Nickel-based superalloys have been widely used in gas turbines, aerospace, and other fields owing to their excellent high-temperature strength and creep resistance. Advanced directional-solidification techniques allow crystals to grow along specific directions, which can eliminate most or all of the transverse grain boundaries to obtain columnar- or single-crystal superalloys, which further improve the high-temperature mechanical properties. A strong magnetic field can modify the mass-transfer behavior during solidification via magnetic-damping or thermoelectromagnetic effect without contacting the material, thus improving the microstructure and microscopic segregation. In order to further refine the microstructure of nickel-based single crystal superalloys and improve the degree of homogenization of element distribution, the influence of longitudinal static magnetic field with a magnetic field intensity (B) that ranges from 0 to 4 T on the microstructure and microsegregation of liquid-metal-cooling directionally solidified nickel-based single-crystal superalloy DD98M was investigated. OM and SEM were applied to characterize the microstructure. Microsegregation was evaluated using a microsegregation coefficient and isoconcentration contour maps based on different data collection modes embedded in EDS. The results showed that with an increase in B, the primary dendrite spacing, average size of γ/γ' eutectic organization, and size of the γ' phases decreased. Meanwhile, the γ' phase in the interdendrite became more regularized. The microstructure refinement under static magnetic fields was attributed to the decrease in ΔT' / G (ratio of the temperature difference between the nonequilibrium solid-phase line and dendrite tip to the temperature gradient based on the Kurz-Fisher model) or the increase in subcooling of the melt surrounding the dendrites due to thermoelectric-magnetic convection. The relationship between ΔT' / G and B was revealed. The reduction in the γ' phase size was caused by the increase in the nucleation rate of the γ' phase due to the introduction of magnetic free energy difference (ΔG_M) under a magnetic field. The magnetic field depressed the microsegregation of solutes, i.e., as B increased, the segregations of Al, Ta, Co, and W decreased. The effective partition coefficient (k_e) of the dendritic scale and the average effective partition coefficients of the dendritic and interdendritic areas were obtained. It was found that the decrease in macrosegregation was essentially due to the effective distribution coefficient that approached 1 that due to the magnetic field.

Titanium and its alloys are highly susceptible to surface oxidation during laser processing. To address this issue, a cathodic electric protection laser processing technique based on an inert electrolyte is proposed. Further, to investigate the effectiveness of this technique, the microscopic morphology and the O content of laser processed area were characterized using SEM and EDS under different operating currents and electrolytes. The results prove that the O content of the laser processed area can be reduced by applying the following two approaches: current competition and the enhancement of the electrolyte's inertness. For an electrolyte obtained by dissolving 0.2 mol/L KNaC₄H₄O₆ (potassium sodium tartrate) in 40%EtOH and at an operating current of 600 mA, the processed area exhibited minimal defects, such as cracks and porosity, and the O content was reduced to 4.9%. A voltmeter and a reference electrode were used to determine the working circuit volt-ampere characteristic curve and the cathodic polarization curve. The results revealed that the curves exhibit an evident linear relationship within the operating current range of 150~900 mA. Further analysis supports the relationship between the electrolyte inertness and the O content: enhancing the electrolyte's inertness reduces the supply of H₂O in the processing area, thereby preventing the reaction between H₂O and Ti through the method of reducing reactants. Consequently, the O content is reduced.

The fluidity of superalloy is an important property in the manufacture of large thin-walled and complex structure castings, but superalloys show high viscosity and a wide solidification temperature range, which may lead to serious defects, low yield, and poor performance. Therefore, the manufacturing of these castings is important to improve the fluidity by regulating the alloy composition. B and Zr, as common elements in superalloys, have important effects on solidification, microstructure, and mechanical properties. However, the effect of B and Zr on the fluidity and mechanism of superalloys remain unclear. In this study, the spiral fluidity test, high-temperature confocal laser scanning microscopy, and double-thermocouple method were used to investigate the fluidity, solidification, dendrite coherency point temperature, and stress rupture property of the IN718 superalloy with various B and Zr contents, whereas the mechanism of the effect of B and Zr on fluidity was also discussed. Results show that the combined addition of B and Zr can improve the fluidity and high-temperature stress rupture property of the IN718 superalloy. At different pouring temperatures, the fluidity of the alloy increases with the increase of B and Zr contents. The optimum fluidity is obtained with 0.0059%B and 0.042%Zr (mass fraction), respectively, which is about 90% higher than that of the original alloy and increases the stress rupture life by 77%. In the IN718 superalloy with a high content of B and Zr, the dendrite growth rate in the mushy zone is low, which reduces the dendrite coherency point temperature (T_DCP), increases the difference between liquidus temperature (T_L) and T_DCP (T_L- T_DCP), delays the dendrite coherency, and improves the melt fluidity.

