Microstructure And Properties Of AlTiCrNiCuSi_x Low-Density High Entropy Alloys Prepared By Powder Metallurgy

The low-density high entropy alloy has the characteristics of low density,high hardness,high specific strength,corrosion resistance,high temperature resistance and other properties.It has promising application potential in aerospace,machinery,automotive and other fields,and has become a hot research topic recently.The main components of new low-density high entropy alloys are light metal elements such as Al,Mg,Ti,Li and Be.Because the chemical properties of the above elements are relatively active,it is difficult to synthesize high entropy alloys and has low safety.Studies have shown that the use of non-metallic elements such as Si,C,N,and B instead of partially active low-density metal elements can produce low-density high entropy alloys with excellent performance,high manufacturing process safety,and lower costs.In this paper,Si element is selected as the main element of low density and high entropy alloys,Al Ti Cr Ni Cu Si_x low-density high entropy alloys were prepared by mechanical alloying?MA?and spark plasma sintering?SPS?processes,and the effects of SPS sintering temperature on the microstructure and mechanical properties of Al Ti Cr Ni Cu?Si₀?high entropy alloys were analyzed;The effect of Si element on the phase structure,microstructure,mechanical properties,and friction and wear properties of Al Ti Cr Ni Cu Si_x?x=0,0.25,0.5,0.75,1?high entropy alloys were studied,and the following conclusions were drawn:In the mechanical alloying process of Al Ti Cr Ni Cu?Si₀?high entropy alloys powders,the alloying sequence of its main elements is:Al?Cu?Ni?Ti?Cr.The synthesized high entropy alloys powders material have a single-phase BCC structure,the average particle size of the powder is about 20?m,and the average size of its internal grains is 14.56 nm.The microstructure of the bulk high entropy alloy material after SPS sintering is mainly composed of matrix phase?BCC1?,Cr-rich phase?BCC2?,Cu-rich phase?FCC?and a small amount of Al₂O₃ oxide.As the sintering temperature increased,the average grain size of the high entropy alloys gradually increased from 1.0?m at 950?to 2.4?m at 1050?,but the alloy phase structure remained unchanged.The relative density of Al Ti Cr Ni Cu?Si₀?high entropy alloy increases with sintering temperature and then remains basically unchanged.The compressive strength and compression rate continue to increase and the hardness decreases slightly.The fracture modes are mainly brittle fracture.In this paper,when the sintering temperature is1050?,the comprehensive mechanical properties of Al Ti Cr Ni Cu?Si₀?high entropy alloy material are the best,its yield strength is 1410 MPa,compressive strength is 2000 MPa,compression rate is 9.13%,hardness is 525 HV,The relative density and density were 6.30g/cm³ and 97.60%,respectively.The addition of Si has a significant effect on the microstructure and properties of Al Ti Cr Ni Cu Si_x high entropy alloys powders and high entropy alloys bulk materials.The results show that the average particle size of Al Ti Cr Ni Cu Si_x?x=0,0.25,0.5,0.75,1?high entropy alloys powders decreases with increasing Si atom content,and the crystal structure is single-phase BCC,but the lattice constant decreases and the lattice distortion increases.TEM analysis shows that the microstructure of Al Ti Cr Ni Cu Si_x high entropy alloys bulk material after SPS sintering is mainly composed of matrix phase?BCC1?,Cu-rich phase?FCC?and a certain amount of silicides.As the Si content continues to increase,the composition of the silicide becomes more complex.When x=0.25,x=0.5?0.75,and x=1,the silicides are Cr₃Si,Cr₃Si+Ti₂Cr Si,Cr₃Si+Ti₂Cr Si+Ti₂Ni Si,respectively.The density of Al Ti Cr Ni Cu Si_x high entropy alloys gradually decreases with the increase of Si content.When x changes from 0 to1,its density decreases from 6.30 g/cm³ to 5.91 g/cm³.The compressive strength of Al Ti Cr Ni Cu Si_x increases first and then decreases,the compression rate gradually decreases,and the hardness gradually increases.In this paper,the density of Al Ti Cr Ni Cu Si_0.75 high entropy alloy material is 6.01 g/cm³,the maximum compressive strength is 3228 MPa,and the highest specific strength is 537 MPa·cm³·g^-1.As the Si content increases,the average friction coefficient and wear rate of Al Ti Cr Ni Cu Si_x?x=0,0.25,0.5,0.75,1?high entropy alloys decrease first and then increase.The wear mechanism is mainly delamination wear and oxidative wear with a low degree of abrasive wear.In this paper,Al Ti Cr Ni Cu Si_0.75 high entropy alloy has the smallest average friction coefficient and wear rate,respectively 0.30 and 9.50×10^-6 mm³·N^-1·m^-1;As the loading frequency increases,the average friction coefficient of Al Ti Cr Ni Cu Si_0.75 high entropy alloy appears to rise first and then decrease,but the change range is not obvious.The wear rate decreases with increasing loading frequency;As the loading load increases,the average friction coefficient and wear rate of Al Ti Cr Ni Cu Si_0.75 high entropy alloy continue to decrease.Changes in frequency and load do not change the wear mechanism of the alloys.