工业纯钛TA2中低温蠕变特征研究

Creep Behavior of CP-Ti TA2 at Low Temperature and Intermediate Temperature

摘要:

工业纯钛TA2中低温蠕变行为存在显著的温度及应力相关性。基于外加应力水平和蠕变应变的变化关系，确定不同蠕变温度下的门槛应力水平。根据短时蠕变实验数据，利用包含稳态蠕变速率的本构方程外推稳态蠕变速率，而后进行两组相对长时的蠕变实验，证明了工业纯钛中低温蠕变是存在稳态蠕变阶段的。利用稳态蠕变速率与应力关系，计算出工业纯钛室温蠕变应力指数为6.96，也说明了外推稳态蠕变速率的可靠性。由中低温蠕变激活能随着蠕变进行变化不大（≈60KJ/mol），且一直大于以位错为变形主导机制的变形激活能（30-40KJ/mol），表明孪晶对于工业纯钛中低温蠕变发展整个阶段均起重要作用。根据蠕变后试样孪晶结构随温度的变化解释了TA2蠕变行为的温度相关性，同时也证明了孪晶对于TA2蠕变行为的重要性.

Abstract:

Significant temperature and stress dependent creep behavior of commercial pure titanium TA2 was observed at low and intermediate temperature. According to the variation of creep strain with applied stress level, the relationship between threshold stress level and the corresponding creep temperature was determined. Based on short time creep tests, the constitutive equation containing steady state creep strain rate was used to extrapolate the minimum creep rate. The existence of steady state creep of commercial pure titanium TA2 was confirmed by subsequent long time creep experiments. Through the minimum creep strain rates, creep stress exponent was obtained which also indicates the accuracy of the extrapolated minimum creep strain rates. The activation energy of primary creep (approximately 60KJ/mol) at different creep strains level was higher than the activation energy for slip controlled creep, which demonstrates the importance of twinning for the development of creep behavior of commercial pure titanium TA2 at low temperature. Moreover, according to the variation of twinning structure with deformed temperature in creep tested specimens, the temperature dependent creep behavior was interpreted and the importance of twinning for creep behavior of TA2 was confirmed.