| High strength, high conductivity copper alloys are candidate materials for high heat flux applications in fusion systems. In these applications, copper alloys must withstand exposure in extreme irradiation and thermal conditions. Most studies have concentrated on the influence of temperature, environment, irradiation exposure and microstructure on tensile properties. Relatively few studies have been performed on fatigue and fracture behavior of these alloys. This work aims to characterize and understand fracture, fatigue and creep-fatigue for three copper alloys, dispersion-strengthened CuAl25, and precipitation-hardened CuCrZr and CuNiBe.; The role of temperature and environment on the fracture behavior of copper alloys was examined in vacuum between 20 and 300°C. This was accomplished through mechanical tests, microstructural examination and in-situ TEM straining experiments. The results showed that all three copper alloys experienced a loss of fracture resistance at elevated temperatures. Environment is not the single, or even most important, factor contributing to poor toughness at high temperatures. The evaluation of fracture mechanisms revealed that grain boundaries have a significant impact on the fracture behavior of copper alloys.; The influence of irradiation on the fatigue behavior of two selected copper alloys, CuAl25 and CuCrZr, was evaluated. The fatigue lives were estimated from tensile properties using the Universal Slopes method. It was found that the influence of irradiation on fatigue performance was not as severe as on tensile properties. The Universal Slopes method provides a reasonable prediction of fatigue response for most unirradiated and irradiated conditions.; The fatigue performance of CuAl25 and CuCrZr and OFHC copper was also evaluated under creep-fatigue loading conditions. It was found that creep and stress relaxation have a major impact on fatigue behavior. Fatigue lives were reduced notably with hold time even at room temperature. Hold times are most damaging at low strain ranges and long fatigue lives. This effect was observed with hold periods as short as 10 seconds. Analysis revealed that the stress relaxation behavior during hold is comparable to transient creep behavior where dislocation glide is the dominant creep deformation mechanism. It was also determined that crack initiation and propagation at grain boundaries was accelerated under creep-fatigue loading conditions. |
