To enhance the surface wear resistance of aluminum alloy,TiC/WC ceramic-reinforced coatings were fabricated in situ on a 7075 aluminum alloy substrate via laser melt injection.The microstructures and mechanical properties of the coatings with varying numbers of laser remelting cycles were investigated using metallographic microscope(OM),field emission scanning electron microscope(FESEM),X-ray diffractometer(XRD),Vickers hardness tester,nanoindenter,and ball-on-disk tribometer.The results indicate that in the TiC-reinforced coating,a small portion of the remelted TiC particles adhere to the surface,while the majority sediment at the bottom,leaving the intermediate region devoid of TiC.The grains of the TiC coating coarsen after remelting,exhibiting a columnar morphology.In contrast,the WC-reinforced coating shows nearly complete aggregation of the remelted WC particles at the bottom,forming a distinct ceramic layer.With increasing remelting cycles,the grain size of the WC coating decreases.However,after five remelting cycles,cracking of WC particles results in visible cracks within the coating.Both types of coatings exhibit significantly lower hardness compared to the aluminum alloy substrate,with a general decreasing trend as the number of remelting cycles increases.Similarly,the fracture toughness of both coatings decreases with additional remelting.In terms of wear resistance,both coatings demonstrate lower wear rates than the substrate,with the TiC coating showing a notably lower wear rate than the WC coating.As the number of remelting cycles increases,the wear rates of both coatings rise.Therefore,increasing the number of laser remelting cycles adversely affects key mechanical properties,namely hardness,fracture toughness,and wear resistance,in TiC/WC ceramic-reinforced coatings,thereby compromising the overall performance of the coatings.This study achievement can provide a reference for improving the wear resistance of aluminum alloy surface.

Niobium alloy is widely used in aerospace and nuclear industry because of its high melting point,excellent high-temperature performance and low density.For the production of complex-shaped or thinwalled components in these applications,additive manufacturing technology has obvious advantages.In this paper,the spheroidization process and mechanism of spherical niobium alloy powder for additive manufacturing were analyzed through theoretical calculations.And the influences of particle size and atmosphere temperature on the spheroidization process were obtained.The results show that the heating and melting process of the particles during spheroidization takes much longer than the droplet spheroidization process,making it the limiting step in the spheroidization process.Increasing the atmosphere temperature and reducing the particle size are both beneficial for spheroidization of particles.Subsequently,using Nb521 alloy powder as the raw material,the effects of spheroidization power and carrier gas flow rate on the powder spheroidization rate were further investigated through high-frequency induction plasma spheroidization experiments.The results indicate that both increasing the spheroidization power and decreasing the carrier gas flow rate improve the powder spheroidization rate,and the spheroidization rate exceeds 95% when the spheroidization power is 80 kW and the carrier gas flow rate is 5 L/min.

To regulate the microstructure of the boundary region of the melt-spun ribbons in hot-deformed Nd-Fe-B magnets,ultrasonic vibration was applied during the hot deformation process of the Nd-Fe-B magnets.The microstructure of the melt-spun ribbon boundary region in the hot-pressed precursor was studied.The effects of conventional hot deformation and ultrasonic hot deformation on the distribution of the Nd-rich phase and the grain size in the melt-spun ribbon boundary region of Nd-Fe-B magnets were investigated,and the morphological evolution laws of the melt-spun ribbon boundary region were summarized.The results show that the microstructure of conventional hot-deformed Nd-Fe-B magnets retains the quasiperiodic distribution characteristics of the hot-pressed precursor's microstructure,with the continuously distributed strip-like Nd-rich phase at the periodic interface being wider.However,in the melt-spun ribbon boundary region in ultrasonic hot-deformed Nd-Fe-B magnets,the strip-like distribution of the Nd-rich phase is weakened.Instead,the Nd-rich phase gradually disperses and spreads toward the interior of the melt-spun ribbons,tending to distribute around the internal grains,which is conducive to improving the intergranular exchange coupling.In addition,compared with conventional hot-deformed Nd-Fe-B magnets,the grains in the coarse-grained region of the melt-spun ribbon boundary region in ultrasonic hot-deformed magnets are refined to a certain extent:the average grain size decreases from 2.17μm(conventional hot deformation)to 1.96μm(ultrasonic hot deformation),with a reduction of approximately 9.6%.

