Influence of Superheat on Microstructure and Mechanical Properties of Ductile Cu47.5Zr47.5Al5 Bulk Metallic Glass-Matrix Composite

Abstract

Generally bulk metallic glasses (BMGs) posses very less ductility and toughness at room temperature. Over the recent past years to improve up on these properties in many alloy system BMG composites have been developed. It was also reported that Cu 47.5 Zr 47.5 Al 5 BMG composite shows a very high strength together with an extensive work hardening-like behavior of large ductility around 18%. In this study, the influence of superheat on microstructure and the resulting mechanical properties in Cu 47.5 Zr 47.5 Al 5 bulk metallic glass-matrix composite alloy has been studied. The Cu 47.5 Zr 47.5 Al 5 melt solidifies into a composite microstructure consisting of crystalline precipitates embedded in an amorphous matrix. The crystalline phase consists of B2 CuZr (cubic primitive with CsCl structure) with a small amount of monoclinic CuZr martensitic structure embedded in an amorphous matrix. The volume fraction of crystalline phases varies with melting current as well as position along the length of the as-cast rod, depending on the local cooling condition. The volume fraction and the distribution of the crystalline precipitates are heterogeneous in the amorphous matrix. Room temperature uniaxial compression tests revealed high yield strength ranging from 796 to 1900 MPa depending upon the volume fraction of the crystalline phases present. The presence of the dendritic B2 CuZr significantly improved the ductility. The BMG composites show a pronounced plastic strain up to 14% for the higher volume fraction of crystalline phase.

Cryo-Casting for Controlled Decomposition of Cu–Zr–Al Bulk Metallic Glass into Nanomaterials: Implications for Design Optimization

“…The final state of the cast rod depends on a number of factors, including casting temperature T cast , mold temperature T mold , rod diameter, thermal conductivity and thickness of the mold material, and the heat transfer coefficient between the cast rod and the mold. − For the same Zr-based composition, it was confirmed that the formation of a number of eutectoid phases or a fully amorphous structure depends only on T cast . In our case, increasing T cast leads to the formation of two martensitic CuZr phases ( Cm and P 2 1 / m ) and CuZr 2 crystals in rods of 2 and 3 mm diameter (Figure S6).…”

“…28−30 For the same Zr-based composition, it was confirmed that the formation of a number of eutectoid phases or a fully amorphous structure depends only on T cast . 31 In our case, increasing T cast leads to the formation of two martensitic CuZr phases (Cm and P2 1 /m) and CuZr 2 crystals in rods of 2 and 3 mm diameter (Figure S6). Thus, glassy phase separation may be useful in controlling the length scales also in crystalline or partially crystalline microstructures.…”