The effect of Si addition on the creep properties of Al-10Ti was investigated. Research areas can be divided into three fields: mechanical alloying behaviors of Al-Ti-(Si) alloys; microstructural changes of as-extruded alloys; creep behavior and mechanism of Al-Ti-(Si) alloys. The supersaturated Al(Ti)powders were obtained in Al-10Ti alloy by MA processing. The maximum solid solubility of Ti in Al was about 6%. It was calculated from the change of Al lattice parameter using XRD results. The residual Ti was embedded in Al(Ti) powders as a nanosize of about 30nm. In MA of Al-10Ti-xSi alloys, Si crystal were not dissolved but distributed uniformly in Al(Ti) powders as a crushed state with a size of 0.1∼1㎛,because of the negligible solid solubility of Si in Al at an ambient temperature and the brittleness of Si crystal compared to Al and Ti crystal.
After hot extrusion processing, the formation of the stable $Al_3Ti$ of $DO_22$ structure occurred, and Si particles in MA Al-10Ti-xSi alloy powders were dissolved into $Al_3Ti$ dispersoids to replace Al, and shrinked the lattice parameters of $Al_3Ti$, i.e. from a=3.84Å to a=3.79Å, from c=8.59Å to c=8.55Å, respectively, up to an addition of 4% Si. In an addition of 6% Si, the $Ti_5Al_7Si_12$ silicide phases were observed due to the excess Si over the solid solution limit of Si in $Al_3Ti$. All alloys consist of fine grains of 0.1~0.2㎛ and dispersoids of 0.05~0.1㎛.
The creep properties of MA Al-10Ti-xSi alloys were investigated in a wide range of stress($50-310MP_a$) and temperature(300~450℃). Two distinctive creep mechanisms have been observed depending on the test stress and temperature, i.e. Coble creep at low stresses and temperatures and dislocation creep at high stresses and temperatures. Coble creep equation taking into account of the threshold stress well predicted creep data in a diffusional creep regime. True creep activation energies in dislocation creep regime calculated using modified semi-empirical creep equation taking into account of the threshold stress were reasonable agreement with that for self lattice diffusion in pure aluminum.
The transition stress and temperature from diffusional to dislocation creep in a MA Al-10Ti alloy tends to increase as a result of Si addition. This was due to the comparatively larger threshold stress in a Si containing alloy as a result of Si incorporation in the Al3Ti particles. Thus the addition of Si has an effect to enhance the creep resistance of MA Al-10Ti alloy.
The origin of threshold stress in diffusional and dislocation creep was compared with the theoretical ones. The calculated threshold stress in diffusional creep regime could be farely well explained by the interfacial dislocation climb and glide model. In dislocation creep regime, the model based on dislocation detachment from dispersoids was the best estimate of threshold stress in MA Al-10Ti-xSi alloys.
