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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]

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]

Additive manufacturing (AM) has various independent parameters that affect the mechanical properties and quality of the produced parts that are not linearly the function of each other. Process parameters in metal AM are very hard to control, analyse and optimise because they affect each other even though they can be independently changed. Changing process parameters in a wide range is not possible due to the formation of problems such as cracks, balling, unmelted powders, porosity and distortion. In this paper, a numerical model to predict the value of tensile strength of selective laser melting (SLM) Ti-6Al-4V parts and analyse the effect of process parameters on the results has been proposed. Taguchi L25 Design of Experiment (DOE) across 125 samples to create a comprehensive and general overview of influential parameters on the build process was investigated. Specifically, parameters included laser power, scan speed, hatch spacing, laser pattern angle and heat treatment (HT). To evaluate and analyse the build process according to established statistical variances, a minimum of five samples based on ASTM standard (for tensile test) were prepared. Heat treatment was added to the DOE to analyse the combined process and post-process effects. Results were compared (cross-validated) against existing values found in the literature and were found to effectively predict and explain the behaviour of tensile strength when changing process parameters. [ABSTRACT FROM AUTHOR]

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]

Explosive welding (EXW) has advantages in joining metallurgically incompatible metals due to its high quality and simple process. Successful titanium/steel clad plates fabricated by explosive welding have been extensively reported in recent years. However, no research has been reported on the fabrication of explosively welded TA2/15CrNi3MoV clad plates and the effect of subsequent heat treatment processes on the clad plates. This study aims to clarify the microstructure evolution and mechanical behavior of explosively welded TA2/15CrNi3MoV clad plates during the subsequent heat treatment process. The explosively welded TA2/15CrNi3MoV clad plates were heat-treated in the temperature range of 700–1000 °C for 30 min. The results elucidated that the heat treatment process accelerated the interdiffusion of constituent elements (e.g., Fe, Ti, and C) at the TA2/15CrNi3MoV interface, which formed FeTi, Fe2Ti, and TiC. For the samples heat-treated at 700 °C, a continuous TiC layer was generated at the TA2/15CrNi3MoV interface, which hampered the formation of FeTi and Fe2Ti. However, for the samples heat-treated at 800 °C, the continuous TiC layer was broken up, which resulted in a significant increase in the Fe-Ti layer to 1.21 μm. This microstructure evolution dramatically dropped the tensile strength to 329.2 MPa. For samples heat-treated in the temperature range of 900–1000 °C, the thickness of the brittle Fe-Ti layer dramatically increased and caused a rapid drop in tensile strength. [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]

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]

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]

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]