Formation of periodic patterns in the (Ni,W)/Al diffusion couples

Formation of periodic patterns was observed in the (Ni,W)/Al finite diffusion couples after annealing at 600 °C. The individual layers in the patterns grew parallel to the original interface between the counterparts of the diffusion couples. A combination of the scanning electron microscopy, energy dispersive analysis of characteristic X-rays and X-ray diffraction revealed that the periodic patterns consisted of Al4W/Al5W layers, which were embedded either in the Al3Ni or in the Al3Ni2 matrix depending on the local Al concentration. The Al3Ni matrix developed in the Al-rich part of the sample, the Al3Ni2 matrix in the (Ni,W)-rich part of the sample. The microstructure analysis was accompanied by nanoindentation experiments that were performed in selected phases, which developed in the samples. The kinetic of the formation of the periodic patterns was investigated with the aid of diffusion couples that were annealed for 1, 3, 6 and 24 h. It was confirmed that the formation of the periodic patterns in the (Ni,W)/Al diffusion couples at 600 °C is a diffusion-controlled process. A model was suggested to describe this process and compared with existing models from literature.