In Situ High-Energy X-ray Diffraction during Hot-Forming of a Multiphase TiAl Alloy

Andreas Stark,Florian Pyczak,Norbert Schell,Aristide Tchouaha Tankoua,Michael Oehring,Lars Lottermoser,Marcus Rackel,Andreas Schreyer

doi:10.3390/met5042252

Abstract

Intermetallic γ-TiAl based alloys exhibit excellent high-temperature strength combined with low density. This makes them ideal candidates for replacing the twice as dense Ni base super-alloys, currently used in the medium temperature range (~700 °C) of industrial and aviation gas turbines. An important step towards the serial production of TiAl parts is the development of suitable hot-forming processes. Thermo-mechanical treatments often result in mechanical anisotropy due to the formation of crystallographic textures. However, with conventional texture analysis techniques, their formation can only be studied after processing. In this study, in situ high-energy X-ray diffraction measurements with synchrotron radiation were performed during hot-forming. Thus, it was possible to record the evolution of the phase constitution as well as the formation of crystallographic texture of different phases directly during processing. Several process temperatures (1100 °C to 1300 °C) and deformation rates were investigated. Based on these experiments, a process window can be recommended which results in the formation of an optimal reduced texture.

Highlights

The demand to reduce both fuel consumption and greenhouse gas emissions from gas turbines and combustion engines is continuously increasing
The experiments facilitate a direct observation of the high-temperature state that is not masked by post process alterations
Formation of the deformation texture at elevated temperatures could be directly observed during the experiments

Summary

Introduction

The demand to reduce both fuel consumption and greenhouse gas emissions from gas turbines and combustion engines is continuously increasing. With conventional texture analysis techniques the texture formed can only be studied by post process metallographic methods [8,9] This means that the real high temperature material conditions are often masked by lower temperature phase transformations or recrystallization. First texture measurements after hot compression of γ-TiAl based alloys were performed by Fukutomi et al [10] and Hartig et al [11] They discussed either pure deformation or dynamic recrystallization (DRX) as the dominant texture forming mechanism. New high-energy synchrotron sources were constructed, which, in combination with advanced sample environments, provide novel tools and analysis methods for engineering and materials science [16,17,18] Such synchrotron sources offer the possibility for time-resolved in situ studies during materials processing [19,20]. We have been able to systematically analyze texture evolution of a multi-phase alloy in different phase fields, both in situ and time resolved

Experimental Section

Results and Discussion

Microstructures before and after Deformation

Texture Formation

Summary