Journal of Materials Engineering and Performance最新文献

Dual-phase heterostructured metals have excellent mechanical properties. This study systematically evaluated the impact of varying Ga concentrations on the microstructural evolution and mechanical response of dual-phase heterostructured Ag-49 wt.%Cu-xGa (x = 0, 5, 7, and 10 wt.%) alloys. The study utilized scanning electron microscopy (SEM) and nanoindentation experiments to analyze the structure evolution and hardness changes in Ag-Cu-Ga alloys. The results revealed that the volume fraction of the hard domains (Cu-rich phases) and the hardness increased as the Ga content increased. This increase in Ga content led to a greater degree of mechanical incompatibility between the soft and hard domains, ultimately enhancing the mechanical properties of Ag-Cu-Ga alloys. Through the implementation of a loading–unloading–reloading (LUR) test, it was shown that the Ag-49Cu-7Ga specimens exhibited higher levels of hetero-deformation-induced (HDI) stresses compared to the Ag-49Cu specimens that did not contain Ga elements. This difference can be attributed to the solid solution strengthening effect of Ga. Through the use of digital imaging technique (DIC), it has been discovered that the introduction of Ga element into the Ag-Cu-Ga specimen results in the formation of dispersed strain bands on the surface. These strain bands effectively absorb and distribute the applied strains, resulting in the Ag-49Cu-7Ga specimen exhibiting both high strength and good plasticity.

ISO coded K06 cemented carbides are gradually becoming a commonly used tool materials for machining difficult-to-machine materials such as superalloy due to their excellent cutting performance. Researchers are exploring advanced manufacturing processes that can further enhance the performance of this material. Therefore, the cryogenic treatment of ISO coded K06 WC–Co cemented carbide was studied by uniform design experiment. The equation of the effect of cryogenic treatment on the properties of cemented carbide was fitted by multivariate quadratic nonlinear regression. The phase composition, grain size, and residual stress of the material were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicate that cryogenic treatment significantly changes the residual stress of WC grains, accompanied by a phase transition of the bonding phase (Co phase). However, cryogenic treatment has no significant effect on the grain size of the material. The wear resistance and impact toughness of cemented carbide have been significantly improved. At the same time, the wear scar and impact fracture of the material were observed, and the mechanism of impact fracture was analyzed. The residual compressive stress of the WC phase increased by about 120% and the rockwell hardness of the material increased by about 2.61% after cryogenic treatment, but the increase was insignificant. However, the wear resistance increased by about 88.89% and the impact toughness increased by about 19.30%.

In this study, the effects of deep cryogenic treatment on the microstructure and mechanical properties of 316L stainless steel fabricated by selective laser melting were investigated. Two types of samples were subjected to comparative experiments: (i) as printed (AP), and (ii) deep cryogenic treatment (DCT). Microstructural analysis revealed that DCT reduced the sample porosity from 1.05 to 0.36%. In terms of mechanical properties, the DCT samples exhibited tensile and yield strengths of 736 MPa and 541 MPa, respectively, which are significantly higher than those of conventionally cast parts. The elongation reached 59%, a crucial factor for applications requiring material flexibility. However, fatigue test results showed a reduction in the fatigue performance of DCT samples. The fatigue limit was predicted using extreme value statistical analysis and sample sectioning methods, with the prediction error within 10%. The Kitagawa–Takahashi diagram and EI-Haddad model were used to evaluate the safety performance of the material, and the critical defect sizes of the samples were determined. The prediction results were consistent with the statistical analysis of crack source defect sizes in fractured samples.

Ti₂AlNb/TiAl composite columnar specimens without defects were fabricated by using direct laser deposition (DLD) process. In this study, the microstructure and mechanical properties were comprehensively investigated. Results revealed that each deposited layer contains two microstructure bands: the equiaxed grain band and the lamellar colony band. These two bands appeared as γ/α₂ lamellar with random lath orientation under high magnification, with different lamellar spacing of 210 and 380 μm, respectively. Unmelted Ti₂AlNb particles could be found in the lamellar colony band, which could decrease the dislocation density further to increase the strength. The tensile strength at room temperature reaches 541-543 MPa, with a corresponding elongation of 0.6-0.8%, while the fracture occurs mainly in the equiaxed grain bands with a translocation fracture mechanism. Hardness tests also showed higher hardness values in the lamellar colony bands than in the equiaxial grain bands. CT characterization tests did not reveal that fracture cracks started or passed through the Ti₂AlNb grains. These results demonstrate an in-depth understanding of the microstructure and properties of Ti₂AlNb/TiAl composites prepared by DLD, and provide a pioneering reference for further investigations of the strengthening effect of Ti₂AlNb on TiAl-based alloys.

This research seeks to create tube-based aluminum foam using friction stir tube deposition (FSTD) process. In this process, AA6063 consumable rods, pre-filled with a mixture of titanium hydride and aluminum powder, are deposited into a hollow mild steel tube using a conventional vertical milling machine. The results indicate that consumable rods with 12 pre-drilled holes ensure a more uniform distribution of the foaming agent. Furthermore, the study shows that increasing the tool’s rotational speed and the weight percentage of titanium hydride results in larger pore sizes and greater porosity. Specifically, for the same TiH₂ composition and rpm levels, the 12-hole filling strategy enhances porosity by 42.62 and 10.12% compared to the 8-hole and 10-hole methods. The optimal process parameters for developing aluminum foam are identified as using consumable rods with 12 holes containing 60% TiH₂ and a rotational speed of 1400 rpm.

