一种[011]取向镍基单晶合金的蠕变断裂

研究了[011]取向的镍基单晶高温合金在750~980℃温度范围和200~680 MPa应力下的蠕变断裂特征。在扫描电镜上对各种实验状态下的蠕变断口和纵向剖面进行了详细观察。研究发现：在低温750℃和中温870℃不同初始蠕变应力条件下，枝晶间区亚晶界处不规则γ＇/γ界面是裂纹主要萌生场所，这些已萌生的裂纹在与外加应力轴垂直的(011)面上沿＜110＞和＜100＞两个方向扩展；980℃不同初始应力条件下，裂纹主要在合金中显微疏松孔洞处萌生，沿与外应力轴垂直的方向扩展。观察750℃和870℃不同应力状态蠕变试样的纵向剖面，对亚晶界区不规则γ＇相面积分数的测量和计算表明，用面积分数表征该合金[011]取向在中低温状态下的蠕变损伤程度是可行的。

Creep fracture of a nickel base single crystal superalloy along [ 011 ] orientation

The creep fracture behavior of a [011] oriented single crystal nickel base superalloy was investigated in the tempera-ture range of 750 to 980℃ and the stress scope of 200 to 680 MPa. The fracture surfaces and longitudinal sections of crept specimens were examined by scanning electron microscopy ( SEM) . It is found that under different initial stresses at 750℃ and 870℃, creep cracks seem always to initiate at theγ'/γinterface on the interdendritic sub-boundary and propagate along the sub-boundary trace, and their cleavage planes expand along<110> and<100> on the (011) plane. But under different stresses at 980℃, creep cracks initiate at inherent casting pores and slowly propagate perpendicular to the axis of stress applied up to the final fast fracture. After observing the longitudinal sections of specimens crept under different stresses at 750℃ and 870℃, it is feasible for the area fraction of irregularγ' phase in the sub-boundary to characterize the creep damage level before collapsing of the superalloy along the [011] direction at the moderated and low temperatures.