Influence of environment, loading frequency and temperature on fatigue crack growth mechanisms in titanium lamellar microstructures

Document Type

Conference Proceeding

Date of Original Version

12-1-2005

Abstract

High temperature fatigue crack growth experiments were carried out on Ti6242 alloy with large colony size in both air and vacuum environment. The alloy was heat treated to provide two different lamella size; fine and coarse. Tests were conducted at two temperatures, 520°C and 590°C, using two loading frequencies; 10 Hz and 0.05 Hz in air and 0.05 Hz in vacuum. All tests were performed at a stress ratio of 0.1. This study shows that at 520°C/air, the fatigue crack growth rate is not significantly influenced by changes in the lamella size microstructure. For 0.05 Hz / low ΔK, however, the fatigue crack growth rate is higher in the fine lamellar microstructure and is accompanied with the appearance of a plateau. In air environment, the fatigue process is predominantly controlled by one single mechanism associated with transcolony fracture and formation of quasi-cleavage facets. In Vacuum conditions, the crack growth rate is not greatly influenced by temperature or lamella size. In comparing the fatigue crack growth rate in air and vacuum, the vacuum results are generally lower than the corresponding ones in air within the ΔK= 18-25 MPa√m. Above this level, the CGR data in both air and vacuum coincides thus indicating the role of environment in the low ΔK growth stage. A general hypothesis explaining the crack growth mechanisms in both air and vacuum is made in this study on the basis of scanning electron microscopic observations of the crack growth path in relation to the lamella direction as a function of loading frequency, temperature, lamella size and test environment.

Publication Title, e.g., Journal

11th International Conference on Fracture 2005, ICF11

Volume

6

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