Dynamic fracture behavior of additively manufactured Scalmalloy®: Effects of build orientation, heat-treatment and loading-rate

Abstract

Scalmalloy® specimens are fabricated using Laser Beam Powder Bed Fusion to investigate the role of build orientation, loading-rate, and heat-treatment on critical energy release rate and crack growth resistance behaviors. Four build orientations - horizontal, vertical, flat, and diagonal - are assessed under dynamic loading conditions. The experiments are carried out in a split-Hopkinson pressure bar apparatus on edge-notched three-point bend geometries. The specimens with the horizontal build are studied also under quasi-static loading conditions to gain some insight into strain-rate sensitivity. The horizontal and flat build specimens are heat-treated for dynamic tests to study the effect of heat-treatment on high strain-rate fracture performance. The in-plane surface displacements near the crack are directly measured using Digital Image Correlation and ultrahigh-speed photography to evaluate the fracture parameters in each of these cases. A hybrid experimental-numerical approach that combines DIC measurements with finite elements is employed to evaluate the fracture behavior. The differences in the critical energy release rates and post-initiation fracture behaviors of Scalmalloy® under different conditions are quantified. The diagonal and horizontal builds outperform the vertical and flat builds in terms of dynamic crack initiation and growth characteristics. The quasi-static crack initiation and growth of the horizontal build specimens show significant strain-rate sensitivity relative to the dynamic counterparts. The heat-treatment of specimens result in marginal improvement of the dynamic fracture performance but does not affect the crack growth resistance behavior. Based on microstructural analyses, the melt-pool boundary orientation relative to crack front extension direction correlates well with the measured dynamic crack initiation and growth performance metrics.