块状碳化物的形态演化及对镍基合金蠕变性能的影响

Configuration evolution of carbides and its influence on creep property of nickel-based superalloy

通过不同工艺热处理、蠕变性能测试及组织形貌观察,研究了固溶温度对一种定向凝固镍基合金中碳化物形态演化与蠕变性能的影响.结果表明:铸态DZ125合金中存有粗大块状MC型碳化物,热处理期间合金中MC型碳化物可发生分解和形态演化,逐步转变成粒状M23C6型碳化物.随固溶温度提高、时间延长,碳化物发生分解及形态演化的几率增加,并使细小粒状M23C6型碳化物沿晶界不连续析出.与低温固溶处理合金相比,高温固溶处理合金在780℃具有良好的蠕变抗力.其中,以共格方式嵌镶在γ基体中的立方γ′相均匀分布在枝晶干和枝晶间区域,并有细小粒状碳化物沿晶界弥散析出,可抑制晶界滑移,是大幅度提高合金蠕变抗力的主要原因.在近780℃蠕变后期,与应力轴呈45°角的晶界承受较大的剪切应力.裂纹在沿与应力轴呈45°角的晶界处萌生与扩展,直至断裂是合金的蠕变断裂机制.

By means of heat treatment at different regimes,creep properties measurements and microstructure observations,an investigation has been made into the influence of solution temperature on the carbides configuration evolution and creep properties of a directionally solidified nickel-based superalloy.The results show that the thicker bulk-like MC-type carbide is distributed in the as-cast DZ125 superalloy.And the decomposition and configuration evolution of the MC-type carbide occur gradually,during heat treatment,to transform into the particle-like M23C6-type carbides.As the solution temperature enhances and time prolongs,the probability of the MC-type carbide occurring decomposition and morphology evolution increase,which may promote significant amount of particle-like M23C6-type carbide precipitating along the grain boundary of alloy.Compared with the alloy solution treated by lower temperature,the alloy solution treated at higher temperature displays a better creep resistance at a temperature near 780 ℃.Wherein,the fine γ′ precipitates embedded coherent in the matrix phase are homogeneously distributed in the dendrite/ inter-dendrite regions,and some M23C6-type carbide particles along the grain boundaries may restrain the slipping of boundary,which is thought to be the main reasons of alloy having better creep resistance.At the latter stage of creep at a temperature near 780 ℃,the bigger shearing stress applying in the boundaries at about 45 angles relative to the stress axis results in the initiation and propagation of the micro-cracks along the ones up to fracture,which is thought to be fracture mechanism of the alloy during creep.