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

Michael Bergman 9909333这是一个实验研究六方最紧密堆积(Hcp)富锌锡合金凝固过程中熔体中剪切流动的影响的项目。已经观察到这样的流动导致凝固的海冰(也称为HCP)的c轴位于切变流的方向，并导致颗粒向上倾斜。然而，还没有关于金属合金的这样的研究。这项研究的动机是，由于对流和科里奥利力，地球凝固的外核可能存在剪切流；内核的旋转就是一个例子。尽管内核条件下铁的物相不确定，但HCP是一个可能的候选者。此外，外芯是一种合金。在拟议的实验中，流体剪切将由Couette流动提供，锌合金熔体包含在旋转的圆柱形熔炉中。金属在其上凝固的热交换器将是一个不旋转的同轴圆柱体。在凝固到达侧壁之前，铸件将从熔体中拉出，从热交换器上切开，然后切分。将使用背反射X射线衍射来确定晶向，并将使用标准金相学和光学技术来确定晶粒倾斜，作为合金百分比、流动(旋转)速度和振荡而不是稳定旋转的函数。尽管实验室实验的时间尺度和时间尺度与与岩芯相关的实验非常不同，但这些实验将深入了解熔体中的剪切流动如何影响凝固过程中形成的纹理。凝固织构被认为是内核地震各向异性的一种解释，但剪切流效应还没有被考虑到任何模型中。

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.