Ex and in situ investigations on the role of persistent slip bands and grain boundaries in fatigue crack initiation

Abstract

Abstract

Early damage and fatigue crack initiation at ambient and elevated temperatures in heat resistant austenitic steel

“…8). In this regard it is interesting to note that some authors [5,6] propose a similar mechanism for initiation of fatigue cracks in room temperature cyclic straining without dwells. However the conditions in room temperature cyclic straining are less favorable for the accumulation of point defects since dislocation density is high and point defects created during cyclic plastic straining migrate preferentially to dislocations.…”

“…Preferentially intrusions represent crack-like defect from which fatigue cracks were proposed to initiate [4]. Alternative mechanism of crack initiation coming from the observations of the cracks in copper single and bicrystals [5,6] is based on the nucleation of the cracks on the grain boundary or on the PSB/matrix interface by direct condensation of vacancies.…”

Introduction

“…The relatively new possibilities of FIB imaging allow quite simple investigations of the crack initiation sites as shown on the cover image of the first part, where extrusions formed by PSBs and their interaction with grain boundaries as discussed in the paper by H.W. Höppel et al 4 are visible. In recent years the field of fatigue has been extended to cover also the very high cycle fatigue regime (VHCF).…”

Initiation and growth of short fatigue cracks in austenitic Sanicro 25 steel

“…[15][16][17][18] Different views on the mechanisms of the initiation of fatigue cracks were expressed. 13,[19][20][21][22][23][24] Physically based models propose an important role of point defects in fatigue crack initiation. While EGM model 19 and Polák model 21,23 consider the indirect role of point defects in formation of the pronounced surface relief, Li et al 13 and Höppel 24 propose the crack embryo forms as a consequence of clustering of vacancies along the PSB/ matrix interface.…”