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The objective of this work is to study the microstructure and the texture evolution in welded joint of X70 steel with duplex stainless steel joined by gas tungsten arc welding (GTAW) process and heat treated at 200 °C and 600 °C. Then, the microstructural evolutions are correlated to their hardness mechanical property. The characterization techniques used are optical microscopy, scanning electron microscopy, EDS, Vickers microhardness, tensile tests, X-ray diffraction, and electron backscatter diffraction (EBSD) technique. Two heat affected zones were observed in welded joint with different microstructures. Heat affected zone on the X70 steel side and another on the duplex stainless steel side. A solidification microstructure was observed in the fusion zone such elongated ferritic grains and a growth direction < 100 > was found. The most microstructural transformations were observed in the vicinity of the interface which connects the heat affected zone to the fusion zone either on the X70 steel side or on the duplex stainless steel side. The effect of heat treatment on the hardness of the welded joint was noticed in the side of the duplex stainless steel. The fusion zone is the hardest zone of the welded joint (309.4 Hv) and which is not affected by the applied heat. X-ray diffraction analysis did not reveal the formation of new phases after the heat treatments applied to the welded joint. The tensile tests have shown that the welded joint treated at 200 C presents the highest value of ultimate tensile strength (667 MPa). [ABSTRACT FROM AUTHOR]

This research aims to investigate the effects of as-casted and proposed in situ heat-treated squeeze casting of Al-3.5 % Cu alloy. The effects of squeeze pressure, melt temperature and die temperature on ultimate tensile strength, percentage elongation and hardness were modelled and analysed for as-casted and in situ heat-treated squeeze casting using the Box-Behnken design. Response surface methodology was used for experimental design, empirical modelling and analysis. Adequacy and validation of the developed models were verified using ANOVA and confirmation experiments, respectively. The results revealed squeeze pressure as the most significant input variable followed by die temperature under as-casted and in situ heat-treated squeeze casting conditions. The comparative analysis suggested in situ heat-treated squeeze casting conditions as the best alternative which resulted in 7.9~11, 6.7~25.7, and 2.2~7.7 % improvement for ultimate tensile strength, percentage elongation and hardness, respectively. A considerable increase in mechanical properties provided a great evidence to reveal a new technique for foundry men to enhance the quality of squeeze casted Al-Cu alloys. Furthermore, the empirical model will aid practitioners to predict the desired mechanical properties prior to examination. [ABSTRACT FROM AUTHOR]

2219 aluminum alloy thin-walled tubes were fabricated by multi-pass spinning process, and then heat treatments were employed to optimize the mechanical properties of the spun tubes. It is shown that severe deformation during the spinning leads to the formation of large number of nanoscale subgrains, which causes the decrease of work hardening rate, ultimate tensile strength, and fracture strain. The solid solution at 530℃/30 min results in the full recrystallization and leads to the disappearance of the nanoscale subgrains. Besides, the micron scale precipitates in the as-spun tubes are refined to be nanoscale via the further aging process conducted at 175℃/18 h. It is why the ultimate strength of the tubes is enhanced from 245 to 435 MPa. By using of the spun tubes, 2219 aluminum alloy bellows with four circumferential waves were successfully formed by multi-step single wave hydroforming process. [ABSTRACT FROM AUTHOR]

As one of the important additive manufacturing techniques, selective laser melting (SLM) has shown great advantage in the production of metal matrix composite components with complex geometry. However, the layer-by-layer manufacturing procedure causes a nonnegligible thermal accumulation and cycling. Thus, the SLM-deposited component always presents gradient microstructure and mechanical properties. In this work, the dense TiB2p/2024Al composite prepared by SLM was employed to investigate the heat-induced microstructure evolution and mechanical properties. The as-deposited composite presents a uniform distribution of TiB2 reinforced particle in α-Al matrix with an oriented < 100 > texture α-Al dendrite microstructure. The yield strength (YS), ultimate tensile strength (UTS), and the elongation of as-deposited sample increase from 230.06 MPa, 302.52 MPa, and 4.49% to 244.17 MPa, 365.36 MPa, and 11.48% from the bottom to top regions. According to the TEM results, this phenomenon is attributed to the high cooling rate induced low content of θ-Al2Cu phase at the bottom of the sample. In addition, agglomeration of the TiB2 particles due to the insufficient convention is responsible to the poor elongation at the bottom of the sample. After the solid solution and aging heat treatment (T6), thanks to the uniform distribution of S strengthening phases, this gradient in microstructure and mechanical properties in the deposit can be eliminated, and the deposit presents higher YS, UTS, and a lower elongation of 380.23 MPa, 421.50 MPa, and 3.14%. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) is a metal additive manufacturing (AM) process for fabricating high-performance functional parts and tools in various metallic alloys, such as titanium, aluminium and tool steels. One specific AM application is fabricating conformal cooling channels (CCC) in plastic injection moulding tool inserts to improve cooling efficiency. This article reports the development of a novel hybrid powder-wrought alloy steel combination intended for injection mould inserts use. In this investigation, cylindrical parts made of 18Ni300 steel powder and wrought 17-4 PH steel were additively fabricated using a hybrid-build LPBF AM technique, followed by various post-build heat treatments. Standard mechanical and microstructural techniques were employed to examine the bonded powder-substrate interface. Microstructure analysis revealed defect-free, fully dense, homogenous powder-substrate fusion across a 280-µm-thick region. Tensile tests confirmed strong powder-substrate bonding due to solid solution strengthening within the region. All tensile fractures were ductile under all heat treatment conditions and occurred about 8 mm from the interface, at the side where the materials were of lower strength. The hybrid-built parts exhibited an ultimate tensile strength of 1009–1329 MPa, with 16.1–17.4% elongation at fracture. Hardness values on the AM-deposited and substrate sides were 31–55 HRC and 32–43 HRC, respectively. A direct post-build 490 °C/1 h age-hardening treatment achieved the best combination of hardness, tensile strength and ductility. The overall result demonstrates that hybrid-built powder 18Ni300-wrought 17-4 PH steel can be a material choice for manufacturing durable and high-performance injection mould inserts for high-volume production. [ABSTRACT FROM AUTHOR]

Mechanical properties and tensile fracture behavior of normal 7075 aluminum alloy produced by rheoforming were investigated. The rheoforming applies limited angular oscillation (LAO) technique for semi-solid slurry preparation and rheological squeeze casting with transverse moving injection feed semi-solid slurry. The microstructures of as-cast rheoformed 7075 alloy are composed of fine spherical α-Al grains with average size of 26 μm surrounded by eutectic mixture. T6 heat treatment (solution treatment for 4 h at 838 K (465 °C) and aging for 12 h at 393 K (120 °C)) causes a slight increase of grain size and the formation of fine semi-coherent precipitation of η′ phase in α-Al matrix. Good elongation to fracture (10.1%, which is quite close to the wrought target (11%)) is obtained for rheoformed 7075 alloy after T6 heat treatment, with average yield strength of 461 MPa and average ultimate tensile strength of 514 MPa. Pores and voids are main defects observed in rheoformed 7075 alloy. The fracture surface of as-cast rheoformed 7075 alloy consists of large and deep dimples showing the growth and coalescence of voids. After T6 treatment, the fracture surface is composed of large dimples, flat areas containing super-fine dimples and tear ridges. Pores are present in the form of large dimples in fracture surface. The crack initiates at pores and propagates by the coalescence of pores and voids. [ABSTRACT FROM AUTHOR]

