DZ417G镍基定向凝固高温合金的再结晶

来源期刊：金属学报2010年第8期

论文作者：彭胜 周兰章 侯介山 郭建亭

文章页码：907 - 912

关键词：定向凝固高温合金； DZ417G； 再结晶； 力学性能

Key words：directionally solidified superalloy； DZ417G； recrystallization； mechanical property

摘    要：研究了喷砂和机加工后DZ417G合金在热处理过程中的组织演化及其对拉伸、持久性能的影响.结果表明:喷砂和机加工后,DZ417G合金样品热处理后表面发生了再结晶.扫描电镜观察发现固溶处理样品中的再结晶晶粒呈等轴晶晶粒,而在时效处理后再结晶晶粒呈胞状形式生长.表层再结晶使室温拉伸强度有一定程度的降低,对高温拉伸强度影响不大.表面再结晶厚度在持久过程中增加.表层等轴晶再结晶组织使持久性能降低,二次胞状再结晶组织将导致持久性能的进一步降低.

Abstract: DZ417G is a directionally solidified (DS) superalloy developed for low-pressure blade applications in gas turbine engines.The crystallization microstructures of DZ417G samples caused by sand-blasting and machining were investigated.The tensile properties of the alloy after crystallization were tested at room temperature and 900℃and its stress-rupture performance was examined under conditions of 980℃/216 MPa and 760℃/725 MPa.The results show that after solution treatment equiaxed recrystallization grains form on the surface of specimens machined from directionally solidified alloy bars.After aging treatment,cellular recrystallization takes place on the surface of specimens pretreated by sand blasting.Both the yield strength and tensile strength at room temperature decrease after recrystallization,while those at 900℃ are slightly affected by recrystallization.The recrystallization depth increases after stress-rupture tests,which may be attributed to migration of recrystallization boundaries driven by high temperature and stress.For samples without recrystallization microstructure,the fracture mode is transgranular,which is controlled by the propagation rate of the cracks initiated both on surface and at inner microstructure discontinuities.While for samples with recrystallization microstructure,the cracks prefer to be initiated on transverse recrystallization grain boundaries and propagate along the recrystallization boundaries into the matrix,which may accelerate the propagation rate.TRF (transverse recrystallization area fraction) is a factor to evaluate the effect of recrystallization on the stress-ruptured performance.The stress-ruptured performance is decreased with the increase of TRF between 0 and 0.5.For samples with a TRF of 0.5,second cellular recrystallization forms in the first equiaxed recrystallization grain.The cracks initated at interfaces of cellular microstructure have a high density,which impair the stress-ruptured performance of DZ417G alloy.