Creep behavior of in-situ Al2O3 and TiB2 particulates mixture-reinforced aluminum composites

Tensile creep tests were carried out at 573, 623 and 673 K on in-situ formed Al₂O₃ and TiB₂ particulates mixture-reinforced aluminum (Al-Al₂O₃.TiB₂) composites fabricated from TiO₂-Al-B and TiO₂-Al-B₂O₃ systems, respectively. The composite fabricated from TiO₂-Al-B system exhibited an apparent stress exponent of 15.8-17.4 and an apparent activation energy of 242 kJ mol^-1 at 56 MPa whereas the composite fabricated from TiO₂-Al-B₂O₃ system had an apparent stress exponent of 16.5-17.9 and an apparent activation energy of 305 kJ mol^-1 at 55 MPa. Two composites exhibited essentially identical creep resistance for all three testing temperatures, though the composite fabricated from TiO₂-Al-B₂O₃ system had lower in-situ particulate content due to the formation of strip-like Al₃Ti. It was demonstrated, by incorporating a threshold stress into the analysis, that for these two in-situ composites, the true stress exponent was equal 8 and the true activation energy was close to the value for lattice self-diffusion of aluminum. The results suggested that the creep of two in-situ composites was controlled by the lattice diffusion with a constant structure.