An innovation for microstructural modification and mechanical improvement of TiAl alloy via electric current application.

In this article, microstructural evolution during the solidification of Ti-48Al-2Cr-2Nb with current density, as well as the formation mechanisms, are discussed, along with the impacts on microhardness and hot compression properties. The applied electric current promotes the solidification from the α primary phase to a largely β solidification in Ti-48Al-2Cr-2Nb. With an increase in supercooling, the solidification process have a tendency to change from an α-led primary phase to (α + β)-led primary phase. The primary dendrites, grain size, and lamellar spacing show a tendency to decrease first before increasing with increasing current density. Microhardness and high-temperature yield strength increase with a decrease in primary dendrite spacing, grain size, and lamellar spacing. Correlations between primary dendrite spacing, lamellar spacing, microhardness, yield strength, and current density are described by a fitting formula. An increase of α phase, due to the application of electric current, results in improved microhardness. The yield strength of Ti-48Al-2Cr-2Nb alloy increases linearly with microhardness. Yield stress increases with a decrease in microstructure parameters, in accordance with the Hall-Petch equation. The predominant modification mechanism with electric current application for TiAl solidification is the variation of supercooling and temperature gradients ahead of the mush zone due to Joule heating.