Cross wedge rolling (CWR) has unique advantages in the production of shaft preforms with refined grains and improved mechanical properties. Considering the sensitivity of Ti-6Al-4V(TC4) alloy to heat treatment temperature, the effect of different initial deformation temperatures (IDTs) on the forming quality, mechanical properties, and microstructure evolution of the TC4 alloy lower arm preforms in CWR forming was studied in this work. The flow stress curves of TC4 alloy in the two-phase region were obtained by isothermal compression experiments. The Arrhenius constitutive model was established and applied to DEFORM-3D finite element (FE) software to simulate the CWR forming process of TC4 alloy lower arm preforms. The forming quality of TC4 alloy parts was compared and analyzed by 3D FE simulation and experiment. And their mechanical properties at room temperature were tested by tensile test. The results showed that the rolled part has well forming quality (no steps and necking defects) and higher geometric dimension accuracy at the IDT 885°C. Moreover, with the increase of IDT, the radial force and torque in the rolling process decrease. In addition, there were no internal defects in the parts rolled by different IDTs, because the die gap reduces the number of alternating cycles of tensile-compressive stress in the rolled workpieces. Compared with the initial state, the microstructure was refined. When the IDT is 885 °C, the ultimate tensile strength (UTS), yield strength (YS), and elongation (EI) of the parts were 987 MPa, 924 MPa, and 16.8%, respectively, which was able to ensure the mechanical performance requirements of the lower arm preform. The results provide theoretical guidance for the actual production of lower arm preform by CWR. [ABSTRACT FROM AUTHOR]

In order to explore the possibilities enabled by laser beam powder bed fusion of metals (PBF-LB/M), reliable material models are necessary to optimize designs with respect to weight and stiffness. Due to the unique processing conditions in PBF-LB/M, materials often develop a dominating microstructure that leads to anisotropic mechanical properties, and thus isotropic material models fail to account for the orientation-dependent mechanical properties. To investigate the anisotropy of 18Ni300 maraging steel, tensile specimens were built in seven different orientations. The specimens were heat treated at two different conditions and tested for their tensile properties using digital image correlation (DIC) technique. The microstructure and fracture surfaces are investigated with scanning electron microscope and electron backscatter diffraction. The tensile properties are typical for the material, with a yield strength in the range of 1850 MPa to 1950 MPa, and ultimate tensile strength in the range of 1900 MPa to 2000 MPa. The elastic modulus is 180 GPa, and the elongation at fracture is in the range of 2–6% for all specimens. The strain fields analysed with DIC reveals anisotropic straining in both the elastic and plastic parts of the flow curve for both direct ageing and solution treatment plus ageing specimens. In the former condition, the elastic anisotropy is dictated by the fraction of melt pool boundaries on the transverse surfaces of the specimens. When the material is solution treated prior to ageing, the melt pool boundary effect was supressed. [ABSTRACT FROM AUTHOR]

This study investigates the microstructure and mechanical properties of 316L stainless steel (316LSS) samples fabricated by additive manufacturing (AM), in order to optimise the process for improving the properties of 316LSS parts built by laser powder bed fusion (LPBF). Accordingly, a substrate heating was performed on an SLM 280HL printer fitted with an experimental heating device. During the process, samples are built on a substrate heated up to 600 ∘C. The substrate temperature significantly influences the microstructural evolution and mechanical properties of manufactured parts. Concerning tensile properties, the ultimate tensile strength (UTS) and yield strength (YS) decrease as a function of the substrate temperature whereas the elongation (El) increases as a function of the substrate temperature. These results are similar to those obtained with a post-heat treatment performed on parts manufactured by forging or LPBF. The tensile and impact energies reach values higher than the minimum requirement for 316LSS manufactured by forging, according to the RCC-MRx code used for materials dedicated to French nuclear applications. When the substrate temperature is equal to 350 ∘C, the UTS, YS, El and impact energy reached 596 ± 5 MPa, 489 ± 3 MPa, 48 ± 3% and 123 ± 20 J, respectively. Finally, this study demonstrates that heating the substrate during the process is a promising solution to optimise the fabrication route by suppressing post-process heat treatment of 316LSS made by LPBF. [ABSTRACT FROM AUTHOR]

This study investigates the mechanical properties of the wire + arc additively manufactured Inconel 625 thin wall. The first part of this study focused on the microstructural features of the material after time-based annealing. This second part discusses the tensile strength and microhardness of the material after the same annealing procedure (980 °C, hold time 30 min, 1 h, and 2 h). It is found that the annealing procedure improved the ultimate tensile strength by 5%. Although the yield strength remains unchanged up to 1-h of annealing, it increases after 2-h of heat treatment. The presence of strengthening elements and precipitation of secondary phases seem to control the tensile strength of the additively manufactured Inconel 625. On the other hand, the average microhardness does not show any significant trend for time-based heat treatment. However, the layer-specific variation of microhardness was observed in the sample, which may have caused high standard deviation in the as-deposited sample. Overall, the annealing procedure with a 2-h hold time presents the best mechanical properties of the Inconel 625 so far. Nevertheless, further improvement in strength and hardness may require a comprehensive study with location-specific microstructure and mechanical properties analysis before and after the heat treatment procedure. [ABSTRACT FROM AUTHOR]

Inconel 625 (In625) is preferred under the circumstances where high strength and corrosion resistance at elevated temperatures are required. However, the restricted thermal conductivity constrains the application of In625 in high heat flux cases. The joining of materials with high thermal conductivity to In625 is capable of improving upon this limitation so as to adapt for temperature-sensitive requirements. In this study, a bi-metallic structure was fabricated by joining In625 on Copper 110 (Cu) substrate with directed energy deposition. Material examination indicated no crack and minor porosity were detected through and along the interface of two materials and the following as-deposited In625. Mechanical performances were characterized at both as-deposited and heat-treated conditions. The resultant yield strength and ultimate tensile strength of as-deposited In625 was 670.97 ± 5.43 MPa and 925.36 ± 9.90 MPa, respectively, with a mean maximum elongation of 0.416 mm/mm. Slightly decreases (by ~ 5%) in tensile strength were observed after heat treatment under 500 °C for 24 h with an enhancement in elongation by ~ 6%. Ductile fracture mode was observed on the fracture surfaces of broken tensile specimens. The impact toughness for as-deposited In625 and heat-treated In625 (under 600° for 24 h) was 118.058 ± 2.285 and 112.045 ± 5.755 J, respectively. A significant improvement in the thermal diffusivity of ~ 100% was experimentally measured when comparing the bi-metallic structure to pure In625. The thickness fraction of Cu played a significant role in the measured thermal diffusivity result. [ABSTRACT FROM AUTHOR]

A complex experimental study of laser welding of the V-1469 Al-Cu-Li alloy is performed for obtaining a high-strength welded joint. The phase composition, microhardness, and strength characteristics of the alloy and welded joint in various regimes of heat treatment are studied. It is found that heat treatment of the welded joint increases its ultimate tensile strength. After complete heat treatment, microhardness values of the alloy and the welded joint become close to each other. Standard heat treatment of samples after welding allows recovery of the structure and phase composition of the entire sample at the micrometer size level. The use of heat treatment allows one to obtain the welded joint strength equal to 0.85 of the base alloy strength in the as-received T1 state. [ABSTRACT FROM AUTHOR]

