Abstract
Castings of 70–30 cupronickel (NES 824) often contain an undesirable amount of porosity, which leads to a high rejection rate for components made from this type of alloy. The possibility of removing such porosity by the application of hot isostatic pressing (hipping) to the castings has been investigated. Part of this investigation involved the hipping of artificial porosity specimens of controlled geometry and a comparison of the results obtained with the predictions of certain well known models for pressure assisted sintering. The results obtained were complicated by the effect of the specimen design on the rate of compaction which is not taken into account in any of the models. However, where the pores are truly internal the degree of agreement with both models is reasonable. It is evident that for internal porosity the removal of porosity in a typical industrial hipping operation occurs during the initial application of pressure and temperature rather than during the subsequent isothermal stage. This applies for up to 10% porosity in the form of a single hole but may not be true of large castings with uneven distributions of pores.MST/3268
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