Recrystallization Involving a Second Phase

Abstract

Many commercial alloys, such as steels and aluminium alloys, are phase mixtures rather than homogeneous solid solutions. Their recrystallization behaviour depends on whether they were deformed in the supersaturated single-phase condition or in the two-phase state. In a deformed and supersaturated alloy, particles of the second phase precipitate in the same temperature range over which recrystallization can proceed. The precipitating particles hinder both the rearrangement of the dislocations to form recrystallization fronts and the migration of the latter. Only discontinuous precipitation increases the velocity of a recrystallization front. If the particles are present in the alloy before cold working, the recrystallization behaviour depends on the nature, volume fraction, and dispersion of the second phase. Independent of the alloy type, an acceleration of recrystallization (compared with the behaviour of the particle-free matrix) is observed for wide interparticle spacing and large particle diameter; for close spacing and small particles the reverse is the case. Very little was known until recently about the recrystallization behaviour of coarse two-phase alloys in which the phases effectively form separate grains and are present in almost equal proportions. Only two examples are presented: recrystallization of Cu–Ni–Zn alloys deformed in the single-phase state and of coarse two-phase Cu–Zn alloys (α/β-brass) deformed in the two-phase state.