Preparation, Microstructure And Properties Of NiAl Composites

As a potential substitute for the new generation of aero engine vanes,NiAl exhibits good properties in terms of density,high temperature oxidation resistance and high melting point,but its practical application was severely limited by low room temperature ductility and high temperature strength.In this paper,NiAl-6.5wt.%Fe-0.3wt.%Y₂O₃ composite was designed.NiAl composites were prepared by gas atomized NiAl alloy powder and elemental Fe powder and Y₂O₃ powder by mechanical ball milling and SPS sintering.The sintering temperatures were set as 1000,1050,1100,1150,1200 and 1250°C,respectively.The effect of SPS sintering temperatures on microstructure and mechanical properties of NiAl composites were studied.The experimental results show that the powders after mechanical ball milling were severely broken and the average grain size is decreased.Fe is still present in the composite powder.The powders were sintered into bulk composites using different SPS sintering temperatures.The diffraction peaks of element Fe disappear around 1100°Cs,and the diffraction peak intensity of NiAl increases obviously with the increase in sintering temperature.Under the sintering condition of 1100°C,the TEM results showed that a solid solution with BCC structure was formed between the phase interfaces.The relative density and hardness first increase and then decrease.The best compression performance is obtained at 1200°C.The composites under the conditions have the best compressive strength and strain,which is 1846 MPa and 28%,respectively;according to the effect of sintering temperature on the microstructure and properties,it is determined that 1200°C is a suitable sintering temperature.CrMnFeCoNi high-entropy alloy with good ductility and high temperature stability was selected as the reinforcing phase.The effects of different enhanced phase contents of the microstructure and properties of NiAl/HEA composites were studied.The NiAl alloy powders and the high-entropy alloy powders were mixed in a certain ratio by ball milling,and the composite powder were sintered at 1200°C into a bulk composite.Microstructure analysis showed that the high-entropy alloy phases were uniformly distributed among the NiAl matrix,but non-uniform diffusion of elements occurred during the high-temperature sintering.The results of TEM showed that the grain size of the composite was decreased after the addition of the reinforcing phase.In addition,a large amount of nano-Al₂O₃particles are formed into the grain boundaries;the density and hardness have a consistent change trend,and both increases.After the addition of the CrMnFeCoNi high-entropy alloy reinforcement phase,the compression properties of the NiAl/HEA composites changed significantly.The experimental results show that the composite with 10wt.%HEA reinforcing phase has good room temperature compression performance,and the yield strength increases from 749 MPa to 1347 MPa compared with NiAl alloy（0wt.%HEA）.The compressive strength increased from 2121 MPa to 2692 MPa,and the compressive strain was 34.5%and 34.2%,respectively.The main fracture mechanism of the composite was cleavage fracture.The friction and wear test results show that the friction coefficient and wear losses of the composites are obviously increased after adding the high-entropy alloy reinforcement phase.The room temperature wear resistance is decreased.On the one hand,the oxide film area of the composite is reduced,resulting in a decrease in the lubricating effect of oxidative wear.On the other hand,the nano-Al₂O₃ particles are obviously increased in the microstructure,which leads to an increase in the friction coefficient and the wear losses.The oxidative wear and abrasive wear of NiAl occurred under the low load,while the wear mechanism of other composites with high-entropy alloy reinforcement phase was abrasive wear.