Intermetallics最新文献

Deep cryogenic cycle treatment (DCT) is a significant rejuvenation method, critically important for research to enhance the room-temperature plasticity and associated properties of bulk metallic glasses (BMGs). In this study, Zr₄₆Cu₄₆Al₄Ti₄ bulk metallic glass (BMG) underwent 5, 10, and 15 cycles of DCT to investigate its effects on the microstructure and mechanical properties. DCT essentially does not change the thermodynamic parameters of BMG, such as T_g, T_x, and ΔT_x. The relaxation enthalpy reaches a maximum value of 14.94 J/g after 10 cycles. The results show that enhanced, reaching three to four times that of the as-cast specimens. Conversely, after 15 cycles, the BMG transforms into a low-energy relaxation state, ultimately resulting in embrittlement. This phenomenon can be attributed to the sensitivity of Zr₄₆Cu₄₆Al₄Ti₄ BMG to the number of DCT cycles. The decrease in hardness and increase in free volume resulting from DCT lead to a decline in the wear resistance of the BMG. There may be a delicate balance between the effects of DCT on the room-temperature plasticity and wear resistance of Zr₄₆Cu₄₆Al₄Ti₄ BMG. The relationship between the mechanical properties and structural heterogeneity of the BMG after DCT is also discussed.

Ti-Zr-Pd-Pt alloys have been considered as potential candidates for high-temperature shape memory alloys (HT-SMAs). In this study, nine alloys were prepared to investigate the effect of multi-component alloying on the phase transformation and shape memory effect. The structural phase diagram of martensite in Ti–Zr–Pd–Pt quaternary alloys was firstly systematically investigated to provide insights and predictions for further research. The phase transformation is divided into three groups: typical martensitic transformation (MT) area, supercooling-controlled phase transformation area and diffusion-assisted phase transformation area. The martensite structure changes from B19 to B33 with the addition of Zr over 25 %. The contribution of Pt contents to raising the martensitic transformation temperature (MTT) became less pronounced with increasing Zr contents. As for shape recovery, over 87 % shape recovery was obtained even under 300 MPa in Ti-10Zr-Pd-Pt alloys, among which Ti-10Zr-15Pt-35Pd presents the highest recovery ratio of over 97 %.

Ta-10W alloy has the advantages of excellent high temperature strength, high ductility, good weldability and excellent corrosion resistance, and is widely used in chemical and aerospace fields. At present, the commerical tantalum-tungsten alloy products are mainly prepared by vacuum electron beam melting method, but the processing costs a lot which is attributable to its cumbersome processing process. Compared with it, although the tantalum alloy prepared by powder metallurgy is slightly less plastic, it has higher strength. In this work, Tantalum-tungsten (10 wt% W) mixed powder was used as raw material, and Ta-10W alloy was prepared by spark plasma sintering (SPS) technology, and high-performance Ta-10W alloy was prepared by changing the sintering parameters. The test results indicated that the sample had the best mechanical properties at the sintering process 2 (1900 °C, 40 MPa, 10 min). Its hardness was 434.38 HV_0.2, the yield strength of compression at room temperature was 1370 MPa, and it had a good elongation (44.8 %). Its average friction coefficient was 0.677 and abrasive wear was the dominant wear mechanism. Besides, the Ta-10W alloy prepared by SPS exhibited brittle fractures, and the presence of brittle phases, W phase, Ta₂O₅ and Ta₂C further deteriorated sintered Ta-10W's mechanical properties.

Recently, laser powder bed fusion (LPBF) has emerged as a potential technique for manipulating chemical short-range order (CSRO) in high-entropy alloys (HEAs), eliminating the need for homogenization treatment. The application of the magnetic field in LPBF has shown promise in refining the microstructure and optimizing the mechanical properties. However, the precise influence of magnetic field on the CSRO of LPBF-processed HEAs remains inadequately understood. Therefore, in this study, we investigate the impact of the static magnetic field on the CSRO of LPBF-processed HEAs. The findings reveal that the presence of the static magnetic field results in a reduction in CSRO, including the size and area fraction. This behavior can be attributed to the influence of the static magnetic field on the melt flow, which is perturbed by the electromagnetic damping effect and thermos-electromagnetic forces, thereby impeding the free diffusion of atoms and ultimately leading to a decrease in CSRO.

A novel NiAlCrFeMo high entropy superalloy was prepared using the vacuum arc melting method, followed by annealing at 800 °C, 1000 °C, and 1200 °C for 10 h. The microstructural characteristics and mechanical properties of the alloy after annealing were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Vickers hardness testing, and high-temperature tensile testing. The results indicate that the as-cast alloy consists of dendritic γ+γ′ phases and interdendritic B2-type β phase, with hemispherical α-Cr phases present within the β phase. Compared to the as-cast status, the volume fraction of the β phase in the annealed state increased from 18.52 % to 26.13 %. Notably, at 800 °C/10h, acicular γ_p’ phases precipitated within the β phase. The alloy exhibited varying degrees of improvement in both strength and ductility after annealing. The specimen annealed at 800 °C/10h showed the highest strength (σ_YS = 181.06 MPa) and good ductility (ε_EI = 12.45 %), with strength increasing by approximately 13.10 % compared to the as-cast status. This improvement is attributed to the coarsening of the α-Cr phase, the transformation in γ′ morphology, and the precipitation of acicular γ_p’ phase. At 1200 °C/10h, all precipitates dissolved into the matrix, resulting in the lowest strength (σ_YS = 134.08 MPa) and the highest ductility (ε_EI = 15.54 %).

