Effect Of Aluminum Content On Microstructure And Properties Of Powder Metallurgy Oxygen-rich Bi-phase Titanium Alloy

(? + ?)bi-phase powder metallurgy titanium alloys have been widely used in medical,aerospace and biological materials because of their excellent properties.Titanium has a strong affinity with impurity elements such as oxygen,carbon,chlorine,and fluorine,among which oxygen is the most easily introduced impurity element.Oxygen-rich raw materials,poorly enclosed processing and service environments that are prone to oxidation will greatly increase the oxygen content of the alloy.However,Ti-6Al-4V alloy has an oxygen content threshold of 0.32 wt.%.Exceeding this value will cause the alloy's plasticity to decline in a cliff-like manner.This phenomenon has become a major obstacle to the application of dual-phase powder metallurgy titanium alloys.In response to this problem,this article reduces the aluminum content in the alloy under the condition of oxygen-enriched alloy.Prepare Ti-4V-x Al-y O(x=0,1.5,2.5,3.5,6 y=0.18,0.35,0.5,0.65,0.8)samples,comparing the mechanical properties of the alloy under different oxygen content and aluminum content,the relationship between the alloy microstructure ? phase,? phase volume fraction,lamellar ? phase thickness and mechanical properties was systematically constructed,and the temperature,temperature,The relationship between holding time and cooling rate on microstructure and performance changes.Studies have shown that when the content of O is 0.18 wt.%,as the content of Al in the alloy decreases,the tensile strength of the alloy decreases but the plasticity presents an increasing trend,which changes from 857 MPa and 11.8 % of Ti-6Al-4V-0.18 O It is 595 MPa and 13.9 % of Ti-4V-0.18 O,and the alloy is ductile fracture.When the O content is increased to 0.35 wt.%,the microstructure of Ti-6Al-4V-0.35 O alloy will lead to increased strength but poor plasticity,such as needle-like ?' and tiny second phase.Ti-6Al-4V-0.35 O alloy has the highest tensile strength of 898 MPa,but the elongation is only 3.9 %,and the fracture surface is characterized by brittle fracture.By reducing the Al content,the volume fraction of ?phase in the structure can be increased,the strength of the alloy is reduced but the plasticity is increased,and the needle-like ?' phase with high strength and low plasticity is not found in the Ti-4V-0.35 O alloy.The appearance is typical ductile fracture characteristics,the obtained tensile strength is 697 MPa,and the elongation can reach 12.5 %.When the oxygen content exceeds 0.5 wt.%,the plasticity of the alloy is significantly reduced,and almost all of them are brittle fracture.After 1000*0.5h+890*3h(oil cooling)heat treatment,Ti-4V-0.35O-x Al titanium alloy has obvious mesh basket structure characteristics.The tensile strength of the alloy is increased by 697 MPa due to the fracture of the coarse ? grain boundary.It is reduced to 652 MPa,and the Ti-6Al-4V alloy prepared by powder metallurgy cannot be oil-cooled due to the vacuum sintering furnace.It is difficult to obtain the characteristics of the basket structure after sintering,and the Widmanstatten structure with poor plasticity is usually obtained.The Ti-4V-0.35 O titanium alloy was kept at400 ? to explore the influence of the ?/? phase boundary on the mechanical properties of the alloy.It was found that the strength of the alloy increased from 705 MPa to 895 MPa as the holding time increased.The number of secondary ? phases with smaller size increases,and the replacement of the primary lamella ? phase with the same content of secondary ? phases will increase the number of ?/? phase boundaries.The dislocations of the titanium alloy need to pass through the interface during deformation.The increase in stress acts to strengthen the alloy.