Eddy current loss, which produces Joule heat and reduces transmission efficiency, is inevitable when the magnetic coupling is running. Magnetic couplings with high electrical resistivity alloys, such as titanium alloy, have been proven to be effective in suppressing the eddy currents. The Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet was a α + β titanium alloy for marine engineering with high specific strength and electrical resistivity, which was used in magnetic couplings to suppress the eddy currents. In this study, the effect of annealing temperature on the microstructure, mechanical properties, and electrical conductivity of the Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet was investigated. The results revealed that the band structure was arranged along the rolling direction (RD), and the as-rolled titanium alloy sheet showed a typical T-type texture with the c-axis of the α phase approximately parallel to the transverse direction (TD). A considerable increase in tensile strength and decrease in elongation after α ＋ β region (850-920^oC) annealing was thought to result from the strengthening of secondary α/β interfaces in the bimodal structure. Simultaneously, the α phase showed both T-type and R-type textures, which also resulted in higher yield strength along the TD of the sheet. Additionally, when the sheet suffered a β phase region annealing (950-1000^oC), the elongation immediately decreased due to the coarseness and precipitation of the secondary α and grain boundary α phases, respectively. Meanwhile, the annealed sheet showed an R-type and a new B-type texture components with basal poles rotated 20°-30° away from the normal direction (ND) toward the RD under the influence of variant selection of secondary α phase. However, the yield strength along the TD was still higher than that in the RD, indicating that the effect of texture on yield strength anisotropy was reduced. Finally, the electrical resistivity analysis of the titanium alloy sheet indicated that the electrical resistivity along the RD of the sheet was higher when the band structure was formed and the c-axis of the α phase was concentrated in the TD. However, the disappearance of the band structure and the increase in the volume fraction of the R-type texture will reduce the anisotropy of electrical resistivity.

During the friction welding process of TiAl turbine and shaft used in engines, brittle intermediate phases will be generated in the welding zone, which affects the joint performance. To reveal the formation rules of the intermediate phases in the friction-diffusion double welding zone between TiAl-based alloy and GH3039 alloy, and investigate the crystal structure and fracture properties of the intermediate phases, the joints at different stages of the double welding were obtained by interrupting welding during the welding process, respectively. The morphology and evolution law of the intermediate phases of these joints in the welding zones were analyzed using SEM; the crystal structures of the intermediate phases and the crack growth behaviors of Al-Ni-Ti ternary intermetallic compound phases were analyzed using TEM and an in situ nanomechanical testing system.Results showed that during friction welding and heat treatment, phase transformation and nucleation occurred on the welding interface and preliminarily grew up to form the following new intermediate phases: Ni₃(Al, Ti), (Ni, Cr)_SS, Al₃NiTi₂, AlNi₂Ti, and Ti₃Al. In the subsequent diffusion welding process, the pressure and high temperature promoted the formation of a stable two-phase zone between Ti₃Al and Al₃NiTi₂. The amplitude-modulated decomposition in the (Ni, Cr)_SS zone formed fcc (Ni)_SS and bcc (Cr)_SS that are staggered and distributed in a column. Dispersions of pure Ti with the α phase could hardly be found in the Al₃NiTi₂ and AlNi₂Ti phases, and the phase boundary between α-Ti and Al₃NiTi₂ was in an incoherent state. Furthermore, Al₃NiTi₂ and AlNi₂Ti exhibited hexagonal and bcc structures, respectively. During the in situ compression process, neither obvious plastic deformation nor dislocation movement was observed in the nucleation and propagation of cracks in the Al₃NiTi₂ phase. However, the lattice surface near the crack tip underwent microdeformation, and the ordered structure of atomic arrangements became disordered.

