INTERNAL FRICTION IN TERNARY α-CuNiZn ALLOYS

Internal friction measurements have been carried out for a number of face-centred cubic CuNiZn alloys, especially the alloys around the composition Cu2NiZn. Damping measurements are carried out using an inverted K6-type pendulum equipped with an optical detector. With an extrapolation in the ageing time relaxation data for the disordered structure were obtained. Also shear moduli and Young's moduli are reported on the same alloys. Introduction. The anelastic damping in disordered CuaNiZn below the critical temperature for ordering is measured. In earlier papers measurements in ordered material (Van Der Veen et al. 1979) as well as on a Cu2NiZn single crystal were reported (De Rooy et al. 1980). For a detailed description of the structure types in this alloy reference should be made to Vrijen et al. 1976 and 3 e Rooy et al. 1980. The main features will be outlined below. In this alloy the order-disorder transformation takes place in two steps. The first step from a fully ordered A2BC (L10) structure to a ternary ordered A3B (LIZ) structure has a critical temperature of about 625 K . After this transformation the Cu and Ni atoms are disordered, while the Zn atoms are still on their own sublattice. The second step, from the partially ordered A3B structure to the completely disordered structure has a critical temperature of about 770 K . There is a little difference in atomic size of Cu and Ni. In comparison with the atomic radius of Zn, the atomic size difference of Cu and Ni can be neglected (the experimental c la for AzBC i s (1.0002). This gives rise to the expectation that there will be hardly any effect on the internal friction when the critical temperature for A2BC-A3B is passed by. Due to the difference in size of Zn compared with the other two elements it may be expected that the second transformation will be more drastic. Since tAe internal friction measurements are related to the elastic moduli, also the shear modulus and the Young's modulus are measured. In the following section the theory is summarized, especially the formulae needed to explain the results. In section two the sample preparation and experimental technique are described. In the third section the experimental results are reported, followed by a discussion in the last section. 1. Theory. When suddenly a stress is applied to an anelastic solid, this solid will show creep. In a torsional pendulum this creep behaviour is demonstrated when we follow the creep angle y as a function of time, that obeys approximately the exponential equation : 1 1 ~ ) . Y= ~ ~ ( 1 e (1) When the applied stress is removed, the anelastic strain relaxes and so the angle changes according to the equation: Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19815142