Sintered NdFeB,as a key rare earth permanent magnetic material,has been widely used in many fields such as aerospace,new energy vehicles and so on.However,its toughness is not good,and this defect has an adverse effect on the machining performance.In order to improve the processing properties of the material,the influence of powder particle size on the mechanical properties and magnetic properties of Nd-FeB magnet with a composition of Re_30.5B_0.9Fe_balM_1.1was studied in this paper.The experimental results show that after increasing the particle size of NdFeB powders,the average bending strength of the magnet decreases,but the fracture toughness is improved.When the particle size of NdFeB powders increases from 2.97μm to 3.37μm,the average grain size of the magnet increases from 4.206μm to 6.382μm.The fracture toughness of the magnet increases by 22.1%from 2.94 MPa·m^1/2to 3.59 MPa·m^1/2.The average bending strength of the magnet decreases by 15.4%from 367.39 MPa to 310.83 MPa.The powder particle size has no obvious influence on the residual magnetism of the magnet,but the coercive force decreases as the powder particle size increases.

Titanium-bearing blast furnace slag-based porous ceramics were prepared with titanium-bearing blast furnace slag as the raw material,borax as the flux and stearic acid as the porogen by mixing,molding and sintering.The effects of borax and stearic acid addition on the microstructure and properties of the prepared porous ceramics were studied,respectively.The results show that the main phases of porous ceramics prepared by adding borax and stearic acid are perovskite,clinopyroxene,calcium borate,and sodium titanium silicate.Varying the addition amounts of borax and stearic acid does not change the phase composition of porous ceramics.With the increase of borax addition,there is no significant change in the total porosity of the prepared porous ceramics,but their closed porosity and compressive strength increase,and their thermal conductivity decreases.With the increase of stearic acid addition,the total porosity of porous ceramics increases,while their density,compressive strength and thermal conductivity decrease.The prepared porous ceramics with the addition of 9%borax and 40%stearic acid exhibit excellent overall properties:a total porosity of 75.03%,a density of 0.85 g/cm³,a compressive strength of 2.29 MPa,and a thermal conductivity of 0.25 W/(m·K).

The creep behavior of refractory high-entropy alloys(RHEAs)during service significantly limits their engineering applications.To address this issue,the effects of varying Al content on the microstructure and creep properties of(Ti_39.5Zr_39.5Nb_9.7Ta_4.3Mo₇)_100-xAl_x(x=0,5,10,15,20,molar fraction,%)RHEAs were investigated.The results indicate that the alloy exhibits a single BCC phase at low Al content,while B2 and Al₃Zr phases precipitate at high Al content,with partial solid solution of Al into the BCC matrix causing lattice contraction.The Al addition enhances nanohardness of the alloy,and the nanohardness of the alloy with 20%Al addition reaches 6.85 GPa under a peak load of 50 mN.Furthermore,Al addition reduces the total creep displacement of the alloy.The alloy with higher Al content exhibits a lower strain rate sensitivity exponent and superior creep resistance.This study provides a theoretical basis for optimizing the composition and enhancing the creep properties of refractory high-entropy alloys.

Beryllium-aluminum alloy was fabricated using selective laser melting(SLM)technology,and then the alloy was subjected to hot isostatic pressing(HIP)at 700℃or HIP at 700℃followed by annealing at 500℃for 12 h.The microstructure of SLM beryllium-aluminum alloy in both deposited and heattreated states was analyzed using FESEM,EDS,and EBSD methods,and their hardness was also tested.The deformation and fracture behaviors of HIP-treated SLM beryllium-aluminum alloy were studied using FESEM and in-situ tensile stage.Microstructural analysis reveals that the as-deposited microstructure of SLM beryllium-aluminum alloy consists of a small amount of stable beryllium/aluminum crystalline structure,microcrystalline structure,and a large amount of metastable structure.Severe lattice distortion and metastable structure collectively result in large residual internal stress in the material.After HIP treatment of SLM beryllium-aluminum alloy,the beryllium and aluminum phases in the as-deposited microstructure are fully diffused,and the metastable structure is transformed into a stable structure.EBSD orientation analysis shows that the grain orientation distribution of beryllium and aluminum phases in the alloy after HIP treatment is random,and the material properties tend to be isotropic.After the SLM beryllium-aluminum alloy is subjected to HIP treatment,subsequent annealing treatment has no significant improvement effect on the alloy microstructure.The hardness of both heat-treated alloys decreases from 258 HV(asdeposited state)to about 200 HV.In-situ tensile test results indicate that the SLM beryllium-aluminum alloy after HIP treatment has high strength but poor plasticity.The generation and propagation time of the main crack during tensile is very short.Before fracture,the aluminum phase activates slip deformation along a specific slip system with coarse aluminum phases showing relatively noticeable deformation,while the beryllium phase barely parti-cipates in the deformation.In the late stage of deformation,the main crack likely first initiates at the phase boundary and then propagates through the interior of the beryllium phase to grow.The crack expands ra-pidly and leads to instantaneous unstable fracture.The fracture mode is a mixed fracture of interphase fracture and transgranular fracture,with transgranular fracture in the beryllium phase being the dominant mechanism.