Additive manufacturing is a powerful process to build complex geometry. Besides the numerous process parameters influencing the mechanical part performances, other parameters related to the initial powder feedstock or component machining are of most importance. In this study, the combined effect of a wide particle size distribution, surface machining and stress-relief heat treatment on the microstructure and mechanical properties (tension and fatigue) of a stainless steel AISI 316L, produced by laser powder bed fusion, is investigated. In order to correctly investigate those parameters separately, the netshape/machined character of the sample, alongside with the heat treatment, is studied for two kinds of powder having different particle size distributions, i.e. narrow and widely spread. Results show that a large spread of particle size is only slightly detrimental to the fatigue life, in particular in high-cycle conditions due to a larger porosity related to a weakly more uneven particle spatial distribution in the bed. Nevertheless, this effect is of a second order compared to machining or heat treatments which greatly affect the mechanical behaviour. Surface machining and moderate heat treatment are then the best post-operational steps to increase the fatigue life in high-cycle fatigue conditions independently of the particle size distribution. Results are discussed in terms of defects, microstructural modifications, surface roughness, martensitic transformation and mechanical loading. [ABSTRACT FROM AUTHOR]

The present work focused on the densification behaviour and heat treatment effect on the mechanical properties of spark plasma sintered Ni–Fe–Al–Cr alloys. Five initial alloys were prepared by mixing of elemental compositions of each alloy followed by sintering. The five alloys, Ni–30Fe–20Cr, Ni–30Fe–15Cr–5Al, Ni–30Fe–10Cr–10Al, Ni–30Fe–5Cr–15Al, and Ni–30Fe–20Al, were sintered at sintering temperature of 950 °C, pressure of 50 MPa, heating rate of 150 °C/min, and at a holding time of 10 min and heat-treated. Microstructure and mechanical properties of the sintered alloys were investigated prior to and after heat treatment by scanning electron microscopy (SEM) and a Future-tech Vickers microhardness tester respectively. Results showed that the relative density of the alloys increases as the aluminium content increases. The microhardness increases at 800 °C for 2 h ageing time and decreases after prolonged ageing. Therefore, optimum strengthening of sintered nickel alloys can be obtainable within short duration of ageing as prolonged results in adverse hardness values. [ABSTRACT FROM AUTHOR]

The friction deposition process is well known for surface repairs and depositing corrosion and wear resistant coatings. In this study, we explored friction deposition additive manufacturing (FDAM) for producing alloy 718 components. The microstructure evolution, temperature distribution during the process, and room temperature tensile properties of the FDAM processed alloy 718 were studied. Multi-layer deposits with sound metallurgical bonding at the layer interfaces were obtained. The deposits showed fine equiaxed grains with grain size varying from 4 to 7 μm across the deposit height, having finer grains (~4 μm) closer to the substrate and coarser grains (~7 μm) at the top of the deposit. Thermography analysis was employed to analyze the temperature distribution during friction deposition, revealing a maximum peak temperature of 1121°C on the deposited material. Subsequently, the material cooled rapidly at a rate of 30°C/s. The FDAM sample in the as-deposited condition exhibited higher tensile strength than the wrought alloy 718 in the solution-treated (ST) condition. The post-direct aging (DA) of the FDAM sample resulted in a 41% improvement in tensile strength than the as-deposited condition and met the tensile properties of wrought alloy 718 in aged condition as per aerospace material specifications (AMS). Furthermore, there were no significant variations observed in the tensile properties across different regions of the FDAM deposit height. [ABSTRACT FROM AUTHOR]

In applications where a combination of good strength and corrosion resistance is required, 17-4 precipitation hardenable (PH) stainless steel is a common material choice. This alloy is traditionally processed through a combination of casting, rolling, and machining. A variety of heat treatments are used to anneal and harden the material via precipitation strengthening. While additive manufacturing (AM) removes many geometric design constraints from these traditional forming processes, until recently, structures fabricated via laser powder bed fusion (L-PBF) were porous and contained undesirable columnar grain structures that contributed to unpredictable and anisotropic mechanical properties. Recent advances in L-PBF processing technology including improved gas flow, powder atomization, and print parameter optimization enable printing of high-quality 17-4 PH with properties that are comparable to traditionally processed material. However, it is yet to be determined whether these properties can be reliably reproduced across various machines and if machine-agnostic material property baselines can be established based on data available thus far. If baselines can be established, their implementation should allow for identification of machines that generate non-conforming material. In this work, we evaluate the consistency of mechanical properties in L-PBF 17-4 PH produced by six vendors with the ultimate goal of establishing mechanical property baselines, which is fundamental to modern qualification paradigms. We find non-conforming data from two vendors by examining anomalies in mechanical response (e.g., transformation induced plasticity effects) and demonstrate that typical sources of variation can be detected using qualification testing protocols. Ultimately, after standard solution annealing and heat treating, the microstructure and mechanical properties across vendors converged with very few, easily explainable exceptions. In particular, powder atomized in nitrogen promoted formation of retained austenite that lead to a yield point phenomenon in as-built conditions, and high surface roughness from as-built surfaces reduced the fatigue strength. However, with conventional post-processing heat treatments and surface polishing, AM 17-4 PH behaved comparably and consistently to conventionally processed material. [ABSTRACT FROM AUTHOR]

In this paper, a disk laser welding was developed to join 3-mm thin-Sect. 30Cr3 ultra-high-strength steel which was widely used in aerospace. The microstructure and mechanical properties of welded joint were investigated in detail. The results indicated that the recommended laser linear energy range were between 150 and 165 J/mm to guarantee that the melting width was up to 1 mm as well as less oxidation, spatter, and depression on the weld. Meanwhile, for the as-welded (AW) condition, the base metal (BM) consisted of ferrite matrix with distributing small spherical carbides, also known as spherical pearlite. While, the fine grained region, coarse grained region, and weld metal were all composed of martensite. However, the partially transformed region mainly consisted martensite with a little of spherical pearlite. Meanwhile, the average grain sizes of weld metal, HAZ, and base metal were 1.3 μm, 1.5 μm, and 1.8 μm, respectively. However, for the post-weld heat treatment (PWHT) condition, the whole welded joint was all composed of tempered martensite, and the average grain size of welded joint was about 1.7 μm. The tensile strength of the welded joint was higher than that of the base metal both in the AW and PWHT condition as all the fracture with shrinkage occurred in the BM of the specimens. Additionally, the average yield strength of the AW and PWHT are about 600 MPa and 1700 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a novel gradient-based algorithm named Kernel-based hybrid multi-objective optimization (KHMO) is implemented and coupled with a support vector regression (SVR) model to efficiently optimize the production of a cold rolled hot-dip galvanized TRIP steel. For this purpose, several heat treatments using an isothermal bainitic transformation (IBT) temperature compatible with continuous hot-dip galvanizing were performed. The most significant processing parameters (cooling rate after intercritical austenitizing ( C R 1 ), isothermal holding time at the galvanizing temperature in the bainitic region t 2 , and last cooling rate to room temperature ( C R 2 )) were thus optimized to achieve the required mechanical properties values. In general, SVR model fits in a satisfactory manner the highly non-linear relationship between experimental parameters and resulting mechanical properties; hence, it is used as objective function. Besides, KHMO algorithm reveals an outstanding performance since it found a dense and spread Pareto front. Moreover, the processing window to manufacture TRIP-aided martensitic steels is suggested in a range of 57–63 ∘ C/s, 33–37 s, and 1–2 ∘ C/s for C R 1 , t 2 , and C R 2 , respectively. The developed computational methodology for modeling and optimization of operating parameters is successfully applied for the first time in the experimental processing of advanced TRIP steels. [ABSTRACT FROM AUTHOR]

