Anomalous hardening behavior accompanied by reordering of plastically deformed Ni3(Si,Ti) intermetallic alloy

Anomalous hardening behavior accompanied by reordering of cold-rolled Ni3(Si,Ti) alloy annealed at 723-823 K was investigated by means of hardness test, microstructural observation and X-ray analysis. Hardening similar to that in precipitation reaction in which hardness increases with increasing annealing time and made a peak, followed by a decrease was observed in heavily cold-rolled samples but not in lightly cold-rolled sample. Hardness increment increased with increasing cold-rolled reduction and took place more rapidly as annealing temperature increased. Reordering proceeded more rapidly as annealing temperature increased and also as cold-rolled reduction increased. Lattice strain evaluated from X-ray half width of reflection peak steadily decreased with increasing annealing time in the same manner not only for the heavily cold-rolled samples but also for the lightly cold-rolled sample. TEM deformation microstructures showed that high density of dislocations was rearranged and polygonized by annealing. The hardening owing to ordered gradient from dislocations to the region distant from it was proposed as a most likely mechanism.