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Experiment and analysis of rotating gear pairs coated with TiN prior to plasma nitriding

Raising hardness of gear surface and smooth surface is an important way to improve the wear-resistance and transmission efficiency as well as prolong the lifetime of gear. 32CrMoV, 40Cr, and 0.2%~0.4% carbon were selected to manufacture gear. After been plasma nitrided, 32CrMoV and 40Cr were deposited TiN onto teeth surface by multi-arc ion plating. All of these uncoated gears and coated gear have been running in the gearbox under the same initial conditions (power, lubricant and rotating speed) for 2 hours. After running tests, loss of weigh reveals gears coated TiN had more wear-resistant. Results of the observation of the gear surface show that gear faces of The coated TiN gears did not cause surface abnormalities, contrarily the gears nitrided exhibited wear on the tooth surface. The morphology of the surface indicats that the surface of the TiN film is dense and smooth (Ra<0.4) so that it had higher wear resistance than the uncoated gear. Distribution of hardness gradient of the coated gear subsurface reveals more rational than those of uncoated. Microstructure of substrate observed using scanning electron microscope (SEM) and optical microscope showed that surface of coated gears were more refined. It can be very effective for increasing the wear-resistant to deposit TiN onto nitrided gears.