NiO whiskers growth driven by the presence of Pt nanoparticles during Ni-base superalloy oxidation

Abstract

The formation and growth of NiO whiskers on a platinum-containing nickel-base superalloy was monitored continuously up to 113 hours, at 920°C, under 50 Pa of air, using High-Temperature Environmental Scanning Electron Microscopy. The images recorded revealed that two types of whiskers form and grow at two different stages of the oxidation process. The first type of whisker forms as soon as the isothermal plateau at 920°C is reached. The growth rate is greater than 500 nm/min. After a few hours of isothermal oxidation, these whiskers have grown and are integrated into the oxide layer covering the surface of the sample. The second type of NiO whiskers forms after 20 hours of isothermal stabilization. They grow at a rate of around 1 to 10 nm/min for several tens of hours. The formation and growth of these whiskers is directly linked to the presence of platinum nanoparticles on the surface of the alloy. The mechanisms of whiskers formation and growth are discussed.

Keywords: ESEM, in situ, Superalloy, whisker, oxidation, Ni-base