Advanced structural analysis of a laser additive manufactured Zr-based bulk metallic glass along the build height

Abstract

Additive manufacturing of bulk metallic glasses (BMGs) has opened this material class to an exciting new range of potential applications, as bulk-scale, net-shaped amorphous components can be fabricated in a single step. However, there exists a critical need to understand the structural details of additive manufactured BMGs and how the glassy structure is linked to the mechanical properties. Here, we present a study of structure and property variations along the build height for a laser powder bed fusion (LPBF) processed Zr-based BMG with composition Zr59.3Cu28.8Nb1.5Al10.4 commercially termed AMZ4, using hardness testing, calorimetry, positron annihilation spectroscopy, synchrotron X-ray diffraction, and transmission electron microscopy. A lower hardness, more rejuvenated glassy structure was found at the bottom of the build compared to the middle region of the build, with the structure and properties of the top region between the two. Such differences could not be attributed to variability in chemical composition or crystallisation; rather, the softer bottom region was found to have a larger medium range order cluster size, attributed to heat dissipation into the build plate during processing, which gave faster cooling rates and less reheating compared to the steady-state middle of the build. However, at the top of the build less reheating occurs compared to the middle, leading to a somewhat softer and less relaxed state. Graphical abstract

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

“…Recent research demonstrated that the bottom parts of the printed samples are built with higher cooling rates, resulting in a softer microstructure. [ 117 ] It follows that the reduced reheating and heat accumulation during the procedure, as previously indicated, results in the softer structure of SB samples.…”

“…In the literature it was reported that the bottom part of printed Zr‐based samples exhibits larger MRO sizes as a result of faster cooling rates. [ 117 ] Therefore, it can be concluded that the higher MRO size in SB materials is due to the reduced reheating and probably heat accumulation during the process.…”

EDP2PDF: a computer program for extracting a pair distribution function from an electron diffraction pattern for the structural analysis of materials

“…EDP2PDF is of interest for studying a wide range of materials and has been used in recent studies of various bulk metallic glasses (Nomoto et al, 2021(Nomoto et al, , 2022Best et al, 2022).…”

Controlling the Relaxation Versus Rejuvenation Behavior in Zr-Based Bulk Metallic Glasses Induced by Elastostatic Compression

“…7. Thus, as in our previous work [54,59], each lamella was assumed to have the average hardness of the surrounding four indentations. The calculated MRO cluster size and volume fraction from each lamella and the corresponding hardness values are shown in Table 5.…”