Precipitation behavior of Pt-rich phase in Au72Pt28 alloy during aging process

Gold–Platinum (Au–Pt) alloy demonstrates considerable promise as a material for spacecraft proof mass, due to its ultra-low magnetic susceptibility. This study systematically investigates the effect of heat treatment on the microstructure evolution, magnetic properties, and mechanical performance of the Au72Pt28 alloy. The results indicate that the Pt-rich phase can be precipitated by discontinuous precipitation (DP) and continuous precipitation (CP) reactions. There is a competition between the two precipitation behaviors of Pt-rich phase, which is closely related to their diffusion path. With increasing ageing time and temperature, the discontinuous precipitates gradually coarsen and extend from grain boundaries into grain interior, while the Pt-rich phase nanoparticles precipitated by CP reaction uniformly distribute in the grain interior. Besides, the volume fraction of Pt-rich phase gradually increases, resulting in the increase of magnetic susceptibility. The coarsening of discontinuous precipitates is the main reason for the decrease in the nanoindentation hardness, and it increases rapidly due to a large number of intragranular Pt-rich phase nanoparticles.