Directional solidification of Cr-Si alloys

Directional solidification of chromium silicides has been carried out using a high temperature optical floating zone furnace. The first eutectic in the published Cr-Si phase diagram occurs at 15 a% Si. In this study, it was found that this cutectic actually occurs at 16 a% Si and that a two-phase lamellar microstructure of Cr-Cr3Si is formed at this composition. The study focuses on the influence of growth conditions such as solidification speed and rotation rate on the formation of the lamellar microstructure. The alignment and spacing of the lamellae were found to be a function of these parameters, as verified using both optical microscopy and SEM. By optimizing the growth conditions, a well-aligned and straight lamellar structure can be produced. The mechanical behavior was also studied, using micro hardness testing. Evidence of a toughening effect is shown by the lack of cracking around the indents.