Dilatometry study of the sintering behavior of boron-alloyed Fe-1.5 Pct Mo powder

The effect of different boron concentrations on the sintering behavior of an Fe-1.5 pct Mo (wt pct) prealloyed powder was investigated. Sintering was carried out in a dilatometer so that all dimensional changes involved with the densification process could be followed. Several transformations were found to occur by heating powder compacts to 1200 C and then cooling them to room temperature. At high temperatures, boron promoted the formation of liquid phases that, through a more-efficient sintering kinetics, promoted a satisfactory densification. Faster heating rates also had beneficial effects on the density of the final products. From a microstructural point of view, boron tended to destabilize the ferritic phase and to form iron and molybdenum borides. These borides can be found both in the intergranular regions, with a typical eutectic morphology, and dispersed in the ferritic matrix, in the form of nanometer-sized precipitates. This feature, having a significant effect on the hardness of the bulk material, has been ascribed to a bainite-like precipitation of borides from an undercooled austenitic phase. (Author)