CoNiV is a novel medium-entropy alloy with excellent mechanical properties. Currently, alloying CoNiV with Al has been extensively employed to improve its mechanical strength. Unfortunately, the microstructure of CoNiV changes from a single phase to a dual phase due to the addition of Al, which considerably reduces its corrosion resistance. Therefore, developing new strategies to improve its mechanical properties is imperative. In this study, the microstructure and static tensile mechanical properties of (CoNiV)_{100 - x} B _x alloys (x = 0, 0.1, and 0.2, atomic fraction, %) are systematically investigated. The results revealed that the strength and ductility of CoNiV can be significantly improved by doping a small amount of B. With the introduction of 0.2%B, the yield strength, ultimate tensile strength, and elongation of CoNiV are improved, increasing by 12%, 10%, and 30%, respectively. The crystal structure, grain size, crystallographic orientation, and plastic deformation mechanism of CoNiV are not affected due to microalloying with B. At room temperature, (CoNiV)_99.8B_0.2 exhibits fcc structure. The plastic deformation mechanism during static tensile deformation is manifested as dislocation slip, while martensitic transformation and twin effects induced by stress are not observed. The results of the nanohardness tests indicated that doping with trace amounts of B could remarkably enhance the grain/twin boundary hardness, confirming the grain/twin boundary strengthening effect of B on CoNiV. The strengthening of grain/twin boundaries leads to increased resistance of dislocations and provides the ability to hinder crack expansion, resulting in the simultaneous enhancement of the strength and ductility of (CoNiV)_99.8B_0.2. Moreover, the B element dissolved into the matrix would serve as a pinning site for dislocation, thus contributing to the increased strength of CoNiV.

Low-carbon martensitic stainless steel 0Cr13Ni4Mo is widely used in hydraulic turbine runners, oil and gas storage, high-pressure pipes in power generation, and other fields owing to its high strength, good corrosion resistance, and good welding properties. However, to enhance its performance under different environments, there is a need to improve its strength and corrosion resistance. Previous studies have found that adding Cu to 0Cr13Ni4Mo steel enhances its strength through the formation of Cu-rich precipitation. However, the impact of Cu on the corrosion behavior of the 0Cr13Ni4Mo steel is not yet well understood. This study aims to investigate the effect of adding 3%Cu (mass fraction) on the microstructure and corrosion resistance of low-carbon martensitic stainless steel 0Cr13Ni4Mo using various techniques such as SEM, XRD, TEM, APT, and electrochemical testing. The results show that after solution treatment at 1050^oC, Cu is uniformly distributed on the lath martensite matrix. After tempering at 400^oC, Cu forms minute nanoclusters with a large number of Fe atoms segregated. On the other hand, tempering at 500^oC leads to the growth of Cu-rich precipitates with a size of 5-10 nm, where Cu atoms are mainly segregated at the core of the precipitates and are in a coherent relationship with the martensitic matrix. Carbides grow from Fe-rich nanoclusters to Cr-rich precipitates during the tempering process. The addition of 3%Cu to low-carbon martensitic stainless steel shows excellent corrosion resistance after tempering at 500^oC. This may be due to the emission of Cr atoms to the surrounding matrix during the growth of Cu-rich precipitates, which reduces the Cr-depleted zone caused by Cr-rich carbides in the matrix, thus reducing the corrosion sensitivity of 0Cr13Ni4Mo martensitic stainless steel with 3%Cu addition. These findings provide a better understanding of the role of Cu-rich precipitates on the corrosion performance of low-carbon martensitic stainless steels and provide guidance for the design of corrosion resistant steels.

