Large-strain deformation of Ni 3Al+B: Part III. Microstructure, long-range order and mechanical properties of deformed and recrystallized Ni 3Al+B

Abstract

The mechanical properties, yield-stress, hardening rate, microhardness and fracture of deformed, partially and fully recrystallized Ni 3Al, doped with minor additions of boron, were studied. The change of long range order was investigated as a function of rolling as well as of annealing temperature. At incipient stages of recrystallization, an anomalous behaviour of the mechanical properties was observed. While the yield-stress decreased, the microhardness attained a maximum. The hardness increase is attributed to thermally activated dislocation locking, while the decrease of yield-stress is interpreted in terms of the arrangement of recrystallized grains along former microbands through the sample cross-section. The intermetallic compound Ni 3Al+B can be partially disordered by cold rolling. The observed loss of long range order cannot solely be explained by the dislocation density. It is proposed that microband formation is the main cause for the measured disordering of Ni 3Al+B during cold rolling.