Microstructure And Properties Of Medium Entropy Alloys For Biomedical Applications

In recent years,researchers have put forward a new alloy design concept--multi-principal component HEAs.Under this concept,a series of titanium series high entropy alloys with bcc crystal structure have been developed.HEAs have become research hotspot due to high yield strength,good biocompatibility and good corrosion resistance in the development of biomedical titanium alloys.However,the HEAs with bcc structure shows brittleness at room temperature,which limits the further application in other research areas.Based on the recently proposed alloy design strategy of valence electron theory,which is to reduce the VEC by controlling alloying,HEAs with bcc structure are ductile in nature.In this paper,a new type of medical entropy alloys(MEAs)system is designed Ti_46-xZr₃₇Nb₁₆Fe₁Mo_x(x=0,1,2,3,5,10,at.%).The research focuses on breaking through the brittleness of high entropy alloy at room temperature,and the medical alloy with excellent comprehensive properties is prepared by means of regulating the content of Mo element and cold rolling.The change of Mo element content and the action mechanism of cold rolling process on the microstructure and properties of the alloy are deeply studied.The following researches were carried out in this work:(1)Ti_46-xZr₃₇Nb₁₆Fe₁Mo_x alloys with a single bcc phase were designed.When4.30?VEC?4.40,the alloys exhibit tensile brittle fracture;when 4.20?VEC?4.26,the alloys exhibit tensile ductile fracture.Among them,the alloy with 1at.%Mo added to the base alloy Ti₄₆Zr₃₇Nb₁₆Fe₁ has realized the simultaneous improvement of strength and ductility,exhibiting the best comprehensive tensile mechanical properties.When x?1,the compressive yield strength is greater than 700 MPa,and the strain of the five alloys exceeds 90%without fracture,and the elastic modulus is less than 30 GPa,which has potential biomedical value.(2)The low strength of as-cast Ti₄₅Zr₃₇Nb₁₆Fe₁Mo₁ alloy with the best tensile comprehensive properties can be improved by cold rolling process.The tensile yield strength of cold rolling Ti₄₅Zr₃₇Nb₁₆Fe₁Mo₁ alloy is 1139 MPa,and the elongation at break is still close to 10%.It is attributed to the fact that part of the?''phase turns into twins structure after large deformation,and the grains are continuously refined to the nanometer level under the interaction of dislocation slip and shear bands.(3)The average friction coefficients of Ti₄₅Zr₃₇Nb₁₆Fe₁Mo₁ alloy before and after cold rolling are 0.54 and 0.56,respectively,which are slightly lower than traditional medical Ti6Al4V and Co-Cr-Mo alloys.The as-cast Ti₄₅Zr₃₇Nb₁₆Fe₁Mo₁alloy exhibits the best corrosion resistance in PBS and better than that of Ti6Al4V medical alloy;Ti₄₄Zr₃₇Nb₁₆Fe₁Mo₂ alloy and cold rolling Ti₄₅Zr₃₇Nb₁₆Fe₁Mo₁ alloy and Ti6Al4V alloy have equivalent corrosion resistance.