Study On Performance Response And Microstructure Evolution Of TA32 Titanium Alloy Under Different Heat Deformation Conditions

TA32 is a new near-αhigh-temperature titanium alloy and is expected to have broad applications in the aerospace field.Like a traditional titanium alloy,the forming properties of TA32 are worse in an indoor temperature,so the thermoforming shall be used.The thermoforming can be implemented by using two methods.The first method is to simultaneously heat and cool a blank and mold(hereafter called as thermoforming with furnace).The second method is to first heat a mold to the forming temperature,then place a blank and finally cool with air after forming(hereafter called as temperature-reached thermoforming).Two forming methods will make formed parts have very different mechanical properties,structure and oxidation degree.Less comparative research is conducted on two thermoforming processes of TA32 titanium alloy at home and abroad.With typical complicated purlins and bulkheads inside the tailpipe of a new airplane engine as research objects,some high-temperature stretching and high-temperature oxidation tests are performed to simulate the forming properties in this paper.The performance response and microstructure evolution of TA32 is compared and analyzed in two thermoforming processes to provide basis for selection of better thermoforming process.The common influence factors of thermoforming include forming temperature,strain rate,heat preservation time and deformation,but the characteristic influence factors of the thermoforming with furnace and temperature-reached thermoforming include temperature rise rate and cooling mode.First study the mechanical property response and structural evolution of the TA32 thermoforming common influence factors by using the high-temperature stretching test and then compare and analyze mechanical property response and microstructure evolution of TA32 in thermoforming with furnace and temperature-reached thermoforming in different temperature rate and cooling mode.The results show that the strain is 0.45~0.6 in the 800℃temperature,0.001s~-11 strain rate and 30min heat preservation.When the temperature-reached thermoforming(800℃/5min temperature rise rate and air cooling)is selected,TA32 deformation resistance is low,plasticity is better,particles are uniform,equiaxed grains ofβphase are more,and comprehensive forming properties are better.Oxidation behaviors of TA32 in thermoforming are studied by using high-temperature oxidation tests,oxidation resistance of the graphite and boron nitride and high-temperature oxidation behaviors of TA32 are studied by using the long oxidation test of high-temperature lubricants in different temperatures and heat preservation time,and the oxidation behaviors of the thermoforming with furnace and temperature-reached thermoforming are compared and analyzed by short oxidation test at different temperature rise rates.The research results show that the TA32 oxidation mechanism depends on diffusion.The oxidation resistance of the boron nitride is better than that of the graphite within 750~850℃.The oxidation is less and the oxidation resistance class is class II in case of boron nitride painting in 800℃and the oxidation of temperature-reached thermoforming(800℃/5min temperature rise rate)is inferior to that of the thermoforming with furnace(800℃/6h temperature rise rate).Based on above research results,when the temperature-reached thermoforming(800℃/5min temperature rise rate and air cooling)is selected,TA32 deformation resistance is low,plasticity is better,particles are uniform,and comprehensive forming properties are better.Typical TA32 stringers and bulkheads are formed by using the temperature-reached thermoforming process and properties of the formed parts are evaluated by normal temperature stretching,micro-hardness test,microstructure,oxidation and hydrogen absorption and conductivity.Results show that the tensile strength of the formed parts reduces by about 10%,the yield strength reduces by about 9%and the hardness reduces by about 3.5%.The oxidation film is thinner and denser,the oxygen content is about 0.009%,and the conductivity is about 10~6S/m.They can satisfy the performance requirements.