The influence of matrix microstructure and temperature on cyclic deformation and fatigue of particle-reinforced 2219 aluminum. Ph.D. Thesis
Room temperature and elevated temperature (150 C) fatigue studies were conducted on naturally aged, peak-aged, and overaged 2219/TiC/lSp and 2219 Al. In addition, the grain size of 2219/TiC/15p was altered from 35 micrometers to 276 micrometers in an attempt to understand how grain size influences the room temperature and elevated temperature cyclic deformation and fatigue life behavior. Plastic strain-controlled testing was used to study the low-cycle fatigue and cyclic response behaviors while stress-controlled testing was used to investigate the high cycle fatigue behavior. The cyclic response and dislocation microstructures of both reinforced and unreinforced materials were very similar for comparable microstructures. Naturally aged materials showed evidence of cyclic hardening, and in some cases, cyclic softening, while the cyclic response of peak-aged and overaged materials showed no evidence of cyclic hardening or softening (except for overaged 2219 Al at high plastic strain amplitudes). Decreasing grain size was found to modestly increase the cyclic flow stress of 2219/TiC/15p while providing very little improvement in the fatigue-life behavior. The addition of TiC reinforcement was found to improve the stress-controlled fatigue life provided processing defects were kept low; however, the plastic strain-controlled fatigue life of the composite was inferior to that of the unreinforced material. At 150 C, cyclic softening was observed at all plastic strain amplitudes for the composite materials and at plastic strain amplitudes greater than approximately 2.5 x 10(exp -3) for the unreinforced materials. This softening was attributed to the decomposition of the theta` strengthening precipitates to the equilibrium theta precipitates. This (theta`) decomposition occurred in all materials; however, the combination of cyclic deformation and the presence of reinforcing TiC particles appeared to greatly increase the kinetics, or rate of decomposition.
- Research Organization:
- Univ. of Michigan, Ann Arbor, MI (United States)
- OSTI ID:
- 102045
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: 1994
- Country of Publication:
- United States
- Language:
- English
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