Understanding the relation between creep-fatigue fracture mechanisms and intergranular dislocation accommodation of a high chromium steel using nanoindentation characterization

Abstract

Relying on nanoindentation technology, the effect of intergranular dislocation accommodation on fracture behavior for the P92 steel that had experienced creep-fatigue (CF) loading was studied. The results indicate that the fracture mechanism of P92 steel gradually changes from fatigue-dominating to creep-fatigue interactive damage with increasing dwell time. According to the variations of hardness (H), elastic modulus (E), creep resistance and strain rate sensitivity (m), a normalized damage indicator ln(H/E)/m is proposed to characterize the fracture mechanism. Thermally activated process of intergranular dislocation accommodation results in the formation of creep voids at GBs and a remarkable stress relaxation, leading to a creep-fatigue fracture mechanism for the CF specimens with long dwells. However, mechanically driven of dislocation accommodation contributes to enhanced grain size and lower hardness, resulting in a fatigue-dominated fracture mechanism.