Multi-scale mechanical characterization of an additively manufactured Fe-based glass-forming alloy

Abstract

This work aims to investigate the influence of specimen size and loading direction on the mechanical response of a laser-powder-bed-fused (LPBF) Fe-based metallic glass (Kuamet 6B2). Cuboidal specimens of sizes ranging from 4 to 8 mm were fabricated and then systematically characterized by a range of complementary techniques including optical microscopy, image analysis, differential scanning calorimetry and electron backscattered diffraction (EBSD). All builds exhibited three highly oriented defect families: elongated lack-of-fusion pores perpendicular to BD, oblique internal cracks and large surface cracks normal to BD. These defects, along with limited amorphous retention, dominate the bulk compliance and strength. The mechanical behavior was assessed by room temperature uniaxial compression, both parallel and perpendicular to the build direction (BD), as well as by nanoindentation. A clear, direction-dependent size effect emerges. Under loading parallel to BD, strength and uniform strain diminish with increasing specimen size, consistent with defect closure and the correlation between density and mechanical response. In contrast, when loading is perpendicular to BD, strength and uniform strain increase with size, due to the reduction of normalized defect length scales relative to specimen width. The ensuing drop in stress-intensity at defect tips, suppressing crack propagation. Nanoindentation on defect-free regions revealed substantially higher local stiffness than bulk values, underscoring that the macroscopic response is defect-controlled rather than matrix-controlled.