FABRICATION OF FULLY DENSIFIED NI3AL INTE RMETALLIC COMPOUND AND NI+NI3AL 2 PHASES ALLOY BY PRESSURELESS SINTERING OF NIAL+NI MIXED POWDER COMPACTS

The pressureless sintering densification characteristic of NiAl + Ni m ixed powder, the composition of which was mainly in Ni3Al intermetalli c compound and Ni + Ni3Al two phase alloy, was investigated. It was fo und that completely densified compacts of Ni3Al intermetallic compound and Ni + Ni3Al alloy with a large amount of Ni3Al could be obtained b y controlling the powder particle size and the sintering condition, th ough the densification of Ni-rich (82-100 at%Ni) sintered compacts was incomplete. These results were thought to be explained by the authors ' theory of ''Equilibrium gas pressure'', i.e., ''The densification in the final stage of solid phase sintering is affected by whether the e quilibrium pressure of the gas (CO in this case) generated by the redu ction of oxide is higher or lower than the surface stress (the driving force of the shrinkage) of the closed pores'', which have been report ed in the previous papers. The bending strength and hardness of the co mpletely densified Ni3Al intermetallic compound were 1.3 GPa and 330 H (V), respectively, and those of Ni+Ni3Al alloy were 2.9 GPa and 310 H( V), respectively.