Microstructure, Mechanical, Tribological And Corrosion Properties Of Carbon/Nitride-based Coatings In Aqueous Enviroment

This thesis aimed to release the internal stress, enhance the adhesive strength, increase thehardness of amorphous carbon (a-C) and TiN, CrN coatings by doping transition metal Ti, Cr and Celements, respectively. Moreover, the influence of incorporating contents of Ti, Cr and C elements onthe compositon, microstructure, mechanical and tribological properties in water and electrochemicalproperty in simulated body fluid for a-C and TiN, CrN coatings was investigated systematically. Atlast, the relationship between microstructure variation and wear mechanism was discussed:1) The Ti/a-C coatings with different Ti doping content were deposited by unbalanced magnetronsputtering. When the current of Ti target was0.5A, the low concentration Ti atoms existed inTi/a-C-0.5coatings as solid solution. The lattice deformation increased the hardness of Ti/a-Ccoatings to27.5GPa, and Ti/a-C coatings shortened the running-in distance and decreased the wearrate of a-C coatings. But when the currents of Ti target varied in the range of1A to2A, the metal-likeTi and TiC nanoparticles were formed and dispersed in a-C matrix. The metal-like Ti and TiCnanoparticles broke the continuity of carbon network, and made the hardness decrease to15~17.5GPa.Besides, under abrasive effect of the TiC nanoparticles, the delamination occurred for Ti/a-C-1、Ti/a-C-1.5、Ti/a-C-2coatings sliding against SiC and Al2O3balls in water. However, the lubricationfilms induced from hydration action of Si3N4balls and oxides induced from oxidation of SUS440Cballs adhered on the coatings’ surface, and made the Ti/a-C-1、Ti/a-C-1.5、Ti/a-C-2coatings maintainintegrity.2) The Cr/a-C coatings with different Cr doping content were deposited by unbalancedmagnetron sputtering. When the currents of Cr target varied in the range of0.5A to2A, the metal-likeCr or chromium carbides were formed. The metal-like Cr and chromium carbides broke the continuityof carbon network, and made the hardness of Cr/a-C coatings decrease to11.6~13.7GPa. TheCr/a-C-0.5coatings with better toughness shortened the running-in distance and decreased the wearrate of a-C coatings. However, when the currents of Cr target varied in the range of1A to2A, theformation of chromium oxides originated from hydration reaction of chromium carbides dominatedthe wear mechanism. Thus, whatever the counterparts were, the Cr/a-C-1、Cr/a-C-1.5、Cr/a-C-2coatings occurred delamination.3) The TiN(C) coatings with different C doping content were deposited by unbalanced magnetronsputtering. Owing to the formation of a-CNx, the hardness of TiN(C) coatings increased to27~32GPa.But with the increasing carbon content, the more a-C made the hardness decrease continuously. Since the SiC and Si3N4balls could generate lubrication film due to hydration, the unbroken TiN, TiN(C1),TiN(C2), TiN(C3) coatings with low friction coefficient were obtained. But the TiN(C4) coatingsoccurred delamination due to decreasing hardness. All of the TiN(C) coatings confronteddelamination because of no hydration reaction for Al2O3balls with high hardness. For SUS440C balls,the adhesive wear increased the roughness between contact area and made the friction coefficient highand unstable.4) The CrN(C) coatings with different C doping content were deposited by unbalancedmagnetron sputtering. With the increasing carbon content, the a-CNxand chromium carbides wereformed gradually. The latter would act with water and generated Cr2O3which acted as wear debrisduring wear process. Thus, when the CrN(C) coatings slid against SiC and Al2O3balls with highhardness, the CrN(C) coatings were all worn out. Owing to the protection effect of the silicon oxidesgel originated from hydration action of Si3N4, the CrN(C1) coatings maintained whole. However, themore Cr2O3resulted from chromium carbides in the CrN(C2), CrN(C3) and CrN(C4) coatingsdestroyed the protection effect of silicon oxides gel, and made the CrN(C2), CrN(C3) and CrN(C4)coatings peel off. Similarly, the oxides resulted from oxidation of SUS440C balls would adhere on thecoatings, protected the CrN(C1) coatings, but the CrN(C2), CrN(C3) and CrN(C4) coatings wereworn out.5) Both the Ti/a-C and Cr/a-C coatings could protect the316L stainless steel in simulated bodyfluid. With the increasing Ti content, the increasing conductivity of Ti/a-C coatings due to increasingsp2content and high porosity density weakened the electrochemical properties in simulated body fluid.However, with the increasing Cr target current, the insulativity of Cr/a-C coatings increased becauseof increasing sp3content, and enhanced the electrochemical properties in simulated body fluid. Due tothe formation of CNx, TiN(C1), TiN(C2) and TiN(C3) coatings enhanced the anti-corrosion propertiesof316L, whereas the poor surface quality of TiN coatings and high a-C content of TiN(C4) coatingsmade them exhibit inferior anti-corrosion properties of316L. Similarly, due to favorable surfacequality and chromium oxides passive coatings, the CrN, CrN(C1), CrN(C2) and CrN(C3) coatingsexhibited superior electrochemical properties than316L. But the high a-C content of CrN(C4)coatings weaken the anti-corrosion properties in simulated body fluid.