Hot stamping steels (HSSs) have been widely used in automobiles, to reduce weight and improve safety due to their ultrahigh strength and ease of synthesis at high temperatures. At present, steel sheets with high strength and good ductility are needed to further reduce the weight of manufactured products. The most popular HSS grade in use at present is 22MnB5, which has an ultimate tensile strength (UTS) of 1500 MPa, but it has a ductility of less than 7%, which is quite poor. Driven by the demand for weight reduction in the automotive industries, a 2000 MPa HSS have been developed by employing a new alloying design and an ultrafast heating process. The latter has received much less attention than the former, although it demonstrates huge potential for improving mechanical properties and production efficiency of HSSs. In this study, the effect of heating processes, including conventional and flash heating, at a ramp of 150^oC/s in the temperature range of 850-950^oC before tempering at 150^oC on the microstructures and mechanical properties of a new type of 2000 MPa HSS were studied. Compared with the conventional heating at a relatively low ramp rate, the flash heating improved the strength and ductility of 2000 MPa HSS, simultaneously. Moreover, their best tensile properties were achieved after flash heating to 950^oC: UTS was 2180 MPa and total elongation was 13%, which were approximately 200 MPa and 4% higher than those obtained using conventional heating, respectively. This is because flash heating results in the formation of a more refined hierarchical martensite structure after quenching, with a higher dislocation density and a larger fraction of retained austenite (RA). RA was formed by dissolving cementite particles containing high C/Mn concentrations, which were then inherited in the formed austenite after quenching due to insufficient time for the homogenization of solute C/Mn by diffusion during the flash heating. The volume fraction of RA increased gradually with an increase in the flash heating temperature, then, more cementite particles were dissolved. This was also confirmed by kinetic simulations that reversed the austenitization on the dissolving cementite. Finally, it was proposed that flash heating technology is a promising technology for the production of ultra-strong and ductile HSS sheets.

The distribution characteristics and magnitude of energy density on the cross section of a laser beam are determined by its spatial profile, which directly impacts heat transport during laser material processing. Hence, it is essential to understand the influence of spatial profiles on heat transport during laser directed energy deposition with synchronous material delivery. Herein, a three-dimensional heat transport model that takes into account important physical events such as laser-powder-pool coupling, thermal-fluid coupling, solid-liquid phase change, and multiple heat transfer was established. The model was validated using single-track single-layer deposition experiments. The effects of four spatial laser beam profiles, including Gaussian (GP), super-Gaussian (SGP1 and SGP2), and pure flat-topped (FTP) profiles, on the heat transport and fluid flow within the molten pool were investigated. Simulated results show that peak temperatures of the molten pool decrease sequentially under GP, SGP1, SGP2 and FTP, and the temperature gradients on the solidification interface increase gradually from the top to the bottom of the molten pool. Temperature gradients on the solidification interface positively correlate with the angle between the normal direction of the solidification interface and the laser scanning direction, and negatively correlate with the distances from the beam center on the molten pool surface. Under all four spatial laser beam profiles, temperature gradients at the same positions on the solidification interface near the rear of the molten pool increase, while those at the bottom of the molten pool decrease. The molten pool exhibits an outward annular flow pattern under all four spatial laser beam profiles with fluid flows mainly driven by Marangoni shear stress. Heat transfer within the molten pool is dominated by Marangoni convection and heat conduction. Average fluid velocities within the molten pool decrease successively according to the following order: Gaussian, super-Gaussian, and pure flat-topped profiles.

The presence of a liquid phase, which provides capillary force during viscous sintering, can accelerate the evolution of sintered particles. Due to the difficulty of coupling about the Navier-Stokes equations, however, it is quite challenging to obtain simulation results that meet the laws of physics. In the present study, a phase field model of the viscous sintering process is established, and the morphology, velocity field, and pressure field evolutions of the sintered particles are analyzed. First, the Cahn-Hilliard and Navier-Stokes equations are solved using the finite difference method and the predictor-corrector method. In the finite difference method, the upwind and central difference schemes are combined. The simulation results show that under the drive of surface tension, two circular particles gradually merge into one. The velocity field is divided into a pure straining region and a rigid body motion region inside the particle; the pressure difference between the inside and outside of the particles is proportional to the curvature of the particles. Then, the contact radius and shrinkage of the two circular particles are calculated, and then a curve over time is drawn. The results show that they vary drastically at the beginning stage of evolution and satisfy the law of viscoelastic contact. In the later stage of evolution, the change becomes slower when the contact radius and shrinkage of the two circular particles are close to the values of the equilibrium state. With the increase in mobility, the evolution rate accelerates, but the morphology of the stable state is almost unchanged. The evolution of multiparticles and pores is also simulated. The results show that the pores in the viscous sintering process are initially spheroidized and then slowly disappear, resulting in densification. Under the same simulation conditions, the smaller pores evolve faster.

