EFFECT OF MECHANICAL ALLOYING BEYOND THE COMPLETION OF GLASS-FORMATION FOR NI-ZR ALLOY POWDERS

Elemental powders of nickel and zirconium were mechanically alloyed over a wide concentration range 10 to 90 at % Zr. The amorphous single phase was formed over the range 20 to 80 at % Zr. The effect of the excessive mechanical alloying on the glass formation was studied by continuing ball-milling beyond the completion of the glass formation for the powders with the average compositions Ni30Zr70, Ni50Zr50 and Ni70Zr30. A partial crystallization took place in all three cases and its initiation was the fastest in Ni30Zr70 and was delayed with decreasing zirconium content. The critical factor for triggering the crystallization was attributed to the oxygen contamination for the zirconium-rich Ni30Zr70 powders and to the reduction in glass-forming ability for the nickel-rich Ni70Zr30 powders. The latter conclusion is drawn from the facts that the impurity concentrations arising from the debris of the stainless steel balls and the vial are gradually accumulated with increasing milling time and that the effective zirconium concentration is reduced below the critical concentration of approximately 20 at % as a result of alloying with the elements iron, chromium and nickel in the stainless steel. © 1990 Chapman and Hall Ltd.