Nanoscale inhomogeneities in melt-spun Ni–Al Original Research Article

NixAl100−x material with x=62.5 or 65 was rapidly quenched to room temperature by the melt-spinning technique and studied using X-ray diffraction, different transmission electron microscopy (TEM) modes and calorimetry measurements. Similar to bulk material, the initial B2 structure undergoes a martensitic transformation to the L10 or 14M structure. However, the transformation proceeds very inhomogeneously and results in a mixed microstructure consisting of transformed and untransformed regions. The structure of the transformed regions varies from faulted L10 to faulted 14M and shows a variety of morphologies and features like wave-like interfaces and curvature of twin planes. The potential factors responsible for such an inhomogeneous behaviour, i.e. internal stresses, lattice defects, incomplete atomic ordering and compositional variations, are investigated and discussed. Finally, we conclude that the special structural state of the melt-spun material is explained mainly by solute segregation appearing during the crystallisation process. Thus, contrary to most other melt-quenched materials, in Ni–Al, solute segregation cannot be suppressed by the rapid quenching procedure.