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Abstract Owing to the unique layer-wise production method, additive manufacturing technologies have been widely adopted in rapid prototyping and tooling areas, which often require superior mechanical properties such as tensile strength and hardness. In current literature, most mechanical property studies focusing on additive manufactured materials mainly adopt experimental or simulation-based approaches, and therefore cannot be directly used to accurately estimate and predict the achieved mechanical properties. In addition, information regarding the mechanical properties of photosensitive liquid resin used in the Stereolithography additive manufacturing process is limited. Hence, in this paper, mathematical models are established to quantify the tensile strength and hardness of Stereolithography fabricated materials by estimating the solidification levels of both green parts and Ultraviolet post-cured parts. The established degree of cure model is shown to have an average prediction accuracy of around 94%. In addition, the mechanical property models have an average accuracy of 88% and 90% for tensile strength prediction, and 98% and 95% for hardness prediction of green parts and post-cured parts, respectively. It is also observed that the Ultraviolet post-curing process has the capability of significantly enhancing the studied mechanical properties. Graphical abstract Unlabelled Image Highlights • The tensile strength and hardness of photosensitive liquid resin are modeled based on the degree of cure. • The established degree of cure model has an average of 94% prediction accuracy. • The investigated resin consists of Hexane-1, 6-diol diacrylate, Isobornyl acrylate, Acrylate monomer, etc. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Pt-15Ir-3Hf-0.5Y alloy with good high-temperature strength and ductility is prepared. • No Pt-Hf precipitates but three types of nanoclusters, clusters containing stacking fault, clusters at 1/2 〈0 1 1〉 dislocation core and clusters with short-range order are observed in the alloy matrix. • The alloy has a strong ageing strengthening effect through more and larger clusters formation. A novel ultra-high temperature Pt-15Ir-3Hf-0.5Y (wt.%) alloy was developed for the first time by high vacuum arc-melting, hot rolling and ageing treatment. The microstructures of the as-cast and hot-rolled and then post-aged samples were investigated. The alloy consists of the (Pt,Ir) 5 Y phase and matrix. Through transmission electron microscopy atomic resolution imaging, three types of nanoclusters, clusters containing stacking fault, clusters at 1/2 〈0 1 1〉 dislocation core and clusters with short-range order were observed in the matrix. The hardness at the ambient temperature of the alloy after hot rolling and ageing treatment was up to 443 HV and the tensile strength at 1500 °C was up to 47.8 MPa. Compared with the solid solution strengthened Pt-Ir binary alloys, the addition of Hf and Y can effectively improve the mechanical properties, which were achieved by introducing the combined effects of nanocluster strengthening and grain boundary strengthening of (Pt,Ir) 5 Y phase. Our findings provided new insights into designing the Pt-based superalloy with high strength and ductility. [ABSTRACT FROM AUTHOR]

A successful demonstration of applying integrated strengthening using Hall-Petch strengthening (grains size effect) and precipitation strengthening is shown in the fcc based high entropy alloy (HEA) Al 0.3 CoCrFeNi, leading to quantitative determinations of the Hall-Petch coefficients for both hardness and tensile yield strength, as well as the enhancements in the yield strength from two distinct types of ordered precipitates, L1 2 and B2. An excellent combination of yield strength (~ 490 MPa), ultimate tensile strength (~ 850 MPa), and ductility (~ 45% elongation) was achieved by optimizing and coupling both strengthening mechanisms, resulting from a refined grain size as well as both L1 2 and B2 ordered precipitates. This opens up new avenues for the future development of HEAs, with the appropriate balance of properties required for engineering applications. [ABSTRACT FROM AUTHOR]

