EFFECT OF MECHANICAL ALLOYING ON THE MODE OF INTERMETALLIDE PHASE-FORMATION IN NI-AL SYSTEM ON REACTIVE SINTERING

Studied was the effect of changes in the structure and properties of i nitial Al and Ni powders (50 at% Al, 50 at.% Ni) caused by a short-ter m (less than or equal to 16 h) treatment in an attritor on the charact er of reactive sintering process, exothermal effects, structure and ph ase composition of compacts sintered under conditions of vacuum reacti ve sintering or high temperature self-propagating synthesis. In this p owder mixture the interaction between aluminum and nickel resulting in the formation of an equilibrium NiAl (beta-phase, B2) takes place in several stages at which a succession of aluminides with lower melting points is formed : NiAl3, Ni2Al3, (Ni3Al). Strain hardening of the NiAl powder mixture on short-term (less than or equal to 16 h) mechanica l alloying decreases the the temperature of the beginning of interacti on between Ni and Al to -300 degrees C without altering the sequence o f appearance of the intermediate phases. Strain hardening intensifies mass transfer between Al and Ni and initiates the appearance of small amounts of NiAl already at low-temperature solid-phase reactions (grea ter than or equal to 300 degrees C), whereas in powder mixtures not su bjected to attrition treatment the formation of NiAl is only possible after the appearance of a liquid phase which greatly intensifies mass transfer.