迭加压应力的疲劳蠕变交互作用下的断口分析

Fractography on the Fatigue-creep Interaction under Compressive Overload

对在700℃,迭加压力过载峰sp=-196MPa的复杂波形载荷作用下,试样的显微断口形貌进行了分析。由于Sp的作用使得疲劳条纹呈现有规律性的半圆弧形宽间距条纹,借助于它,测得疲劳裂纹扩展速率da/dN与△K的关系服从Paris公式;疲劳裂纹Ⅱ阶段与Ⅰ阶段扩展交替出现的形貌证实了:在大应力条件下,裂纹的扩展并不是长裂纹的延伸,而是短裂纹的“超前开动”及“跃迁式”连接过程。由于Sp的作用,断口上出现了三种不同形貌的“台阶”结构及宽条纹上的“挤入”、“挤出”、“二次裂纹”形貌,证实了疲劳条纹形成的滑移机制及形成上述形貌的晶体学位向关系。裂纹的疲劳蠕变混合形貌反映了高温下交互作用的影响。

A detailed fractographic analysis was performed on a nickel-based superalloy under complex loading with superimposed compressive peak overload at 700℃. The fatigue cracks were observed to be presented in semicircular striations with relatively wide spacing. The measured fatigue crack growth rate da/dN from the fractography was found to be related to ΔK in the way of paris formula. It also indicated that fatigue cracks were not propagated continuously by extending a long crack but by a successive process of 'stimu- nated nucleation at the front of crack tip' and 'jump connection' with the main crack. Under the effect of the superimposed Sp there were three different types of 'step' morphologies observed on the fracture surface, a crystallographic orientation relationship in the morphologies were proposed. The mixed fatigue and creep morphology reflected the influence of their interaction at high temperature.