Evolution of order in melt-spun Ni–25at.%V alloys

This paper reports the evolution of order in stoichiometric Ni–25at.%V alloys with different thermal histories. In these alloys, the face-centred cubic structure of the disordered matrix transforms to a tetragonal (D022) structure during ordering. In such types of transformation, the process of order evolution involves a number of nucleation and growth processes, which are often competitive in nature. In the present work, evolution of the order has been studied in two sets of samples, one in which samples were subjected to order annealing treatment in the "melt-spun state" and the other in which samples were annealed in the "solid solution state". Different sequences of the order evolution have been observed in the two sets of samples. In the first set of samples, grain boundary aided heterogeneous nucleation and growth of ordered domains dominated the order evolution process, whereas in the second set of samples the intragranular nucleation and growth of ordered domains dominated the ordering process. As a manifestation of different evolution sequences, different morphological changes occurred in the two sets of samples. The difference in the evolution sequences has been rationalized on the basis of driving forces influencing the ordering transformation in the two cases.