In this study, 12Cr12Mo martensitic stainless steel was manufactured using selective laser melting (SLM). The resulting microstructures and mechanical properties were analyzed under optimal process parameters to understand the correlation between the process, microstructure, and properties. The results showed that only a single martensitic phase is present in the SLM samples, attributed to the exceptionally rapid solidification rate and high density of dislocations. It was observed that the 12Cr12Mo microstructure consists of interspersed columnar and equiaxed grains at the microscale, while fine body-centered cubic (bcc) lath martensite with high dislocation density is observed at the submicron scale. SLM-prepared 12Cr12Mo stainless steel exhibits impressive mechanical properties due to its hierarchical microstructure. Under optimal process parameters, the fabricated samples achieved a microhardness of 544.91 HV, with yield and ultimate tensile strengths of 729 ± 24 and 842 ± 19 MPa, respectively, but elongation is limited to 7 ± 0.6%. The cellular and martensitic structures with high dislocation density along grain boundaries are the mean factor for the increased strength but reduced ductility. Observations of a disintegrated surface and river-like patterns suggest a brittle fracture mode in 12Cr12Mo stainless steel prepared by SLM.

This study aims to elucidate the influence of varying TiC particle additions on the mechanical properties of Al-10Si-3.5Cu-2.5Ni-0.3Mg alloys. The alloys were fabricated using the gravity casting technique, with TiC additions of 0, 0.5, 0.75, and 1%. Following T6 heat treatment, the microstructure, tensile strength, and fracture mechanisms of the alloys were comprehensively analyzed. The research findings indicate that the microstructure is primarily composed of α-Al, eutectic Si, Al₃Ni, Al₃CuNi, (Al, Si)₂(Zr, Ti), and (Al, Si)₃(Zr, Ti) phases. Image J quantitative analysis indicated that increasing TiC content resulted in the refinement of both the eutectic silicon and the grains. Additionally, the Al₃Ni and Al₃CuNi phases gradually became spheroidized and had a homogeneous distribution. The 350 °C tensile strength of the alloy increased from 93.7 to 137.8 Mpa with increasing TiC content, an increase of 44.1 MPa (47%). This is mainly attributed to the stability of the (Al, Si)₂(Zr, Ti) phases at high temperatures and the refinement of the grains, eutectic silicon, and intermetallic second phases.

Application of nickel-based superalloys is gradually rising in many sectors such as aerospace, automotive and marine industries due to their exceptional thermo-mechanical properties. Superalloys are predominantly fabricated by casting process. The pursuit of customized materials possessing with exceptional properties has driven the scholars to investigate the possibility of powder metallurgy for preparing them and assess their appropriateness to produce gas turbine components. This study focuses on the use of powder metallurgy approach for synthesizing Nimonic 90 superalloy. Physical properties such as density, microhardness and macrohardness are determined to validate with the standard sample. Mechanical properties like tensile strength and compressive strength are measured and analyzed. Dry sliding wear test is done to study the wear characteristics. Density and hardness of the material are close to that of standard alloy, which is due to the appropriate selection of sintering temperature and stay time. Measured values for the ultimate tensile strength, 0.2% offset yield strength and percentage of elongation are approximately 900 MPa, 386 MPa and 52%, respectively. In microscopic study, it is observed that the material has γ/γ’ phase because of precipitation hardening and solid solution strengthening. Findings establish the fundamental basis for near-net-shape manufacturing by powder metallurgy.

NiMnCrMoW_x (x = 0.2, 0.4, 0.6, 0.8, 1.0 atomic fraction) high-entropy alloys are synthesized by mechanical alloying and conventional sintering techniques. Both alloy powders and the sintered pellets are characterized for microstructural, chemical, and mechanical properties. The phase analysis by x-ray diffraction (XRD) and high-resolution transmission electron microscopy of 70 h milled powder confirmed the dual phase of BCC as a major phase and FCC as a minor phase. Scanning electron microscopy is used for microstructural study of the milled powders and sintered pellets. The differential scanning calorimetry analysis of milled powders confirmed that these are thermally stable below 1000 °C. The XRD of annealed powders didn’t show new phases below 1000 °C, whereas 1000 °C annealed powders showed the presence of σ-phase; the XRD of the sintered pellets confirmed different volume fractions of σ-phase, MoNi₃, and MnNi phase. Results of Vickers hardness and wear studies indicated that the alloy containing 0.6 atomic fraction of tungsten possessed a maximum hardness of 644 HV₅ and maximum wear resistance. This might be attributed to the maximum extent of the σ-phase, MoNi₃, and MnNi phases in the W_0.6 alloy.

Although the self-piercing riveting (SPR) process is widely used in the automotive industry, it faces challenges in achieving mechanical interlock when joining high-strength steel. In this paper, the pre-holed self-piercing riveting (PH-SPR) process is adopted to join high-strength steel to aluminum alloy. This paper aims to investigate SPR joinability and select suitable rivets and dies for different steel–aluminum combinations. A 2D axisymmetric numerical model is developed using LS-DYNA commercial software to simulate the PH-SPR process with varying process parameters (e.g., rivet hardness, geometric dimensions of rivet and die, hole size, and material and thickness of sheet). The accuracy of the FE model is verified by comparing the forming quality parameters between the experimental test and the simulation result. The results show that (i) the rivet with strength of 0.9 GPa is suitable for the bottom sheet with yield stress of 89 MPa, and the rivet with strength of 1.34 GPa is appropriate for the bottom sheet with yield stress greater than 165 MPa. (ii) The increasing rivet diameter, rivet length, and hole size can improve forming quality, and the decreasing die depth and top sheet thickness can enhance the undercut. (iii) The undercut of the joint with 1.2 mm top sheet increases with the increase in yield stress of the bottom sheet, while a decreasing tendency is found for the joint with 1.6 mm top sheet. (iv) The minimum rivet length required for a successful joining increases with the increase in thickness ratio, while the opposite trend is observed for maximum rivet length.