退火预处理对高温合金单晶铸件再结晶的影响

Effect of Annealing Pretreatment on Recrystallization Behavior of Single Crystal Superalloy Castings

为研究退火工艺对单晶高温合金再结晶缺陷的影响,采用静压加载的方式对DD5合金的单晶铸件进行局部变形,经过不同退火工艺预处理后,再进行固溶热处理。结果表明,随着加载压力的提高,固溶热处理中再结晶深度明显增加;当压力载荷较小时,在固溶前进行低温和高温退火预处理对再结晶基本无影响;当压力载荷较大时,低温退火使得铸件中残余应力和最终再结晶程度有所减小,而高温退火反而会增大再结晶倾向,其原因可能是退火温度过高导致铸件在预处理时就已发生再结晶。对样品微观组织的观察分析表明,再结晶组织的产生和生长为亚晶聚合机制,退火预处理对此没有影响。

In order to investigate the effect of annealing process on the recrystallization behavior, the as-cast samples of single crystal superalloy DD5 were locally deformed by applying different loading pressures. Before solution heat treatment, the deformed samples were pretreated with two different annealing processes, called as LTA(lower temperature annealing) and HTA(higher temperature annealing) respectively. It was found that the recrystallization layer formed during solution treatment became thicker significantly with an increase in the loading pressure. For the samples deformed under smaller loads, both annealing processes had little influence on the recrystallization layer thickness. For the samples with larger loads, the recrystallization depth in the LTA samples was slightly reduced due to the correspondent release of the residual stress. In the HTA samples,however, the recrystallization became even serious. The reason may be that the temperature in HTA process is high enough to promote the recrystallization even during the annealing pretreatment. The observation on the recrystallization microstructure confirmed that the formation mechanism of recrystallization is the subcrystalline polymerization, without influence of the annealing process before solution treatment.