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

Abstract

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 2 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.

Review on Progress of Lamellar Orientation Control in Directionally Solidified TiAl Alloys

“…A direct relationship exists between lamellar orientation and the growth direction of the primary phase, as shown in Figure 1 [ 19 ]. Nevertheless, factors affecting solidification paths are complicated and diverse.…”

“… Schematics of the relationship between the lamellar orientation and the growth direction of the primary phases: ( a ) crystal orientation and lamellar orientation of α phase; and ( b ) crystal orientation and lamellar orientation of β phase [ 19 ]. …”

Effect of cavity shape on microstructural evolution of pure aluminum in electrically-assisted solidification

“…To overcome these drawbacks, treatment of liquid metal using external energy, including mechanical vibration 13 – 15 , electromagnetic stirring 16 – 19 , and ultrasonic vibration 20 – 22 , have been introduced, which can be alternative methods to obtain mechanical properties that meet the requirements of the end products. Recently, a casting method using an electric current as an external energy source has been proposed 23 – 26 . In this method, an electric current is applied directly to the liquid metal through the electrodes during solidification.…”

Simultaneous Densification and Improvement of Cold Spray Additively Manufactured Ti-6Al-4V Properties via Electro Plastic Treatment

“…Previous studies suggest that direct resistance heating is highly promising to achieve the best combination of titanium properties compared to the other conventional oven heating and cooling methods such as water quenching [28][29][30][31][32][33][34]. The resistive heating followed by air-cooling leads to formation of ne martensitic microstructure with mechanical properties superior to the costly bimodal α + β titanium microstructure [28].…”