Growth kinetics of W₅Si₃ layer in WSi₂/W system

Growth kinetics of the W₅Si₃ layer in the WSi₂/W diffusion couple was investigated using optical microscopy, field-emission scanning electron microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction. The 62 μm WSi₂/0.3 μm-W₅Si₃/W diffusion couple was made by chemical vapor deposition (CVD) of Si on a W substrate. When the diffusion couple was annealed at temperatures between 1300 and 1500 °C in an argon atmosphere, the W₅Si₃ layer was simultaneously formed both at the surface of the WSi₂ layer and at the interface between the WSi₂ layer and the W substrate. The W₅Si₃ layer observed at the surface of WSi₂ layer was formed by loss of Si released from the decomposition of WSi₂ phase into the W₅Si₃ and Si phases. The growth kinetics of W₅Si₃ layer formed at the interface between the WSi₂ layer and the W substrate obeyed a parabolic rate law, indicating the diffusion-controlled growth. From the change of columnar diameter and texture of W₅Si₃ grains, the dominant diffusion element and growth mechanism of the W₅Si₃ layer was found. The integrated interdiffusion coefficients in the W₅Si₃ phase were determined.