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The Damage Mechanism of Alloy 690TT Caused by Fretting Wear in a Flowing Nitrogen Environment

Abstract The different fretting wear behaviors of alloy 690TT in air and in a flowing nitrogen environment were revealed. Moreover, grain refinement to the nanoscale caused by fretting wear in nitrogen was investigated. The results showed that when compared with an air environment, the coefficient of friction in nitrogen was slightly higher due to direct contact between the metals with strong adhesion, which resulted in a smaller wear width and volume. Fretting in nitrogen ran in the partial slip regime with the wear mechanisms including the formation of fatigue cracks and severe plastic deformation (SPD). The formation of fatigue cracks resulted in the maximum wear depth occurring at the edge of the wear scar. Fretting in air ran in the gross slip regime with the wear mechanisms oxidation, delamination, and SPD. Due to SPD during fretting wear in nitrogen, nanotwins were formed in fine crystals, which caused the original grains to be divided into twin–matrix lamellae. The interaction of nanotwins with the dislocation arrays further subdivided the twin–matrix lamellae into nanoblocks and randomly oriented nanograins.