Fatigue crack growth in additively manufactured Hastelloy X - Influences of crack orientation and post-fabrication treatments

Abstract

Numerous studies have been conducted in the recent past to assess different nickel-based superalloys fabricated using laser-based powder bed fusion (PBF-LB). Most of these works focused on the processability, microstructural evolution, post-fabrication treatments and the mechanical behaviour of components manufactured by PBF-LB under static loading. However, limited efforts have been made to investigate the fatigue crack growth (FCG) characteristics of PBF-LB built alloys, thereby imposing a barrier to their use as critical components. As such, the aim of the present study was to evaluate and understand the effect of build orientations (0° and 90°) and post-fabrication treatments (solution heat treatment and hot isostatic pressing) on the FCG behaviour of Hastelloy X (HX) fabricated by PBF-LB process. The results from the FCG tests showed that the build orientations had no discernible influence on the fatigue threshold and FCG rate within near-threshold and Paris regions. Nevertheless, the post-fabrication treatments led to an increase in the fatigue threshold and crack growth resistance within the near-threshold region because of the alleviation of detrimental tensile residual stress alongside the crack growth direction. In conjunction with FCG tests, scanning electron microscopy and electron backscattering diffraction were used to investigate the crack path and fracture surfaces within near-threshold and Paris regions.