Exploring novel magnetic Heusler alloys is of great significance for the development of a new generation of smart sensing materials. The A₂BC type magnetic alloy, which comprises transition magnetic metal elements A and B and III-V main group element C (p-block element), has gained significant attention due to its various physical and chemical properties, including semimetallic magnetism, ferromagnetic shape memory effect, multicaloric effect, and superconductive effect. In this study, eight new A₂BTi type magnetic functional alloys, including three Co-based alloys (Co₂MnTi, Co₂FeTi, and Co₂NiTi), three Fe-based alloys (Fe₂MnTi, Fe₂CoTi, and Fe₂NiTi), and two Ni-based alloys (Ni₂FeTi and Ni₂CoTi), were investigated for their phase stability against tetragonal distortion using first-principles calculation. The underlying mechanism for the stability of the L2₁ phase was discussed. The results show that valence electron concentration and magnetism are the key parameters in determining the structural stability of L2₁ phase in A₂BTi type alloys. Co₂NiTi, Fe₂NiTi, and Ni₂CoTi alloy samples, whose L2₁ structure is an unstable phase, were prepared, and their crystal structure, phase transformation, magnetic properties, electrical resistance, and mechanical properties were investigated experimentally. The results show that at 298 K, Co₂NiTi is composed of an ordered face-centered cubic L1₂ structured matrix phase and a hexagonal Co₃Ti-type second phase, Fe₂NiTi is composed of a hexagonal Fe₂Ti-type matrix phase and a tetragonal FeNi-type second phase, and Ni₂CoTi has a single hexagonal Ni₃Ti-type structure. The fact that no compound undergoes a first-order structural phase transition may be due to the weak stabilities of their L2₁ phases. Fe₂NiTi and Ni₂CoTi have strong magnetic properties and undergo a second-order Curie magnetic transition during cooling. Fe₂NiTi has high compressive strength (1280 MPa), moderate compressive strain (5%), and large resistance (120 μΩ·cm), while Co₂NiTi and Ni₂CoTi have excellent compressive plasticity and small resistance. This phenomenon may be related to the different proportions of metallic and covalent bonding caused by the difference in valence electron concentration of the three alloys.

The Pb-Al alloy, which undergoes liquid-solid (L-S) phase separation, can potentially serve as a high-performance and low-cost anode material for hydrometallurgy and a grid material for lead-acid batteries. For this purpose, a microstructure containing uniformly dispersed micro/nano Al-rich particles in the Pb matrix is desired. However, during cooling of the Pb-Al alloy melt, Al-rich particles nucleate from the matrix melt first, grow, and migrate in the melt until they are caught by the solidification interface. Consequently, Pb-Al alloys often exhibit a solidification microstructure with coarse Al-rich particles or significant phase segregation. Recent studies have shown that the application of electric current pulses (ECPs) during solidification can effectively modify the microstructure evolution. This research aims to investigate the possibility of controlling the L-S phase separation process and microstructure of Pb-Al alloys. To achieve this, continuous solidification experiments were carried out on Pb-Al L-S phase separation alloy while subject to ECPs. A theoretical model describing the microstructure formation during the L-S phase separation process of the alloy under the effect of ECPs was proposed. The microstructure evolution was simulated according to the experimental conditions, and the effect of ECPs on the L-S phase separation process of the alloy was analyzed. It was demonstrated that ECPs can effectively reduce the energy barrier for the nucleation of Al-rich particles during the L-S phase separation process of Pb-Al alloy, enhance the particles' nucleation rate, and reduce the average radius, thereby promoting the formation of a composite containing in situ micro/nano Al-rich particles embedded in the Pb matrix. The peak current density (j_max) has two critical values (j_{\mathrm{c}\mathrm{1}} and j_{\mathrm{c}\mathrm{2}}). When j_{\mathrm{m}\mathrm{a}\mathrm{x}}\le j_{\mathrm{c}\mathrm{1}}, ECPs have a negligible effect on the nucleation behavior of Al-rich particles. When , the nucleation rate and number density of the Al-rich particles increase rapidly with increasing j_{\mathrm{m}\mathrm{a}\mathrm{x}}. When j_{\mathrm{m}\mathrm{a}\mathrm{x}}\ge j_{\mathrm{c}\mathrm{2}}, the nucleation rate and number density increase continuously with increasing j_{\mathrm{m}\mathrm{a}\mathrm{x}}, but at a lower rate. Furthermore, the electromagnetic force causes migration of the Al-rich particles toward the center of the sample, resulting in the emergence of an Al-poor layer on the surface of the sample and promoting the formation of a special composite composed of a Pb-rich shell and an in situ Al-rich particles reinforced Pb matrix core.

