Development of elevated temperature structural alloys & intermetallics

几类合金被设计用于高温应用。本文主要研究了两类合金：单晶镍基高温合金和钛铝金属间化合物。前者实际上是用于燃气涡轮机的涡轮机级中的叶片的唯一材料。后者正在成为有用的高温材料。拟议的SX研究代表了长期计划的第三阶段。前两个阶段研究了显微偏析和耐火元素对凝固结构的影响，并开发了创新的热处理方法来控制化学均匀化、溶解和初熔。拟议的第三阶段将研究微观结构的稳定性作为耐火材料含量的函数，通过确定元素相分配，γ '形态，和有害的拓扑紧密堆积相的形成方面的热和蠕变暴露的响应。这项研究将提供控制固溶热处理的冶金机制和对后续性能的影响的理解，从而提供机会，大大缩短固溶热处理和改善后续的性能控制，降低这些合金的加工成本和改善性能在燃气涡轮机发动机延长服务。对TiAl的研究将利用这种材料中可能发生的大规模转变来开发一种简单的淬火和回火工艺，该工艺可产生具有适合用作往复式发动机排气阀的性能的微观结构。本研究将研究各种工艺参数的影响，以确定大量的转变和回火反应的动力学，并最终表征热强度，蠕变和疲劳性能。该研究将为TiAl的大规模转变提供更好的基本理解，并开发一种简单的铸造加上易于应用的热处理工艺，以降低TiAl阀门的制造成本，帮助它们从实验室转移到公路车辆。

Several classes of alloys are designed for elevated temperature applications. This research focuses on two classes of these alloys: single crystal (SX) nickel base superalloys and titanium aluminide (TiAl) intermetallics. The former are virtually the only materials used for blades in the turbine stages of gas turbine engines. The latter are emerging as useful high temperature materials. The proposed SX research represents the third phase of a long term program. The first two phases examined microsegregation and the impact of refractory elements on the solidified structure, and developed innovative heat treatments to control chemical homogenization, solutioning and onset of incipient melting. The proposed third phase will study microstructural stability as a function of refractory content by determining the response to thermal and creep exposure in terms of elemental phase partitioning, gamma prime morphology, and formation of harmful topologically close packed phases. This research will provide an understanding of the metallurgical mechanisms controlling solution heat treatments and the influence on subsequent properties and, thereby, offer the opportunity to substantially shorten solution heat treatments and improve subsequent property control, reducing the processing cost of these alloys and improving properties during extended service in gas turbine engines. The research on TiAl will utilize the massive transformation possible in this material to develop a straightforward quench and temper process that produces a microstructure with properties appropriate for application as reciprocating engine exhaust valves. This research will investigate the influence of various process parameters to determine the kinetics of the massive transformation and tempering reactions, and finally characterize the hot strength, creep and fatigue properties. The research will provide a better fundamental understanding of the massive transformation in TiAl, as well as develop a simple cast plus easy-to-apply heat treatment process to reduce the manufacturing cost of TiAl valves helping them move from the laboratory to road vehicles.