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Microstructure and Tensile Ductility of a Ti-43Al-4Nb-1Mo-0.1B Alloy

Published online by Cambridge University Press:  28 August 2018

Laura M. Droessler ,
Thomas Schmoelzer ,
Wilfried Wallgram ,
Limei Cha ,
Gopal Das  and
Helmut Clemens
Laura M. Droessler
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria
Thomas Schmoelzer
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria
Wilfried Wallgram
Affiliation:
Bohler Schmiedetechnik GmbH&CoKG, Mariazeller Str. 25, A-8605 Kapfenberg, Austria
Limei Cha
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria
Gopal Das
Affiliation:
Pratt & Whitney, 400 Main Street M/S 114-43, East Hartford, CT 06108, USA
Helmut Clemens
Affiliation:
Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Franz-Josef-Str. 18, A-8700 Leoben, Austria
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Abstract

The microstructural development of a forged Ti-43Al-4Nb-1Mo-0.1B (in at%) alloy during two-step heat-treatments was investigated and its impact on the tensile ductility at room temperature was analyzed. The investigated material, a so-called TNM™ gamma alloy, solidifies via the β-route, exhibits an adjustable β/B2-phase volume fraction and can be forged under near conventional conditions. Post-forging heat-treatments can be applied to achieve moderate to near zero volume fractions of β/B2-phase allowing for a controlled adjustment of the mechanical properties. The first step of the heat-treatment minimizes the β/B2-phase and adjusts the size of the α-grains, which are a precursor to the lamellar γ/α2-colonies. However, due to air cooling after the first annealing step, the resulting microstructure is far from thermodynamic equilibrium. Therefore, a second heat-treatment step is conducted below the eutectoid temperature which brings the microstructural constituents closer to thermodynamic equilibrium. It was found that temperature and duration of the second heat-treatment step critically affect the solid-state phase transformations and, thus, control the plastic fracture strain at room temperature. Scanning and transmission electron microscopy studies as well as hardness tests have been conducted to characterize the multi-phase microstructure and to study its correlation to the observed room temperature ductility.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1128: Symposium U – Advanced Intermetallic-Based Alloys for Extreme Environment and Energy Applications , 2008 , 1128-U03-08
Copyright
Copyright © Materials Research Society 2009

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