Study On The Structure And Properties Of The Ti-(Zr)-B-N Nano-Composite Coatings

With the development of modern industrial technology,the requirements for cutting tools are getting higher and higher,and the traditional tools can no longer meet the current needs.Therefore,it is necessary to develop coated tools with high-performance to meet the current processing requirements.TiB₂ coatings have many advantages,such as high hardness,high wear resistance,high thermal stability,etc.,which are widely used on the surface of cutting tools.However,they are extremely brittle and easy to break and even to peel off,which limits their application.Therefore,the TiB₂ coatings must be toughened.It has been repored that dopping nitrogen into the TiB₂ coating can form an nc-TiN/a-BN nanocomposite structure,as a result the toughness of the coating can be improved.However,it has also been found that a large amount of amorphous BN phase can be formed even if a small amount of nitrogen was introduced into the coating,which resulted in the lower coating hardness.To resolve the above problem,the reverse design method was put forward.The minimal nitrogen was input during the reactive magnetron sputtering.In the meantime,the coating composition was adjusted by changing the sputtering power of TiB₂ target.So the amount of hard phase in nc-TiB₂/a-BN nanocomposite coating can be increased,which simultaneously improved the hardness and toughness of the coating.In addition,the Ti-B-N coating was doped by Zr atoms,which was expected to further improve the hardness and heat resistance of the Ti-B-N coating.Zr atoms are solid-dissolved in the TiB₂ lattice or react with N to form a ZrN hard phase.Zr atoms are easy to react with O to form a dense ZrO₂ film,which acts as a thermal barrier.So the coating can also be used at high temperatures.In this paper,Ti-B-N coating and Ti-Zr-B-N coating were deposited by pulsed DC magnetron sputtering,respectively.The effects of TiB₂ target power,deposition temperature and nitrogen flow rate on the microstructure,mechanical properties and friction properties of the coatings were studied systematically.The main conclusions were drawn as follows:1.The compositions and structure of Ti-B-N coatings were optimized by adjusting the target power of TiB₂.It was found that all Ti-B-N coatings are uniform and dense without pinhole defects.As the sputtering power of the TiB₂ target increased,the coating became more and more dense;the hardness of Ti-B-N coating increased gradually from 1344 HV To 3463 HV;the critical load varied from 61N to 86N.When the sputtering power of TiB₂ target was 2.4 kw,the friction coefficient and wear rate of the Ti-B-N coatings reached the lowest valus 0.55 and2.1×10^-3?m³N^-1?m^-1,respectively.In this case,the coating was the most wear resistant.2.The effects of deposition temperature on the microstructure and properties of the Ti-B-N coatings were studied.The results showed that the surface of Ti-B-N coating was smooth and compact with increasing deposition temperature.The coating hardness increased from 2855 HV to 3994 HV,and the residual stress gradually decreased from 0.9 GPa to 0.3 GPa.When the deposition temperature reached 400°C,the coating was smooth and dense,and presented the highest hardness and the lowest residual stress.When the deposition temperature was 300°C,the coating possessed the lowest friction coefficient and wear rate.They are 0.5 and 1.1×10^-3?m³N^-1?m^-1,respectively.3.A series of Ti-Zr-B-N coatings were prepared.The effects of nitrogen flow on the microstructure and properties of Ti-Zr-B-N coating were investigated systematically.It was found that the crystallinity of the coating increased with increasing nitrogen flow;the coating hardness first increased and then decreased,varied between 1000 HV and 2200 HV.When N₂=10 sccm,the coating hardness reached about 2200 HV;the adhesion between the coating and substrate were tested by the scratch test.The critical varied in the range of 34⁷0N.As nitrogen flow was 15 sccm,the critical load was about 70N,the wear rate reached a minimum value2.8×10^-3?m³N^-1?m^-1,which showed the best wear resistance.