Effects of ultrasonic vibration on the microstructure and mechanical properties of high alloying TiAl

Abstract

To modify the microstructure and enhance performances, the ultrasonic vibration is applied in the mould casting of TiAl alloy. The effects and mechanism of ultrasonic vibration on the solidifying microstructure and mechanical properties are investigated and the model for predicting lamellar colony size is established. After ultrasonic vibration, the coarse microstructure is well modified and lamellar colony is refined from 534 μm to 56 μm. Most of precipitated phases are dissolved into the lamellar colony leading to a homogenous element distribution. The phase ratio of α2-Ti3Al and γ-TiAl is increased, and the chemical composition is promoted to more close to equilibrium level by weakening the influence of β-alloying elements. The microhardness and yield strength are gradually improved by 23.72% and 181.88% due to the fine grain strengthening, while the compressive strength is enhanced by 24.47% through solution strengthening. The critical ultrasonic intensity (Ib) for TiAl alloy is estimated at 220 W cm−2 and the model for average lamellar colony size is established as . The ultrasonic refinement efficiency exponentially increases as the ultrasonic vibration time with a theoretic limit maximum value of Elim = 88% and the dominating refinement mechanism by ultrasonic vibration is the cavitation-enhanced nucleation rather than cavitation-induced dendrite fragmentation.

On the microstructural refinement in commercial purity Al and Al-10 wt% Cu alloy under ultrasonication during solidification

“…An emerging alternative to addressing the inherent limitations of chemical inoculation is to apply a physical field such as high-intensity mechanical shear [10], electromagnetic [11] or permanent magnetic stirring [12], electric current pulse [13], or low frequency mechanical vibration [14] during solidification. Among the various physical refinement techniques, application of high-intensity ultrasound has shown promising grain refinement results for Mg-alloys [15][16][17], Al-alloys [15,[18][19][20], and TiAl alloys [21,22]. Direct introduction of ultrasound into the melt during solidification could be an alternative grain refinement approach to inoculation for relatively low-melting alloys.…”

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

“…The application of an external energy field to metal liquid during solidification is a new way to change the behavior of nucleation and crystal growth and to modify the structure and enhance the mechanical properties of the solid. These fields, such as ultrasonic 1 , electromagnetic 2,3 , gravitational 4 , and electric current 5 , have shown to have great effects on the structural features and quality of cast metal. Processing technologies involving electric current are efficient, economical, and environmental methods of microstructural modification and have gained great attention in materials science, due to the resulting significant grain refinement, homogeneity and performance improvement.…”

Continuous Casting of TiAlNb Alloys with Different Velocities by Mixing Binary TiAl Ingot and Nb Wire

“…It was the b stable element and expanded b phase region. [20] In research the casting ma-/microstructure, mechanical property, grain size, microstructure homogeneity, and cracking tendency were studied and discussed with the different R. To acquire the TiAl alloys with high Nb will be difficult and with segregation phases by using the easy method of casting.…”