Microstructural Development and Densification During Hipping of Ceramics and Metals

Abstract

Prediction of deformation behaviour during hipping is often difficult because data on complex material properties are required but are not usually available from the literature. From the present work, measurement of the deformation of a single sphere is proposed as a direct and simple method of predicting hipping behaviour. For C1018 steel, copper, and API nickel superalloy, the predictions made from deformation experiments with single spheres were in good agreement with measured hipping behaviour at hipping densities <93% theoretical. In addition, the creep parameters, such as the exponent n for the power law creep relation, of the powder material itself were measured during single sphere deformation. During hipping of C1018 in the density range above 90%, the use of lower pressures, which is favoured for economic reasons, showed that microstructural development and densification during the final stage of hipping are determined by relatively large pores. These large pores may result from irregularities in the initial powder packing and are still present when areas of initially well packed particles were completely densified. Quantitative measurements of this effect in C1018 were supported by two dimensional simulations of the densification process. Additional observations of API, C1018, and W(Ni) emphasised the importance of the differential deformation of individual particles and grain growth on microstructural development during hipping. PM/0452