A Comparison of Microstructural Effects on Fatigue-Crack Initiation and Propagation in Ti-6Al-4V.
Abstract
Fatigue-crack initiation and propagation studies were conducted on commercial purity (0.20 weight percent interstitial oxygen) Ti-6Al-4V rolled plate, heat treated to produce three differing microstructures. The three heat treatments were an as-received mill anneal (MA), a recrystallization anneal (RA), and a beta anneal (BA). The fatigue-crack propagation results show a distinct ordering of crack growth rate (da/dN) versus stress-intensity range (delta K) curves on the basis of microstructure. The coarse-grained Widmanstatten BA material exhibits the greatest resistance to crack propagation, and the finer-grained MA material offers the least crack propagation resistance. For fatigue-crack initiation, results obtained from blunt-notch WOL-type fracture mechanics specimens reveal a different ordering in relation to microstructure. The MA and RA materials are indistinguishable in their resistance to crack initiation; moreover, their crack initiation resistance is moderately superior to that of the BA material in the low-cycle regime (i.e., less than 100000 cycles to crack initiation). However, at approximately 1000000 cycles to crack initiation, the fatigue resistance of the BA material appears equivalent to that of the MA and RA materials. In the crack initiation specimens, a theoretical stress concentration factor (K(t)) of 4.1 was used. This corresponds to Kt values determined for titanium alloy jet engine components. The influence of surface roughness in the crack initiation region of blunt-notch specimens was examined; no difference in cycles-to-initiation behavior was observed for 16 and 72 micron-in. finishes, regardless of microstructure.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 05, 1982
- Accession Number
- ADA111610
Entities
People
- George R. Yoder
- L. A. Cooley
- Thomas W. Crooker
Organizations
- United States Naval Research Laboratory