Cailiao Baohu (May 2022)
Application Research on TiN and DLC Coatings on Plunger for Low-Speed Marine Diesel Engine
Abstract
In order to improve the wear resistance of plunger and the service life of plunger assembly for low-speed marine diesel engine, TiN and DLC coatings were prepared on plunger by ion-plating technology and multiple arc magnetron coupling coating technology respectively. SEM, optical profiler and XRD were used to characterize the micro-morphology, surface roughness and phase composition of TiN and DLC coatings, and nano indentation instrument was employed to detect the nano-hardness and elastic modulus of such coatings. In addtion, the scratch and indentation methods were used to test the binding force of the coatings. And the friction coefficients of such coatings in the air and under the environment of heavy diesel oil were investigated through the reciprocating wear test. Then, the wear degrees of those coatings were qualitatively evaluated with the help of a optical microscope. Furthermore, a bench test was adopted to evaluate the actual wear situation of the coated plunger. Results showed that the crystals of two coatings grew well, and their structures were continuous and dense, and there was no stratification, cracking or peeling phenomenon. The DLC coating was relatively smooth and the roughness R;was about 0.10 μm, while the TiN coating R;was 0.16 μm. The nano-hardness, elastic modulus and poisson ratio of DLC coating were higher than those of the TiN coating. No matter in dry friction or heavy oil friction,the friction coefficient of TiN coating was higher than that of DLC coating,and the wear resistance of TiN coating was lower than that of DLC coating. After the bench test,relatively obvious parallel grooving wear marks appeared on the plunger with TiN coating,and the overall wear was relatively serious,while the wear marks on the plunger with DLC coating were narrow and shallow that not easy to find,further proving that the wear resistance of DLC was superior.
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