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

Zhanxing Chen,Jingjie Guo,Hengzhi Fu,Hongsheng Ding,Ruirun Chen

doi:10.1038/s41598-019-41881-z

Zhanxing Chen, Jingjie Guo + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-41881-z

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Journal: Scientific Reports	Publication Date: Apr 2, 2019
Citations: 3	License type: open-access

Affiliation: Harbin Institute of Technology

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 α2 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.

Highlights

The solidification process of melts controls the crystal growth morphology and, the columnar to equiaxed transition (CET)
We show here that refining TiAl alloys with electric current application leads to a fine-grained microstructure, and gives rise to a higher ductility and improved deformability
The application of a lower direct current density ranging from 32 × 103 A/m2 to 64 × 103 A/m2 generates intensive dendrite morphology at the top and a reduced primary dendritic spacing, which increases with an increase in current intensity (Fig. 1(b,c))

Summary

Introduction

The solidification process of melts controls the crystal growth morphology and, the columnar to equiaxed transition (CET). 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. The correlation between microstructure and microhardness, and the correlation between microstructure and compressive deformation at high-temperatureare discussed

Methods

Results

Conclusion