单晶镍基高温合金的蠕变断裂

CREEP FRACTURE IN SINGLE CRYSTALLINE Ni-BASE SUPERALLOYS

本文研究了〈001〉取向的CMSX—2,SRR99和RR2000三种单晶镍基高温合金,从750-1000℃温度范围和从150—680MPa应力下的蠕变断裂特征;用扫描电镜对上述各种实验状态下的蠕变断口和纵向剖面进行了详细观察。结果表明:单晶的蠕变断裂具有明显的晶体学特征,蠕变裂纹总是从已有的铸造的显微疏松处萌生;对于含碳量较高的材料,碳化物及其与基体的界面也是裂纹萌生的有利位置;这些已萌生的裂纹在外加应力轴垂直的(001)面上各向异性地扩展,直到由于承载截面的逐渐减小而导致最终破坏。虽然在较高的实验温度下,断口被强烈地氧化,但是蠕变断裂特征没有改变,在对三种材料断口上(001)面的大小和面积分数的测量和计算表明,用面积分数来表征蠕变损伤程度是可行的。

Creep fracture behaviour of <001> oriented single crystalline Ni--base superalloys CMSX--2, SRR99 and RR2000 has been investigated in the temperature range of 750--1000℃ and under stress with in the scope of 150--680 MPa. The creep fracture surfaces and logitudinal sections of crept specimens have been examined by SEM. Creep cracks seem always to initiate at inherent casting pores and slowly propa- gate anisotropically along the (001) planes, perpendecular to axis of stress applied, up to the final fast fracture. Creep cracks can also nucleate at fractured carbides or at in- terfaces between carbides and matrix in the alloys containing more carbon. Although at higher testing temperatures, oxidation masked strongly the fracture surface, the creep damage mechanism did not seem to vary in the temperature and stress range explored. The size distribution and the area fraction of (001) facets on fracture surface character- ize the creep crack damage level reached just before the collapse.