Nanoscale inhomogeneities in melt-spun Ni-Al

Abstract

Ni-Al material consisting 62 …65%Ni 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 L1o 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 L1o to faulted 14M and shows a variety of morphological features. EDX and EELS nanoprobes reveal 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 of other melt quenched materials, in Ni-Al, solute segregation can not be suppressed by the rapid quenching procedure. Ageing at 1200°C restores the compositional homogeneity and results in more homogenious martensitic transformation resembling that in bulk Ni-Al material.