Microstructural characterization of subsurface caused by fretting wear of Inconel 690TT alloy

The evolution of microstructures of subsurface caused by fretting wear of Inconel 690 alloy at 20 degrees C has been characterized. The results indicated that there were five layers: oxide layer, mixed layer, tribological transformed structure (TTS) layer, plastic deformation layer and base materials in the subsurface. The topmost layer was the oxide layer consisting of NiCr2O4 and Fe2O3 with an average grain size of 6.8 nm, which was caused by full oxidation and persistent mechanical effect. Tribologically mixed layer was comprised of ultra-fine metal grains and oxides mainly including NiO and Cr2O3 with an average grain size of 15 nm by oxygen diffusion and selective oxidation. Underneath the mixed layer, the equiaxed grain I IS layer with an average grain size of 180 nm without oxidation formed as a consequence of large plastic strain by dynamic recrystallization. The plastic deformation layer contained lots of dislocations. A higher oxygen concentration was found in the oxide layer, and gradually decreased to the almost zero in the TTS layer, corresponding to the gradual increase in the grain size. (C) 2016 Elsevier Inc. All rights reserved.