The thermal cycles necessary to produce galvanized transformation-induced plasticity (TRIP) steels on a continuous hot-dip galvanizing line involve several processing parameters that must be chosen and strictly controlled to achieve the required mechanical properties. The resulting mechanical properties strongly depend on the optimal determination of each heat treatment variable. In this paper, a novel memetic algorithm named kernel-based gradient evolution (KGE) is implemented and coupled with a support vector regression (SVR) model to efficiently optimize the production of a cold rolled hot-dip galvanized TRIP steel. For this purpose, the most significant processing parameters (cooling rate after intercritical austenitizing, isothermal holding time at the galvanizing temperature in the bainitic region, and last cooling rate to room temperature) were thus optimized to achieve the required hardness values. In general, SVR fits in a satisfactory manner the relation between experimental parameters and resulting hardness which is highly non-linear in nature, and hence, it is used as objective function. Besides, KGE algorithm reveals an impressive performance since it solved the problem in less than 10 iterations. As a result, optimal solution is successfully achieved by the proposed SVR-KGE model. [ABSTRACT FROM AUTHOR]

This study investigated the microstructures and tensile properties of as-build and heat-treated (including T6, T2, and T6-T2 treatments) AlSi10Mg samples fabricated by laser powder bed fusion (LPBF). The microstructure analysis revealed that the trend of eutectic Al-Si phase distribution along grain boundaries for heat-treated samples was significantly weakened, and the eutectic Al-Si phase was transformed into Si particles which were uniformly distributed in α-Al matrix. For the T6-T2-treated specimens, the Si content in particles was the highest. Meanwhile, the T6 treatment increased the proportion of equiaxed grains on vertical section most significantly. However, in the wake of heat treatments, the average grain size on horizontal section had little change while the average grain size on vertical section was increased. The properties analysis demonstrated that the T6-T2-treated specimens obtained the best elongation and worst strength. Besides, the T6 treatment eliminated the anisotropy of the LPBFed specimens basically and synergistically obtained the best combination of strength and plasticity. The T6 treatment weakened the direction difference to the greatest extent, whereas the T2 treatment minimized the stress concentration. According to the comparative finding, the Si content in particles played an important part in properties. Besides, the relationship among inverse pole figure (IPF) maps, pole figure (PF) maps, the mass fraction and distribution of Si in Al matrix and Si particle, the grain size, kernel average misorientation (KAM), and mechanical properties under different heat treatments was established, which provided a new idea for the selection of heat treatments on LPBFed parts. [ABSTRACT FROM AUTHOR]

The influence of the scale effect on the strength of mechanically inhomogeneous welded structures with a soft zone was studied. The investigated welded samples were made of two 12Kh18N10T austenitic steel plates and a low-carbon ferritic insert connected between them by two dissimilar welded joints performed by electron beam welding. Tensile strength as a function of soft zone relative thickness for tensile specimens was plotted. It was shown that with a relative thickness of the soft zone in the range from 0.2 to 0.5, the scale effect did not manifest during tension. This can be explained by low plastic compressive deformations in the soft zone after heat treatment, which typically lead to a decrease in the constraint effect due to the Bauschinger effect. [ABSTRACT FROM AUTHOR]

In this study, the optimum process parameters for the manufacture of brake friction linings (BFLs) from palm kernel shells (PKS), periwinkle shells (PWS), and coconut shell (CNS) composites were established using signal–to–noise ratio based on the Taguchi technique. The L9(34) orthogonal array was set up for the investigation of the performance metrics (coefficient of friction, wear rate, and hardness) synergized by multiple criteria evaluation. The manufacturing parameters considered were molding pressure, molding temperature, curing time, and heat treatment time. Consequently, the optimized parameters were utilized for the production of different BFL composites of the PKS/PWS/CNS mix. Finally, entropy and TOPSIS techniques were employed to isolate the best composite for comparative analysis. The results show that the optimum process parameters are 29 MPa (molding pressure), 120 °C (molding temperature), 6 min (curing time), and 2 h (heat treatment time). ANOVA using Minitab 21.1.0.0 shows that the effects of the molding pressure and curing time are statistically significant at α = 0.05, with a total contribution of 94.45%. The entropy-TOPSIS analysis gave sample S2pkpc with a composition of 12% PKS, 15% PWS, and 18% CNS as the best composite. Compared to the asbestos BFL, the composite shows an improvement in friction coefficient (45.7%), wear rate (66%), density (60.2%), and oil and water absorption (233%) (542.8%) respectively. The live test on a Peugeot 301 using S2pkpc BFL confirms the satisfactory performance of the composite. However, an increased wear rate was observed at vehicle speeds above 90 km/h. [ABSTRACT FROM AUTHOR]

Additive manufacturing of composite materials is a promising technology. It could solve one of the most critical drawbacks of 3D-printed fiber-reinforced thermoplastics: their low out-of-plane mechanical properties. Due to this factor, it is still unknown how most design and manufacturing parameters affect the out-of-plane properties of composite materials. As a solution, this paper proposes an experimental methodology to characterize out-of-plane printed composite materials. For this purpose, existing standards for traditionally fabricated composites are adapted, investigated, and validated for 3D-printed laminates reinforced with long fibers using the fused filament fabrication technique. Consequently, the methodology is employed to study the impact of stacking sequence and heat treatment conditions on the composites' out-of-plane mechanical properties. The main results showed that increasing the thickness between stacking layers increases the mechanical response due to reducing the number of fiber/matrix interfaces and, consequently, the reduction of porosity. Compared to the initial sample, a heat treatment at 175 °C for 6 h increased the interfacial strength by 101.09% and reduced the porosity in the fiber produced by the additive manufacturing process by 72%. [ABSTRACT FROM AUTHOR]

This paper studies printing parameters and post-printing heat treatment for laser powder bed fused Inconel 718. The printing scanning speeds and energy densities per unit volume were varied, and each print group was subjected to combinations of three different types of heat treatment: homogenization, hot isostatic pressing, and solution heat treating following with aging. The quality of the samples was measured by the porosity present in the samples, hardness, size/quantity of defects, and identification of phases and defects in the microstructure. Both optical and scanning electron microscopy observations showed that a scanning speed of 1250 mm/s and energy density of 54.5 J/mm3 result in the lowest porosity. Reduction of porosity and precipitation hardening increased material hardness to 470 HV. The Laves phases, normally seen in the as-printed samples, were effectively minimized after these thermal heat treatments. An increment of 550% of fatigue life was seen in axial fatigue testing at 525 MPa on samples after hot isostatic and aging treatment. [ABSTRACT FROM AUTHOR]

