Study Of Friction And Drilling Performance Under Dry And Cutting Fluids Of TiN And TiVN Coatings

In order to improve the cutting performance of the tools,surface coatings are prepared on the tool to ensure the reliability and long-term service of tool under severe working conditions.In this thesis,TiN and a series of TiVN of different V content were prepared by multi-arc ion plating equipment.The tribological and drilling performance of TiN and TiVN were investigated under different temperatures and water-based glycerol cutting fluids conditions.The microstructure and mechanical properties of TiN and TiVN were characterized by XRD,SEM,EDS,nano hardness tester,scratch tester,FTIR and other analysis methods.Additionally,the tribological and drilling properties of TiN and TiVN effects under temperatures and cutting fluids conditions were explored.The main research results were as follows:(1)The TiN and TiVN are face-centered cubic structures and the cross-section of coatings are uniformly dense columnar structure.The V doping improves the hardness and binding force of TiN by refines the grains.During the friction process at room temperature TiN does not oxidize,but oxidation occurs after doping V in TiN.With the increase of temperature coefficient of friction(COF)of TiN and TiVN increase first then decrease,and the COF is the highest at200 °C,and COF of TiVN is lower.When the temperature exceeds 200 °C,the wear resistance of TiVN is worse than TiN.This results because of TiVN undergoes severe oxidation or even phase change.(2)At medium and low speeds,the temperature during the drill bit cutting process is lower than 200 °C,while during the drill bit cutting process the temperature is between at 200 °C ～500 °C when high speed.Therefore,the TiVN has more excellent wear resistance and binding strength than TiN,the TiVN has a better protective effect for the drill bit.(3)Under cutting fluid lubrication,all coatings have a lower COF than dry friction.The coating has no obvious wear under 5 N load,but there is obvious material transfer on the surface of wear tracks.Under 25 N load,the wear rate of TiN decreases with cutting fluid concentration increases,while the wear rate of TiVN increases.This result is related to hardness of coatings and the contact state of tribo-pair during friction process.(4)During the drilling experiment,due to high contact stress,the stable adsorption film and reaction film of the cutting edge surface cannot formed,the coating will be more seriously strip or worn.Under low and medium speed drilling,due to the low temperature of the drilling region,the cooling advantage of water-based cutting fluid cannot be exerted.By compared with dry cutting,the advantage of solid-liquid synergy is not significant.At high speed drilling,the waterbased cutting fluid significantly reduces the drilling temperature and avoids high temperature damage of coating.Therefore,the higher hardness and wear resistance of TiVN shows better protective effect than TiN.All in all,the solid-liquid synergy is more significant at high speed drilling.