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.