1997 年 37 巻 10 号 p. 1010-1015
Textural changes were investigated using X-ray diffraction and orientation imaging microscopy (OIM). During normal grain growth, slight increase in γ-fibre (ND//<111>) was observed. Prolonged annealing and a resultant abnormal grain growth, however, decreased γ and increased α (RD//<110>). The decrease/increase in fibres were mainly caused by corresponding changes in F [{111}<112>] and I [{112}<110>] orientations, while E [{111}<110>] and H [{001}<110>] components did not change significantly. OIM characterization of grain boundary nature indicated an approximate increase in the fraction of low angle (<20°) boundaries with increasing annealing time. At the initiation of abnormal grain growth, the fraction of low angle boundaries (specially those with 1-5° misorientation) were observed to have reached a relatively large value. Such observations may fit well with a simple scheme: the transient strengthening in γ-fibre was possibly caused by normal grain growth of γ-grains. At the later stages of grain growth, the growth of the γ-grains was possibly inhibited/stopped by grains of similar orientations. This, in turn, may increase the fraction of low angle boundaries. When the fraction of low-angle/low-mobility boundaries reached a critical value, growth of certain grains (as F/E in our case) were inhibited/pinned, while few of the more favourable placed/oriented grains could grow abnormally. Measured values of 'free length', defined as the average distance between an i (where i may be F/E/I/H) and a j (where j is less than 20° misoriented with i) grain, showed the highest value for I and the lowest for F. Free length can be considered as an average distance for non-interrupted growth. Highest free length values for I, caused by the spatial locations, possibly favored abnormal grain growth of I grains.