Cemented carbide tools are widely used in machinery manufacturing and other fields due to their excellent hardness,strength,corrosion resistance,wear resistance and impact resistance.However,as the industrial demand for high quality components increases,the output of waste cemented carbide tools has gradually increased,causing serious pollution to the environment.Therefore,researching regenerated cemented carbide and improving the properties of the carbide through applying coating with excellent performance are of great significance.A TiN/MT-TiCN/Al₂O₃/TiN composite coating was applied to a regenerated cemented carbide by chemical vapor deposition(CVD)in this paper.In the process of coating production,it was found that the phenomenon of coating failure existed in regenerated cemented carbide substrate.XRD,SEM and EDS were employed in researching the phase composition and microstructure of the coating to explore the failure reasons.The results show that the holes on the surface of regenerated cemented carbide substrate and the diffusion of impurity elements are the main factors affecting the growth of the coating.The holes on the substrate surface caused by the detachment of fine-grained binder phase after sandblasting treatment will affect the growth and quality of the coating.Impurity elements can lead to slow growth and coarsening of the coating microstructure during the deposition process.Among them,the α-Al₂O₃coating has a growth pause phenomenon,which leads to coating failure,whileκ-Al₂O₃can grow normally.This study provides reference for optimizing the CVD coating of regenerated cemented carbide.

WC-10Co4Cr coatings were prepared on the surface of 45 steel by highvelocity oxygen-fuel spraying technology at different kerosene flow rates(22.0 L/h,22.8 L/h and 23.6 L/h).The effects of kerosene flow rate on the microstructure,mechanical properties(hardness and fracture toughness),friction and wear resistance and electrochemical corrosion resistance were studied.The results indicate that as kerosene flow rate increases,porosity of the coating cross-section decreases at first and then increases,the microhardness of coatings rises and the fracture toughness sinks.After friction and wear tests with a load of 1100 N,both the width and depth of wear scars on the coating surface obviously decrease with increasing kerosene flow rate.When kerosene flow rate is 23.6 L/h,the oxidation degree of wear scars on the coating surface is relatively high and the friction and wear resistance is relatively excellent.The wear mechanism for the three coatings is abrasive wear.As the kerosene flow rate increases,the electrochemical corrosion resistance of the coating ascends at first and then descends.When the kerosene flow rate is 22.8 L/h,the coating exhibits the best electrochemical corrosion resistance.

The low intrinsic electronic conductivity of Na₃V₂(PO₄)₃(NVP)leads to poor rate performance and significant capacity decay during electrochemical reactions.Therefore,in this study a high-entropy doping strategy is adopted by introducing five trace metal ions into the V-site of NVP to design a high-performance sodium-ion battery cathode material,Na₃V_1.9(MnCrCaMgAl)_0.02(PO₄)₃/C(HE-NVP/C)composite,which was synthesized using an improved sol-gel combustion method.The structure of the material was characterized by X-ray diffractometer,specific surface area and porosity analyzer,scanning electron microscope and transmission electron microscope,and its electrochemical performance was evaluated by battery test system and electrochemical workstation.The results show that the synthesized HE-NVP/C composite is composed of micron-sized blocky particles with mesoporous structure and uniform coating of amorphous carbon layer.High-entropy micro-doping preserves the rhombohedral lattice structure of NVP,and the unit cell volume is almost unchanged due to the synergistic effect of five doping elements.High-entropy micro-doping can significantly increase the porous structure of the NVP/C electrode material,thereby shortening the transport path of sodium ions,increasing the specific surface area of the electrode material,and providing more electrochemical active sites,which collectively improve the sodium storage performance.The electrochemical reversibility,electronic conductivity and sodium-ion diffusion rate of HE-NVP/C sample are higher than those of NVP/C.Consequently,HE-NVP/C exhibits excellent rate capability and cycling performance.As the rate increases from 0.2 C to 10 C,the average discharge specific capacity of the HE-NVP/C sample decreases from 113.08 mA·h/g to 103.60 mA·h/g.When the rate is returned to 0.2 C,the capacity recovers 112.02 mA·h/g.At a rate of 1 C,the initial discharge specific capacity of the HE-NVP/C sample is 108.16 mA·h/g and the capacity retention rate is 93.39%after 100 cycles.At a rate of 10 C,the HE-NVP/C sample exhibits an initial discharge specific capacity of 102.16 mA·h/g and maintains a capacity retention of 70.58% after 500 cycles.