Preparation And Properties Of Ni₃Al Alloy By High Temperature Mechanochemical Method

As a typical intermetallic compound,Ni3Al has many advantages,such as high melting point,low density,corrosion resistance and high temperature oxidation resistance,so it is widely used in aviation,machinery,metallurgy,electrochemistry and other fields.However,with the development of society,the demand for Ni3Al-based alloys is increasing day by day.The existing preparation methods can not reduce the preparation cost of Ni3Al-based alloys while large-scale production.Therefore,improving the preparation process of the current Ni3Al alloy has a high research value in reducing the production cost while increasing the yield.Ni3Al powder and bulk materials are successfully prepared by high temperature mechanochemistry method and hot press sintering using Ni powder and Al powder as raw materials.The optimum process conditions for the preparation of Ni3Al alloy powder are determined by studying the parameters of the ball milling process.The effects of hot pressing sintering temperature and the addition of alloying elements on the properties of Ni3Al alloy are investigated.In addition,the effects of high temperature energy ball milling on the lattice constant and grain size of Ni3Al alloy powder,and the effect of process control agent on the microstructure of Ni3Al alloy powder are also studied.The process conditions of preparing Ni3Al alloy powder by high temperature energy ball milling and traditional high energy ball milling are compared.The results show that it is feasible to prepare Ni3Al alloy powder at low ball milling temperature by high temperature mechanochemistry method.By researching on the ball milling process parameters,the optimum process parameters of the initial ball milling are determined:ball milling temperature 500?,ball milling time 20 h,ball-to-powder ratio 20:1,ball milling speed 40 r/min;the optimum process parameters of ball milling after heating are:ball milling temperature 700?,ball milling time 20 h,ball-to-powder ratio 20:1,ball milling speed 40 r/min.During high temperature energy ball milling,the lattice constant of Ni3Al increases with the prolongation of ball milling time,the grain size decreases gradually,and the change rate of grain size increases firstly and then decreases.When the addition amount of PEG 10000 is 1.0 wt.%,the prepared Ni3Al alloy powder has the smallest median diameter,and the median diameter is decreased about 1 ?m compared with the powder to which the process control agent is not added.Compared with the traditional high energy ball milling process for the preparation of Ni3Al alloy powder,the calcination temperature of the high temperature energy ball milling process is reduced by 500?.By studying on the hot pressing sintering process and alloy properties,it is found that with the increase of sintering temperature,the density and hardness of Ni3Al alloy increase significantly,the porosity of the alloy surface decreases,the compressive strength and punching performance increase gradually,and the plasticity is improved significantly.Analysis of the compression fracture shows that the fracture mode of the Ni3Al alloy is intergranular fracture.The average friction coefficient and volume wear of the Ni3Al alloy decrease with the increase of sintering temperature.Observing the surface morphology after wear,it is found that the mechanism of Ni3Al alloy in the process of friction and wear is a typical abrasive wear mechanism.By studying on the corrosion performance,it is found that the open circuit potential curves of Ni3Al alloy are relatively smooth,indicating that Ni3Al alloy is stable in hydrochloric acid(pH=2)and it is not easily to be corroded;the average corrosion rate and self-corrosion current density decrease with the increase of sintering temperature,indicating that increasing the sintering temperature can improve the corrosion resistance of Ni3Al alloy.By adding B,Mo and Cr alloying elements to Ni3Al alloy to improve its properties,it is found that the effect of alloying elements on the hardness of Ni3Al alloy is significant.With the addition of B,the hardness of Ni3Al alloy increases firstly and then decreases.When the addition amount of B is 1.0 at.%,the hardness of Ni3Al alloy reaches 591 HV;after adding 4 wt.%of Cr,the hardness of Ni3Al alloy increases from 487 HV to 643 HV,but the addition of 4 wt.%of Mo has little effect on the hardness of the Ni3Al alloy.Alloying element B can effectively improve the room temperature ductility of Ni3Al alloy.With the addition of B,the plastic deformation of Ni3Al alloy increases firstly and then decreases.When the addition amount of B is 1.0 at.%,the ductility of Ni3Al alloy is the best,but the compressive strength of the alloy is decreased.The analysis of the compression fracture shows that after adding the alloying element B,the fracture mode of Ni3Al alloy changes from intergranular fracture to intergranular and transgranular mixed fracture.The alloying elements Mo and Cr have significant effect on the high temperature oxidation resistance of Ni3A1 alloy.The Ni3Al alloy with Mo is oxidized faster and the oxide film is exfoliated severely,indicating that the alloying element Mo is not conducive to improving the high temperature oxidation resistance of Ni3Al alloy;The addition of Cr can reduce the oxidation rate of the Ni3A1 alloy and promote the formation of the Al2O3 protective film.Therefore,the high temperature oxidation resistance of Ni3Al alloy can be greatly improved by the alloying element Cr.