Microstructural stability and creep of elevated temperature alloys

蠕变指的是在长时间的加载期间依赖于时间的应变或缓慢的形状变化。蠕变变形和失效困扰着工程材料的许多高温应用，例如燃气涡轮机发动机部件和许多热交换器结构。进行实验室蠕变测试相对简单，但了解控制蠕变的物理冶金因素作为施加的温度和载荷的函数更具挑战性。已经发展了几种解释金属晶体结构蠕变的理论，这些理论依赖于晶体缺陷和晶界的响应来解释蠕变期间应变的模拟。提出的研究将系统地调查晶界结构的主要蠕变响应的三种合金设计用于在高温下使用的影响。特别是，晶界结构将从“平面”修改为“锯齿状”形态。锯齿状边界通过阻碍蠕变裂纹沿着垂直于主加载方向的边界的增长来延迟蠕变破坏，这是合理的。然而，很少了解晶界形态的影响的主要蠕变行为-在此期间的应变模拟率不断下降的初始阶段。在许多工程应用中，主要蠕变的持续时间决定了部件的使用寿命。这项研究的结果将是一个更好的理解的因素控制工程合金蠕变。这种理解可以应用于具有改进的抗蠕变性的合金的微观结构设计。

Creep refers to time dependent strain - or slow shape change during extended periods of loading. Creep deformation and failure afflicts many elevated temperature applications of engineering materials, such as gas turbine engine components and many heat exchanger structures. Undertaking laboratory creep tests is relatively straightforward, but understanding the physical metallurgical factors controlling creep as a function of the applied temperature and load is much more challenging. Several theories to explain the creep of metallic crystalline structures have been developed which rely on the response of crystalline defects and crystal grain boundaries to explain the accummulation of strain during creep. The research proposed will systematically investigate the influence of grain boundary structure on the primary creep response of three alloys designed for use at elevated temperatures. In particular, the grain boundary structure will be modified from 'planar' to 'serrated' morphologies. It is reasonably well established that serrated boundaries delay creep failure by hindering the growth of creep cracks along boundaries that are normal to the main loading direction. However, very little is understood regarding the influence of grain boundary morphology on the primary creep behaviour - the initial period during which the rate of strain accummulation continuously decreases. For many engineering applications the duration of primary creep determines component service life. The result of this research will be an improved understanding of the factors controlling creep of engineering alloys. This understanding can be applied to the microstructural design of alloys with improved creep resistance.