The comparative study on nanostructured tribolayers of Alloy 690TT subjected to fretting wear under different oxygen contents

The nanostructured tribolayers of Alloy 690TT subjected to dry fretting wear at 320 °C under different oxygen contents were studied. Results indicated that the low oxygen content (5 vol%) produced the nanostructured tribolayer containing large amount of Cr2O3 with an average grain size of 15 nm, which was mainly due to the limited oxidation and preferential oxidation of Cr, resulting in lower friction coefficient, wear volume, dissipated energy, smoother worn surface and thicker tribolayer. The farther from the worn surface, the weaker was the Cr2O3 concentration. Only a small quantity of microcracks perpendicular to the worn surface were observed in the Cr2O3-rich tribolayer under a low oxygen content, which indicated the Cr2O3-rich tribolayer had a better wear resistance. By comparison, under a high oxygen content (21 vol%), the tribolayer mainly consisted of NiCr2O4 and Fe2O3 with an average grain size of 7 nm due to the sufficient oxidation during fretting wear, resulting in higher friction coefficient, wear volume and dissipated energy. The plenty of microcracks without specific orientation and voids appeared in the oxide layer and along the interface of oxide/metallic grains.