MECHANICS OF HOT ISOSTATIC PRESSING OF A DENSIFIED UNIDIRECTIONAL SIC/TI COMPOSITE

The effect of standard and modified hot isostatic pressing programs on local residual stresses is investigated with an axisymmetric micromechanical model of a unidirectional SCS6/Ti-15-3 composite, made of an elastic fiber and a thermo-viscoplastic matrix. The processing parameters studied include the cooling rate under sustained pressure, the magnitude of the hydrostatic stress, and the ratios of the axial/transverse components. Local stresses in the fiber and in the matrix at their interface are evaluated after cooling from 980 degrees C to room temperature, and during reheating to 500 and 980 degrees C. As in our previous studies, the results indicate that inelastic deformation of the matrix along the cooling path, promoted here by slow cooling rates at sustained pressure, is responsible for reduction of the residual stresses in the fibrous composite. The magnitudes of the local residual stresses at room temperature are nearly linear functions of the logarithm of the cooling rate. Higher processing pressures also contribute to residual stress reduction, and especially so when the transverse pressure component is much higher than the axial.