Effects of R-ratio on the fatigue crack growth of Nb-Si{sub ss} and Nb-10Si in situ composites

Journal Article · Mon Jun 01 04:00:00 EDT 1998 · Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

DOI:https://doi.org/10.1007/s11661-998-0098-x· OSTI ID:634649

Zinsser, Jr, W A; Lewandowski, J J ^[1]

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1. Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Materials Science and Engineering

The effects of changes in R ratio on the fatigue crack growth behavior of a Nb-10 at. pct Si composite as well as bulk Nb-1.24 at. pct Si were determined. Fatigue crack growth experiments were performed over a range of {Delta}K levels at R ratios of 0.1 and 0.4. Qualitative and quantitative scanning electron microscopy studies were performed to characterize the fatigue fracture features of the composites and alloys, in order to determine the factors controlling these fracture features. The results of this work indicate that increases in R ratio reduce the observed threshold stress intensities in both materials. Somewhat higher fatigue thresholds were observed in the Nb-Si{sub (ss)} alloy, which exhibited no evidence of cleavage fracture in fatigue at any R ratio or {Delta}K level, the Nb-Si{sub (ss)} constituent in the Nb-10 at. pct Si composite exhibited a distinct fracture mode transition from ductile tearing near threshold and low {Delta}K to cleavage fracture with an increase in {Delta}K and K{sub max}. Possible reasons for such observations are provided.

• Sponsoring Organization: USDOE
• OSTI ID: 634649
• Journal Information: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 6 Vol. 29; ISSN 1073-5623; ISSN MMTAEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
CRACK PROPAGATION
FATIGUE
FRACTOGRAPHY
FRACTURE MECHANICS
FRACTURE PROPERTIES
NIOBIUM
NIOBIUM SILICIDES