Crack Propagation Properties and Toughening of Wrougt TiAl Alloys based on Our Design Principle

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The effects of lamellar orientation and presence of beta-Ti phase on toughening and strengthening of TiAl alloys with lamellar microstructure using single and polycrystalline materials were systematically investigated. From the single crystal experiments, crack initiation and propagation behavior depends strongly on the lamellar orientation with shear component parallel to the loading direction, and toughening can be achieved by minimizing the component. From the polycrystalline experiments based on our design principle of the wrought alloys, the beta phase present on the lamellar colony boundaries is deformable and resistant to crack propagation, thereby effective in toughening. The creep strengths of the alloys were found to be comparable to the currently used Ni-based alloys. Thus, it is not the presence of beta phase but microstructure stability during creep that governs the creep strength.