铸态TC21钛合金高温热变形行为及加工图

研究了铸态TC21钛合金在温度1000~1150℃,应变速率0.01~10s-1条件下的高温压缩变形行为,基于动态材料模型建立了热加工图,并结合变形微观组织观察确定了该合金在实验条件下的高温变形机制及加工工艺。结果表明:TC21合金在β相区进行热压缩,主要变形机理为动态回复;Ⅰ区(高应变速率,ε≥1s-1),材料落入流动失稳区域,其微观变形机制为局部塑性流动,在制定热加工工艺时应尽量避免;Ⅱ区(1050~1120℃,0.1~1s-1),β晶粒变扁、拉长,晶界平直,为典型的动态回复,功率耗散率为32%~34%;最优加工区,Ⅲ区(低应变速率0.01~0.1s-1),功率耗散为38%~46%,拉长的β晶粒晶界上出现连续再结晶现象,首火次开坯应在高温(1150℃)附近进行,以提高铸态组织的塑性,随后开坯应在中低温进行,以得到细小均匀的β晶粒。

Hot Deformation Behavior and Processing Map of As-Cast TC21 Alloy

The hot deformation behavior of as-cast TC21 alloy was investigated in the temperature range of 1000-1150 ℃ and the strain rate range of 0.01-10 s-1. Based on dynamic materials modeling (DMM), the processing map was established. Combined with the microstructure observation the hot deformation mechanism of TC21 alloy was worked out. The results show that the leading deformation mechanism of TC21 alloy is dynamic recovery in β region. At higher strain rate ( ≥1 s-1), the instability is attributed to flow localization, which should be avoided. The second domain (1050-1120 ℃, 0.1-1 s-1), β grain boundary represents sliding, which is typical dynamic recovery. Optimal processing zone appears at the lower strain rate (0.01-0.1 s-1), which has a peak efficiency of 38%-46%, and a typical continuous recrystallization with serrated grain boundaries occurs. Thus, the first cogging should be at a higher temperature (1150 ℃) to avoid cracking. Later, it should be at a lower temperature to obtain fine and homogeneous microstructure.