Friction stitch welding of S355 steel was conducted under wet conditions to study the bonding quality. The effects of plug material, joint design, and welding variables on the weld defects, microstructural characteristics, hardness levels, and tensile properties were investigated. The underwater stitch welding performed with a S355 steel plug exhibited visible bonding defects at the weld interface, while the weld with LF2 as the plug material yielded a qualified joint without cracks or discontinuities, provided the plug and hole geometries were well-designed. The LF2-plug-stitch weld contained more upper bainite and fewer lath martensite grains, which was consistent with the substantially decreased hardness values in the weld metal. The joint was designed with large initial contact area and gap between the plug and hole, so a higher amount of heat was generated when welding was started. Further, the welding time was extended from 11 to 16 s, resulting in a larger heat affected zone and the flow of the plasticized (or squeezed) material was improved too. Stitch welds realized with a 40 kN forging force exhibited better ultimate tensile strength and elongation than those with a 35 kN forging force, when the other conditions were kept constant. [ABSTRACT FROM AUTHOR]

In this paper hybrid welding of the annealed AA5754 alloy was studied and the role of post weld heat treatment (PWHT) on microstructure and mechanical properties was investigated. The microstructure and hardness of the base material and welds were analyzed. Due to the segregation, the lowest microhardness value was observed at the welding centerline. High microhardness was registered in a narrow zone at the interface between the fusion zone and the heat affected zone where the welding cycle promotes both the strengthening by Mg solid solution and the lowest grain size. The hardness of the heat affected zone was higher than that of the base material due to dissolution of soluble particles (Mg 2 Si and Mg 2 Al 3 ). PWHT at 350 °C increased the microhardness in the fusion zone and the tensile strength with respect to the untreated joint, whereas the strain at fracture was similar showing that the fracture was promoted mainly by the presence of porosity, coarse grain size and insoluble segregated second phases. [ABSTRACT FROM AUTHOR]

This study systematically investigated the microstructural evolution, hot workability, and mechanical properties of the β-γ TiAl alloy Ti-43Al-2Cr-2Mn-0.2Y. The as-cast alloy had a wide hot working window and excellent hot workability. A crack-free pancake was obtained through one-step canned forging with an initial deformation condition of 1200 °C/0.1 s- 1. The coarse lamellar microstructures of the as-cast alloy were broken down into fine γ grains after forging. Residual lamellae were hardly observed even near the edge of the pancake. Dynamic recrystallization of γ grains was the main softening mechanism during hot forging. Tensile tests showed that the as-forged alloy exhibited better room temperature tensile properties than the as-cast alloy because of microstructural refinement and homogenization. The ultimate tensile strength of the as-forged alloy at 700 °C was maintained at 496 MPa, and elongation was 10%. The ductile-brittle transition temperature was between 700 and 750 °C. In addition, the nano-hardness values of the β0 and γ phases were 5.6 and 4.6 GPa, respectively. The hardness of the β0 phase was lower than that of the β0 phase in TNM alloys, indicating that the hardness of the β0 phase highly depended on alloying elements. [ABSTRACT FROM AUTHOR]

Two different microstructures, i.e., fine-grained solute depleted (FGSD) and coarse-grained solute enriched (CGSE), are prepared by thermomechanical processing. The samples are subjected to six pass equal channel angular pressing (ECAP). EBSD indicates formation of an ultrafine grained (UFG) structure within a size range of 632 nm in FGSD in comparison to 727 nm in CGSE which is attributed to more significant grain fragmentation in the FGSD sample with higher surface area of boundaries. In both as-annealed and -deformed conditions, hardness, yield strength (YS) and ultimate tensile strength (UTS) of the CGSE samples are higher than those of FGSD which is attributed to more significant solute enrichment. Elongation is found to reduce by the initial passes of ECAP and gradually improve by further processing. At a similar deformation history, the uniform elongation of the deformed CGSE samples is higher than those of the deformed FGSD samples which is attributed to more significant solute enrichment and work hardening causing a delayed necking and larger uniform elongation. However, the elongation to failure of FGSD samples after 2, 4 or 6 pass ECAP is larger than the CGSE sample with a similar deformation history which may be due to the high capacity of boundaries to accommodate dislocations and postpone fracture. [ABSTRACT FROM AUTHOR]

Highlights: [•] Development of polymer/clay nanocomposites. [•] Compatibility of ABS and montmorillonite nanoclay and composition capability of them. [•] Effect of nanoclay content and process parameters on the mechanical properties of nanocomposite. [•] Analyzing the distribution of nanoclay layers using XRD test. [•] Dependency of tensile strength and hardness to the nanoclay content and processing conditions. [Copyright &y& Elsevier]

