Effects of B2 precipitate size on transformation-induced plasticity of Cu–Zr–Al glassy alloys

• This paper addresses the effects of the CuZr B2 size and distribution on plasticity.
• There is a critical size to induce the martensitic/twinning transformation.
• An analytic model based on melt flow dynamics is settled.

To demonstrate the effect of processing on the microstructure and subsequent mechanical property of bulk metallic glasses, we prepared two alloys, Cu47.5Zr47.5Al5 and Cu47.5Zr48Al4Co0.5, using two different designs of suction mold – one with a sharp inlet and one with a blunt inlet. The two alloys have been demonstrated previously to be ductile via phase transformation of the B2 phase and twin formation during plastic deformation. Microstructures of the as-cast as well plastically deformed samples, in particular, the size and distribution of the B2 phase, were examined using X-ray diffraction, scanning and transmission electron microscopy. Compressive tests were conducted on samples cast by different molds and their properties were found to closely correlate with the B2 morphology. Fluid dynamics during suction casting was also analyzed. Effects of Vena contracta, flow velocity, and Reynolds number were discussed and compared favorably with experimental observations.

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