| Designing a nano-laminated structure is an effective way to improve the mechanical properties of hard coatings. The coatings can possess excellent properties due to the formation of nano-laminated composite structures by the periodic growth of two different nanometer thickness materials. Ceramic/ceramic and ceramic/metal nano-laminated structure are the common two systems. According to the reports, ceramic/ceramic nano-laminated structure has been successfully applied in the design of superhard coatings, and ceramic/metal nano-laminated structure can also has certain toughness in addition to meet the property of superhard coating. Possessing the properties of toughness and hardness means possible good friction and wear perforemance.This paper prepared VC/Ni nano-laminated coatings with modulation periods of3.3nm-53.5nm by non-reactive MF pulsed magnetron sputtering alternating deposition. XRD and SEM were used to characterize the growth structure, laminated structure, phase composition, and stress state of the coatings. Hardness and modulus of the coating was characterized by nano-indentation apparatus. Vickers microhardness tester and SEM have been used to characterize the toughness of thin coating. AFM and scratch instrument were used to measure the surface roughness and binding force. UMT-3multifunctional friction was used to test the friction and wear properties for the laminated structure of thin coating. AFM, SEM and EDS were respectively used to test the wear morphology and debris components. The friction and wear mechanism are discussed in this paper, the main results as follows:1) From the low angle XRD and SEM characterization, the coatings are well deposited as expected. Compared to the normal one layer VC coating, those nano-laminated VC/Ni coatings have less internal stress. And the internal stress in those coating decrease with the modulation period. In addition the nano-laminated structure changes the preferred orientation of normal one layer VC and Ni hard coating, the VC (200) and Ni (111) preferred orientations are found.2) As the modulation period going up, the growth structure of the VC/Ni nano-laminated coating also changes from dense to incomplete columnar structure, then to complete columnar, finally dense again. At the same time, the roughness of the coatings’surface also changes, initially increasing then decreasing, adhesion firstly decreases then increases.3) The hardness and elatic modulus of all those VC/Ni nano-laminated coatings are within the region of one-layer Ni coating (hardness9.17GPa, elastic modulus239.16GPa) and VC coating (hardness32.27GPa, elastic modulus331.15GPa). But both values (hardness and elastic modulus) of those coatings are less than the mixture of the two values of pure VC and Ni (hardness20.72GPa, elastic modulus290.7GPa). As the modulation going up, both values increase at first, after they come to the highest value then decrease a little.4) In the frictional test, apart from the coatings which have a modulation period of3.3nm and30.3nm (they were worn out in the test), all the other coatings have a very steady friction coefficient (about0.59±0.02). And those coatings that were not worn out also have a similar wear rate (about10-15m3/Nm), which is much smaller than the unprotected M2high speed steel. The coating with a modulation period of23.5nm has the smallest wear rate, which is1.1×10-15m3/Nm. After a deep analysis of the wear debris, we find that both mechanical and chemical wear process are involved in the frictional test.If the chemical wear process plays a more important role in the test, the wear rate becomes smaller and vice versa. |
PDF Full Text Request