A deformation mechanism in B2 ordered matrix composites
The B2 ordered intermetallic compound, NiAl, has many attractive properties as a high temperature structural material. However, its lack of creep resistance prevents practical applications. Adding ceramic reinforcements, such as TiB{sub 2} particles, Al{sub 2}O{sub 3} particles or whiskers can significantly improve the strength of binary NiAl. However, the increase in the yield stress of the discontinuous NiAl matrix composites is difficult to explain. The purposes of this research were to understand the deformation mechanisms which cause the increase in strength achieved by adding TiB{sub 2} particles, Al{sub 2}O{sub 3} particles or whiskers to NiAl, and to recognize the principles of the deformation process in NiAl matrix composites. In order to accomplish this objective, mechanical properties and thermal activation parameters in NiAl matrix composites with different types, shapes and sizes of reinforcements have been systematically evaluated. Microstructures and dislocation structures in NiAl matrix composites have also been thoroughly characterized before and after deformation. It was found that the size of the reinforcement had a large influence on the microstructures of the composites, and the nominal activation ;energies for all the composites were the same and within the range of the activation energy of self-diffusion for pure NiAl. This indicated that the deformation mechanism was the same for all NiAl matrix composites. The thermally activated motion of jogged screw dislocations is postulated as the rate controlling mechanism of the deformation of NiAl matrix composites. However, this non-conservative motion of jogged screw dislocation theory requires only the appearance of vacancy producing (VP) jogs. Based on the unique B2 ordered structure, a cross-slip model is proposed to account for the occurrence of VP jogs.
- Research Organization:
- Materials Engineering Associates, Inc., Lanham, MD (US)
- Sponsoring Organization:
- US Department of the Navy, Office of Naval Research (ONR)
- OSTI ID:
- 20014208
- Resource Relation:
- Conference: 1999 TMS Fall Meeting, Julia R. Weertman Symposium: Advanced Materials for the 21st Century, Cincinnati, OH (US), 10/31/1999--11/04/1999; Other Information: PBD: 1999; Related Information: In: Advanced materials for the 21st century: The 1999 Julia R. Weertman symposium, by Chung, Y.W.; Dunand, D.C.; Liaw, P.K.; Olson, G.B. [eds.], 585 pages.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Strengthening of NiAl matirix composites (Annual report October 1, 1994-November 30, 1995)
Evolution of B2 and laves phases in a ferritic steel under Fe2+ ion irradiation at 475 °C