The FeCoNiCr and FeCoNiCrW high-entropy alloy coatings, comprising a single solid solution, were successfully obtained by electro-deposition. The microstructure, microhardness, wear properties and corrosion behaviors of both coatings were investigated. The results revealed that both coatings consisted of amorphous phases and the component elements existed as metals and their oxides. Compared with the FeCoNiCr coating, the FeCoNiCrW coating exhibited superior mechanical properties attributed to solution strengthening. Specifically, the microhardness of the FeCoNiCrW coating was 35.9 % higher, and the width of the worn tracks was 8.3 % smaller than those of the FeCoNiCr coating. However, the FeCoNiCrW coating showed more serious adhesive wear than that of FeCoNiCr coating due to its thinner coating which was worn out during wear. The FeCoNiCrW coating has the highest corrosion resistance and the lowest corrosion rate compared to 304 stainless steel and FeCoNiCr coating in 3.5 % NaCl solution, attributed to the formation of a highly stable and resistant passive film.

To regulate the microstructure of directionally solidified TiAl alloy and improve its service temperature and high-temperature mechanical properties, the large-size single crystal Ti-44.5Al-3Nb-0.6Si-0.2C alloy with full lamellar structure prepared by electromagnetic confinement directional solidification was heat-treated in the α single-phase region. The results show that this alloy has high stability and no recrystallization occurs at 1340 °C for 30 min. The (α₂+γ) lamellar structure formed during the subsequent cooling process is consistent with the orientation of the original as-cast state, and the refinement effect is very significant. The thickness of the α₂ and the γ phases is 1/3 and 1/10 of the original structure, respectively. The dislocation strengthening and the interface strengthening are enhanced with the increase of the dislocation density and the number of α₂/γ phase boundaries in the refined lamellar structure after heat treatment, thus resulting in a substantial increase of compressive strength at 1000 °C. The corresponding compressive peak strength at 1000 °C is 2.6 times higher than that of the as-cast alloy, reaching 709 MPa. This exceeds almost all the TiAl alloys under the same conditions reported so far. This research is expected to increase the service temperature of TiAl alloy to 1000 °C, thereby replacing more Ni-based superalloy components and promoting the lightweight development of aero engines.

Complex alloy systems exhibit some unique properties, many of which are attributed to ordering phenomena. At the atomic scale, this phenomenon refers to the occupancy probability of particles at the lattice sites. From the perspective of symmetry, it corresponds to different space groups. This study uses several machine learning algorithms to predict some common space groups of complex alloy systems. Under a large data set and a difficult classification task, the relevant models achieved excellent results on the test set. In the traditional support vector machine algorithm model, the prediction can reach the first-class level. Further, through the Product-based Neural Networks method under the wide and deep framework, the bottleneck of the traditional algorithm is broken through, and the prediction ability of the model is further improved. The average Area under curve value of the model can reach 99 %, and the prediction ability of multiple space groups has been improved. This study can not only provide more ideas for cross-scale modeling of complex systems, but the related models can also provide guidance for specific alloy design.

In this research, CoMoMnNiV high entropy alloys were successfully prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructure, phases and magnetic properties of the as-milled powders and bulk sample were examined, employing X-ray diffraction, differential scanning calorimeter (DSC), scanning electron microscopy, and Vibrating Sample Magnetometer (VSM) techniques. The resultant phase following MA exhibits a dual-phase microstructure comprising BCC and FCC solid solutions, with individual crystal dimensions below 18 nm. Thermal stability assessment via DSC reveals the alloy robustness up to 1216 °C. The SPS was performed on the MA samples at 980 °C and 50 MPa pressure, and their density was determined to be 89.64 %. The sample subjected to a milling duration of 40 h demonstrated a saturation magnetization of 25.977 electromagnetic units per gram (emu/g) and a coercivity of 371.5 Oersteds (Oe).

In this paper, partial replacement of Ni for Co was adopted in FCC + BCC heterostructure as-cast CrFeNi_1-xCo_xAl_0.28Si_0.09Ti_0.02Cu_0.01 high entropy alloys (HEAs), and the modification in microstructure and mechanical properties of these alloys with the increase in the Co/Ni ratio has been systematically investigated. It was observed that all these designed HEAs consist of FCC sideplates with a surrounding BCC phase, as well as well-dispersed B2 phase in as-cast state. Additionally, higher Co/Ni ratio leads to a larger proportion of BCC phase, which has following impacts on the mechanical properties of this series of HEAs: when such ratio begins to increase, it has obvious enhancement in strength and gradual decrease in plasticity; when it reaches 0.15/0.85, it has high strength of ∼1.4 GPa and good plasticity of >10 %. While further enhancing Co/Ni ratio leads to significant connection of BCC phase, resulting in drastic increase in brittleness. The detailed mechanism for such phenomenon has been discussed in detail. This study provides a novel route on improving the comprehensive mechanical properties of this series of as-cast HEAs.