多面体晶体从金属熔体中生长的形态分析

本文以MC碳化物在镍基高温合金熔体中的生长为研究模型,分析了多面体晶体在合金熔体中的生长过程。结果表明,晶体生长方式是向固液界面已形成的台阶上沉积,其机制属于体扩散生长。由八面体模型分析得出,枝臂的形成是由于多面体晶体各晶面上溶质通量流密度的分布不同所致。这与用球扰动分析所得到的多面体的晶面中心较稳定而顶角处稳定性较差的结论相符。从而解释了八面体顶角处容易长出枝臂的实验事实。对MC碳化物进行Auger表面成分的测试结果,支持了这一论点。

Morphological Analysis for Polyhedral Crystals Growing from Metallic Melts

The growth behaviour of MC carbides in Nickelbase superalloys, as a general pattern of polyhedral crystals growing from melts, is investigated. Chernov deemed that q(Solute flux density) was a constant over {111} faces[4]. Our investigation reveals that q varies over {111} faces. Different viewpoints exist about the growth mechanism of carbides[2]. Our investigation shows that the growth mechanism of carbides is essentially the deposition of growing unit onto the growth steps in a way that depends upon the bulk diffusion in the melt. The calculation of the distribution of the flux density over {111} faces of MC shows the density on the surface of octahedra is max. at the vertexes and min. in the center of faces. As a result, branches form at and extend beyond the vertexes. The results of calculation confirm the authors' conclusion presented in a previous paper[1]. The conclusion in Ref.[1] was that the stability in the center of the octahedral faces is much higher than at the vertexes during solidification. It should be emphasized that the authors' viewpoint about the growth mechanism of carbides and the authors' theoretical conclusion compatible with such a mechanism are supported by the results of measurment obtained with Auger analyzer.