Thermal stability and its effects on the mechanical properties of rapidly solidified Al-Ti alloys

Microstructure and mechanical properties of the rapidly solidified (RS) Al- Ti alloy after thermal exposure treatment have been investigated. It is rev ealed that the Al3Ti particle: which disperses homogeneously within the Al matrix, is coarsened via a volume diffusion controlled growth mechanism des cribed by the LSW equation. The coarsening rate increases with increasing v olume fraction of the particle. The Young's modulus of the Al-Ti alloy incr eases with increasing particle volume fraction, which can be predicted by t he Halpin-Tsai equation and the Eshelby method. The modified shear lag mode l used to estimate Young's modulus of the particulate reinforced composite is hereby re-modified to give a more precise evaluation. The yield strength of the RS Al-Ti alloy is found to increase with increasing volume fraction and decreasing particle size of the reinforcement. It is indicated that th e continuum strengthening mechanists (the modified shear lag model and the Eshelby model) fails to explain the increased yield strength. Therefore, st rengthening mechanisms based on dislocation movement have been taken into a ccount. Considering microstructure changes in the matrix due to the presenc e of the reinforcement. the Eshelby type model is believed to give the yiel d strength of the RS Al-Ti alloy quite accurately. (C) 2000 Elsevier Scienc e S.A. All nights reserved.