Consolidation of low-sinterability powders with applying medium isostatic pressure

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Sintering experiments were conducted on various alloys and ceramics powders using a sintering furnace with controllable atmosphere and pressure of ambient to 10kg/cm^2. The effects of powder characteristics, sintering temperature, applied pressure, sintering time, and heating and cooling conditions on the relative density and grain size of the sintered compacts. Iron alloy and super alloy powder could be densified to full density with pressure of 10kg/cm^2. Tool alloy powder of metal/boride system could not be sufficiently densified with such low pressure, and the higher pressure up to 500kg/cm^2 was necessary for the full densification. The grain structures, distributions of residual pores, shape and size of the precipitate were quantifield with an image analyzer, the sintering mechanisms during the microstructural evolution was studied. The sintering shrinkage rate was measured by non-contact-type dilatometric analyzer, and with the aid of the computer simulation of sintering densification kinetic equations for the shrikage rate were derived. At present the agreement between the simulation and the experimental is not good. However, the nature of the driving force for the densification was clarified, and the semi-quantitative discussion can well be made about the effect of applied pressure on the densification enhancement. For the further understanding of the sintering mechanisms a sintering map which takes into account the effects of sintering temperature, pressure, time and atmosphere has been constructed. With this sintering map the effect of pressurizing has been discussed in correlation with sintering mechanisms.