Reaction sintering of an Fe-6 Wt Pct B-48 Wt Pct Mo alloy in the presence of liquid phases

Abstract

The mechanism of liquid phase sintering of an Fe-6 wt pct B-48 wt pct Mo alloy was investigated by means of thermal dilatometry, differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A fine composite microstructure of Mo2FeB2 and ferrite was produced from powders of Fe, Mo, and FeB by a reaction sintering process involving two liquid phases. The hard phase Mo2FeB2 is produced in the compact prior to liquid formation initially by the reaction 2Mo+2FeB=Mo2FeB2+Fe and later by the reaction 2Mo+2Fe2B=Mo2FeB2+ 3Fe. Above 1365K, considerable densification results from the initial stage rearrangement of the solid phases (austenite and Mo2FeB2) coexisting with the first formed liquid phase (L1). Another liquid (L2) which forms above 1415K, where Mo2FeB2 is the only coexisting solid phase, is required for complete densification. L2, having a high solubility for Mo2FeB2, provides for solution/reprecipitation processes which characterize the intermediate stage of liquid phase sintering. The effective separation of the initial and intermediate stages by L1 and L2 is considered essential for the control of the sintered microstructure of the ternary alloy.