Near Conventional Forging of an Advanced TiAl Alloy
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Near Conventional Forging of an Advanced TiAl Alloy Daniel Huber1, Helmut Clemens2 and Martin Stockinger1 1 Business Development, Research & Innovation, Böhler Schmiedetechnik GmbH & Co KG, Mariazellerstrasse 25, A-8605 Kapfenberg, Austria 2 Department Physical Metallurgy and Materials Testing, Montanuniversität Leoben, A-8700 Leoben, Austria ABSTRACT Balanced mechanical properties are needed for TiAl low pressure turbine blades envisaged for use in new generation aircraft engines. However, thermomechanical processing of J-TiAl based alloys is a challenging task due to a small “processing window”. Isothermal forging, as state of the art process for this class of material, results in high productions costs and lower productivity. Due to these facts Bohler Schmiedetechnik GmbH & Co KG has developed a higher efficient “near conventional” thermomechanical processing technology. Lower die temperature and processing at standard atmosphere as well as the use of standard hydraulic presses with higher ram speed result in a highly economical process. Subsequent heat treatment strategies can be used to tailor microstructure and, therefore, mechanical properties according to customer needs. The paper summarizes our effort to establish a near conventional forging route for the fabrication of TiAl components for aerospace industry. INTRODUCTION The strong demand for higher efficiency, reduction of fuel consumption, CO2 and NOx emissions as well as weight reduction in aircraft engines lead to a substitution of presently used materials by novel light-weight, high-temperature materials like γ-TiAl based alloys. Turbine blades are engine parts that are subjected to high mechanical and thermal loading. Thus alloys are required which provide high strength and good fatigue properties at elevated temperatures as well as a sufficient ductility at room temperature. Presently, Ni-base alloys are state of the art. World-wide fundamental research conducted over the last two decades has clearly shown that balanced material properties can be obtained by hot-working and subsequent heat treatment of TiAl alloys. Due to a small “deformation window” hot-working of TiAl alloys is a complex and challenging task and, therefore, isothermal forming processes are favored so far [1]. In order to expand the process window, a novel Nb and Mo containing γ-TiAl based alloy (TNMTM alloy) was developed [2]. As a result of a high volume fraction of disordered bcc β-phase at elevated temperatures this alloy can be hot-die forged under near conventional conditions, which entails that conventional forging equipment with minor and inexpensive modifications can be used. By means of subsequent heat treatment a significant reduction of β-phase can be achieved and mechanical properties can be tailored to customer requirements. The paper summarizes our effort to establish a near conventional forging route for the fabrication of TiAl components for aerospace industry. The path from lab scale compression tests for material data generation via finite element modeling to ind
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