H13 die steel easily fails under friction and wear due to its low purity, poor homogeneity, and unreasonable matching between strength and toughness. The preparation of wear-reducing and wear-resistant coatings through extra high-speed laser cladding (EHLA) is important for the restoration and remanufacturing of metallurgical spare parts. This method provides an solution for the in-service life extension of H13 die steel. However, cracking at the EHLA interfaces induced by residual stresses due to low substrate dilution rates, remarkable cooling rates, and differences in thermal expansion between dissimilar metals acts as a limitation to the application of EHLA. This work aimed to alleviate stress mutation at the fusion interface of EHLA coatings, improve the fusibility of EHLA coatings on H13 die steel, and obtain wear-reducing and abrasion-resistant features on the surfaces of EHLA coatings. In this study, a Ti(C, B)/Ni60A composite coating was prepared with almost defect-free microstructures on an H13 die steel substrate by coupling EHLA with direct reaction synthesis to introduce an in situ exothermic reaction into EHLA cladding to achieve the above aims. The obtained material was compared with the pure Ni60A coating prepared through EHLA alone. Residual stress distribution at the fusion interface of the Ti(C, B)/Ni60A composite and Ni60A coatings was determined using the Giannakopoulos & Suresh (G&S) energy method based on nanoindentation. SEM, EDS, and EBSD were performed to investigate the microstructures, phase compositions, and characteristics of the two coatings and cladding interfaces. A focused ion beam setup was used to obtain information on the superficial wear of the two samples, and double spherical aberration TEM was conducted to analyze the superficial wear characteristics of the two coatings. The superficial wear mechanism of the Ti(C, B)/Ni60A composite coating was determined along with the changes in the surface microhardness of the two coatings.Results revealed that the Ti(C, B)/Ni60A composite coating interface was affected by the emission of approximately 670 kJ Joule heat by the in situ reaction of Ti and B₄C. The interfacial width of the coatings reached 22 μm, which was 11 times that of the Ni60A coating prepared through EHLA (2 μm). This increase effectively reduced the stress gradient in the interfacial region and alleviated the stress mismatch on both sides of the interface. However, the surface hardness of the Ti(C, B)/Ni60A composite coating was only 360-400 HV_0.2, which was less than half of that of the Ni60A coating. The wear losses of the two materials were in the same order of magnitude owing to the support provided to the Ti(C, B)/Ni60A composite coating matrix by the in situ authigenic TiCB, Ti₃B₄, and other phases. Such support reduced abrasion and conferred wear resistance. The above observation was also a result of the formation of equiaxed ultrafine grains at a depth of 180 nm below the wear surface area through the coupling of the plastic rheology-heat-force fields. This phenomenon dynamically strengthened the worn surface.

