| Due to excellent comprehensive properties, titanium and its alloys have been widely used in aviation, aerospace, shipbuilding, chemical industries and other fields. In order to meet different application requirements, the development of new titanium alloys is a very active domain in recent 20 years in China. Among them, TA17 titanium alloy is one of near α titanium alloys which was modelled on ΠT-3B titanium alloy of Russia, and has been as shell material for warship. Due to poor thermal conductivity, high temperature oxidation, flow stress and microstructure should be very sensitive to the temperature and strain rate of the TA17 titanium alloy, prone to defects large plate crown, plate cracking, poor organization uniformity in the hot deformation process, so it is necessary to research on TA17 titanium alloy thermal deformation characteristics of the system. In this paper, the deformation mechanisms and microstructure evolution law of TA17 titanium alloy were studied by isothermal compress test at constant strain rate and metallographic method. Based on that, the deformation behaviors of TA17 medium plate were simulated by Deform-3D soft. The results of this study have significant value in theory and practice to establish and optimize hot working process and microstructure control techniques for TA17 titanium alloy. The main conclusions are as follows:(1)The main deformation mechanism of TA17 titanium alloy is dynamic recrystallization in(α+β) phase region, and dynamic recovery in β single phase region.(2)The influence laws of hot deformation process parameters to flow stress have been revealed. The results show that the flow stress of TA17 titanium alloy are particularly sensitive to temperature and strain rate. With the increase of temperature and the decrease of strain rate, the flow stress decrease gradually. It exhibits strong softening effects in the temperature range from 800 ℃ to 900 ℃. In the(α+β) phase region, the critical deformation for dynamic recrystallization gradually decreases as the temperature increases and flow stress decreases. In β single phase region, the temperature and strain rate have little influence on flow stress.(3)The material parameters(material constant A, hot deformation activation energy Q, etc.) are obtained by using linear regression method. And then, constitutive equation of TA17 alloy is established, which will lay the foundation for simulation model of hot rolled plate.(4)The influence laws of microstructure caused by T, ε? and ε have been revealed. The dynamic recrystallization mainly occurs in(α+β) region, recrystallized grains quantity increase and well distribute with increasing temperature. The structure uniformity is sensitive to strain rate. With the increase of ε?, the number of bending of lamellar α phase increase and the structure uniformity become worse. The deformation amounts also have a significant effect on grain breaking. When the deformation amount is 0.4, most grains are not broken; when the deformation amount reaches to 0.8, the grains are broken completely and have a good uniformity. In the β single phase region, the microstructures become easily coarse.(5)The processing maps of TA17 titanium alloy suggest that the safe processing region are in 800 ℃ ~ 1000 ℃ with the primary strain rate of 1 s-1 ~ 10 s-1, the rheological instability region are in 700 ℃ ~ 800 ℃ with the primary strain rate of 1 s-1 ~ 10 s-1 and 1000 ℃ ~ 1100 ℃ with the primary strain rate of 5 s-1 ~ 10 s-1.(6)Through the rolling models of TA17 medium plate, built by using Deform soft, the deformation characteristics have been revealed. In this rolling model, the maximum error was 8.7%. By studying on the section parameters of medium plate, we found there is a great difference in strain rate and temperature on the section, which will cause uneven microstructure. |
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