Hot consolidation of mechanically alloyed nanocrystalline powd in Ni-, Fe- and Mo-Based systems

Abstract

The sinterability and hot-pressing behavior of mechanically milled metastable powders with nanocrystalline structures were examined in Ni-, Fe- and Mo-based systems. The nanocrystalline powders exhibited a poor sinterability in spite of very high grain boundary energy induced during mechanical milling. High applied pressures in the order of several GPa are likely to be necessary for achieving full density. The addition of third metals to mechanically alloyed powders can markedly improve both compressibility and densification in pressureless sintering or in hot pressing with re1atiw:ly low pressures below 60 MPa. Near full densification was obtained by the proper selection of the additive metals and their content while retaining a nanocrystalline structure in the inner layer. In Mo₃₃Si₆₇ retarded grain growth was observed when applying pressure during hot consolidation.