Effect of Yttrium on microstructure, thermal properties and damping capacity of Ni41Ti50Cu9 alloy

In this paper, investigations of Yttrium effects on Ni41Ti50Cu9 alloy are presented. In particular, Yttrium was added to the ternary alloy in substitution of Ni and in the content of 1, 3 and 5 at%. Electron microscope observations, pure thermal measurements by differential scanning calorimetry and electrical resistivity analysis, dynamo-mechanical tests were used to study the thermo-mechanical properties of samples in as cast and annealed conditions. It was found that two main matrixes form after casting, where Yttrium aggregates in cluster with Copper. Despite of this, Yttrium does not change the path and the product of the phase transition (i.e. B2-B19-B19') except for 5 at% Yttrium sample where a single-step B2-B19' transition was found. Yttrium allows for higher transition temperatures with respect to the ternary NiTiCu sample and it does not change the good thermal stability of the alloy. Dynamo-mechanical tests show that Yttrium depresses the relaxation peak in all samples. Furthermore, Yttrium does not allow for significant improvements of the damping response of the NiTiCu ternary alloy. Finally, substantial change of micro-hardness is visible in samples with Yttrium content higher than 3 at%.