This study intends to evaluate the strain-based fatigue parameters of Ti–6Al–4V alloys fabricated through additive manufacturing (AM), considering the effects of AM methods, building direction, and post-processing techniques, including heat treatment and surface finishing. The investigated parameters were fatigue strength coefficients and exponents, as well as the fatigue ductility coefficients and exponents. These parameters are crucial for fatigue life predictions. Fatigue data of different AM specimens were employed to obtain the aforementioned strain-based fatigue parameters under various circumstances. Finally, several case studies dealing with fatigue predictions have been fulfilled using the calculated fatigue parameters to evaluate the accuracy of these parameters. To this end, the effects of notch and loading conditions were assessed through the modified Morrow's criterion. A reasonable agreement was observed between the available fatigue test data with the predicted results. [ABSTRACT FROM AUTHOR]

This study presents a bimetallic additively manufactured structure (BAMS) of Inconel 625 (In625) and austenitic stainless steel 316L (SS316L) manufactured by a gas-metal-arc-welding (GMAW) based on wire-arc additive manufacturing (WAAM) technology. A BAMS was heat treated at 970 °C for improvement of the mechanical properties. The heat treatments resulted in a microstructural change from delta-ferrite to austenite in SS316L and enhanced tensile strength compared to the as-built sample. The same crystal structure and similar lattice constant between In625 and SS316L led to an epitaxial growth at bimetallic interface, which developed coherent columnar grains with the same crystallographic orientation. During the heating and cooling sequence, different thermal expansion coefficients of both materials generated localized strains at the bimetallic interface, from which dynamic strain hardening was achieved exhibiting a higher hardness at the interface. [ABSTRACT FROM AUTHOR]

Mitigation of residual stress in additive manufactured metal parts through post-heat treatment helps enhancement of life during service. The present work aims to investigate the effect of stress-relieving heat treatment (SRHT) at 1065 °C on microstructural changes, residual stress patterns, and mechanical properties of Inconel 718 (IN718) blocks fabricated through use of the laser-based powder bed fusion (L-PBF) process. The X-ray diffraction technique known as cos α method was used to capture the Debye ring for the measurement of surface residual stress. Dissolution of the columnar dendrites along with laves phases in the interdendritic region was seen after SRHT. The resultant microstructure showed partially recrystallized grains along with the formation of annealing twins and strengthening phases such as γ', γ", and tiny metal carbides. The residual stress on the top surface of as-built sample was found to be 77% higher on the corners compared to the center region. The distribution of residual stress was seen as not uniform in the as-built condition. The SRHT sample showed uniform distribution of compressive residual stresses in all the locations. This phenomenon was due to the diffusion of atoms present in the high-stress regions migrated to low-stress regions until attaining their equilibrium. The combination of face centered cubic (FCC) and hexagonal lattices in as-built microstructure led to misfit strain between the grains. After SRHT, microstructure of IN718 experienced relaxation of residual stresses due to the transformation of hexagonal structured laves phase into the body-centered tetragonal (BCT) γ"and FCC-structured γ' phases. Furthermore, SRHT significantly alters the mechanical properties of IN718 alloy causing a 23.03% increase in average hardness and a 21.04% increase in tensile strength. [ABSTRACT FROM AUTHOR]

To minimize the carbon footprint of the transportation industry, manufacturers and engineers are continuously trying to improve the efficiency of the combustion engine. However, due to the presence of iron cylinder liners in the engine block, high tensile residual stresses are generated during the manufacturing process which leads to a large reduction of the alloy's useable strength. Thus, the present study utilized neutron diffraction to study, for the first time, the evolution of residual stress of sand-cast aluminum engine blocks that have eliminated the iron cylinder liners from the casting process and mechanically inserted them after heat treatment and machining operations. Moreover, this study also examined the effects that cylinder bore chills have on the resulting residual stress profiles. The replacement of the iron liners shifted the stress mode from purely tension to purely compression until the bore chills were removed. Following the removal of the bore chills, the maximum tensile stress at the top of the cylinder bridge was ~ 70% lower than the engine's predecessor which was produced with iron liners. Moreover, in the production-ready state (i.e., T7 heat treated and press-fit liners inserted), the stress mode maintains the partially compressive nature, thereby lowering the material's susceptibility to crack growth and propagation. [ABSTRACT FROM AUTHOR]

Aluminium matrix composites (AMCs) have a high strength-to-weight ratio, high stiffness, and good damage resistance under a wide range of operating conditions, making them a viable alternative to traditional materials in a variety of technical applications. Because of their high strength, composite materials are hard to deform to a desired shape and depth at room temperature. As a result, additional treatments are required to enhance the composite's ductility at room temperature prior to deformation. In this investigation, as-received 6092Al/silicon carbide particle (SiCp) composite sheets (T6-condition) are heat-treated to O-condition annealing to enhance its ductility in order to assess the formability and fracture behaviour of the Al/SiC particle composite sheets under single point incremental forming (SPIF) using different forming parameters at room temperature. The annealed sheets are heat-treated to T6-condition to enhance the strength and achieve properties equivalent to as-received sheet properties. The results demonstrate that the Al/SiC particle composite sheets with T6 treatment could not be deformed to the specified depth due to low ductility at room temperature. Further treatment, such as O-condition annealing, is required to enhance its ductility to enable successful deformation of the Al/SiCp sheets using SPIF. After SPIF processing, the annealed Al/SiCp composite sheets are heat-treated back to T6. The sheets exhibit properties comparable to the as-received sheets. Al/SiC particle composite sheets with low values of SPIF parameters, i.e. small tool diameter, low step size and feed rate, are able to achieve greater formability and fracture depth with low strain hardening under SPIF processing conditions. [ABSTRACT FROM AUTHOR]

The local residual stresses (tensile) generated on the surface of a component during its manufacturing (machining, welding) cause deterioration of its service life. To eliminate the negative effect of the stresses, the surface is treated using different methods (shot peening, laser shock peening, heat treatment, water jet peening). The application of ultrasonic technology to modify the continuous jet has been intensively researched for treating advanced stages of erosion. In this work, the modifications in the mechanical properties (tensile strength, micro-hardness and residual stress measurements) of AISI 304 Tungsten inert gas welded joints were investigated after ultrasonic pulsating water jet treatment in the incubation stage of erosion. This revealed that the initial tensile residual stress in the welded joints was converted to compressive stress after the treatment. The micro-hardness of the joints after the treatment increased about 40% in the heat affected zone in the near-surface region. Also, the tensile properties increased by about 37.8% and 34.6% in yield strength and ultimate strength, respectively. The microstructural examination of the near-surface region showed the grain reformation mechanism. [ABSTRACT FROM AUTHOR]

This article reports the impacts of the powders morphologies and post-processing heat treatment on microstructure and mechanical properties of cold-sprayed commercial pure (CP) Ti deposits. The results show that cold-sprayed CP Ti deposited from spherical-shape powder exhibit lower porosity and hardness than that produced from irregular-shape powder. According to LECO analysis, cold-sprayed CP Ti deposits made from irregular-shape powder had higher oxygen and nitrogen contents than those made from spherical-shape powder. The results indicated that irregular-shape powder was more reactive with oxygen and nitrogen than spherical-shape powder, owing to differences in particle velocity and surface area. Post-processing heat treatment in a high-vacuum furnace at 920, 990, and 1100 °C dissipates particle boundaries, removes sub-micron pores, and greatly enhances the tensile characteristics of cold-sprayed CP Ti deposits. After post-heat treatment, cold-sprayed CP Ti deposits made from spherical powder have a higher elongation to break and a slightly lower tensile strength than cold-sprayed CP Ti made from irregular-shape powder. Furthermore, SEM microstructure images reveal that grain size increases when the temperature of the post-heat treatment rises. On the other hand, cold-sprayed CP Ti manufactured with spherical-shape powders has a larger grain size than cold-sprayed cp-Ti made with irregular-shape powders. [ABSTRACT FROM AUTHOR]

