Influence of process parameter variation during thermo-mechanical processing of an intermetallic β-stabilized γ-TiAl based alloy

Abstract

The effort of weight reduction in modern aircraft engines, while improving performance and efficiency, demands novel light-weight high temperature materials to replace heavy nickel-based superalloys for low pressure turbine blades. Low density, high specific stiffness, elevated-temperature strength retention as well as good environmental resistance make γ-TiAl based alloys a promising substitute. The requirement for high and balanced mechanical properties of low pressure turbine blades in next generation aircraft engines favors a hot working strategy. Thermo-mechanical processing, however, of γ-TiAl based alloys is a challenging task due to a narrow “processing window”. Isothermal forging, state-of-the-art process for this material class, leads to high tooling and forging costs. With this in mind, Böhler Schmiedetechnik GmbH & Co KG has developed a “near conventional” thermo-mechanical processing technology. A die temperature about 400°C to 800°C below billet temperature and processing under standard atmosphere as well as usage of a conventional hydraulic press with high ram speed result in a more economical process. Subsequent heat treatment strategies can be used to tailor microstructure and, therefore, mechanical properties according to customer requirements.This paper summarizes industrial forging trials as well as mechanical testing and shows the effect of process variations on the final components' properties.