Crystallization kinetics and consolidation of mechanically alloyed Al₇₀Y₁₆Ni₁₀Co₄ glassy powders

Abstract

Al₇₀Y₁₆Ni₁₀Co₄ glassy powder was produced by mechanical alloying of elemental powder mixtures and the thermal stability as well as the crystallization kinetics was investigated using differential scanning calorimetry in both isochronal and isothermal modes. The isochronal and isothermal activation energies have a similar value (~280 kJ/mol). Similar activation energy was obtained for the process from the viscosity measurements. In addition, JMA analysis shows that the transformation is diffusion controlled three-dimensional process and the crystallization proceeds with increasing nucleation rate at annealing temperatures within the supercooled liquid region, while it proceeds with decreasing nucleation rate at temperatures below the glass transition temperature. Metal matrix composites were synthesized through powder metallurgy methods by hot extrusion of commercial 6061 Al alloy powder blended with different amounts of Al₇₀Y₁₆Ni₁₀Co₄ metallic glass reinforcement. The mechanical properties of the 6061 matrix are remarkably improved by the addition of the glass reinforcements. The ultimate compressive strength increases from 260 MPa for the 6061 alloy to 350 MPa for the composite with 50 vol.% of glassy phase.