ORIENTATION-DEPENDENT CRACK PATTERNS IN ALUMINA FILMS ON NIAL SINGLE-CRYSTALS DUE TO SPHERICAL INDENTATION

Spherical indentations on (100), (110) and (111) oriented NiAl at room temperature caused anisotropic surface topographies around the indent s which revealed the highly anisotropic plastic deformation of NiAl. N o cracks were observed at the surface of non-oxidized samples. For oxi dized samples, radial and circumferential-like cracks in the alumina f ilm around the indent indicated circumferential and radial tensile str ains at the NiAl surface depending on the in-plane crystal direction. Unlike the case of isotropic plastic deformation, on (100) NiAl, a sin king-in of the surface at the periphery of the indent was connected wi th circumferential tensile strains in special directions as indicated by the appearance of radial cracks. Copyright (C) 1996 Acta Metallurgi ca Inc.