Abstract: Polypropylene (PP) is one of the most common thermoplastic materials in the world. There is a need to recycle the large amount of this used material. To overcome the environmental problems, related to the polymer waste, PP was recycled and used as a matrix material in different composites that can be used in high value applications. In this paper, composites made of recycled polypropylene (RPP) reinforced by glass fibres and/or wood flour of the palm tree were prepared, characterized and modeled. The mechanical and thermal properties of these recycled polymer matrix composites (RPMCs) were measured experimentally and modeled theoretically. The mechanical properties included tensile modulus, tensile strength and hardness, whereas thermal properties included thermal stability, melting and crystallinity percentage content were studied. In addition we applied the functionally graded materials concept, the elastic finite element analysis of a layered functionally graded pressurized pipe, which is one of the practical industrial applications, was accomplished in order to have some insight on the performance of such RPMCs. The results reveal that the desired mechanical and thermal properties met the requirements of a wide range of practical applications which can be attained by adding the considered fillers. Also, the proper selection of the layers of the pressurized pipe, which was made of RPMCs, led to decrease of the induced stresses and accordingly increased the operational safety. [Copyright &y& Elsevier]

Highlights: [•] Specific design recommendations for bobbin friction stir welding tools. [•] Pin with four flats feature best for thin plate aluminium. [•] Shoulder gap affects hence vertical flow motion. [•] Clamped side has higher hardness and lower tensile strength. [•] Developed a conceptual model representing the underlying physics. [Copyright &y& Elsevier]

Highlights: [•] Functionally graded steel and nickel super-alloy structures have been developed. [•] Mechanical properties of FGMs can be controlled by process input parameters. [•] SDAS is strongly dependent on the laser power and powder mass flow rate. [•] Carbides provide a mechanism to control the hardness and wear resistance of FGM. [•] Tensile strength of FGM is dependent on the laser power and powder mass flow rate. [Copyright &y& Elsevier]

Highlights: [•] Microstructure and properties of the HAZ were analyzed. [•] Delta ferrite morphology changed, and ferrite content decreased. [•] Adverse effect on yield and ultimate tensile strength was negligible. [•] The absorbed energy and hardness decreases with increasing number of weld-repair. [•] The sensitivity to pitting corrosion was increased. [Copyright &y& Elsevier]

Highlights: [•] Mg effects on microstructure and mechanical properties of Al–Si–Mg were studied. [•] Three alloys with different amounts were cast, homogenized and exposed to T6. [•] Intermetallic compounds were formed on the microstructure by increasing Mg amount. [•] Hardness and tensile strength increased with increasing Mg content. [•] Elongation and density decreased with increasing Mg content. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of ESR process on microstructure of Cu–Cr–Zr alloy was investigated. [•] The hardness, strength and electrical conductivity are sensitive to thermomechanical treatment. [•] The microstructure of the alloy can be optimized for obtaining the best combination of mechanical and electrical properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] T-lap and T-butt joints were fabricated by friction stir welding. [•] Original joint line with severe deformation (OJLwSD) in T-joints was studied. [•] Hardness and microstructures in different zones of T-joints were investigated. [•] Distribution and statistic data length of OJLwSD were analyzed. [•] Relationships of welding parameters, OJLwSD and properties were studied. [ABSTRACT FROM AUTHOR]

Highlights: [•] A sound FSW joint of rolled SiCp/AA2009-T351 sheet was achieved. [•] Precipitation sequences of phases varied in different regions of the joint. [•] Coarsening of precipitates and reduction of dislocation density occurred in HAZ. [•] HAZ had the lowest hardness and strength with the fracture occurring in this zone. [•] The FSW joint exhibited a good combination of strength and ductility. [ABSTRACT FROM AUTHOR]

