DEFORMATION STRUCTURE OF MICROINDENTATIONS IN W(100) - A TRANSMISSIONELECTRON-MICROSCOPY STUDY

The deformation structure induced by Vickers indentations with diagona l sizes from 2 to 4 mu m in the (100) surface of W single crystals was studied by means of transmission electron microscopy (TEM). Dark-held imaging of the area around an indentation, performed at different til t angles around an axis perpendicular to the diffraction vector, revea ls the presence of lattice misorientation in the region adjacent to in dentation. The angles of rotation around the axes in the plane of the foil are in the range 1-2 degrees. The surface strain associated with this amount of rotation is comparatively small, from 0.01 to 0.03%. Th e estimate of the dislocation contribution to the surface strain, as o btained from the analysis of the TEM results, is 0.4+/-0.1%. This valu e is in good agreement with that in the pile-up region calculated from scanning tunnelling microscopy profiles, which is in the range from 0 .1 to 0.7%. It follows that the deformation in the pile-up region can be accounted for by the dislocation mechanism.