The tensile and compressive creep properties of coarse- and fine-grained dispersion-strengthened aluminum with 25 vol.% submicron alumina dispersoids are presented for temperatures between 335°C and 500°C and stresses between 30 MPa and 110 MPa. For all stresses investigated, the minimum creep rate is higher in tension than in compression, because cavitation is the main deformation mechanism in tension. In compression, however, dislocation creep is the dominant deformation mechanism at all stresses for the large-grained material and at high stresses for the fine-grained material, while diffusional creep dominates in the fine-grained material at low stresses. The apparent stress exponents for both diffusional creep and dislocation creep are much higher than for unreinforced aluminum, indicating that the dispersoids strongly inhibit both mechanisms. The threshold stresses determined experimentally for dislocation creep are significantly higher than those predicted by existing climb or detachment models, which consider the interaction of a single dislocation with dispersoids. Since transmission electron microscopy reveals that several dislocations typically interact with a single dispersoid, the modified threshold stress model presented in the theoretical companion article  is applicable, whereby the stress of dislocation pile-ups upon the threshold-controlling dislocation is taken into account. Good agreement is found between the experimentally determined threshold stresses and theoretical predictions from that model. The same model can also satisfactorily explain the very high measured values of the apparent activation energy.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys