Study On Prepartion?microstructure And Properties Of NbMoTaW/Ni Composites

Metal matrix composites have attracted wide attention due to their convenience and simplicity in preparation and excellent comprehensive mechanical properties.Ceramic or amorphous phase is the most common reinforcing phase in the previous research,but the thermal expansion coefficient of ceramic reinforcing phase is quite different from that of metal matrix,and amorphous tends to crystallize under high temperature or large deformation,which significantly reduces the reinforcing effect of metal matrix composites.In this paper,based on the preliminary study of Al Co Cr Fe Ni reinforced Al or Cu matrix composites by the research group,it is found that this kind of high-entropy alloy is easy to diffuse with the matrix at a high temperature,leading to the transformation of some high-entropy alloys of BCC structure into FCC structure due to element diffusion,which affects the mechanical properties of the composites.NbMoTaW refractory high-entropy alloy has excellent high temperature mechanical properties,high temperature oxidation resistance,good wear resistance,corrosion resistance and many other advantages.If it is used as the reinforcing phase of Ni matrix composites,the properties of the composites are expected to be improved greatly.In this paper,NbMoTaW high-entropy alloy powders were prepared by mechanical alloying,and NbMoTaW/Ni composites were prepared by Spark plasma sintering.The X-ray diffraction was used to calibrate its phase composition,its microstructure was characterized and analyzed by scanning electron microscope and energy dispersive spectrometer,and its mechanical properties were evaluated by vickers microhardness tester and universal testing machine.The following research results were obtained:The optimal process for preparing NbMoTaW high-entropy alloy powder obtained by mechanical alloying.The ball-to-powder ratio is 10:1,ball grinding time is 50 h with the speed of 350r/min.The protective atmosphere is argon and N-heptane is the process control agent.NbMoTaW high-entropy alloy powder is prepared successfully and its structure is single BCC,with average particle size about 600 nm.The grain size and the lattice distortion rate of NbMoTaW powder are 8.75 nm and 1.14%,respectively.NbMoTaW high-entropy alloy reinforced Ni matrix composites were prepared by Spark plasma sintering.The composites' diagram is composed of the reinforced phase high-entropy alloy with small particle size,which wraps the nickel matrix with large particle size and presents a grid shape.Phase diffraction peaks only exist Ni element diffraction peaks.When the volume fraction of the NbMoTaW increased from 20vol% to 30vol%,at room temperature,thecompressive yield strength of the composites increased from 490.9MPa to 958.6MPa,while the compressive strength also increased to 1739.8MPa.However,the plastic strain decreased from42.68% to 25.86%.When the sintering temperature increases,all the compressive yield strength,compressive strength and plastic strain of the composites can be improved.The density and hardness change rule is consistent with the strength.The high temperature mechanical properties of NbMoTaW/Ni composites were explored by means of high temperature compression test.It turns out,at 600? test temperature,for the composites with 30vol% volume fraction and 1200? sintering temperature,the yield strength and compressive strength reached 678.66 MPa and 1165.29 MPa,respectively.The cracks and defects of composites increase with the increase of compression temperature,resulting in a slight decrease in compression yield strength and compressive strength,and a significant increase in plastic stress.There is no obvious change of composites' phase and composition before and after high temperature compression.