Alloy Design Concepts for Wrought High Temperature TiAl Alloys

Abstract

Wrought TiAl alloys provide more possibility to control the microstructure and give a balanced mechanical properties than cast alloy. Titanium aluminides based on the general composition Ti-45Al-(6-9)Nb (in at.%) exhibit several desired properties for higher temperature applications. N b addition changes the Ti-Al phase diagram and the segregations of N b and other elements are easy to form, which induces formation of B2 phase. B2 phase worsens the mechanical properties at both room temperature and elevated temperatures. The new idea is that the P phase is can be used to improve the hot-workability, and the segregations can be lightened during the deformation and finally disappeared, so stable B2 phase is avoided at room temperature. Otherwise, high Nb addition significantly reduces the stalking fault energy (SFE), resulting in abundant twinning and twin intersections, which plays an important role for accommodating heterogeneous deformation and avoiding formation of microcrack at boundaries. The basic compositional characteristics of the high temperature TiAl alloys are high Nb and low A1 content, typically 6/9 N b and 44-46A1. Carefully microalloying using the elements B, W, Y , C may further optimize the properties of the alloys. These wrought alloys have excellent oxidation resistance, balanced mechanical properties and good workability.

Additive Manufacturing of Ti-48Al-2Cr-2Nb Alloy Using Gas Atomized and Mechanically Alloyed Plasma Spheroidized Powders

“…One of the most widely known γ-TiAl alloys is the Ti-48Al-2Cr-2Nb (at. %) alloy, which is currently used by General Electric for low-pressure turbine blades [3,4]. While TiAl alloys possess high strength, their poor ductility and brittleness at room temperatures severely complicate their processability by conventional manufacturing techniques and limit their application [5].…”