No abstract

The creep behavior of 15 vol pct TiBw/Ti composite and unreinforced Ti was investigated at 873 to 923 K. The 15 vol pct TiBw/Ti composite exhibited a stress exponent of 4.6 to 4.7 and an activation energy of 300 kJ/mol, which were close to those for the lattice diffusion of ␣-Ti. Finally, the creep resistance of the composite was about one order of magnitude higher than that of unreinforced Ti.

Static and cyclic creep tests of Al-15 vol% TiB 2 in situ composite were carried out at 573-623 K. The values of apparent stress exponent and activation energy for cyclic creep of the composite were much higher than that for static creep. Furthermore, the cyclic creep rate tended to decrease with increasing percentage of unloading amount but was independent of the loading frequencies under the frequency ranges investigated. Finally, the true stress exponent of the composite was equal to 8, and the true activation energy was close to the value for the lattice self-diffusion of aluminum by incorporating a threshold stress for the analysis.

Aluminum-borate (AlBO) whisker-reinforced AA6061 composite fabricated by squeeze casting was subjected to both tensile and creep investigations. The whisker exhibited a significant reinforcing effect on as-extruded AA6061, but not for T6-treated specimen. The yield strength of the composite decreased slightly after T6 treatment. This was caused by the degradation of the whiskers and the microcrack initiation. The incorporation of the AlBO whisker into the AA6061 improved the creep resistance of the alloy by several orders of magnitude. Moreover, the composite exhibited higher values of apparent stress exponent and apparent activation energy for both the static and cyclic creep. Finally, cyclic creep retardation behavior was observed for both reinforced and unreinforced AA6061.