熔模铸造条件下K424合金枝晶间缩松及微观偏析研究

Study on Interdendritic Shrinkage Porosity and Microsegregation of Superalloy K424 Under Investment Casting Process

摘要:

本文结合熔模铸造条件下K424高温合金出现的高温持久性能下降的问题,对所存在的一些缺陷进行了研究,对缺陷的形态、成因以及对高温持久性能的影响进行了阐述。借助扫描电子显微镜、显微硬度计等仪器对K424合金试棒进行了观察和测试。观察结果表明,试棒的枝晶间存在显微缩松。显微缩松附近有呈规则正八面体的MC碳化物聚集。Cr元素发生了较严重的偏析。显微缩松是相邻枝晶臂搭接,剩余液相被封闭在晶间区域收缩而成。显微缩松在高温持久测试时引起应力集中,作用于薄弱的晶间组织,导致高温持久性能不足。

Abstract:

To understand the reason of creep rupture life of superalloy K424 drops sometimes under investment casting process, the defects in the test bars were investigated on the shape, distribution with the help of scanning electron microscope (SEM) and microhardness tester. The causes of the defects and influences on creep rupture were analysed. The results show that there are micro shrinkage porosities in interdendritic regions and intact regular octahedron shaped MC carbides can be founded nearby. The microsegregation of the elements is in different degrees which the most serious element is Cr. The cause of the micro shrinkage porosities is that the adjacent dendrite arms join each other and split liquid alloy into closed parts. The micro shrinkage porosities cause stress concentration in the test bars and thus cause the lower high temperature creep rupture life.