Localisation of plastic strain at the microstructurlal level in Hastelloy X subjected to monotonic, fatigue, and creep loading: the role of grain boundaries and slip transmission

The localisation of plastic strain in polycrystalline metals is influenced by the microstructure. In this work, we study the localisation and heterogeneity of the plastic response using high resolution strain measurements via digital image correlation and microstructural characterisation using electron backscattering diffraction in monotonic tension, fatigue, and creep. We focus on the role of grain boundaries acting as barriers to dislocation motion. More specifically, we address slip transmission across grain boundaries and the importance of the residual Burgers vector in determining the cross-boundary reaction. We provide insight into how these cross-boundary reactions influence the accumulation of plastic strains across interfaces, dictate the locations of fatigue cracks, and affect the length of fatigue microcracks. The scope of the paper is partially a summary and overview of most recent published work as well as presenting new experimental results, particularly at elevated temperatures. The main outcomes of the agglomerate of experimental and analysis results are discussed with the intent to provide a deep understanding of the plastic response of the nickel-based superalloy, Hastelloy X, at different length scales and different loading and temperature conditions.