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

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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.