INTRINSIC FEATURES OF FE-40WT-PERCENT NI POWDERS PREPARED BY CENTRIFUGAL OR VACUUM GAS ATOMIZATION

Centrifugal atomization (CA) and vacuum gas atomization (VGA) were used to produce a series of Fe40Ni powders (where the composition is in approximate weight per cent) with and without niobium and carbon additions. For the CA powders, the rate of the helium flow used for convective cooling was varied; two different gases, helium and argon, were used for VGA processing. Powder characterization included particle size distribution, structure and microstructure, surface films and noble gas content. Substantial quantities of noble gases are entrained in the powders and accompanied by a large population of porous particles. There was no discernible correlation between processing parameters and particle features, except for the microstructures observed for CA- and VGA-processed powders. The importance of powder features in determining the mechanical behavior of consolidated powder products is discussed; no influence on yield stress and creep rupture for the Fe40Ni powders without niobium and carbon additions was observed. Powder characterization needs to address vacancy condensation during rapid crystallization and the role and control of noble and reactive gas entrainment during processing. © 1990.