Glass transition behavior and viscous flow working of Pd40Cu30Ni10P20 amorphous alloy

Abstract

The viscous flow of the supercooled liquid for a bulk amorphous Pd40Cu30Ni10P20 alloy was examined as a function of temperature and applied stress. The flow rate increases linearly with increasing applied stress, but the viscosity is independent of stress. Thus, the viscous flow of the supercooled liquid occurs via the Newtonian flow mechanism. The viscosity at the temperature just before crystallization is as low as 8.3 × 105 Pa·s and the low viscosity reflects the high resistance of supercooled liquid against crystallization. The viscosity (η) measured by thermomechanical analysis is independent of applied stress and heating rate and can be expressed as a function of temperature by equation; η=9.34 × 10-3 exp [4135/(T-447)] (Pa·s). The Pd-based amorphous alloy heated at a heating rate of 0.33 K/s up to 600 K can retain the supercooled liquid state with a low viscosity of about 108 Pa·s for 1 ks. The die-forging into a three-stage die with pitch circle diameters of 4, 5 and 6 mm and a module of 0.3 was made for 120 s at 610 K under a compressive stress of 10 kPa and a three-stage gear was formed. The shape and dimension of the gear agree with the inner size of the die within a scattering of ±1%. The utilization of viscous flow in the supercooled liquid was found to be useful for secondary working of the bulk amorphous alloys which can produce a final product with near-net shape.