Crystallization kinetics of Zr₆₅Ag₅Cu_12.5Ni₁₀Al _7.5 glassy powders produced by ball milling of pre-alloyed ingots

Abstract

Ball milling was employed to produce Zr₆₅Ag₅Cu_12.5Ni₁₀Al _7.5 glassy powder from pre-alloyed mixtures of crystalline intermetallic compounds. Differential scanning calorimetry (DSC) in isochronal as well as in isothermal modes was used to study the thermal stability and the crystallization kinetics of the glassy powder. The activation energy for crystallization was calculated using isothermal and isochronal DSC data as well as from viscosity measurements, which lead to values of the activation energy ranging between 298 and 314 kJ/mol. Johnson-Mehl-Avrami analysis shows that the transformation is a diffusion controlled three-dimensional process and the crystallization proceeds with increasing nucleation rate at annealing temperatures within the super-cooled liquid region. To test the effectiveness of the glassy powder as reinforcement in Al-based metal matrix composites, bulk specimens consisting of pure Al powder blended with 50 vol.% of Zr₆₅Ag₅Cu_12.5Ni₁₀Al _7.5 glassy powder were synthesized by powder metallurgy. Room temperature compression tests reveal that the strength increases from 155 MPa for pure Al to 235 MPa for the composite with 50 vol.% of glass reinforcement.