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Role of Microstructure in Promoting Fracture and Fatigue Resistance in Mo-Si-B Alloys

Published online by Cambridge University Press:  26 February 2011

J. J. Kruzic*
Affiliation:
Department of Mechanical Engineering, Oregon State University, Corvallis, OR 97331, U.S.A.
J. H. Schneibel
Affiliation:
Oak Ridge National Laboratory, Metals and Ceramics Division, Oak Ridge, TN 37831, U.S.A.
R. O. Ritchie
Affiliation:
Department of Materials Science and Engineering, University of California, and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, U.S.A.
*
* Tel: +1–541–737–7027; fax: +1–541–737–2600. E-mail address: jamie.kruzic@oregonstate.edu
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Abstract

An investigation of how microstructural features affect the fracture and fatigue properties of a promising class of high temperature Mo-Si-B based alloys is presented. Fracture toughness and fatigue-crack growth properties are measured at 25° and 1300°C for five Mo-Mo3Si-Mo5SiB2 containing alloys produced by powder metallurgy with α-Mo matrices. Results are compared with previous studies on intermetallic-matrix microstructures in alloys with similar compositions. It is found that increasing the α-Mo phase volume fraction (17 – 49%) or ductility (by increasing the temperature) benefits the fracture resistance; in addition, α-Mo matrix materials show significant improvements over intermetallic-matrix alloys. Fatigue thresholds were also increased with increasing α-Mo phase content, until a transition to more ductile fatigue behavior occurred with large amounts of α-Mo phase (49%) and ductility (i.e., at 1300°C). The beneficial role of such microstructural variables are attributed to the promotion of the observed toughening mechanisms of crack trapping and bridging by the relatively ductile α-Mo phase.

Type
Research Article
Copyright
Copyright © Materials Research Society 2005

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