This paper aims at analyzing the effect of heat treatment using Concentrated Solar Energy (CSE) on the martensitic microstructure evolution of Ti-6Al-4V alloy manufactured by Selective Laser Melting (SLM) technology. The application of CSE, a renewable energy sources, in post-processing of SLMed Ti-6Al-4V alloy is discussed based on heat treatments performed at Plataforma Solar de Almeria, Spain, using solar furnace SF40. In SLM process of Ti-6Al-4V powder because of local high heating followed by a rapid cooling the microstructure consists of an acicular martensite (α′ phase). Decomposition of α′ martensite of SLMed Ti-6Al-4V after heat treatment in solar furnace, using CSE, by SEM, EDX, TEM, SAED, and XRD analyses, was investigated. It has been found that for treatment below β-transus at 705 °C, because of low temperature, the α′ martensite was not fully converted into α + β and the β phase was not identified by XRD analysis. Heat treatments below (940 °C followed by 650 °C) and above (1050 °C) β-transus have revealed that α′ martensite was converted into a lamellar α + β mixture and also β phase was identified by XRD and TEM analysis. In the analyzed areas, middle areas of the samples contain an area fraction of β phase greater than the top areas. Area fraction of β phase, after heat treatment above β-transus, at 1050 °C, is greater than that obtained after treatment below β-transus. [ABSTRACT FROM AUTHOR]

The effect of solution heat treatment on the mechanical and microstructural properties of 316L stainless steel parts fabricated through hybrid additive and subtractive process (HASP) is explored. These techniques synergistically combine additive manufacturing directed energy deposition (DED) with subtractive manufacturing (SM) technique in a single machine, and they provide an important opportunity to improve material utilization, part complexity and quality management in functional components. Thin-wall specimens were manufactured by HASP to investigate the effect of the solution heat treatment at different temperatures and different holding times on the microstructure and the resultant mechanical properties, such as the Vickers micro-hardness and tensile property. The results show that the content of δ and σ phases can be optimized via heat treatment. While the solution treatment temperature and time increase, the content of the σ and δ phases in the γ matrix can distinctly decrease, which causes the strength to degrade but the ductility to increase. These results suggest that the microstructure and the resulting mechanical properties of HASP-fabricated samples can be adjusted through the adjustment of solution heat treatment. [ABSTRACT FROM AUTHOR]

Stainless steel (SS) alloys produced by laser-based powder bed fusion (LPBF) offers comparable and sometime superior mechanical properties compared to conventionally processed materials. Some of these steels have been extensively studied over the last decade; however additively manufactured martensitic SS, such as AISI 420, need further research in characterizing their post-built quality and mechanical behaviour. This lack of information on martensitic SS is not consistent with their growing demand in the automotive, medical and aerospace industries due to their good corrosion resistance, high hardness and good tensile properties. Selection of the appropriate process parameters and post treatments plays a fundamental role in determining final properties. For this reason, the effect of LPBF process parameters and different heat treatments on density, defect characteristics and locations, roughness and mechanical properties of AISI 420 were investigated in this paper. A first experimental campaign was carried out to establish a set of suitable process parameters for industrial applications. Starting from this result, detected defect properties were investigated by computed tomography (CT) scans. Dimensions, sphericity and distributions of defects inside the volume were analysed and compared between samples manufactured with different parameters. In the second part of the paper, the influence of process and post-process conditions on mechanical properties was investigated. The final presented results establish a correlation between the employed production cycle and the resulting properties of LPBF AISI 420 specimens. [ABSTRACT FROM AUTHOR]

Maraging steels (MS) are widely used materials for heavy-duty applications and are considered an alternative to carbon hardened steels when high strength and good toughness is needed. Their processing through additive manufacturing (AM) technologies offers additional high-value opportunities, for instance, in the rapid prototyping or fabrication of tooling and inserts, and in the repair of molds and dies as well as in maintenance applications. This work studied the maraging 300 steel (18Ni-300) deposited by the laser cladding (LC) process. The experimental design was based on a 23-full factorial design used to determine the optimum processing windows, using a constant powder feed rate. After that, samples with optimal process parameters were manufactured to determine the influence of deposition strategy and aging heat treatments on structural and mechanical properties (i.e., macrohardness). Results indicated the influence of crucial process parameters (i.e., laser power, velocity, and laser spot size) on the track's geometrical characteristics. The processing windows also revealed that particular combinations of these parameters' values produced LC tracks with the minimum dilution with either maximum height or maximum width, which is desirable for manufacturing and repair applications. Although the as-built samples did not show significant differences in their hardness, they showed a considerable difference in their austenitic phase content due to a combined effect between the sample's geometry and deposition pattern. Aging heat treatments between 460 and 490 °C (4–8 h) resulted in the maximum hardness value (~55HCR) with an austenite content below 6 wt% calculated by Rietveld analysis. Finally, SEM and EDS analysis were carried out; it was found that the austenite located in the boundaries of the solidification structures is rich in Mo, Ti, and Ni for the samples in the as-built condition, while for the samples with aging, the highest content of austenite rich in Ni and Mo was obtained with aging at 530 °C. [ABSTRACT FROM AUTHOR]

In the present work, 2024-T351 Al alloy reinforced with alumina particulates (Al2O3p) was elaborated using friction stir processing (FSP). The effect of solution heat treatment followed by subsequent aging on microstructure, hardness, and tribological behavior is discussed. It was noticed that the hardness of the as-FSPed 2024-T351/Al2O3p was slightly enhanced in comparison to the as-received AA2024-T351 material, whereas the resulting wear resistance was remarkably improved. After heat treatment process, the composite volume increased, and swelling and pores were created at the processed area. The heat treatment caused a degradation in wear resistance compared to as-FSPed composites. The precipitation mechanism changed for AA2024/Al2O3p; reactions occurred at grain boundaries between Al2O3 and Cu or Mg, causing their depletion from the Al matrix. Intriguingly, the precipitation mode in heat-affected zone of the matrix also changed to grain boundary precipitation. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is a unique manufacturing process that disrupted completely the way which components are made, since this process is capable of producing complex parts layer after layer. As a matter of fact, one of its distinct technologies is metal laser beam powder bed fusion (mLB-PBF), also known as selective laser melting (SLM) or direct metal laser sintering (DMLS), which creates metallic parts with the aid of a high-energy laser beam. One of the most employed superalloys in this technology is the Inconel 718 (IN718), a precipitation-hardened alloy that is used in the marine, nuclear power plants, gas turbines, and aerospace field due to its capacity of retaining good mechanical properties at high temperatures. The research novelty of this review manuscript is the compilation of all kinds of information from the last 15 years of investigation about IN718 parts produced via mLB-PBF, namely, information related to distinct heat treatments and the influence they have in increasing mechanical properties of the manufactured components, as well as reducing residual stresses (RS) and part porosity. Throughout the review, it can be seen that the expected microstructure in the as-built state is characterized by fine columnar grains and a saturated γ matrix with the presence of the Laves phase and carbides. However, distinct heat treatments can be employed which lead to the dissolution of the undesired phases (Laves and carbides), the precipitation of the strengthening phases (γ' and γ"), and the porosity decrease. Furthermore, it was also shown that heat treatments as well as optimized process parameters can be held accountable for lowering the RS of the IN718 manufactured parts. Nevertheless, there are still some problems to overcome, namely, the mechanical properties variability when subjecting IN718 powder to different process parameters. Moreover, the RS evolution under different heat treatments needs to be further investigated. [ABSTRACT FROM AUTHOR]

