Mechanisms of ambient temperature fatigue crack growth in Ti-46.5Al-3Nb-2Cr-0.2W
- Univ. of Dayton Research Inst., OH (United States). Structural Integrity Div.
- Wright Lab., Wright-Patterson AFB, OH (United States)
- Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering
Fatigue crack growth studies have been conducted on a two-phase alloy with a nominal composition of Ti-46.5Al-3Nb-2Cr-0.2W (at. pct), heat treated to produce duplex and lamellar microstructures. Fatigue crack growth tests were conducted at 23 C using computer-controlled servohydraulic loading at a cyclic frequency of 20 Hz. Several test methods were used to obtain fatigue crack growth rate data, including decreasing-load-range-threshold, constant-load-range, and constant-K{sub max} increasing-load-ratio crack growth control. The lamellar microstructure showed substantial improvement in crack growth resistance and an increase in the threshold stress intensity factor range, {Delta}K{sub th}, when compared with the behavior of the duplex microstructure. The stress ratio had a significant influence on crack growth behavior in both microstructures, which appeared to be a result of roughness-induced crack closure mechanisms. Fractographic characterization of fatigue crack propagation modes indicated a highly tortuous crack path in the fully lamellar microstructure, compared to the duplex microstructure. In addition, limited shear ligament bridging and secondary cracking parallel to the lamellar interfaces were observed in the fully lamellar microstructure during fatigue crack propagation. These observations were incorporated into a model that analyzes the contribution of intrinsic vs extrinsic mechanisms, such as shear ligament bridging and roughness-induced crack closure, to the increased fatigue crack growth resistance observed for the fully lamellar microstructure.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 484838
- 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: 3A Vol. 28; ISSN MMTAEB; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
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