Tribology of incoloy 800HT for nuclear reactors under helium environment at elevated temperatures

Abstract

Nickel-based alloy 800HT is considered one of the main candidate alloys for nuclear reactors with gas cooled high-temperature environment and, therefore, it is necessary to have a thorough understanding of the alloy tribological response for obtaining optimum operating and loading conditions. The current study investigated the wear and friction behavior of alloy 800HT using a customized high temperature tribometer to simulate the environment of helium cooled reactor up to 750 °C. The effect of temperature, contact load, environment, sliding distance and sliding speed on the alloy friction and wear were studied. To generalize the study for other applications, an investigation is also performed in air environment. The friction and wear coefficients have the highest values at high temperature helium atmosphere where the formation and stability of the oxide scales play an important role. Optical and contact profiling, scanning electron microscopy, as well as energy dispersive spectroscopy techniques were utilized to study the surface oxide. The analysis showed the presence of Fe-Cr-Ni rich oxide both in air and helium. The protective glazed layer did not form in helium in any condition, whereas in air and under specific conditions a stable protective oxide layer was observed.