ECI Digital Archives

Title

Enhanced oxidation resistance of Ti-rich Mo-Si-B alloys by pack-cementation process

Authors

Camelia Gombola, Karlsruhe Institute of TechnologyFollow
Daniel Schliephake, Karlsruhe Institute of Technology
Martin Heilmaier, Karlsruhe Institute of Technology
John H. Perepezko, University of Wisconsin - Madison

Conference Dates

July 17-21, 2016

Abstract

To increase efficiency by higher combustion temperatures of aircraft engines and energy generation, new high temperature materials are inevitable. Mo-Si-B alloys for example satisfy several requirements such as good oxidation and creep resistance. Recently, novel Ti-rich Mo-Si-B alloys have shown an increased creep resistance compared to Ti-free Mo-Si-B alloys by the formation of Ti-silicide precipitates during processing. However, due to the formation of a duplex SiO₂ – TiO₂ oxide layer, where fast inwards diffusion of oxygen takes place, the oxidation resistance is poor.

In this study we show that oxidation resistance of Mo-Si-B-Ti alloys can be enhanced drastically at temperatures ranging from 800 to 1200°C for several hundreds of hours by pack-cementation application of a borosilica based coating. The Mo-12.5Si-8.5B-27.5Ti (in at.%) substrate was produced by repetitive arc-melting of high-purity metals, Si and B in a high-purity argon atmosphere. After homogenization treatment at 1600°C for 100h slices of this alloy were prepared for pack-cementation. The pack-cementation was done in an atmosphere of high-purity argon at 1000°C for 40h, followed by a conditioning step at 1400°C for 10h in air. The resulting layer consists of an outer borosilica layer followed by an inner MoSi₂ and Mo₅Si₃ layer. To study the oxidation behavior, both isothermal and cyclic oxidation tests were carried out. After an initial mass loss during the first hours of oxidation, a steady state is reached for tests up to 1000 hours. To demonstrate the high stability of the outer borosilicate layer SEM cross-sections were prepared after different times of oxidation.

Recommended Citation

Camelia Gombola, Daniel Schliephake, Martin Heilmaier, and John H. Perepezko, "Enhanced oxidation resistance of Ti-rich Mo-Si-B alloys by pack-cementation process" in "Beyond Nickel-Based Superalloys II", Chair: Dr Howard J. Stone, University of Cambridge, United Kingdom Co-Chairs: Prof Bernard P. Bewlay, General Electric Global Research, USA Prof Lesley A. Cornish, University of the Witwatersrand, South Africa Eds, ECI Symposium Series, (2016). https://dc.engconfintl.org/superalloys_ii/22