Design,Preparation And Properties Of CrTiMo High-entropy Alloys System With Wear And Oxidation Resistance

High-entropy alloys(HEAs)have received widespread attention due to their special structure and better performance,and they are expected to become a new generation of high-temperature candidate materials.As the branch of HEAs,refractory high-entropy alloys(RHEAs)composed of some refractory elements are a new branch in the past ten years,but the research on the properties of RHEAs is still in the initial stage.Therefore,we start with the design and preparation of RHEAs,and conduct the main research on its high-temperature properties.In this paper,the research based on the application of high temperature and other harsh conditions,several types of RHEAs with potential are designed on the basis of matrix alloys.They are prepared by spark plasma sintering(SPS),and researched on its structure,mechanical properties,high temperature oxidation resistance and tribological properties.The effects of different element contents on the structure,mechanical and physical properties of the alloy are analyzed,and the mechanism of high-temperature oxidation behavior of the material and the friction and wear mechanism are explained,which provides data support for the development of RHEAs.The main research contents and results of this article are as follows:1.Three metal powders of Cr,Ti and Mo are mixed to prepare raw materials,and Cr Ti Mo ternary alloy is prepared by SPS.The alloy has a BCC single-phase structure,and its microstructure is evenly distributed and dense.Cr Ti Mo failed to form a dense protective layer during the high-temperature oxidation test at 1000?,resulting in weight loss.The oxidation was more serious when the test was carried out for 10 h.The wear test results of Cr Ti Mo show that as the test temperature rises from 25 to 800?,its wear rate shows a downward trend,which is mainly due to the self-lubricating effect of Mo O₃produced in a high temperature environment.2.The Al element was introduced on the basis of Cr Ti Mo alloy,and Al_xCr Ti Mo(x=0.25,0.5,0.75,1)quaternary high-entropy alloy was prepared by SPS technology.This system of alloys is composed of BCC single phase.As the Al content of the alloy increases,the density and strength of the alloy gradually decrease,and the hardness first increases and then decreases.The high temperature oxidation test at 1000?shows that the Al Cr Ti Mo high-entropy alloy has better oxidation resistance due to the formation of a dense Al₂O₃oxide protective layer.Wear tests show that the wear rate of Al_xCr Ti Mo RHEAs gradually decreases with the test temperature increasing from 25 to 800?.Among them,Al_0.25Cr Ti Mo alloy has a low wear rate at 800?due to the formation of Cr and Mo oxides on the worn surface.3.On the basis of Al Cr Ti Mo high-entropy alloy,Ta element was introduced,and Al Cr Ti Mo Ta_x(x=0.25,0.5,0.75,1)five-element high-entropy alloy was prepared by SPS technology.As the Ta content decreases,the XRD diffraction peaks change accordingly.Al Cr Ti Mo Ta is composed of BCC,B2 and Cr₂Ta three phases,Al Cr Ti Mo Ta_0.75and Al Cr Ti Mo Ta_0.5are composed of BCC and B2 phases,and Al Cr Ti Mo Ta_0.25is composed of single phase BCC.With the increase of Ta content in the alloy,the density and hardness of the alloy gradually increase,and the strength first increases and then decreases.Among them,the compressive strength of Al Cr Ti Mo Ta_0.75is the highest.After the introduction of Ta,the high-temperature oxidation resistance of the alloy at 1000?is significantly improved.The test results show that Ti O₂,Al₂O₃,Cr₂O₃,Cr Ta O₄and other oxide protective layers are formed in the oxide layer of the Al Cr Ti Mo Ta_xhigh-entropy alloy.The Cr Ta O₄formed on the surface of Al Cr Ti Mo Ta and Al Cr Ti Mo Ta_0.75is relatively dense,which effectively prevents the invasion of oxygen atoms,which is the key to the enhancement of its oxidation resistance.Friction and wear tests show that the wear rate of Al Cr Ti Mo Ta_xRHEAs gradually decreases with increasing temperature in the test temperature range of 25-800?.At the test temperature of 800?,the same oxides were detected on the wear marks of the four alloys.Among them,the content of oxides generated on the wear marks of the Al Cr Ti Mo Ta alloy was low,and the material did not produce serious oxidation,which made the alloy have a relatively low wear rate at high temperature.