Abstract:
Hot isostatic pressing is now an accepted material processing technique for the
consolidation of metal powders to near-net-shape components. This thesis examines
the use of coatings as in-situ envelopes to overcome the problems associated with
traditional containerisation of powder. The application of metallic coatings by physical
vapour deposition, involving resistive and electron beam evaporation and ion plating,
onto green powder metal compacts has been studied as a potential method for
encapsulating powder metal products prior to hot isostatic pressing. The coating
structures are discussed in terms of processing conditions and surface roughness
influence. The most promising approach is a combined sinter-hot isostatic, pressing
cycle, which utilises the formation of a transient liquid phase to defect-heal the
coating during the sinter cycle prior to the application of pressure. The influence of
particle size distribution on densification has also been studied. This included both
monosized and bimodal powders. The results of this study has been incorporated into
a modified Ashby model computer program and it is shown that the model results in
a shift of the dominance of the mechanism fields and gives good correlation between
the predicted and measured values of density.
