| TC4 titanium alloy has the characteristics of low relative density,high specific strength,good corrosion resistance,good biocompatibility,outstanding high temperature heat resistance and high temperature creep,and is widely used in the aerospace field.With the development of the times,it is gradually involved in light industry fields such as sports products,medical appliances and precision structural parts of watches.However,TC4 titanium alloy is a dual-phase alloy,which has a complex phase transition process.It is sensitive to temperature parameters and is difficult to control the structure;it has large deformation resistance at room temperature and difficult plastic processing.Main paper work contents and results are as followings:(1)Using high-temperature confocal experiment,the effects of process parameters such as heating temperature,holding time and heating and cooling rates on the evolution and phase transition rate of TC4 were studied.During heating at 1050℃ in the single-phase region,β grains began to grow.As the heating temperature increased to 1200℃,the grain size became larger,the grain boundaries that provided the nucleation sites of the structure were reduced,and the growth rate of the structure was reduced by 0.63μm/s;When the secondary heating temperature was increased from 870℃ to 885℃,the degree of subcooling and equilibrium crystallization temperature decreased,resulting in a decrease in the micro structure growth rate;After adjusting the process parameters such as temperature and holding time,it is concluded that when the temperature range of TC4 titanium alloy in the two-phase region is from 850℃ to 900℃,as the holding time is extended to 15min,the microstructure growth is complete and the growth rate is 2.99μm/s.And the micro structure is fine needle-shaped and has good stability,which is conducive to improving the growth rate of the microstructure.(2)Through DIL experiment and XRD diffraction analysis,the effect of different process parameters on the content of β phase in TC4 titanium alloy and the effect of different β phase content on the micro structure and properties of TC4 titanium alloy were studied.The results showed that as the heating temperature increased to 900℃,and it was heated to 1020℃ at a rapid heating rate of 80℃/s,maintained for 2s,and cooled at a faster cooling rate of 40℃/s,a higher β remained in the microstructure about 26.76%.According to the resistance furnace simulated annealing experiment,it can be known that under this temperature parameter,the microstructure when the cooling method is water cooling is fine needle-like,and the strength is 987 MPa.(3)The TC4 titanium alloy hot-rolled sheets were subjected to rolling experiments at different temperatures to avoid the phenomenon of cold rolling cracking and the edge shape was good.The effects of different rolling temperatures and reduction processes on the microstructure and properties of TC4 alloy were studied.The results show that the structure tends to be equiaxed as the rolling temperature increases;comparing the experimental results of each rolling process,it can be seen that when the rolling temperature is 800℃and the rolling amount is 40%,the strong plastic properties match.The results for the rolled plate heat-treated at 900℃ in the two-phase zone show that the structure is more uniform,fine and equiaxed;EPMA experiment analysis of alloy element distribution of TC4 sheet after each heat treatment,the results show that as the rolling temperature of the original sheet increases,both Al and V elements undergo diffusion movement.Among them,the Al element is enriched in the center of α grains,and the V element is enriched in the two-phase grain boundaries and the β-transformed matrix.Based on the comparison of mechanical properties before and after heat treatment,it is found that the strength of the annealed rolled sheet is higher than that of the unannealed rolled,the plate is slightly reduced,and the elongation is increased by 5%. |
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