There has been growing interest in studying the formation of the structure and properties of aluminum alloys in a solid-liquid state, which is practically not used in domestic metallurgy and mechanical engineering, those at temperatures slightly higher than the eutectic, which leads to a change in the eutectic structure of the acicular type to a more dispersed equiaxial one. Therefore, the purpose of this work is to study structure formation during thixotropic treatment of an aluminum-silicon alloy, which takes place with the participation of a liquid phase, the modes of which can be adapted for thixotropic casting, which will allow changing the shape and size of eutectic crystals, which ultimately affects the mechanical properties of products. In the course of the work, the Al-12%Si alloy was studied, which underwent heat treatment at temperatures from 572 to 600 °C. During heating, isothermal holding, and cooling at a temperature above the eutectic temperature, melting and recrystallization processes occur in parallel. It was found that since the change in the state of the system is determined by a decrease in the thermodynamic potential (Gibbs energy), it is necessary to take into account the change in the volumetric energy and the change in the surface energy associated with melting (the appearance of new melt/α-solid solution and melt/Si interfaces). But it is also important to take into account that during isothermal exposure, the total surface energy will change in such a way as to minimize the final surface energy. [ABSTRACT FROM AUTHOR]

Cold spray additive manufacturing (CSAM) is relatively a new additive manufacturing technology that does not employ heat to achieve bonding between metal particles and the substrate. The CSAM process operates at a temperature lower than the melting temperature of the metal particle and the substrate. Hence, the constraints associated with high-temperature processing such as oxidation and phase change can be minimised, as well as the requirement of energy can be significantly reduced. This technology offers promising solutions for a wide range of applications in industries such as automotive, aerospace, and nuclear power generation. In this study, the effects of build orientation and post-build heat treatment on additively manufactured (AM) copper were investigated. Copper deposits were fabricated using a novel spraying system where stationary nozzle propels metal particles by compressed air onto a substrate clamped on a moving robot arm. The deposits were built in two different orientations (XY—0° and Z—90° to the build platform, respectively) and then mechanically tested in the as-deposited (AD), annealed at 400 °C (400 M), and sintered at 1000 °C (1000 M) conditions. The results strongly suggested that Z-build orientation samples had substantially lower inter-particle bonding strength compared with the XY-build direction samples due to the presence of porosity network. This pore network was created when the spray angle was abruptly changed from 90 to 45° orientation. The metallurgical bonding between particles improved with subsequent heat treatment. The 400 M samples consisted of recrystallised microstructure leading to an increase in tensile strength and ductility. Although the metallurgical bonding in the 1000 M samples was comparably better than the as-desposited samples, the formation of grossly large pores along grain boundaries acted as crack initiation sites, thereby resulting in very poor mechanical properties. This study has provided insights into the CSAM processing parameter selection and potential post-processing route to improve the mechanical properties of cold-sprayed copper parts. [ABSTRACT FROM AUTHOR]

Vehicle weight reduction has been discussed by automotive industry for decades. The current solution for weight reduction purpose is the use of aluminum stamping and casting parts to replace the steel parts. However, joining aluminum with aluminum or aluminum with steel parts would be difficult to select a proper joining technology to ensure a qualified joint. Self-pierce riveting (SPR) as a mechanical joining technique has been used by automotive industry owing to its simplicity, versatility, and environment friendly nature. Although SPR can avoid the joining quality problems caused by welding to join aluminum with steel parts, the other joining problems from SPR still hinder the industry to widely use this joining technology. This article analyzed the cause of cracks on joint button from the understanding of joined material. The modified heat treatments were used to investigate the relationship between eutectic silicon morphology and cracking condition on joint button. In addition, the lap-shear strength according to the samples with various heat treatments was also tested and analyzed. Eventually, the results indicated that silicon content and its morphology take main responsibility on crack initiation and propagation on SPR joint button. But the influence of cracks on joining strength still needs to be investigated and studied in the future work. [ABSTRACT FROM AUTHOR]

The aim of this study is to explore the wear performance of AISI 316L stainless steel fabricated via selective laser melting along different directions with respect to the building direction and via post annealing. The wear behavior of the alloy under high-speed sliding was investigated with high sliding velocities of up to 1 m/s. It was shown that the wear behavior of the alloy was completely different from that in quasi-static wear environments. The high-speed wear resistance was significantly affected by the building direction. After the annealing heat treatment of the alloy at 800 °C for 4 h, the high-speed wear resistance significantly decreased. Therefore, special care must be taken in using SLM 316L alloys when subjected to wear environments with high sliding velocities. [ABSTRACT FROM AUTHOR]

Despite ongoing optimization, selective laser melting (SLM) technology still cannot guarantee the production of completely defect-free components. This work investigates hot isostatic pressing (HIP) in a nitrogen environment and solubilization heat treatment as methods for improving the quality of 316L stainless steel components produced by SLM. The characteristics of HIP-treated specimens are firstly correlated with the initial density of samples obtained with different SLM process parameters, showing that HIP is effective at eliminating pores in components with high initial density (above 99%) but not in those with low initial density (approximately 94%). Subsequently, the mechanical properties and microstructure of 316L stainless steel specimens produced by SLM are examined in the as-built state and after various post-process conditions including solubilization heat treatment and HIP at pressures from 50 to 2000 bar. The observed effects of post-processing on the porosity and microstructure of each specimen are consistent with hardness and tensile test results, with the benefits and limitations of HIP clarified for future implementation. [ABSTRACT FROM AUTHOR]

Production rate is an increasingly important factor in the deployment of metal additive manufacturing (AM) throughout industry. To address the perceived low production rate of metal AM systems based on single-laser powder bed fusion (L-PBF), several companies now offer systems in which melting has been parallelised by the introduction of multiple, independently controlled laser beams. Nevertheless, a full set of studies is yet to be conducted to benchmark the efficiency of multi-laser systems and, at the same time, to verify if the mechanical properties of components are compromised due to the increase in build rate. This study addresses the described technology gaps and presents a 4-beam L-PBF system operating in "single multi" (SM) mode (SM-L-PBF) where each of the four lasers is controlled so that it melts all of a particular components' layers and produces specimens for comparison with standard L-PBF specimens from the same machine. That is all four lasers making all of some of the parts were compared to a single-laser manufacturing all of the parts. Build parameters were kept constant throughout the manufacturing process and the material used was Inconel 625 (IN625). Stress-relieving heat treatment was conducted on As-built (AB) specimens. Both AB and heat-treated (HT) specimen sets were tested for density, microstructure, tensile strength and hardness. Results indicate that the stress-relieving heat treatment increases specimen ductility without compromising other mechanical properties. SM-L-PBF has achieved a build rate of 14 cm3/h when four 200 W lasers were used to process IN625 at a layer thickness of 30 μm. An increase in the build rate of 2.74 times (build time reduction: 63%) has been demonstrated when compared to that of L-PBF, with little to no compromises in specimen mechanical properties. The observed tensile properties exceed the American Society for Testing Materials (ASTM) requirements for IN625 (by a margin of 22 to 26% in the 0.2% offset yield strength). Average specimen hardness and grain size are in the same order as that reported in literatures. The study has demonstrated that a multi-laser AM system opens up opportunities to tackle the impasse of low build rate in L-PBF in an industrial setting and that at least when operating in single mode there is no detectable degradation in the mechanical and crystallographic characteristics of the components produced. [ABSTRACT FROM AUTHOR]

