Accelerated shrinkage of creep cavities by thermal cycling of dispersion-strengthened aluminum

High-temperature engineering materials which develop creep cavities in service can be rejuvenated by intermediate annealing, with or without external hydrostatic pressure, to close creep cavities. We report here experimental data of creep cavity shrinkage for dispersion-strengthened-cast aluminum with about 23% submicron Al₂O₃ dispersoids, annealed isothermally or subjected to thermal cycling without applied stress. We demonstrate that thermal cycling increases the rate of cavity shrinkage relative to isothermal annealing, allowing for recovery of full theoretical density in a shorter time. Isothermal and thermal cycling densification is considered in light of diffusive cavity shrinkage mechanisms, and a simple model considering thermal mismatch stresses is employed to estimate the enhanced rate of densification during thermal cycling.