Linear growth of reaction layer during in-situ TEM annealing of thin film Al/Ni diffusion couples

During reactive layer growth in binary diffusion couples new phases can nucleate and grow. In the present work we perform in- and ex-situ interdiffusion studies in the system Ni-Al using X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM). We investigate the reaction between 270 degrees C and 500 degrees C. We show that in the early stages of the solid-state reaction a small polycrystalline aluminide layer forms, while preferential grain growth follows in the later stage. In the reaction layer we detect the presence of Al3Ni by XRD and electron diffraction. Local chemical analysis by EDX in the TEM suggests that a second aluminide phase forms simultaneously. An in-situ TEM study at 380 degrees C shows layer growth of about 0.042 nm/s with a linear time dependence. We interpret this rate law on the basis of an interface-controlled reaction and discuss our results in the light of what is known about layer growth in thin film diffusion couples (presence/absence of predicted phases, linear/ parabolic rate laws) and in view of results from the Ni-Al system published in the literature. Areas in need of further work are identified.

Automated summary

In this study, the process of layer growth in the Ni-Al system was investigated through experiments and observations. The results showed that a polycrystalline aluminide layer formed in the early stage of the solid-state reaction, followed by preferential grain growth in the later stage. It was also found that two different aluminide phases formed simultaneously. In-situ TEM study revealed the time dependence of layer growth rate. The findings provide insights into the growth mechanism of reaction layers and suggest areas for further research.