Study On The Friction And Wear Properties Of CrN-based And TiN-based Hard Coatings

Nitride coating has high hardness,good wear resistance,good oxidation resistance,antiadhesion and other properties,commonly used as tool protection coating.304 stainless steel and titanium alloys are widely used in life due to their excellent performance,but they are more typical difficult to machine materials due to defects such as process hardening,high cutting temperature,and tool bonding during processing.The use of coated tools can effectively improve the cutting performance of the tool and prolong the service life of the tool.Al CrN and Al TiN coatings are commonly used in the market to cut these two materials.However,these two materials are easy to create adhesion layer on the tool surface,which will reduce the tool life.In order to solve the "adhesion",it is necessary to understand the adhesion mechanism of different tools on different coatings.In this thesis,CrN?TiN?Al CrN and Al TiN coatings were prepared on cemented carbide by arc ion plating,the coatings were polished and unpolished,the friction and wear experiments were carried out on the four coatings,the adhesion of them in the initial running-in stage was studied,and then the adhesion of the two materials on different coatings was analyzed,surface energy was used to explain the difference of adhesion.The specific work is as follows:(1)The hardness,elastic modulus and bonding force of the four nitride coatings were measured by nano-indentation,scratch tester,etc.Among them,the CrN coating had the lowest hardness and the Al TiN coating had the highest hardness.However,the binding force of CrN coating is the best,and the binding force of TiN coating is the worst,while the binding force of Al CrN and Al TiN is not much different,which are 87.1N and 82.9N respectively.The surface roughness of the coating was measured by AFM,and it was found that the surface roughness of Al TiN coating was the largest,followed by Al CrN coating,and the surface roughness of CrN coating was the lowest.The XRD patterns show that all four coatings have a single-phase face-centered cubic structure.(2)Through the ball-disk friction experiment at room temperature,the initial adhesion of CrN?TiN?Al CrN and Al TiN coatings against two different metals of 304 stainless steel and TC4 under different coating surface roughness was investigated.It was found that 304 stainless steel was greatly affected by the surface roughness of the coating and adhered seriously in the unpolished coating.After the coating is polished,the adhesion on the coating will be reduced.TC4 is less affected by roughness,but the adhesion on the polished TiN and Al TiN coatings will increases,and the adhesion of TC4 is related to the affinity between the coating and the material.After polishing,the friction coefficient is very low in the first 50 laps,and the friction coefficient starts to increase sharply between 50-75 laps.The wear mechanisms of the coating when abrasive against these two metals are: adhesive wear,abrasive wear and oxidative wear.(3)The adhesion of the material is related to the surface energy.The surface energy of the material was calculated by owens-Wendt-Kaelble' method,and the surface energy of two different metals and four kinds of nitride coatings(unpolished and polished)of 304 ss and TC4 was analyzed,and it was found that the surface energy of the coating would be reduced after polishing.According to the Owens-Wendt surface free energy model,interactions occur only between forces of the same nature,while different interactions(polarity/dispersion)of the maximum proportion present in the pairs may indicate a low adhesion between materials.The anti-adhesion order of these four coatings on the two metals is obtained by calculating the relationship between the surface energies: Al CrN(29)CrN(29)Al TiN(29)TiN.