Anomalous growth of Ni3Si2 in bulk Ni/Si interdiffusion

Abstract

In the case of reactive interdiffusion of a binary system, growth interfaces between phases generally adopt plane front morphology. However, a few cases exist, as in the binary diffusion couples Ni–Si, Mo–Si, and Fe–Al, for which an intermediate phase may grow with an irregular needlelike morphology. We present an analysis of the Ni3Si2 formation by reactive interdiffusion in the Ni–Si system, characterizing the needles and their growth by optical and scanning electron microscopy, x-ray diffraction, and microtomography. The observations are consistent with a diffusion-controlled mechanism with preferred direction of very fast diffusion, from which it follows that the Ni3Si2 needle morphology is due to an anisotropic diffusion mechanism.