Effects of Al and Mo on Microstructure and Hardness of As-Cast TNM TiAl Alloys

Gang Yang,Yuewen Zhai,Yongfeng Liang,Yongsheng Wang,Junpin Lin,Xiangjun Xu,Guojian Hao

doi:10.3390/met11111849

Abstract

The effects of Al and Mo elements on the microstructure and hardness of TNM TiAl alloys (Ti-43.5Al-4Nb-1Mo-0.1B) were studied by decreasing 0.5 at.% Mo and/or increasing 1.5 at.% Al. The results showed that the changed composition of the alloy had a slight influence on the morphology, but had important effects on the volume fraction, size, and composition of each phase. All the alloys had nearly full lamellar (NL) microstructures, with a few βo phases at the boundaries of the colony or in the lamellar colony. The lamellar colony size and the lamellar spacing increased with the decrease in Mo and the increase in Al. The reduction in Mo content reduced the content of each phase in proportion, but the increase in Al content in the alloys led to the corresponding increase in Al content in the α2 and γ phases. The hardness of the alloys decreased with the increase in Al content and the decrease in Mo content. This is mainly due to the increase in lamellar spacing caused by the change in composition. Therefore, the increased content of Al and decreased Mo content are unbeneficial for the microstructure. The relationship between the Vickers hardness and the lamellar spacing obeyed the Hall–Petch relationship.

Highlights

Published: 17 November 2021Due to their low density, relatively high specific strength, etc., TiAl-based alloys have been successfully applied as turbocharger wheels in car engines and low-pressure turbine blades in aero engines [1,2]
Comparing our microstructures with those of Burtscher [32], we find that the effect of colony boundaries exists for their testing, but the effect of the βo phase is an additional phenomenon for the present alloy; we have a similar formula with a different coefficient
The lamellar colony size and the lamellar spacing have inincreased with the decrease in Mo alloy (Mo) and the increase in Al

Summary

Introduction

Published: 17 November 2021Due to their low density, relatively high specific strength, etc., TiAl-based alloys have been successfully applied as turbocharger wheels in car engines and low-pressure turbine blades in aero engines [1,2]. TiAl alloys with an excess of the Al element have poor mechanical performance, due to rapid grain growth in the single phase region. It has been found that TiAl alloys with a lower Al content have changed the overall properties [7,8,9]. Numerous elements, such as Nb, W, Mo, Zr, Ta, and Cr, or interstitial elements, such as C, B, and N, have been introduced into TiAl alloys in order to obtain useful phases for increasing their service temperature [10,11,12]. The Nb element increases the oxidation resistance, melting point, and high-temperature strength of TiAl

Methods

Discussion

Conclusion