ON THE MECHANICAL PROPERTIES AND DAMPING BEHAVIOUR OF THERMALLY AGED UNMODIFIED AND Ni MODIFIED Cu-Zn-Al SHAPE MEMORY ALLOYS

The effect of thermal ageing on the mechanical properties and damping behaviour of CuZnAl(x)Ni shape memory alloys (SMAs) (where x = 0, 0.1, 0.3 wt. % Ni), produced via liquid metallurgy processing was investigated. The strength and fracture toughness parameters were observed to increase with increase in Ni concentration and ageing temperatures, while the ductility increased with Ni concentration but decreased with increase in ageing temperature. For the unmodified CuZnAl alloy, damping capacity improved with ageing treatment in comparison with the unaged condition. In contrast, the damping capacity decreased for the Ni modified CuZnAl alloys in the aged condition (0.015 - 0.025 at 250oC and 0.012 - 0.038 at 400°C, for the 0.1Ni modified CuZnAl alloy; and 0.012 - 0.018 at 250°C and 0.016 - 0.0284 at 400°C for the 0.3Ni modified CuZnAl alloy) compared with the unaged condition (0.0376 - 0.050 for unaged 0.1Ni modified CuZnAl alloy, and 0.0428 - 0.062 for the unaged 0.3Ni modified CuZnAl alloy). The results indicate that Ni modification within the range 0.1 - 0.3 wt.% could have a more favourable effect on mechanical properties but could adversely affect the damping capacity of CuZnAl based SMAs in comparison with the unmodified condition.