The Role of Carbon in Solidification of Nickel-Base Single Crystals

添加碳对降低高温合金单晶凝固过程中晶粒缺陷的发生率有有益的作用。本研究考察了这种效应的基本基础。该项目是卡内基梅隆大学与通用电气公司研发和通用电力系统之间的合作项目，隶属于由DMR金属研究项目和MPS多学科活动办公室资助的GOALI项目。这项高温合金研究的具体目标有两个：(1)确定碳添加物在定向凝固过程中影响晶粒缺陷形成的机制；(2)更好地了解碳作为有益添加物的合金成分范围。本研究旨在更好地全面了解导致镍基合金单晶凝固破裂的过程。这是通过一个实验程序来完成的，该程序检查了影响凝固过程的合金结构和化学的许多不同方面。首先，由于富含耐火材料的碳化物在液相温度附近析出，碳化物的结构和成分作为合金化学的功能进行了研究。差热分析用于测量固相、液相和碳化物溶液温度。为了检查合金元素在糊状区的分布，并获得固体分数随温度的函数，进行了淬火中断的定向凝固实验。电子探针分析用于表征这些样品中的偏析。为了研究合金化学成分对晶粒缺陷形成的影响，我们使用多种成分进行了单晶定向凝固实验，这些成分在se聚类、碳化物密度和碳化物析出温度方面具有明显不同的特征。本研究探讨高温合金铸件的缺陷形成，并涉及在涡轮发动机上的应用。教育方面的好处包括学生与通用电气公司的实验室互动。＊＊＊

9807648 Pollock Carbon additions have a beneficial effect on reducing the incidence of grain defects that develop during solidification of superalloy single crystals. This research examines the fundamental basis for this effect. The program is a collaboration between Carnegie Mellon University and General Electric Corporate Research and Development and General Electric Power Systems, and falls under the GOALI program funded by the DMR Metals Research Program and the MPS Office of Multidisciplinary Activities. The specific goals of this research on superalloys are twofold: (1) to determine the mechanisms by which carbon additions influence grain defect formation during directional solidification, and (2) to obtain an improved understanding of the range of alloy composition over which carbon serves as a beneficial addition. This research aims to develop a better overall understanding of the processes which result in the breakdown of single crystal solidification in nickel-base alloys. This is accomplished with an experimental program that examines a number of different aspects of alloy structure and chemistry that influence the solidification process. First since refractory-rich carbides precipitate in the vicinity of the liquidus temperature, carbide structure and compositions are examined as a function of alloy chemistry. Differential thermal analysis is employed to measure solidus, liquidus, and carbide solution temperatures. To examine the distribution of alloying elements in the mushy zone and to obtain measurements of fraction solid as a function of temperature, directional solidification experiments interrupted by quenching are conducted. Electron microprobe analyses are used to characterize segregation in these samples. To examine the influence of alloy chemistry on grain defect formation, single crystal directional solidification experiments are conducted with a number of compositions that have distinctly different characteristics in terms of se gregation, carbide density, and carbide precipitation temperatures. %%% This research examines defect formation in high temperature superalloy castings and relates to applications in turbine engines. Educational benefits include student interaction with General Electric Corporation laboratories. ***