Effect of heat treatment on microstructures and mechanical properties in a full lamellar PM TiAl alloy

Meike Su,Jie Yan,Kai Guan,Hu Zhang,Lijing Zheng,Zebao Lang

doi:10.1590/s1516-14392012005000059

Abstract

The effect of heat treatment on the microstructures and tensile properties of a powder metallurgical (PM) TiAl based alloy has been investigated in this paper. The near gamma (NG) microstructure is transformed to a full lamellar (FL) microstructure with an average grain size of 100 μm by heat treatments. The lamellar spacing of FL structure decreases with the increase of cooling rate. For cooling rates of 5, 10 and 50 °C/min, the lamellar spacing is 1.9, 1.0 and 0.8 μm respectively. The room temperature tensile properties exhibit an increasing trend with decrease of lamellar spacing.

Highlights

TiAl alloys are attractive for aerospace and automobile applications because of their low density, good hightemperature strength and acceptable oxidation resistance
The formation of lamellar structure after heat treatment indicates that near gamma (NG) microstructure is transformed into single α phase during holding at 1340 °C, and lamellar structure is formed during cooling via the precipitation of γ plates in the α grains during cooling after heat treatment[16]
When three different cooling rates are compared, it is evident that cooling rate has no marked influence on the optical microstructure morphology; fully lamellar structures with the same average grain size of about 100 μm are produced by heat treatments

Summary

Introduction

TiAl alloys are attractive for aerospace and automobile applications because of their low density, good hightemperature strength and acceptable oxidation resistance. The mechanical behavior of these alloys strongly depends on their crystallographic texture and microstructure, evolve during the fabrication processes[9]. The TiAl alloys can be fabricated by traditional casting and ingot metallurgy, but the process may cause of coarse-grained lamellar, a sharp casting texture, and chemical inhomogeneity in the microstructure[10]. In compared of common ingot metallurgy, PM have advantage in eliminating compositional segregation, realizing the macro net-shape forming, and can effectively solve the TiAl intermetallic shaping of difficulty[11,12,13]. It is one of the main preparations for TiAl alloys. PM technique has attracted more and more interest due to the improvement in powder production and consolidation techniques such as hot isostatic pressing and current auxiliary sintering[14,15]

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Conclusion