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Physical and Mechanical Properties of Mo5X3+α (X=Si, B, C) Single Crystals

Published online by Cambridge University Press:  11 February 2011

Taisuke Hayashi ,
Kazuhiro Ito ,
Katsushi Tanaka  and
Masaharu Yamaguchi
Taisuke Hayashi
Affiliation:
Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606–8501, Japan
Kazuhiro Ito
Affiliation:
Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606–8501, Japan
Katsushi Tanaka
Affiliation:
Department of Advanced Materials Science Faculty of Engineering, Kagawa University, Takamatsu 761–0396, Japan
Masaharu Yamaguchi
Affiliation:
Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606–8501, Japan
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Abstract

Mo5X3+α (X=Si, B, C) intermetallic compounds such as Mo5SiB2 (D8l), Mo5Si3 (D8m) and Mo5Si3C (D88) have a great potential for ultra-high temperature applications. The present study was undertaken putting greater emphasis on clarifying how their physical and mechanical properties are similar or different in terms of a structure type. Some interesting features are summarized in this paper.

The resistivity of Mo5SiB2, Mo5Si3 and Mo5Si3C single crystals exhibited a negative curvature (d2ρ(T)/dT2<0), with a tendency towards saturation. In the Mo5Si3C with large ρ0 due to impurity carbon atoms, resistivity saturation is pronounced. In contrast, a much higher temperature is required to reach saturation in the Mo5SiB2. The anisotropy ratio of CTE (αc/αa) for the Mo5SiB2 is about 1.2–1.6 and is significantly reduced from about 2 of the Mo5Si3 and Mo5Si3C. On the other hand, the Young's modulus of the Mo5SiB2 is more anisotropic than those of the Mo5Si3 and Mo5Si3C. Plastic anisotropy was observed in the Mo5SiB2, because only slip on [001] {100} is operative at 1500°C. On the contrary, plastic deformation was observed at temperatures above 1300°C for the Mo5Si3C and Mo5Si3. Anisotropy of their plastic deformation was much less than that of the Mo5SiB2, presumably because more than two slip systems can be activated. Creep resistance of the Mo5SiB2 is much better than that of the Mo5Si3 as well as the most advanced materials such as MoSi2 and Si3N4 based structural ceramics.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 753: Symposium BB – Defect Properties and Related Phenomena in Intermetallic Alloys , 2002 , BB5.27
Copyright
Copyright © Materials Research Society 2003

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