Ambient to high temperature fracture toughness and fatigue-crack propagation behavior in a Mo-12Si-8.5B (at.%) intermetallic

Citation
H. Choe et al., Ambient to high temperature fracture toughness and fatigue-crack propagation behavior in a Mo-12Si-8.5B (at.%) intermetallic, INTERMETALL, 9(4), 2001, pp. 319-329
Citations number
49
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Material Science & Engineering
Journal title
INTERMETALLICS
ISSN journal
0966-9795 → ACNP
Volume
9
Issue
4
Year of publication
2001
Pages
319 - 329
Database
ISI
SICI code
0966-9795(200104)9:4<319:ATHTFT>2.0.ZU;2-8
Abstract
Boron-containing molybdenum silicides have been the focus of significant re search of late due to their potentially superior low-temperature "pest" res istance and high-temperature oxidation resistance comparable to that of MoS i2-based silicides; however, like many ordered intermetallics, they are pla gued by poor ductility and toughness properties. Of the Various multiphase Mo-Si-B intermetallic systems available, alloys with compositions of Mo-12S i-8.5B (at.%), which contain Mo, Mo3Si, and T2 phases. are anticipated to h ave higher toughnesses because of the presence of the relatively ductile Mo phase. In this study, we examine the ambient to high (1300 degreesC) tempe rature fracture toughness (R-curve) and fatigue-crack growth characteristic s of Mo-12Si-8.5B. with the objective of discerning the salient mechanisms governing crack growth. It is found that this alloy displays a relatively h igh intrinsic (crack-initiation) toughness at 800 up to 1200 degreesC (simi lar to 10 MPa rootm), but only limited extrinsic R-curve (crack-growth) tou ghness. Although the lack of extrinsic toughening mechanisms is not necessa rily beneficial to quasi-static properties, it does imply in a brittle mate rial that it should show only minimal susceptibility to premature failure b y fatigue, as is indeed observed at temperatures from ambient to 1300 degre esC. Of particular significance is that both the fracture toughness and the threshold stress intensity for fatigue are increased with increasing tempe rature over this range. This remarkable property is related to a variety of toughening mechanisms that become active at elevated temperatures, specifi cally involving crack trapping by the alpha -Mo phase and extensive microcr acking primarily in the Mo5SiB2 phase. Published by Elsevier Science Ltd.