Microstructure Evolution of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y Alloy during Long-Term Thermal Exposure.

Zhiyuan Chen,Song Chen,Xiaosong Jiang,Zhengkun Cai,Hongliang Sun,Zewen Huang

doi:10.3390/ma13071638

Abstract

The hot-rolled alloy Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y was exposed to 700 °C air for up to 10,000 h. The changes in microstructure were observed using scanning and transmission electron microscopies. It was found that the α2 laths, α2 + γ lamellae, and B2(ω) structure of the alloy showed thermodynamic instability. There were three types of phase transformation in the alloy during long-term thermal exposure. The first was α2 → γ, which occurs in the interior and boundary of the α2 + γ lamellae. The second was α2 + γ → B2(ω), which occurs on the α2 + γ boundary. In addition, B2(ω) also precipitates on the γ/γ interfaces. The third was B2(ω) → γ, which describes the precipitation of micron-scale γ phases in the B2(ω) area after thermal exposure of 5000 h. The volume fraction and size of the B2(ω) area and equiaxed γ grains continued to increase throughout the exposure process. Large-sized γ grains and a B2 area of tens of microns appeared in the microstructure after long-term thermal exposure. The volume fractions of the B2 area and the equiaxed γ grains after thermal exposure of 10,000 h reached 16.8% and 63.2%, respectively.

Highlights

Introduction γTiAl-based intermetallic alloys have been widely used in aero-engine and automobile applications to replace Ni-based and Ti-based alloys and steels [1,2,3,4]
The high-Nb-containing TiAl alloys are typically used at high temperatures ranging from 600 ◦ C to 900 ◦ C
This alloy had a duplex microstructure (DP) after hot rolling and cooling to room of the α2 + γ lamellae is almost parallel to the direction of the original α2 laths, and the lamellar temperature

Summary

Introduction

TiAl-based intermetallic alloys have been widely used in aero-engine and automobile applications to replace Ni-based and Ti-based alloys and steels [1,2,3,4]. TiAl alloys, high-Nb-containing TiAl alloys have higher tensile strength, better oxidation resistance, and high-temperature creep resistance, which have received high attention and in-depth research from various circles [5,6,7,8,9,10]. The high-Nb-containing TiAl alloys are typically used at high temperatures ranging from 600 ◦ C to 900 ◦ C. The basic characteristics of TiAl-based alloys require long-term thermal stability in the presence of air. It is very important to study the long-term thermal stability of high-Nb-containing TiAl alloys under high-temperature conditions

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