Title

Influence of loading frequency on fatigue crack growth path in α/β titanium lamellar microstructures at elevated temperatures

Document Type

Conference Proceeding

Date of Original Version

12-1-2008

Abstract

An experimental study is conducted to examine the crack tip/microstructure interactions in lamellar Ti6242 alloy. A series of heat treatments was carried out in order to produce microstructures that vary in their lamella and colony size. Fatigue crack growth experiments were performed on these microstructures at 520 and 590 °C with two loading frequencies; 10 and 0.05 Hz. The lower frequency was explored with and without hold-time imposed at the peak stress level. Results show that variations in lamella and colony size have no effects on the fatigue crack growth rate except for the early stage of crack propagation. It is also shown that the addition of a holdtime, did not alter the fatigue crack growth rate. The crack growth behavior is found, however, to be sensitive to the loading rate. For the same microstructure, the crack growth rate is lower at 10 Hz than at 0.05 Hz. The mechanism responsible for these differences is explained in terms of the slip process along two prism directions in the hexagonal αphase; a 1 and a 2 as well as the slip transmission at the alpha/beta interfaces within the crack tip plastic zone. At 0.05 Hz, the low slip density along the prism slip directions results in a1-type crack path being a predominant fracture mechanism. At 10 Hz, both a1-type and a2-type crack paths are possible fracture mechanisms. Analysis of these mechanisms is made through fracture surface examinations and measurements of the crack path orientation with respect to the long axis colony direction.

Publication Title

17th European Conference on Fracture 2008: Multilevel Approach to Fracture of Materials, Components and Structures

Volume

2

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