15-5PH parts that are fabricated using direct metal laser sintering (DMLS) has shown mechanical properties comparable to conventionally manufactured parts. However, DMLS-fabricated 15-5PH parts have shown high anisotropy in their mechanical properties due to the layering nature of additive manufacturing process. In addition, the fatigue life and strength of DMLS 15-5PH varies significantly between horizontally and vertically fabricated parts and both orientations are inferior to conventionally manufactured parts. Reliability and large variations in performance remain as a barrier from employing 15-5PH parts fabricated using DMLS. Standard heat treatment of 15-5PH is insufficient to eliminate the anisotropy and homogenize the DMLS parts. Modified precipitation hardening heat treatments did not show further improvement in published literature. Therefore, in this paper, we investigate the influence of different solution annealing heat treatments on the microstructure and mechanical properties of 15-5PH steel produced using DMLS. Three different solution annealing heat treatments were investigated: the standard solution heat treatment, the second heat treatment extended the time from 1 to 3 h, the third heat treatment increased the temperature from 1038 to 1200 °C. For each heat treatment, three patches of specimens were fabricated each in one of the three principal orientations X, Y, and Z. In addition, three patches, one of each orientation, were tested in as-built condition. The specimens were tensile tested and their microstructure and fractured surfaces were imaged. It was found that extending the time of the heat treatment improved the homogenization while increasing the temperature of the heat treatment to 1200 °C had detrimental effects, especially on vertically fabricated specimens. [ABSTRACT FROM AUTHOR]

The present study was performed on an Al-6% Cu-0.7%Si alloy, and 319 and 356 alloys following different heat treatments. The main task was to evaluate the drilling and tapping characteristics of the Al-Cu alloy with respect to the Al-Si-based 319 and 356 alloys. The drilling work was carried out on a Huron K2X8five CNC machine at 15,000 rpm with continuous cooling to absorb the heat and to clean the holes from the chips formed during the drilling operation. The results show that the addition of Si coupled with T6 aging treatment produces the highest cutting forces (about 360 N) among the alloys studied (approximately 270 N) after 2500 holes. Considering the Al-Cu-based alloys, varying the aging treatment has practically no significant bearing on the cutting forces. Apparently, a high Cu content acts as a self-lubricant, facilitating the drilling process up to 2700 holes, with no sign of tool wear. However, due to the low level of Si in the Al-Cu-based alloy, built up edge (BUE) is more frequent, with conical chips, which would affect the precision of the size of the drilled hole. The chips are normally dull and characterized by their rough surfaces compared to those obtained from A356.0 alloy. Tapping of the drilled holes was carried out using Guhring 971 H6 M6 6HX- HSSE taps. The HT200-based alloys revealed excellent machinability with no sign of tool wearing after 2500 holes. In contrast, the tool failed after 1600 holes in the case of 356 alloy and 2160 holes for 319 alloy. Thus, it is concluded that the presence of 3.5% Cu in the 319 alloy helped in reducing the severity of wearing due to eutectic Si particles. However, the tapping forces reached 120 N prior to failure compared to about 75 N in the case of T200-based alloys. [ABSTRACT FROM AUTHOR]

The work presented here was carried out on an Al-6%Cu-0.7%Si alloy (used in as cast, T5 and T7 aged conditions), in comparison with B319.0 (T7 by treated at the two places where treatment appears) and A356.0 (T6 treatment) alloys. Wet milling was carried out on 15 blocks of each alloy using new inserts for 120-m machining distance. A total of 75 blocks were employed. The results show that the cutting forces for the Al-Cu based alloys are not affected by the applied heat treatment. The presence of Cu in the B319.0 neutralized, to some extent, the harmful effect of the hard Si particles. Maximum cutting forces were obtained from machining the A356.0 alloy treated in the T6 condition, due to the presence of a high density of hard eutectic Si particles (~ 41500 particles/mm2), in addition to the dense precipitation of ultra-fine Mg2Si particles. Thus, the presence of 6%Cu in the Al-Cu-based alloy may act as a self-lubricant leading to much smoother finishing surfaces compared with those exhibited by B319.0 and A356.0 alloys. Similar observations were reported on the wearing of the drilling tools. Moreover, after 120-m machining distance, tiny burrs were found adhered to the outer edges of the workpiece, whereas burrs in the case of the A356.0 alloy were separated from the block. [ABSTRACT FROM AUTHOR]

In the present study, the effect of various heat treatments on the microstructure and micromechanical properties of a Ti-6Al-4V alloy processed by a laser powder bed fusion (L-PBF) technique is investigated. Heat treatment cycles employed in this study include solutionizing at 950 °C (for 1 h) followed by three different cooling rates (water quenching, air cooling, and furnace cooling) as well as solutionizing followed by water quenching and artificial aging. To assess the small-scale properties, a nanoindentation testing technique is employed. Microstructural quantitative analyses (i.e., optical microscopy and scanning electron microscopy) were performed extensively on the as-fabricated and heat-treated samples. Artificially aged specimens showed the highest microhardness of all the heat-treated samples, followed by air-cooled and furnace-cooled samples. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study of the tensile performance, heat treatment, fracture, decrease of residual stress, second-phase particle and microstructures of a 316L stainless steel fabricated by directed laser deposition (DLD) and thermal milling (starting milling temperature at 250 ± 50 °C), a typical hybrid additive and subtractive manufacturing process. Experiments of different post-heat treatment temperatures and tensile tests at room temperature were performed. The residual stress was eliminated with heat treatment at 400 °C for 2 h, and the average residual stress decreased 53.7% while the yield strength and ultimate strength decreased slightly. The fracture surfaces of different heat treatment temperatures were observed. The typical ductile fracture microstructures of dimples were seen in almost all specimens whenever the heat treatment temperature was low or high. The evolution of dimples from formation to destruction by heat treatment was analyzed. The different morphology and composition of the second-phase particles of different heat treatment temperatures were compared. The yield strength of 427.5 MPa, the ultimate strength of 599.27 MPa, and the elongation of 36.48% showed the new hybrid manufacturing technology could be used for further fabrication of components. [ABSTRACT FROM AUTHOR]

The anisotropy of wire-arc additively deposited nickel-aluminum bronze alloy is studied by microstructure observation and room temperature mechanical property testing. The applied heat treatments have effectively modified the as-fabricated {0 1 1} <2 1 1>, {1 1 1} <1 1 0> texture into {1 1 1}. According to the microstructures, the single tempering has resulted in lowest anisotropy while heat treatment with prior homogenization and quenching process induces even intensified annealing textures. However, as shown by the tensile tests, the quenching process is necessary for favorable mechanical properties in the wire-arc additive manufacturing fabricated nickel-aluminum bronze component; therefore, a balance between homogenization annealing and κ-phase precipitation is indicated. Meanwhile, the function of κ-phase precipitates on grain rotation and growth during post-production heat treatment is explained in detail. [ABSTRACT FROM AUTHOR]