Spinodal decomposition and ordering in Au-Pt-Pd alloys

Au-Pt alloys are widely used as spinnerets for producing textile fibres due to their excellent corrosion resistance. Component lifetime is limited by their susceptibility to mechanical damage due to their low strength. A widely used alloy, Au30Pt1Rh at.%, can be aged to a hardness of 255 HV. While higher Pt containing alloys can achieve higher hardness values, the narrow gap between solvus and solidus temperatures (heat treatment window) introduces a risk of incipient melting during homogenisation. We have developed an AuPtPd alloy with high hardness (338 HV) and a wide heat treatment window. STEM images reveal that the alloy has a modulated microstructure after cooling, while XRD patterns show evidence of an additional low symmetry phase. To optimise alloy composition and processing, the crystal structures of all phases, and their precipitation sequences, must be understood. It is thus proposed that synchrotron X-ray diffraction be used in situ to track the microstructural evolution.