Mechanical spectroscopy of 18-carat AuCuPd white gold alloys

The mechanical loss and dynamic modulus temperature spectra of two 18-carat white gold alloys, Au58%Cu24%Pd18% without (grade A) and with alloying additions (grade B), were measured in the 400-1000 K temperature range. A peak interpreted as a Zener relaxation peak is found at about 630 K in both alloys. In the as-quenched state the peak shifts to lower temperatures due to excess vacancies, creating a transient peak at 520 K visible only upon the first heating. In grade A, a relaxation peak is observed at 750 K and is attributed to grain boundary relaxation, since it is absent in monocrystalline sample. in the same temperature region, the grade B features a peak with a large hysteresis between heating and cooling. A sharp peak observed in heating at 830 K is accompanied by a strong modulus decrease. In cooling, we observe a peak at 750 K, below which the mechanical loss abruptly decreases, accompanied by a modulus recovery. The peak hysteresis is interpreted as being due to dissolution or precipitation, respectively. The internal friction spectrum is correlated with the alloy's mechanical properties, namely the hardening of the grade B upon tempering at a temperature below the dissolution peak. (C) 2009 Elsevier B.V. All rights reserved.