Rapid solidification of Au alloys

Rapid solidification (RS) of crystalline Au alloys is described with attention to disorder trapping phenomena. For 18 karat AuCu, RS is the most effective technique to suppress order-disorder transformations of the first order type. On the contrary, disorder cannot be retained in the P phase of the Au-Cu-Al ternary where the transformation is of the second order type. The ordered P phase undergoes a further displacive transformation in the temperature range from 45 degrees C to 80 degrees C which can be exploited for a shape memory effect. Rapidly solidified ribbons prove useful for tailoring thermal treatments to this goal. Amorphisation of metals was first achieved with a Au-Si alloy. Other systems have then been obtained as glassy solid, even in quasi-bulk form. Examples include Au-Ge-Si, Au-Sb-Pb and Au-Cu-Y. Results are reviewed with reference to the concept of melt fragility.