THE INFLUENCE OF HYDROSTATIC-PRESSURE ON GRAIN-BOUNDARY SLIDING IN SUPERPLASTICITY - IMPLICATIONS FOR CAVITATION

It has been established that the occurrence of cavitation during super plastic deformation may be reduced substantially by the superimpositio n of a hydrostatic pressure of the order of the flow stress. Careful i nspection of the available data suggests that both cavity nucleation a nd cavity growth are retarded by the superimposition of hydrostatic pr essure. The present experimental study demonstrates that the grain bou ndary sliding activity occurring during superplastic deformation is no t affected by hydrostatic pressure. Experimental measurements also rev eal that the grain boundary sliding contribution to superplastic strai n is more than 75%. both at low elongations of approximately 50% and a t large elongations of over 200%. It is concluded that the imposition of hydrostatic pressure retards cavity nucleation during superplastic deformation by increasing the size of a stable cavity nucleus.