A Laboratory Study On The Effects Of A Mean Shear Fluid Flow During Solidification of Hexagonal Closest Packed Metallic Alloys

点击翻译按钮获取中文摘要

Michael Bergman 9909333 This is a project to study experimentally the effects of a shear flow in the melt during the solidification of a hexagonal closest packed (hcp) zinc-rich tin alloy. Such a flow has been observed to cause the c-axes of solidifying sea ice, which is also hcp, to lie in the direction of the shear flow, and to cause the grains to tilt upstream. However, there have been no such studies on metallic alloys. The motivation for this study is that shear flows are likely in the Earth's solidifying outer core because of convection and the Coriolis force; rotation of the inner core is one example. Although the phase of iron under inner core conditions is uncertain, hcp is a likely candidate. Moreover, the outer core is an alloy. In the proposed experiments the fluid shear will be provided by Couette flow, with the zinc alloy melt contained in a rotating, cylindrical furnace. The heat exchanger onto which metal solidifies will be a non-rotating coaxial cylinder. Before solidification reaches the sidewall, the casting will be pulled from the melt, machined off the heat exchanger, and sectioned. Back reflection X-ray diffraction will be used to determine grain orientation, and standard metallography and optical techniques will be used to determine grain tilting, as a function of alloy percent, flow (rotation) rate, and oscillation rather than steady rotation. Although the timescale and lengthscale of laboratory experiments are very different from those associated with the core, the experiments will give insight into the ways in which a shear flow in the melt can impact the texture that develops during solidification. Solidification texturing has been suggested as an explanation for the inner core seismic anisotropy, but shear flow effects have not been incorporated into any models.