Abstract: A high strength Mg–8.0Zn–1.0Al–0.5Cu–0.5Mn(wt.%) magnesium alloy with outstanding ductility was developed using a common casting technique and heat treatment. The microstructure of the as-cast alloy is composed of α-Mg, MgZn, MgZnCu and Al–Mn phases. After the solution treatment and subsequent two-step aging treatment, the yield strength (YS), ultimate tensile strength (UTS) and elongation of the alloy at peak hardness reach 228MPa, 328MPa and 16.0% at room temperature, respectively. The comprehensive mechanical properties of the alloy are superior to almost all other high performance casting Mg alloys. [Copyright &y& Elsevier]

Abstract: In present paper, an attempt was made to examine the effect of different concentrations of Fe (0.5, 1, 1.5, 2 and 3wt.%) on the microstructure and tensile properties of an in situ Al–15wt.%Mg2Si metal matrix composite (MMC). The composite was made by casting process and characterized by optical microscope, scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy. The results depicted that the addition of 2wt.% Fe to the MMC changes the morphology of primary Mg2Si from irregular to polyhedral shape and reduces its average particle size from 33μm to 15μm. The microstructural studies also showed that the addition of Fe leads to the formation of Fe-rich intermetallics with polyhedral, plate-like and star-like morphology. Hardness results demonstrated that Fe addition to Al–15%Mg2Si composite has a positive effect on the hardness improvement. Further investigations on tensile tests revealed optimum Fe (1wt.%) level for improving tensile properties. In the point of fracture behavior of the composite, Fe-containing specimens showed a brittle mode of failure. [Copyright &y& Elsevier]

Abstract: Sn–0.7wt%Cu–1.0wt%Ag and Sn–0.7wt%Cu–2.0wt%Ag alloys were directionally solidified under transient conditions undergoing cooling rates varying from 0.1 to 25K/s. The microstructure was characterized along the castings lengths and the present experimental results include the secondary dendrite arm spacing (λ 2) and its correlation with: the tip cooling rate () during solidification and microhardness (HV), yield tensile strength (σ y), ultimate tensile strength (σ u) and elongation to fracture (δ). The aim is to examine the effects of Ag content and tip cooling rate on both the microstructure and mechanical properties. The initiation of tertiary branches within the dendritic arrangement, as well as the distinct morphologies of the intermetallic compounds (IMC) related to the solidification cooling rate was also assessed for both examined alloys. While the Cu6Sn5 phase appeared as large faceted crystals along the entire casting length, very fine Ag3Sn spheroids prevailed at higher cooling rates (>7.5K/s and>4.0K/s for 1.0wt%Ag and 2.0wt%Ag alloying, respectively) with a mixture of Ag3Sn coarser spheroids and fibers predominating at lower cooling rates. The Sn–0.7wt%Cu–2.0wt%Ag alloy exhibited smaller dendritic spacings and HV of about two times higher than the corresponding values of the Sn–0.7wt%Cu–1.0wt%Ag alloy. A single Hall–Petch equation is proposed relating δ to λ 2 for both alloys, which means that the increase in Ag content from 1.0 to 2.0wt% does not affect the elongation. It is shown that δ decreases with the increase in λ 2. [Copyright &y& Elsevier]

Abstract: The evolution of crystallographic texture and the mechanical properties of copper subjected to severe plastic deformation (SPD) using equal channel angular pressing (ECAP) were investigated. Samples were subjected to ECAP under two different processing routes: B 60 and BC . As the cross sections of the samples were circular, a new route with a rotation angle of 60° in the same direction between consecutive passes was introduced. The material exhibited texture development similar to the simple shear texture in both routes and the most significant changes in texture strength in both processing routes took place after the second pass. Microstructure of ECAP processed samples were investigated using electron backscatter diffraction (EBSD) analysis. Comparison of the EBSD data with optical micrograph of the initial sample confirmed that ECAP process has led to a significant decrease in grain size. Significant increases in hardness and tensile strength were observed after the first pass of ECAP. Variations of tensile strength as a function of the number of passes were related to the dislocation densities and the average boundary spacing. [Copyright &y& Elsevier]

