Shear ligament phenomena in Fe{sub 3}Al intermetallics and micromechanics of shear ligament toughening
- Univ. of Calgary, Alberta (Canada). Dept. of Mechanical Engineering
The environment-assisted cracking behavior of a Fe{sub 3}Al intermetallic in an air moisture environment was studied. At room temperature, tensile ductility was found to be increased with strain rate, from 10.1 pct at 1 {times} 10{sup {minus}6} s{sup {minus}1} to 14.3 pct at 2 {times} 10{sup {minus}3} s{sup {minus}1}. When tensile tests were done in heat-treated mineral oil on specimens that have been heated in the oil for 4 hours at 200 C, ductility was found to be recovered. These results suggest the existence of hydrogen embrittlement. Shear ligaments, which are ligament-like structures connected between microcracks, were observed on the tensile specimens. They undergo ductile fracture by shearing and enhance fracture toughness. This toughness enhancement (represented by J{sub l}) was estimated by a micromechanical model. The values of the unknown parameters, which are the average ligament length {bar l}, the area fraction V{sub l}, and the work-to-fracture {tau}{sub 1}{gamma}{sub 1}, were obtained from scanning electron microscopy (SEM) observation. The total fracture toughness K{sub c} and J{sub l} were reduced toward a slower strain rate. The experimental fracture toughness, K{sub Q}, was found to be increased with strain rate, from 35 MPa{radical}m at 2.54 {times} 10{sup {minus}5} mm{center_dot}s{sup {minus}1} to 47 MPa{radical}m at 2.54 {times} 10{sup {minus}2} mm{center_dot}s{sup {minus}1}. The fact that strain rate has a similar effect on K{sub Q} and K{sub c} verifies the importance of shear ligament in determining fracture toughness of the alloy. With the presence of hydrogen, length and work-to-fracture of the shear ligament were reduced. The toughening effect caused by shear ligament was reduced, and the alloy would behave in a brittle manner.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 438547
- 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: 12 Vol. 27; ISSN MMTAEB; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
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