Enhance the thermal stability and glass forming ability of Al-based metallic glass by Ca minor-alloying

In order to stabilize the supercooled liquid and enhance the glass forming ability of Al-based glass forming alloy, the alloying design based on minor Ca substitution for Al was examined to retard the precipitation of face-centered-cubic (FCC) Al. Calcium was selected as the alloying element, because it has a large negative mixing heating with Al but a positive value with the other components. This is anticipated to facilitate formation of Al-Ca clusters and then inhibit the diffusion of Al atoms which is thought to be the dominant reason that limits the glass forming ability (GFA) of Al-based alloys. The proposed strategy was confirmed in experiments by the observation of a greatly increased reduced glass transition temperature, T-rg = T-g/T-l (T-g the glass transition temperature and T-l the liquidus temperature), the increased the activation energy for crystallization, and the increased activation energy for diffusion. The Al85-xY8Ni5Co2Cax (x = 0.5-5) system is found to possess extraordinarily high T-rg = 0.613 far exceeding that for any known Al-based glass forming alloys. (C) 2012 Elsevier Ltd. All rights reserved.