Strengthening Mechanism and Alloy Design for a Heat-Resisting Light Intermetallics Titanium Aluminide

铝化钛比重小，高温强度高，是耐热材料的候选材料之一。本研究旨在阐明钛铝化物的强化机理，开发耐热材料的合金设计系统。主要研究结果如下：1.钛铝化物的高温变形：随着应力水平的不同，γ-TiAl表现出三种不同的蠕变机制。在高应力区，蠕变由动态再结晶控制，而在低应力区，位错运动本身控制蠕变。测定了α-Ti固溶体合金、α_2-Ti_3Al和γ-TiAl的相对强度随温度和应变速率的变化关系。Theta概念的发展：为了分析高温下复杂的蠕变行为并评估长期蠕变性能，我们需要本构蠕变方程。提出了一种非稳态蠕变方程，即theta概念。利用这个概念，我们可以用简单的方式理解复杂的行为，并高精度地预测长期蠕变特性。文中还讨论了蠕变方程的物理基础。耐热材料合金设计的概念：通过对蠕变曲线的分析，利用theta概念得到三个材料常数。为了开发合金设计系统，必须解决以下问题：如何将材料常数与高温蠕变性能关联起来，以及如何通过冶金处理来控制材料常数。通过简单的方程，可以将theta概念中的材料常数与蠕变特性联系起来。分析了冶金因素对材料常数的影响，提出了合金设计的概念。

Titanium aluminide is one of candidates for heat resisting materials because of its low specific gravity and high elevated temperature strength. This study aims at elucidating strengthening mechanism of the titanium aluminide and developing an alloy design system for heat resisting materials. The results are summarized as follows:1. High temperature deformation of titanium aluminide : gamma-TiAl shows three different creep deformation mechanisms depending on stress level. At high stress regime creep is controlled by dynamic recrystallization,whereas dislocation motion itself controls creep at low stresses. Relative strength of alpha-Ti solid solution alloy,alpha_2-Ti_3Al and gamma-TiAl was determined as functions of temperature and strain rate.2. Development of theta concept : In order to analyze complicated creep behavior at high temperature and to evaluate long term creep properties,we need constitutive creep equation. A creep equation for non-steady state creep,i.e.theta concept was proposed in this study. By using this concept,we could understand the complicated behavior in a simple manner and predict long term creep properties with high accuracy. Physical basis of the creep equation was also discussed in this study.3. A concept of alloy design for heat resisting materials : Three material constants are obtained from creep curve analysis by means of the theta concept. In order to develop alloy design system,the following problems have to be solved: How to correlate the material constants to high temperature creep properties,and how to control the material constants by means of metallurgical treatments. The material constants of the theta concept are related to the creep properties by simple equations. It was shown how metallurgical factors effect the materials constants,suggesting a concept of the alloy design.