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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 57616 (07)
- University: Sharif University of Technology
- Department: Materials Science and Engineering
- Advisor(s): Serajzadeh, Siamak
- Abstract:
- In this study, the creep behavior of an Al-Cu alloy (AA2017) was investigated to examine mechanisms associated with cavitation, including cavity nucleation, growth, and coalescence, at intermediate temperatures. Initially, 2000-series aluminum alloy sheets underwent solution heat treatment at 495°C for 1 hour. Subsequently, the samples were subjected to artificial aging heat treatment at 210°C for 6 hours. Following the preparation process, creep tests were conducted within the temperature range of 120°C to 210°C and an applied stress range of 120 MPa to 290 MPa. Based on the stress exponent of 6.8 and activation energies of 169.9 kJ/mol and 194 kJ/mol obtained from the creep tests, dislocation climb was identified as the dominant creep mechanism within the specified temperature range. Additionally, the morphology and distribution of cavities in the microstructure were examined using optical microscopy (OM) and scanning electron microscopy (SEM). X-ray diffraction (XRD) results confirmed the presence of Al-Cu, Al-Cu-Mg, and Fe₂MnSi precipitates. The influence of second-phase precipitates on the kinetics of cavitation and cavity growth was analyzed using uniaxial tensile tests and physical creep models. Favorable sites for cavity nucleation and growth were identified, with the highest probability of nucleation observed at the interface between the precipitate and matrix, followed by quadruple junctions, triple junctions, and grain boundaries. The alloy exhibited significant sensitivity to cavitation during creep testing, with cavity coalescence notably occurring at 290 MPa and creep strains exceeding 0.015. In another part of this research, based on the experimental results, cavity growth was simulated using a two-dimensional Cellular Automata technique, considering diffusion-controlled and localized deformation-driven growth mechanisms. Quantitative analysis was performed to evaluate the microstructure's average cavity size, volume fraction, and spatial distribution. The volume fraction of cavities increased from 0.154% after one day of creep to 0.635% after seven days. Furthermore, the simulation model was employed to predict the effects of temperature, stress, second-phase precipitate distribution, and initial grain size on the alloy's cavitation rate
- Keywords:
- Creep Behavior ; Coalescence ; Simulation ; Cellular Automata ; Aluminum Alloy 2017
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