The X20Co martensitic heat-resistant steel (X20Co) has notable characteristics such as elevated high-temperature strength, as well as commendable resistance to oxidation and corrosion. The X20Co has been extensively employed as high-temperature working components of die-casting machines for Mg-alloys. Nevertheless, the prolonged exposure of die-casting machine components to high-temperature magnesium alloy liquid might result in deformation and fracture failure due to the occurrence of high-temperature creep. Therefore, it is imperative to enhance the high-temperature creep resistance of X20Co and prolong the operational lifespan of hot-work components in die-casting machinery. Rare earth (RE) elements, including Ce, are seen as potential means to improve the creep properties of X20Co. However, the effect of Ce on the microstructure and creep performance of X20Co have not been reported yet. In this study, the impact of Ce on the creep properties and microstructural characteristics of X20Co by applied stress within 100~200 MPa at 680~720^oC is investigated by means of electronic creep testing machine, scanning electron microscope (SEM), transmission electron microscope (STEM), and energy-dispersive X-ray spectroscopy (EDS). The findings indicate that the incorporation of Ce can enhance the creep resistance of X20Co. Moreover, as a subsequence of the increase of Ce concentration, there is a remarkable and substantial improvement in the creep life of X20Co. As an illustration, by the testing condition of 700^oC/150 MPa, the X20Co steel with 0.005% and 0.012%Ce (mass fraction) presents enhanced creep rupture time c.a. 33% and 103% respectively superior to that of the plain X20Co. The creep stress exponent, activation energy, and threshold stress of the plain X20Co are determined to be 5.05, 572.3 kJ/mol and 58.3 MPa, respectively. Correspondingly, those of the X20Co with 0.005% (mass fraction) Ce are 4.76, 595.0 kJ/mol and 87.8 MPa, respectively. Whereas, those of the X20Co with 0.012% (mass fraction) Ce are 4.49, 642.1 kJ/mol and 82.5 MPa, respectively. It is indicated that the creep processes of the three X20Co steels all follow the mechanism of dislocation climbing. It is a fact that the addition of Ce has not changed the creep mechanism but clearly raised the creep activation energy and threshold stress for X20Co steels. Furthermore, the microstructural evolution analysis compared before creep and after fracture reveals three distinct precipitates appear in X20Co. These precipitates are the large W-rich M₆C phases and Cr-rich M₂₃C₆ phases on grain boundaries, as well as fine V-rich MC phases within grains. It is suggested that Ce reduces the number of large-size massive M₆C phases, which significantly improves the creep properties of X20Co.

The oxidation behavior of Ni-Fe-Cr-Al alloys with Cr content of 20%Cr, 24%Cr and 28%Cr (mass percentage) respectively at 1200^oC in air for 100 h were studied by intermittent weighing method. The microstructure and phase composition of the alloys and oxide scales were also characterized. The results show that the oxidation kinetics curves of the three alloys all conform to the parabolic law. The oxidation resistance of the alloys is enhanced with the increasing Cr content. A two-layered oxide scale is formed on the surface of the three alloys after oxidation at 1200^oC for 1 h, i.e. the outer layer was composed of Cr₂O₃ and a small amount of spinel oxide NiCr₂O₄, and the inner layer was Al₂O₃ layer. After 100 h oxidation, the oxide scale still has a two-layered structure, which is slightly different from those of the 1 h oxidation, namely, the outer layer is mainly composed of mixed spinel and a small amount of Cr₂O₃, the mixed spinel is NiCr₂O₄ and NiFe₂O₄, and the inner one is continuous Al₂O₃ layer. The three Ni-Fe-Cr-Al alloys with different Cr content showed obvious internal nitriding during air oxidation. When oxidized for 1 h, the increase of Cr content presents a certain inhibitory effect on internal nitriding. With the extension of oxidation time (100 h), the nitriding depth of the three alloys is similar, and the increase of Cr content has little effect on the internal nitriding.

A high entropy alloy CoCrFeNiSi _x (x = 0.2, 0.6, 1) coating was deposited onto 40Cr steel surface by means of laser cladding technique. The phase composition, microstructure, hardness, friction and wear behavior, as well as electrochemical corrosion properties of the coating in 3.5%NaCl solution were systematically investigated with emphasis on the effect of Si element on the high entropy alloy coating. Results reveal that with the increasing in Si content, the high entropy alloy coatings experienced transformation of phase composition from single face-centered cubic structure to face-centered cubic structure with silicide σ phase and finally to face-centered cubic structure with body-centered cubic structure and σ phase. The microstructure of the coating evolves from equiaxial to columnar and dendritic morphology. The microhardness of the coating increases with the increasing Si content; when x = 1, it reaches the maximum value 498.92HV, which is about 2.52 times higher than that of the substrate, which may be due to solid solution strengthening caused by lattice distortion induced by Si addition and second-phase strengthening resulting from intermetallic compound σ phase formation within the coating matrix. Moreover, with the increasing Si content, the wear rate and average friction coefficient reduced gradually; when x = 1, the friction coefficient decreases significantly to around 0.309, indicating that the improved tribological performance mainly attributed to changes in wear mechanism from adhesive wear or delamination wear towards abrasive, so that the wear resistance is enhanced under dry sliding conditions. The corrosion resistance of alloy coatings in 3.5%NaCl solution is also improved gradually with the increasing Si content, reaching its optimum value by x = 1.

