Aj. Fletcher et S. King, RELATIONSHIPS BETWEEN DENSITY, PRESSURE, AND TEMPERATURE IN POROUS CUPRONICKEL ALLOYS, Materials science and technology, 12(6), 1996, pp. 477-482
Castings of 70-30 cupronickel (NES 824) often contain an undesirable a
mount of porosity, which leads to a high rejection rate for components
made from this type of alloy. The possibility of removing such porosi
ty by the application of hot isostatic pressing (hipping) to the casti
ngs has been investigated. Part of this investigation involved the hip
ping of artificial porosity specimens of controlled geometry and a com
parison of the results obtained with the predictions of certain well k
nown models for pressure assisted sintering. The results obtained were
complicated by the effect of the specimen design on the rate of compa
ction which is not taken into account in any of the models. However, w
here the pores are truly internal the degree of agreement with both mo
dels is reasonable. It is evident that for internal porosity the remov
al of porosity in a typical industrial hipping operation occurs during
the initial application of pressure and temperature rather than durin
g 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 wi
th uneven distributions of pores. (C) 1996 The Institute of Materials.