Sintering Mechanisms of Iron Containing Multiple Boride Base Hard Alloys

Abstract

The ternary Fe-6%B-x%Mo alloys have a composite microstructure consisting mainly of a complex boride Mo₂FeB₂ as a hard phase and a ferritic binder. The mechanism of liquid phase sintering of this alloy was investigated by means of dilatometry, differential thermal analysis, X-ray diffraction, and scanning electron microscopy. 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. Above 1, 365K, 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 1, 415K, where Mo₂FeB₂ is the only coexisting solid phase, is required for complete densification. L2 having a high solubility for Mo₂FeB₂, provides for solution/reprecipitation process 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 microstrucure of the ternary alloy.