CRYSTALLOGRAPHIC FEATURES AND GROWTH OF CREEP CAVITIES IN A NI-18CR-18FE ALLOY

The crystallographic nature and growth of creep cavities in a Ni-18Cr- 18Fe alloy were examined as part of the study of behavior of nickel ba se superalloyys at high temperatures. Creep experiments were carried o ut at 973 K and 52 MPa, and grain boundary cavitation damage was exami ned in polished sections, as well as by scanning electron microfractog raphy of surfaces exposed after hydrogen charging. Well developed cavi ties, whose development tended to favor one side of the grain boundary , were observed and identified with vacancy condensation on {111} plan es. The preference is attributed to cavity nucleation in the grain in which the carbide-matrix interface is incoherent and vacancy condensat ion is energetically favored. A model for cavity growth patterned afte r crystal growth is suggested and discussed. (C) 1997 Acta Metallurgic a Inc.