FRACTOGRAPHY OF EMBRITTLED COPPER BICRYSTALS

The grain boundaries of SIGMA33a copper bicrystals are examined by mea ns of transmission electron microscopy. Two kinds of grain boundaries have been found in the as-grown bicrystals: one is the exact (118)1-(1 18BAR)2 boundary and the other is the zigzag boundary composed of (001 BAR)1-(334)2 and (885)1-(114BAR)2. Having been permeated with bismuth, the bicrystal is easily broken down in an intergranular mode. The fra cture surfaces are examined by means of scanning electron microscopy, as well as reflection electron microscopy, using a conventional transm ission electron microscope. The fractographic observations indicate th at the grain boundary of an embrittled copper bicrystal has a well-dev eloped facet structure and that the boundary is mainly composed of (00 1), (120BAR) and (210) facets. Some macrofacets on the (010) plane, re sulting from fluctuation during bicrystal growth, are also observed. T he holes which appear at the grain boundary are related to titanium in clusions, which have an effect on the local orientations of the grain boundary near these holes. Experimental results show that reflection e lectron microscopy is a useful technique for the observation of the fa ceted fracture surfaces.