Evolution and thermal stability of Ni3V and Ni2V phases in a Ni-29 at. pct V alloy

Abstract

Eutectoid decomposition of the disordered fcc Ni-V solid solution in the composition range of 25 to 33.3 at. pct V gives rise to a mixture of the ordered Ni3V and Ni2V phases. In the present work, the evolution and thermal stability of these phases were studied in a Ni-29 at. pct V alloy. Solution-treated and water-quenched specimens, when aged at 850 °C, were found to exhibit two types of microstructure. In the first, the Ni2V phase precipitated in a lamellar Ni3V matrix where a pair of conjugate lamellae corresponded to two variants of the Ni3V phase. In the second morphology, the Ni2V phase precipitated within a Ni3V matrix comprising a single variant of the Ni3V phase. The Ni2V phase was observed to precipitate in a plate-shaped morphology, exhibiting {120}fcc-type, habit planes. The precipitation of the Ni2V plates in the Ni3V lamellae resulted in zigzag interfaces between adjacent Ni3V domains. Both the microstructures were found to be thermally quite stable and did not coarsen appreciably on prolonged aging. However, the prolonged aging caused the renucleation of the Ni3V and the Ni2V phases in the vicinity of the grain boundaries in a manner similar to “recrystallization.” The stability of the aged microstructure could be attributed to the nature of the interfaces between different domains of the Ni3V and Ni2V phases.