Abstract
Additive manufacturing of bulk metallic glasses (BMGs) through laser powder bed fusion (LPBF) has drawn growing interest in the last years, especially concerning industry-relevant alloys based on iron or zirconium. The process-inherent high cooling rates and localized melting pools allow to overcome geometrical restrictions given for the production of BMGs by classical casting routes. Yet, the achievable surface qualities are still limited, making an adequate post-processing necessary. In this work, we report on applying thermoplastic forming on LPBF-formed parts for the first time to decrease surface roughness and imprint finely structured surface patterns without the need for complex abrasive machining. This BMG-specific post-processing approach allows to functionalize surface areas on highly complex LPBF-formed specimens, which could be of interest especially for medical or jewelry applications.
Highlights
Bulk metallic glasses (BMGs) are a relatively new class of engineering materials
Instead the diffractograms show a typical broad halo, indicating an overall amorphous structure within the detection limits of this method. Both DSC curves show a glass transition from the initial glassy state into the supercooled liquid state at glass transition temperatures Tg of 683 K (LPBF-AB) and 680 K (LPBF-thermoplastic forming (TPF)). Crystallization occurs for both samples at Tx = 758 K, integration over the respective exothermal events reveals the enthalpies of crystallization ΔHx that are found to be 4.02 kJ/g-atom (LPBF-AB) and 3.91 kJ/g-atom (LPBF-TPF)
Overall amorphous AMZ4 specimens were produced by laser powder bed fusion (LPBF) additive manufacturing according to previous studies
Summary
Bulk metallic glasses (BMGs) are a relatively new class of engineering materials. Their combination of high strength and hardness on the one hand and elastic limits up to 2% similar to polymers on the other hand offers significant advantages over crystalline metals [1]. As the glassy specimen is monolithically produced by dissipating the heat of the liquid through the mold interface, the achievable cooling rates in the inner volume of a cast part decrease with sample thickness. This results in an upper size boundary for fully amorphous cast specimen that can be quantified by the critical casting thickness, which is the maximum diameter in which an amorphous rod-shaped sample can be cast. The layer-wise manufacturing approach with very small and localized melt pools, features high cooling rates up to 106 K/s [6] This allows to create large and complexly shaped parts that cannot be produced by casting. The development of adequate postprocessing routes for complex surface structures is in high demand
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