Study On Tribological Behaviors Of Nitrided Coatings Under MoDTC Lubrication

With the purpose of improving the tribological properties of nitride coatings in the practical application, three series of nitride coatings were prepared using vacuum cathodic arc ion plating equipment, including Ti N coatings, Ti Al N coatings and Al Ti N coatings. Tribological behaviors of the three nitride coatings in the lubrication of Mo DTC were examined on a MS-T3000 model ball-on-disc tribo-tester. Some surface analysis techniques like Nano-Map-D profilometer, SEM and XPS was utilized to analysis the morphologies of the wear tracks on the nitride coatings and the element combination states of the tribo-films formed on the worn surfaces. Triboligical behaviors and mechanisms of the three coatings under Mo DTC lubrication were studied. The results are as follows:1) Ti N coating, Ti Al N coating and Al Ti N coating were successfully prepared on the 316 L stainless surface by vacuum cathodic arc ion plating technology. The micro-hardness of the coatings was 2393 ± 42 HV, 2480 ± 169 HV and 3096 ± 112 HV, respectively. The roughness of the coatings was 19.1 nm, 27 nm and 12 nm, respectively. Phase structure of Ti N coating is face-centered cubic Ti N phase, with(111) preferred orientation; Phase structure of Ti Al N coating was face-centered cubic(Ti, Al) N phase, with(200) preferred orientation; Phase structure of Al Ti N coating was hexagonal structure Al N, face-centered cubic structure(Ti, Al) N and Ti, has a(200) preferred orientation;2) The wear rate of Ti N gradually decreased with the Mo DTC concentration increased from 0 up to 1.5 %.When Mo DTC concentration exceeded 1.5 %, the wear rate was increased. When Mo DTC concentration was 1.5 %, the friction performance of Ti N coating was better than the other lubricated conditions. Mo DTC lubrication was found to have more significant influence on improving the wear resistance and friction-reducing property of Ti Al N coating than PAO lubrication. The friction coefficient and wear rate of Ti Al N coating gradually decreased with the Mo DTC concentration increased from 0 up to 1.0 %. When Mo DTC concentration exceeded 1.0 %, the friction coefficient and wear rate would not have obvious changes basically. The wear rate of Al Ti N coating gradually decreased with the Mo DTC concentration increased from 0 up to 1.0 %, then increased with the Mo DTC concentration increased from 1.0 up to 2.0 %. The friction coefficient of Al Ti N coating gradually decreased with the Mo DTC concentration increased from 0 up to 1.0 %, then would not have obvious changes basically with the Mo DTC concentration increased from 1.0 up to 2.0 %, fluctuated in the rang of 0.086 and 0.088.3) The basic principle of the friction-reducing and wear resistance ability of nitride coatings is the formation of tribofilm containing Ti Ox, Al2O3, Mo S2, Fe Sx and Mo O3. Mo S2 is a well-known lamellar solid lubricant with a hexagonal crystal structure. The Fe S2 layer could slip layer by layer easily with close-packed hexagonal structure. Mo O3 as hard oxides has played a good role in the wear resistance ability. The wear mechanism of Ti N coating was changed from the furrows into spalling and plastic deformation with adding Mo DTC. The wear mechanism of Ti Al N coating was changed from spalling and furrows into spalling, furrows and plastic deformation with adding Mo DTC. The wear mechanism of Al Ti N coating was changed from spalling, furrows and plastic into spalling and abrasive wear with adding Mo DTC.