High‐Entropy Alloy‐Induced Metallic Glass Transformation: Challenges Posed by in situ Alloying via Additive Manufacturing

Abstract

In situ alloying and fabricating glassy structures through a layer‐by‐layer fashion approach are challenging but have high potential to develop novel‐graded materials. For the first time, this cost‐effective approach is applied to additive manufacturing (AM) of a Zr‐based bulk metallic glass (BMG) from high‐entropy alloys (HEAs). A newly developed composition of Zr40Al20Cu20Ti20 is fabricated through laser powder bed fusion (LPBF). Process parameters are optimized within a wide range of laser power (50–200 W) as well as scanning speed (50–800 mm s−1). In all printed samples, microscopic and compositional examinations reveal no glass formation, but very fine grains and CuTi and AlTi nanocrystals. Some glassy transitions at the interfaces may be encouraged to occur with proper melting and mixing. However, the main reason for not obtaining a glassy matrix is the substantial proportion of unmelted Zr raw powder throughout the structure as spherical particles. Consequently, glass formation can be hindered by a considerable amount of compositional deviation. During LPBF, in situ alloying poses significant challenges to developing BMGs. Hence, the various stages of the process, including raw material specifications, laser settings, and process parameters, should be investigated further.

Single-Bead Microstructures of an AlCrFeCoNi High Entropy Alloy Processed by the Laser Directed Energy Deposition

“…Generally, the formation of melt pool can lead to a positive impact as it strengthens the bonding between a formed bead and a substrate [19]. However, in the case of the AlCrFeCoNi HEA, the melt pool area was no longer identified as the AlCrFeCoNi HEA with the equiatomic compositions due to the incorporation of substrate elements into the HEA compositions, resulting in deviation from the equiatomic compositions [20]. Furthermore, the including substrate elements lead to changes of the microstructures in the formed beads, resulting in alterations in its properties [21].…”

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

“…[ 14 ] The LPBF technology has recently been used in several studies dealing with the manufacturing of BMGs. [ 15–35 ] Simulations show that substantial differences exist between simulated cooling/heating rates using LPBF (10 5 /10 6 K s −1[ 36 ] ) and critical cooling/heating rates (2500/45 000 K s −1[ 37 ] ), for the nucleation rates upon cooling and heating. [ 38–40 ] However, the nature of the process involves reheating overlapping regions of adjacent tracks, hence generating a complex thermal history.…”