Wear Resistance And Toughening Mechanism Of MeC/a-C Nanocomposite Coating In Seawater

Friction and wear of key tribo-pairs is the bottleneck for long-life stable operation of mechanical system in seawater.Improving the surface properties of a material is an important method that extends service life of machine parts under harsh condition.In this work we fabricated MeC/a-C nanocomposite coating for the applications to protect key tribo-pairs in seawater by multi-arc ion plating deposition.Firstly,coatings with different composition and microstructure are achieved by process designs.Then,the tribological mechanisms on atmosphere and seawater environment are discussed further.Main results are listed as follows:1.Carbon-rich CrC coating was deposited on 316L stainless steel to improve its protective properties.The tribological behavior of CrC coating and 316L sliding against WC-Co ball under dry friction,the lubrication of distilled water and seawater were comparatively studied.Whatever the conditions,the CrC coating has a more advanced protective performance than 316L.Friction coefficients and wear rates of these samples sliding in three different conditions decrease in the following order:dry friction,sliding in distilled water and seawater.As a result,the CrC coating can be treated as a good anti-corrosion material due to its dense and compact structure,chemical inertness to aggressive seawater and formation of oxide passivation layer.2.Cr-C nanocomposite coatings were deposited at various argon/acetylene mixtures.By increasing the flow rates of argon/methane mixtures,multi-arc ion plating of Cr-C coatings can give different microstructures ranging from a nanocomposite of C clusters in a chromium carbide matrix to a nanocomposite with crystallites of carbide in an amorphous matrix.And the binary nanocomposite coating tends to be completely disordered and amorphous under the condition of high flow rate of the mixtures.Experiment findings and theoretical calculations reveal phase segregation of sp~2-carbon from carbides in which the excess amounts of carbon are incorporated.A significant improvement of adhesion and toughness is achieved by increasing C content at the expense of hardness.The wear resistance of Cr-C coatings is controlled by the friction rather than hardness.Compared to dry friction,lower friction coefficients but higher wear rates are obtained under seawater condition.The coatings with higher Cr content display excellent anti-corrosion properties in seawater.3.VC nanocomposite coatings with high carbon content were deposited at varied substrate bias voltages.It is found that carbon bonding is significantly affected by bias voltage.For the coatings deposited at high bias voltage,the appropriate combination of inducing compressive stress and manipulating the nanostructure accounts for the effect of hardening and toughening.The hard yet tough nanocomposite structure makes the coatings have favorable wear resistance.Moreover,the smooth surface and dense structure obtained at high bias voltage jointly improve capacity of anti-corrosion resistance.The results are beneficial to the potential application of VC nanocomposite coating in seawater.