Grain boundary character distribution in B2 intermetallics

This paper reports the results of the experimental studies of the effect of chemical composition, texture and processing methods on the grain boundary character distribution evaluated by the electron back-scatter diffraction pattern (EBSD or EBSP) technique, in B2 FeAl and NiAl intermetallic compoun ds. An alternative method based on the grain boundary surface area for calc ulating the unbiased fraction of grain boundaries of a given character (Sig ma CSL) is proposed. It is shown that the proposed method gives different r esults than the classical method based on the counting of grain boundary se gments. It is found for both FeAl and NiAl that the fraction of low-angle b oundaries (Sigma1 LABs) increases with increasing percentage of the <100> a nd to a lesser extent the <111> texture, up to the upper limit of similar t o 20%. In B2 FeAl the fraction of so-called "special" grain boundaries (SGB s) (Sigma3-29) seems to be independent of the percentage of the <100> textu re. In B2 NiAl and NiAl+2wt.%HfC alloy the fraction of SGBs decreases conti nuously with increasing percentage of the <111> texture. The <110> texture does not have strong effect on LABs. Processing of B2 FeAl by shock-loading and subsequent annealing can increase the fraction of LABs to 90-97%. This effect is not observed in B2 NiAl. Instead, the premature abnormal grain g rowth occurs, accelerated by the accumulated shock strain energy. In B2 com pounds the fraction of LABs seems to increase nearly linearly up to the lim it of similar to 20% with decreasing grain size from similar to 400 to simi lar to 100 mum. For grain sizes smaller than similar to 100 mum the fractio n of LABs seems to be independent of grain size. The fraction of SGBs does not exhibit any dependence on grain size. (C) 2000 Elsevier Science Ltd. Al l rights reserved.