Solute segregation improves the high-cycle fatigue resistance of nanocrystalline Pt-Au

Fatigue-induced grain growth has been shown to drive high-cycle fatigue crack initiation in nanocrystalline metals. As a potential strategy to suppress such grain growth, particular solute additions are known to stabilize grain boundaries through both thermodynamic and kinetic mechanisms. In previous work, Au additions in nanocrystalline Pt were confirmed to stabilize grain boundaries against thermally-driven grain boundary migration, however, the corresponding effect on fatigue resistance was unknown. The present work compared the high-cycle fatigue performance of stabilized Pt-10at%Au to reference pure Pt with a similar initial grain size, using a combination of ex-situ and in-situ scanning electron microscope fatigue tests. Ex-situ tests revealed that the Pt-10Au exhibits substantial improvement in overall fatigue life over Pt, including a 75% elevation of the fatigue endurance limit. The improvement was attributed to enhanced crack initiation resistance, since the Pt-10Au exhibited diminished resistance to crack propagation compared to Pt. Electron backscatter diffraction, transmission kikuchi diffraction, and transmission electron microscopy showed that the pure Pt exhibited extensive fatigue-induced abnormal grain growth, with the largest grains growing to 10 times the size of the initial grain size, whereas the Pt-10Au exhibited inhibited grain growth, with the largest grains growing by approximately a factor of two. This study provides clear evidence that thermodynamic strategies used to impart thermal stability can also contribute to improved high-cycle fatigue resistance via suppression of grain-growth induced crack initiation.