Fabrication Of Ultrafined Ti6Al4V And Their Microstructure And Mechanical Properties

Titanium alloy Ti6Al4V is wildly used in areas such as aerospace,chemical equipment and automobile industry because of its good combination of strength and elongation,excellent fatigue and corrosion resistance and good formability.Nowadays,how to further enhance its strength become a research focus.It is an important method to produce high strength ultrafined materials by severe plastic deformation.In this research,ultrafined Ti6Al4 V alloys are fabricated by severe hot rolling.And the effects of rolling reduction ratio and heat treatment condition on the microstructure evolution and mechanical behavior of ultrafine-grrained Ti6Al4 V are investigated.Then the inner relationship of processing parameter,microstructure and mechanical properties is analysed.The results show that,with the rolling reduction ratio increasing,the strength of hot rolled Ti6Al4 V increases,and after 90% hot rolling ultrafined Ti6Al4 V with an average grain size of 150 nm is successfully fabricated,the ultimate tensile strength of this ultrafined Ti6Al4 V is 1135 MPa,30% promoted when compared to the as received sample without obvious decreasing of plasticity.The as hot rolled Ti6Al4 V presents anisotropy of mechanical properties arises from the(0002)texture,which leads to the RDTD plane displaying highest microhardness value.The severely hot rolled ultrafined Ti6Al4 V shows aging effects when annealed at 200°C-500°C for 1h and leads to the appearing of dispersion strengthening.The ultrafined Ti6Al4 V shows recrystallization When annealed over 600°C for 1h,and with increasing of annealing temperature the grain size grows significantly.The high temperature annealed sample displays the microstructure of equiaxed α phase,intergranular β phase and recrystallized α phase.With the increasing of annealing temperature,the mechanical properties of ultrfien-grained Ti6Al4 V increase first and then decrease.It exhibits good combination of strength and elongation with the yield strength,ultimate tensile strength and elongation of 1065 MP,1080MPa,10% respectively.The hot stability of severely hot rolled ultrafined Ti6Al4 V is investigated.The results shows that when annealed at 700°C for 120 min,the average grain size still below 1 μm and the microhardness and ultimate tensile strength remain to and 331.7Hvand 963 MPa.when annealed at 800°C,the ultrafine grained Ti6Al4 V shows obvious recrystallization of both α and β phase,and the mechanical properties decease with the increasing of annealing time.The plasticity of ultrafined Ti6Al4 V shows good stability when annealing at 700°C and 800°C.