On the Morphology of Massive and Martensitic Phases with 2H Structure in Ni₆₇Cu₈Sn₂₅ Alloy

Abstract

The morphology of the 2H phase in a Ni₆₇Cu₈Sn₂₅ alloy that was treated by different cooling rates was studied by means of electron microscopy. The transformation from the high temperature DO₃-type cubic phase to the 2H(β-Cu₃Ti)-type orthorhombic structure was found to be massive in the case of furnace cooling and martensitic in the case of quenching. In the massive 2H phase of the furnace cooled specimen, defects such as stacking faults, planar defects terminated by dislocations and stacking faults with antiphase boundaries were observed. A few plates of 2H structure were also observed as growth faults in a massive grain. Some of such plates were (121)_2H twins. If the cooling rate of specimen was decreased, the morphology of the 2H phase was considered to change gradually from the martensite-like structure to the massive one due to the migration of interfaces.