Silver (Ag)-matrix-composite electrical contact materials (ECMs) are widely used in railway, manufacturing, electric power distribution, and aerospace systems, owing to their excellent electrical and thermal conductivities and good mechanical and anti-erosion properties. In particular, they play a key role in low-voltage switches, which are vital in the global electrical economy. To date, substituting the toxic Ag/CdO ECMs has become a bottleneck in the development of low-voltage switches. Over the past decades, Ag/SnO₂, Ag/ZnO, Ag/Ni, and Ag/C have been exploited as substitutes for Ag/CdO ECMs, but their intrinsic defects make them unsuitable; therefore, there is still an urgent need to develop eco-friendly substitutes for CdO. Recently, MAX-phase materials, which combine attractively dual metal and ceramic properties, have shown potential in replacing CdO as a reinforcement for Ag-matrix composites. Moreover, arc erosion is a common cause of the premature failure of low-voltage switches in applications. To aid the further development of MAX-reinforced Ag-matrix-composite contacts, there is a need to understand the mechanism of arc erosion and degradation of the microstructural and mechanical properties of the composites. Nano-indentation is the most common and stable method of evaluating the micromechanical properties of materials. In this study, micro-/nano-indentation tests were performed along the cross-section of Ag/Ti₂SnC contacts (from the arc erosion layer to the near arc erosion layer and then to the matrix interior). The gradient variation of the microhardness, nanohardness, modulus, creep behavior, and plastic/elastic depth in different areas was analyzed and contrasted in the direction of the electrical arc erosion. The micromorphology and elemental composition were comprehensively analyzed, and the structural and compositional evolution of the Ti₂SnC reinforcement phase and Ag matrix were investigated. The relationship between the gradient structural change and micro-/nano-mechanical properties of the Ag/Ti₂SnC composites was analyzed. COMSOL simulations were employed to further demonstrate the physical characteristics of multi-field coupled erosion in the Ag/Ti₂SnC composites; based on these analyses, we propose an erosion mechanism for the composites. This study not only provides insights into the intrinsic relationship between the structure and properties of Ag/MAX composites under arc erosion but also paves the way for the future design and development of eco-friendly contact materials for low-voltage switches.

Metal matrix composites reinforced with micro-nano particles have emerged as a promising avenue for the development of advanced structural materials. Such composites can considerably enhance the strength and toughness of metals. TiAl composites with reinforced micro-nano Ti₂AlC particles exhibit excellent mechanical properties at room temperature and impressive oxidation resistance at high temperatures. However, there is limited study on the tensile behavior of micro-nano particles reinforced TiAl composites. The impact of micro-nano particles on the tensile fracture of TiAl composites at high temperatures remains largely unexplored; hence, it is crucial to investigate the high-temperature strengthening and toughening mechanisms of micro-nano Ti₂AlC particles reinforced TiAl composites. In this study, micro-nano Ti₂AlC particles reinforced TiAl composites were in situ synthesized by spark plasma sintering (SPS) at 1250-1350^oC using Ti-48Al-2Nb-2Cr prealloyed powders with addition of 0.5% graphene oxide. With increase in sintering temperature, various microstructures of Ti₂AlC/TiAl composites were observed, ranging from near fully lamellar to coarse fully lamellar. The high-temperature tensile properties of these composites with varying microstructures at 800 and 850^oC at a strain rate of 0.0001 s^-1 were systematically studied. The corresponding strengthening and toughening mechanisms were discussed based on the observed fracture morphologies. The findings revealed that the composites reinforced with micro-nano Ti₂AlC particles, especially those with near and fine fully lamellar structures, exhibited a synergy between strength and ductility at high temperatures. For instance, the fine fully lamellar Ti₂AlC/TiAl composite displayed ultimate tensile strength of 496 MPa and a fracture strain of 10.7% at 850^oC and 0.0001 s^-1. This represents a 50^oC increase in working temperature compared to that of the fully lamellar Ti-48Al-2Nb-2Cr alloy (The ultimate tensile strength and fracture strain at 800^oC and 0.0001 s^-1 were 467 MPa and 4.5%, respectively). The enhanced high-temperature properties of the Ti₂AlC/TiAl composites were primarily attributed to the micro-nano Ti₂AlC particles, which refined the lamellar colonies and hindered dislocation movement and crack propagation.