Tensile and Impact Toughness Properties of a Zr-Based Bulk Metallic Glass Fabricated via Laser Powder-Bed Fusion

Abstract

In the past few years, laser powder-bed fusion (LPBF) of bulk metallic glasses (BMGs) has gained significant interest because of the high heating and cooling rates inherent to the process, providing the means to bypass the crystallization threshold. In this study, (for the first time) the tensile and Charpy impact toughness properties of a Zr-based BMG fabricated via LPBF were investigated. The presence of defects and lack of fusion (LoF) in the near-surface region of the samples resulted in low properties. Increasing the laser power at the borders mitigated LoF formation in the near-surface region, leading to an almost 27% increase in tensile yield strength and impact toughness. Comparatively, increasing the core laser power did not have a significant influence. It was therefore confirmed that, for BMGs like for crystalline alloys, near-surface LoFs are more detrimental than core LoFs. Although increasing the border and core laser power resulted in a higher crystallized fraction, detrimental to the mechanical properties, reducing the formation of LoF defects (confirmed using micro-computed tomography, Micro-CT) was comparatively more important.

Mechanical Properties of Bulk Metallic Glasses Additively Manufactured by Laser Powder Bed Fusion: A Review

“…The highest fracture strength measured was 1326 MPa. Sohrabi et al [100] investigated the tensile performance of LPBF-fabricated AMZ4 BMG samples, and a high fracture strength of 1180 MPa was obtained, although no macro plastic deformation was detected in the tensile tests. It was also found that the loading direction has a noteworthy influence on the fracture strength of LPBF-fabricated BMG specimens, which may be related to the layered structure obtained with 3D printing.…”

“…There has been very little research into the tensile properties of LPBF-prepared BMGs, with only three studies reported so far, and all of them were carried out on the industrialgrade alloy Zr 59.3 Cu 28.8 Al 10.4 Nb 1.5 (AMZ4) BMG [99][100][101]. Best et al [101] conducted tensile tests on LPBF-fabricated AMZ4 BMG, and the samples underwent a typical brittle fracture with a fracture strength of only 1.08 GPa, which is considerably lower than the compressive strength of the material of 1.8 GPa [82], as shown in Figure 12.…”

“…The highest fracture strength measured was 1326 MPa. Sohrabi et al [100] investigated the tensile performance of LPBF-fabricated AMZ4 BMG samples, and a high fracture strength of 1180 MPa was obtained, although no macro plastic deformation was detected in the tensile tests.…”

“…Due to the fact that the shape of LoF is mostly irregular and its size can reach hundreds of micrometers, it may lead to stress concentration and damage mechanical properties [64]. Currently, several studies on the LPBF of BMG attribute LoFs to premature failure in tensile [100,101] and compressive [40] tests. Pauly et al [40] reconstructed LPBF-prepared compression test specimens by µ-CT and found that the presence of large holes in the center of the specimens, i.e., LoF defects, shown in Figure 14a, which pass through several layers' thicknesses and usually contain unmelted powder particles inside, may have contributed to the premature failure of LPBF-fabricated BMGs in compression tests compared to as-cast specimens.…”

Controlling the Glassy State toward Structural and Mechanical Enhancement: Additive Manufacturing of Bulk Metallic Glass Using Advanced Laser Beam Shaping Technology

“…As predominantly brittle intermetallic phases crystallize in the HAZ, a significant detrimental impact on the mechanical response, particularly upon deformation at room temperature is observed. [50][51][52][53][54] Some authors exploit (B2 to B19) martensitic to enhance the plastic deformability of bulk metallic glass composites (BMGCs). However, even for those systems, crystallization and consequently reduced ductility remain a challenge for the printing of BMGs.…”