Selective laser melting of an Al86Ni6Y4.5Co2La1.5 metallic glass: Processing, microstructure evolution and mechanical properties

Abstract

In this study, single line scans at different laser powers were carried out using selective laser meting (SLM) equipment on a pre-fabricated porous Al86Ni6Y4.5Co2La1.5 metallic glass (MG) preform. The densification, microstructural evolution, phase transformation and mechanical properties of the scan tracks were systematically investigated. It was found that the morphology of the scan track was influenced by the energy distribution of the laser beam and the heat transfer competition between convection and conduction in the melt pool. Due to the Gaussian distribution of laser energy and heat transfer process, different regions of the scan track experienced different thermal histories, resulting in a gradient microstructure and mechanical properties. Higher laser powers caused higher thermal stresses, which led to the formation of cracks; while low power reduced the strength of the laser track, also inducing cracking. The thermal fluctuation at high laser power produced an inhomogeneous chemical distribution which gave rise to severe crystallization of the MG, despite the high cooling rate. The crystallization occurred both within the heat affected zone (HAZ) and at the edge of melt pool. However, by choosing an appropriate laser power crack-free scan tracks could be produced with no crystallization. This work provides the necessary fundamental understanding that will lead to the fabrication of large-size, crack-free MG with high density, controllable microstructure and mechanical properties using SLM

Effect of Process and Post-Process Conditions on the Mechanical Properties of an A357 Alloy Produced via Laser Powder Bed Fusion

“…LPBF is one of the most used AM processes, owing to its ability to produce functional near net shape metallic parts with enhanced mechanical properties [3]. Furthermore, LPBF is very attractive thanks to its extremely high cooling rates that can reach 10 6 Ks −1 [4], that make it possible, as recently reported in some studies, to obtain metastable structures and supersaturated solid solutions [5][6][7].…”

A selective laser melting and solution heat treatment refined Al–12Si alloy with a controllable ultrafine eutectic microstructure and 25% tensile ductility

“…SLM fabricates components layer by layer, which enables the fabrication of complex-geometry components [28]. Due to the laser heating only a very small volume of material and the short laser interaction time, the process has very high heating and cooling rates (10 3 -10 8 K/s) [29] which has been shown to result in the formation of metastable phases [30,31]. Following this, the high heating and cooling rate would induce large super heating and undercooling and this will tend to enhance the nucleation rate and suppress the grain growth in the Al-Si alloy.…”

Additive manufacturing of Cu–10Sn bronze

“…SLM not only is a flexible technique for the fabrication of parts with intricate shapes, but also offers the possibility to produce metastable phases and microstructures, due to the small μm-sized melt pool and the corresponding high cooling rates. Examples are high-strength Al-Si alloys with refined microstructures [5,6], nanostructured Al-Nd-Ni-Co [7], amorphous Al-Ni-Y-Co-La [8] and Fe-based bulk metallic glasses [9].…”