TEM studies of the ternary Ti 36 Al 62 Nb 2 alloy
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TEM studies of the ternary Ti36Al62Nb2 alloy V.S.K. Chakravadhanula1, K. Kelm2, L. Kienle1*, V. Duppel3, A. Lotnyk1, D. Sturm4, M. Heilmaier5, G. J. Schmitz6, A. Drevermann6, F. Stein7, M. Palm7 1 Christian-Albrechts University Kiel, Institute for Materials Science, Synthesis and Real Structure, D-24143 Kiel, Germany 2 German Aerospace Center, Institute of Materials Research, D-51147 Cologne, Germany 3 Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany 4 Otto-von-Guericke University Magdeburg, Institute for Materials Joining and Technology, D39104 Magdeburg, Germany 5 Technical University Darmstadt, Physical Metallurgy, D-64287 Darmstadt, Germany 6 ACCESS e.V., D-52072 Aachen, Germany 7 Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany ABSTRACT Al-rich Ti-Al alloys attracted some attention during the past years due to the possibility of their application as light-weight, high-performance materials at elevated temperatures. The effect of the addition of Nb to Al-rich Ti-Al alloys has been studied for Ti36Al62Nb2 by a combined approach of transmission electron microscopy (TEM) techniques for unraveling the structure and composition at the nanoscale. Structural analyses on as-cast ternary alloys revealed the presence of h-TiAl2-, Ti3Al5- and Ȗ-TiAl-type phases. After heat treatment, phase transformations like the replacement of the metastable h-TiAl2-type by the stable r-TiAl2-type were identified. Additionally, changes of the microstructural features like the formation of interfaces with different orientation relationships are apparent. The orientation and interfacial relationships involved are compared to those of binary Ti-Al alloys rich in Al. INTRODUCTION The potential of Al-rich Ti-Al alloys as light-weight, high-performance materials at elevated temperatures attracted scientific attention during the past years [1]. While it is possible to produce lamellar microstructures in Al-rich Ti-Al alloys [2], comparable to those in near ȖTiAl alloys which are nowadays entering technical applications, their mechanical properties remain unsatisfactory. Refractory elements like Nb improve creep resistance as well as tensile ductility of the Ti-Al alloys. Moreover, besides the beneficial effect of lamellar microstructures in improving mechanical properties, the fracture toughness, elevated temperature strength and oxidation resistance are further more enhanced by the addition of Nb [3]. In the present work, the effect of the addition of Nb on the microstructure of Al-rich TiAl alloys has been examined. Binary Al-rich Ti-Al alloys have been studied to some extent and thus microstructures, phase relations and orientation relationships are basically established [4,5]. To our knowledge, no study has been published until now concerning the influence of niobium additions on the microstructure and phase evaluation of Al-rich Ti-Al alloys. EXPERIMENTAL Samples of the alloy Ti36Al62Nb2 have been studied in the as-cast state and after heattreatment at 1000 °C in Ar for 100 h and subsequent
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