Abstract: The effects of deep cryogenic treatment (DCT) on the static mechanical properties of the AISI 302 austenitic stainless steel were investigated through experimental testing. The results of the tensile and hardness tests are discussed and compared to data and microstructural observations from the DCT literature concerning the same class of steel. In addition, the influence of two important treatment parameters, such as the soaking-time and the minimum temperature, is analysed through a full factorial design of experiments (DOE) and by means of a first approximation model in order to obtain confirmation and suggestions about the possible use of the DCT as a standard practice to improve the mechanical properties of stainless steels. A particular focus is given to the registered changes of the elastic modulus and of the hardness as representative measures of two different deformation mechanisms. [Copyright &y& Elsevier]

Abstract: Advanced high strength steels (AHSS) are essential to meet the demands of safety and fuel efficiency in vehicles. In this paper, we present the results of laser welding of two AHSS steels, TRIP780 and DP980. A 2kW Trumpf TRUDISK 6002® Yb:YAG laser beam was utilized to join 1mm thick TRIP780 with 1.5mm thick DP980 and 1mm thick mild steel. Optical metallography was used to characterize the weld profile and microstructures. Microhardness, tensile and fatigue tests were performed to evaluate the mechanical properties. Results indicate that the laser welds exhibit excellent strength and hardness with minimal defects which are attributed to the high beam quality, disk type of laser. In addition, there is a distinct effect of pre-straining of TRIP780 steels on the energy absorption. [Copyright &y& Elsevier]

Abstract: Sintered and forged low-alloy P/M steels containing Cr, Ni and Mo were subjected to tensile, hardness and impact tests, in order to understand the influence of the alloying elements and microstructure on their mechanical properties. Elemental powders of atomized iron, graphite, chromium, nickel and molybdenum were mixed in suitable proportions using a ball mill, compacted and sintered in order to yield the following alloy compositions: Fe–0.2%C, Fe–0.2%C–1%Cr, Fe–0.2%C–1%Cr–2%Ni, Fe–0.2%C–2%Ni and Fe–0.2%C–2%Ni–1.5%Mo. Cylindrical compacts of 24mm diameter and 32mm height were prepared from the powder mixes in a 1000kN hydraulic press using suitable cylindrical die-punch combination. Sintering of the ceramic-coated cylindrical preforms was carried out at 1000±10°C in a muffle furnace for a period of 120min. Immediately after sintering, the cylindrical compacts were hot upset forged and drawn into square cross-section bars of density values to near-theoretical using a 2000kN friction screw press. The size of the bars was maintained as 10×10×110mm for preparing tensile specimen and 12×12×70mm for impact specimen. Standard tensile and impact specimens were machined off from the forged square rods. Standard procedure was followed for conducting tensile test and impact test on the forged alloys. Hardness of the hot forged alloys was also measured using Rockwell hardness tester. Microstructures of the alloys were examined for correlating with the mechanical properties. Fractographs of the fractured surfaces of the tensile specimens were obtained using a scanning electron microscope. From the present study, it is contended that the alloying elements Cr, Ni and Mo have strong influence on the tensile and impact properties of the low-alloy steels studied. Among all the five alloys considered, the steel with chromium addition has exhibited the highest tensile strength with the corresponding impact strength being the least. The same alloy has also been found to have the highest hardness value, compared to the rest of the alloys. The plain carbon steel specimens exhibit a ferrite–pearlite structure whereas carbides of Cr and Mo were observed along with ferritic and bainitic microstructure in the case of the hot forged alloys with Cr, Ni and Mo additions. [Copyright &y& Elsevier]

Abstract: Aluminum (Al) matrix composites reinforced with 0–2.0wt.% multi-wall carbon nanotubes (MWCNTs) were prepared by thorough mixing of the composite powders in a roller mill and then sintered using a spark plasma sintering (SPS) machine followed by hot extrusion. Fully dense Al–MWCNT composites were obtained. The microstructure and mechanical properties of these composites were characterized: there is a significant enhancement in the Al–MWCNT composite properties at initial loadings 0.5wt.% of MWCNTs when compared to Al samples without much increase in cost. [Copyright &y& Elsevier]