Investigation On The Microstructure And Mechanical Properties Of VC And VC_xN_y Thin Films

The magnetron sputtered transition metal carbides and nitrides thin films have attractednumerous attentions due to their exotic properties such as excellent hardness,high meltingpoint,good chemical stability and high conductivity.Although there is a growing interest in theuse of hard transition metal carbides and nitrides as functional coatings, a literature surveyshows that very few researches exist about the microstructure and properties of thin filmsprepared by PVD in the vanadium–carbon system.In this thesis,a series of VC and VC_xN_ythinfilms were deposited by magnetron sputtering.The effect of reactive gas flow rate,substrate biasand substrate temperature on the microstructure and mechanical properties of films wasinvestigated systematically.The main works of this thesis are summarized as two parts:（1） VC thin films were deposited on Si（100） substrates by using direct current （DC）reactive magnetron sputtering in discharging mixed CH₄/Ar gases. The effects of CH₄flowrate，substrate bias and substrate temperature on the structure, morphology, intrinsic stress,hardness, fiction and wear resistence for the obtained films have been explored.As CH₄flow rate is increased，the deposition rate for the VC films decreases and stressincreases. The ball-on-disk tests yield low friction coefficients with values of0.2and high wearresistance for the film which was deposited at CH₄flow rateof10sccm. The low frictionbehavior can be attributed to the the formation of a graphite-like lubricious phase which iscomposed of amorphous a-C.As substrate bias increases properly，the deposition rate of the VC films increases,andmaximum value of deposition rate obtaions at substrate bias of60V.With substrate biasincreasing，the preferred orientation changes from （111）to （200）. In addition, the hardnessof VC films increases with substrate bias increasing, which can be ascribed to densification andincreament of sress. When substrate bias changes，the friction coefficients of the films do notchange significantly,this also illustrates that there is no significant effect of hardness on thefriction coefficients. The wear resistance of films has been significantly improved withincreasing of bias, the important effects of hardness on the wear resistance of flims can beproposed. With increasing substrate temperature， the deposition rate of the VC filmsdecreases.Substrate temperature has almost no effect on the phase structure of films.However，when substrate temperature increases, the stress in the films have a significant downwardtrend,at the same time the hardness and friction coefficient of the films increase to someextent.In addition，the surface roughness of the films decreases with increasing the substratetemperature.（2） VC_xN_ythin films with different N concentration were deposited on Si（100） substratesusing direct current （DC） reactive magnetron sputtering in a mixture of CH4/N₂/Ar at asubstrate temperature of700℃. The effects of N₂flow rate on the structure, intrinsic stress,hardness, and fiction and wear resistence for the obtained films have been explored. With N₂flow rate increasing，the content of N in the VC_xN_ythin films increases from16at.%to37at.%,while the deposition rate keep on decreasing.The preferred orientation of films changeswith the introduction of Nitrogen，texture of（200）can be observed in all the VC_xN_ythin filmsalmostly. While the enhancement in hardness is observed for the film with highest nitrogencontents due to fine grain and solid solution hardening.The maximum hardness value of thefilm can reach34GPa.