SmFeN has received a lot of attention in recent years because of its exceptional wave-absorbing characteristics. Herein, nitro-SmFeN alloy powders were prepared by gas nitriding at 550^oC for 2 h and 3 h. Then the effect of nitriding treatment on their microstructure and electromagnetic parameters (including the dielectric real part ε′, the dielectric imaginary part ε″, the permeability real part μ′ and the permeability imaginary part μ″), attenuation constants, and impedance matching, as well as the influence on wave-absorbing properties were studied in detail. The findings indicate that the N content of SmFeN alloy powders can be increased due to the nitriding treatment, as a subsequence the the nitride structure of SmFeN is changed to Fe₃N and Fe₂N, therewith its wave absorbing performance is enhanced. Following nitriding, SmFeN's reflectivity value is significantly increased (with a minimum reflection loss value of -52.49 dB). Additionally, the effective absorption bandwidth is widened and moved to a lower frequency, with a maximum value of 4.3 GHz in the 10.4~14.7 GHz frequency range. The study's findings offer a useful concept for the ensuing relevant applications.

The pack cementation aluminizing method is a common process for preparing tritium barrier coatings. A dense and continuous Fe-Al coating can be prepared on the surface of stainless steels, while the microstructure of the aluminide layer has an important effect on the barrier properties of the top Al₂O₃ film formed on the coating. Herein, Fe-Al aluminide coating was prepared on 316L stainless steel via pack cementation method with NH₄Cl as activator. The surface, cross-sectional morphology, phase composition of the Fe-Al coating was characterized by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results show that the aluminized coatings prepared at different temperatures are mainly composed of Fe₂Al₅ and FeAl₃. The thickness of the aluminized coating increases with the increase of temperature, and shows a multi-layered structure. When the aluminizing temperature is between 650^oC and 750^oC, the aluminizing coating shows a serrated structure embedded in the substrate. As the temperature increases, the serrated morphology gradually disappears and the surface quality of the aluminizing coating deteriorates; With the increasing aluminizing time, the thickness of the aluminized coating gradually increases, but does not affect its phase structure. In addition, the formation process of the aluminizing coating was analyzed in terms of the thermodynamics stabilities of its structure and conponents. The FeAl₃ phase was formed on the surface of the substrate at the initial stage of the reaction, however, the growth rate of the Fe₂Al₅ phase was much higher than that of the FeAl₃ phase, thereby, the former will inhibit the growth of the later once the former emerges at the initial stage, which led to the growth of the FeAl₃ phase was suppressed. The Fe₃Al phase begins to form only when the temperature is lower than 422^oC. On the basis of kinetics, a kinetic model of aluminizing process was established and the diffusion activation energy was calculated.

A low-density steel Fe-29.96Mn-9.56Al-1.01C was isothermal compressed in a temperature range of 850~1100^oC and strain rate range of 0.01~10 s^-1, meanwhile, the microstructure evolution and dynamic recrystallization process of the steel were studied by OM, EBSD and TEM. On this basis, the corresponding constitutive equation of the steel is constructed based on strain compensation, and the effect of Z parameter on the dynamic recrystallization of the steel was analyzed. The results show that the conditions of low temperature and high strain rate are beneficial to the formation of fine dynamic recrystallization grains, but the recrystallization is not sufficient. In comparison, the conditions of decreasing strain rate while increasing temperature are more favorable to the completion of the dynamic recrystallization process of the steel. The Z-value has an important relationship with the dynamic recrystallization of the steel, i.e. the deformation condition of high temperature and low strain rate is conducive to the recrystallization and the grain growth for the steel with low Z-value. For the steel with middle and high Z values of, the same condition may be conductive to the formation of fine dynamic recrystallization grains, the retention of the original band-structure, and thereby a low degree of recrystallization. The grain boundary orientation difference of the steel shows a bimodal structure during thermal deformation. The main dynamic recrystallization mechanism of the steel is discontinuous dynamic recrystallization. The degree of continuous dynamic recrystallization and geometric dynamic recrystallization is weak under different thermal compression conditions.

Herein, the effect of deformation rate on the residual stress distribution, carbide precipitation behavior and hardness of the cold rolled expanding deep groove ball bearing rings of GCr15 steel were studied by means of microstructure observation, residual stress and mechanical property measurements as well as finite element simulation. According to the finite element simulation with three different feed rates of 0.50, 0.70 and 0.90 mm/s respectively for the cold rolling process, it follows that the mean residual compressive stress on the outer surface of the bearing ring is -170.49 MPa when the feed rate is 0.50 mm/s, which is only 6.49% different from the experimental result of -160.10 MPa, indicating the reliability of the simulation. With the increase of feed rate, the deformation rate of the ring increases, the relative deformation between the core and the surface layer increases, and the residual stress also increases. The carbides in the inner surface layer of the ring are uniformly distributed and fine. The distribution of carbides is the densest and their average size is the smallest and their average size is the smallest in the groove. The hardness of the ring varies along the radial direction, the inner surface has greater hardness than the outer surface, and the groove position has the maximum hardness.

Transitional metal dichalcogenides (TMDs) materials have attracted great interest as a potential multifunctional material. However, the synthesis method of 1T-WS₂ is limited and complex. In this paper, 1T/2H phase WS₂ nanomaterials were prepared by a simple solvothermal method. For the first time, the content of 1T phase in WS₂ could be adjusted by controlling the ratio of WCl₆/TAA in the precursor and the reaction temperature. The effect of reaction conditions on the content of 1T phase in the product was confirmed by XRD, XPS and SEM, while the co-catalytic degradation test result confirmed that W-200 (W-12) had the best co-catalytic effect. Finally, TEM and Raman spectroscopy confirmed that W-200 had the best content of the 1T phase. By comparing the state of the material before and after the reaction, it is proved that sulfur vacancies will be generated during the use of WS₂ and it has excellent recyclability.