Nanoscale inhomogeneities in melt-spun Ni-Al

NixAl100 - x material with x = 62.5 or 65 was rapidly quenched to room temp erature by the melt-spinning technique and studied using X-ray diffraction, different transmission electron microscopy (TEM) modes and calorimetry mea surements. Similar to bulk material, the initial B2 structure undergoes a m artensitic transformation to the L1(0) or 14M structure. However, the trans formation proceeds very inhomogeneously and results in a mixed microstructu re consisting of transformed and untransformed regions. The structure of th e transformed regions varies from faulted L1(0) to faulted 14M and shows a variety of morphologies and features like wave-like interfaces and curvatur e of twin planes. The potential factors responsible for such an inhomogeneo us behaviour, i.e. internal stresses, lattice defects, incomplete atomic or dering and compositional variations, are investigated and discussed. Finall y, we conclude that the special structural state of the melt-spun material is explained mainly by solute segregation appearing during the crystallisat ion process. Thus, contrary to most other melt-quenched materials, in Ni-Al , solute segregation cannot be suppressed by the rapid quenching procedure. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rig hts reserved.