Journal of Materials Engineering and Performance最新文献

This study aims to examine the dry reciprocating wear behavior of stir–squeeze cast AA6061-B₄C composites under the synergistic effect of ex situ B₄C particles and in situ formed Al-Ti intermetallic phases due to the use of K₂TiF₆ salt as flux and Mg₂Si precipitates formed after T6 heat treatment process. The K₂TiF₆ flux content in the composites varied between 40 and 100% of a constant B₄C content (6 wt.%). The heat treatment consisted of solutionizing at 540 °C for 8 h, followed by water quenching and then artificially aging at 180 °C for 4 h. While at any applied load, the wear rate decreased with increasing ex situ B₄C particle retention, at applied loads more than 20 N, the wear performance deteriorated due to increased fracture and dislodgement of B₄C particles. In situ Al-Ti intermetallics were more effective in lowering the wear rate at high applied loads. A mechanically mixed layer (MML) consisting of self-lubricating boron oxide and boric acid was formed in composites with high B₄C particle retention, lowering the friction coefficient up to 20 N applied load. However, the friction coefficient increased at a higher applied load of 30 N due to increased peeling off the MML and three-body wear.

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.