Experimental Studies On The Phase Equilibria Of Au-Cu-Pd Ternary System

As the Au-Cu-Pd ternary alloy is of vital applications in nanocatalysis and as a kind of dental material and a brazing material,its phase diagram plays an important guiding role in the research and development of alloys.However,due to the high research cost of precious metal alloys,the study of this system so far is still very weak.Therefore,it is necessary to study on the phase equilibria of the Au-Cu-Pd ternary alloys.In this work,a diffusion-coupled method was used for phase equilibrium measurement;two diffusion-coupled Au46Cu46Pd8/Au3Pd and Au46Cu46Pd8/AuPd3 samples were subjected to equilibrium diffusion treatment at 350?.Scanning Electron Microscopy(SEM)was used to observe the morphology of the diffusion couple.The Energy Dispersive Spectrometer(EDS)and the Electron Probe Micro-Analyzer(EPMA)were used to determine the compositions of the diffusion layers,plot the distribution curve of the elemental components,and to analyze on the diffusion paths so that there are supplements of the phase equilibria at the rich-Au side and the Au-Pd region of the controversial Au-Cu-Pd ternary alloy phase diagram at the isothermal section of 350?.X-ray Diffractometer(XRD)and Transmission Electron Microscopy(TEM)were also used in this work to analyze the structure of Au3Pd,AuPd3 and Au46Cu46Pd8,which are three special alloys in this system.The Differential Scanning Calorimetiy(DSC)was used to determine the order-disorder transition temperature of the Au46Cu46Pd8 alloy.The experimental results show that Au3Pd,AuPd3 and Au46Cu46Pd8 are all single-phase structures.Au46Cu46Pd8 is in the region of AuCu L10 ordered-structure phase,whose orderdisorder transition temperature is 506.2 ? and both Au3Pd and AuPd3 are in the fcc_Al disordered phase.Both Au46Cu46Pd8/Au3Pd and Au46Cu46Pd8/AuPd3 samples have only one diffusion layer.The diffusion layer of the Au46Cu46Pd8/Au3Pd sample was identified as the Au3Cu L12-type ordered phase,while the ternary solid solution phase formed in the Au46Cu46Pd8/AuPd3 diffusion couple has not been reported yet,and is tentatively named as the X phase.The composition range of the single-phase region on the diffusion path and the conjugate line of the two-phase region were determined according to the composition distribution curve of each element of the diffuse diffusion regions.In this work,the rich-Au side and the Au-Pd region of the Au-Cu-Pd ternary alloy at the isothermal section of 350?was modified,so that pieces of information on a more scientific and accurate phase diagram were thereby obtained.