Intermetallics最新文献

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.

We measured the shear viscosity of 14 metallic glasses (MGs) differing with their mixing entropy ΔS_mix. It is found that the viscosity at the glass transition temperature T_g significantly increases with ΔS_mix. Using calorimetric data, we calculated the excess entropy ΔS of all MGs with respect to their maternal crystalline states as a function of temperature. It is shown that the excess entropy ΔS both at room temperature and at T_g decreases with ΔS_mix. It is concluded that glasses with ‘high mixing entropy’ ΔS_mix correspond to MGs with low excess entropy ΔS. The origin of the increased shear viscosity at T_g of glasses with high ΔS_mix is determined by their reduced excess entropy ΔS.

The γ′-strengthened NiCoCr-based superalloys are extensively used in aerospace, energy, and chemical industries. This work focuses on tensile properties and evolution of deformation mechanism in a newly developed NiCoCr-based superalloy, designated K439B, at temperatures ranging from 25 °C to 1000 °C. The results demonstrate that the deformation mechanisms of this alloy are temperature-dependent. Slip bands and strongly-coupled dislocation pairs shear γ′ precipitates at 25 °C, resulting in high yield strength and work hardening rate. At 600 °C and 700 °C, the Lomer-Cottrell (L-C) locks are observed, and stacking faults shearing γ′ precipitates become the primary deformation mechanism. At temperatures reaching 800 °C, the yield strength exhibits an anomalous increase originating from the formation of Kear-Wilsdorf (K-W) locks. When the temperature exceeds 800 °C, the primary deformation mechanism is transformed into dislocations bypassing γ′ through the Orowan mechanism. The present study elucidates the deformation mechanism of this novel designed superalloy, thereby furnishing a theoretical foundation for the further development of the alloy system.

A new rare earth-free low-alloyed Mg-0.5Bi-0.8Ca-0.8Mn (wt.%) alloy was prepared at three extrusion temperatures (225, 250 and 275 °C). The effects of low-temperature extrusion on the microstructure and mechanical properties of the alloy were studied. Experimental results show that the dynamic recrystallization (DRX) grains are significantly refined by low-temperature extrusion, and the dynamic recrystallization process is further delayed by the Mn precipitate phase, resulting in a bimodal structure composed of ultrafine DRXed grains and coarse undynamic recrystallized (unDRXed) regions. At an extrusion temperature of 225 °C, the grain size was significantly refined, with an average DRXed grain size of 0.84 μm and a tensile yield strength of 418 MPa. Compared with other extruded magnesium alloys, the ultra-fine DRXed grains, strong basal fiber texture, high Schmid Factors of pyramidal <c + a> slip in the unDRXed regions, and along with a certain amount of second phase (Mg₂Ca) distributed along the grain boundaries and nano-Mn particles uniformly distributed in the matrix, are the main reasons for the strength enhancement of low-temperature extruded magnesium alloys. The orientation of the DRXed grains in the alloy after extrusion at 250 °C is more random, which improves ductility. In addition, when the extrusion temperature reaches 275 °C, the alloy shows a fully recrystallized structure and exhibits rare earth (RE)-texture, obtaining high ductility but decreasing strength. This study provides a new idea for the development of high-strength Mg-Bi-based magnesium alloys by adjusting the extrusion temperature and alloying elements. This new high-strength and low-alloyed Mg-Bi-based alloy will help to enrich the series of high-performance, rare-earth free, low-cost extruded Mg alloy with certain application prospects.

The search for new high-entropy alloys (HEAs) with desired properties is an urgent problem that is hardly solvable experimentally due to the extremely large number of possible alloy compositions. Thus, methods for theoretical prediction of HEA's properties play a key role. Currently, effective predictive models are based on machine learning methods and modern data analysis algorithms. Here we address developing data-driven machine learning models (DDML) to predict the ductility of HEAs. We have built several DDMLs and found that the best approach is based on the Support Vector Classifier, which significantly outperforms phenomenological models (balanced accuracy of 0.784 and F-score of 0.824). By combining this model with a previously developed yield strength prediction model, we have predicted and fabricated novel HEAs of the Al-Cr-Nb-Ti-V-Zr system with good mechanical properties. An obtained Al₁Cr₉Nb₃₅Ti₅V₄₀Zr₁₀ alloy demonstrates a combination of high strength at room and elevated temperature, combined with good ductility at room temperature.

Al₂O₃/Fe-Al coatings are favored for their excellent comprehensive properties in nuclear fusion power applications. A critical step in fabricating Al₂O₃/Fe-Al tritium-resistant coatings via “aluminizing + oxidation” method is the formation of Fe-Al intermetallic layer on the substrate surface at high temperatures. The present work aims to investigate the influence of chromium (Cr), a prevalent alloying element in Fe-base alloys (such as austenitic stainless steels, RAFM steels) used in fusion reactors, on the formation of Fe-Al intermetallic layers. The Fe-Al phase composition and microstructure of Fe-Cr alloys with different Cr content (0, 9, 19 wt%) were investigated by combinations of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that Cr significantly influences the phase structure and microstructure of Fe-Al intermetallic layers, despite minimal effects on its overall thickness. Cr exists in the form of Cr-rich second phase in Fe₂Al₅, which reduces the transformation rate of an aluminum-rich phase to an iron-rich phase, and also delays the generation of zigzag- or tongue-shaped structure between the intermetallic layer and the substrate, resulting in the formation of a smooth interface.