| Transition metal nitride coatings（such as CrN and TiN）have excellent mechanical,friction and corrosion properties,which can improve the surface properties of the workpiece and extend the service life of the workpiece.Compared with single-layer coatings,nano-multilayer coatings have been extensively studied due to their superior comprehensive properties.However,these coatings have higher hardness and rigidity than soft substrates,and in many cases are affected by the plastic deformation of the substrate,which may cause the coating fail.The composite treatment system combined with plasma nitriding（PN）and hard coating can effectively improve the hardness of the coating and the bonding strength between the film and base,and reduce the possibility of damaging or cracking the coating,so it has a very high research prospect.In the paper,Cr-Al-Ti-N and W-Cr-Al-Ti-N nano-multilayer coatings were prepared on the AISI 4140 steel by multi-arc ion plating technology.The microstructure and mechanical properties of the nanomultilayer coating were analyzed after adding W element.AISI 4140 steel was subjected to plasma nitriding pretreatment,W-Cr-Al-Ti-N nanomultilayer coating was deposited on nitrided AISI 4140 steel.The morphology,hardness,film-base bonding force and corrosion resistance of the samples treated with different surface technologies were studied.The structure,mechanical property and corrosion resistance were tested by X-ray diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,automatic scratch tester,Vickers hardness tester,friction and abrasion tester and electrochemical workstation.The main research contents are as follows:（1）AISI 4140 steel is mainly based onα-phase,Cr-Al-Ti-N nano-multilayers are mainly dominated by CrN,AlN and TiN phase,W-Cr-Al-Ti-N nanomultilayer films are mainly based on W2N,CrN,AlN and TiN phase,and both coatings haveα-Fe phase diffraction peaks.W-Cr-Al-Ti-N nano-multilayer film has a clear modulation interface,from the substrate to the top are the bottom CrN layer,the middle periodic Cr-Ti-Al-Si-N gradient layer and the top W-Cr-Al-Ti-N nano-coating composition.The nano-hardness and elastic modulus of W-Cr-Al-Ti-N nano-multilayer film reached the maximum value of47.9 GPa and 425 GPa,respectively,with super-hard effect,significantly higher than Cr-Al-Ti-N nano-layer film（24.3 GPa and 350 GPa）and substrate（6.8 GPa and 227 GPa）.The H3/E*2 value of the Cr-Al-Ti-N coating is 0.09,and the plastic deformation ratio H3/E*2 of the W-Cr-Al-Ti-N nano multilayer coating reaches a maximum 0.609,higher than the ordinary transition metal nitride hard coating（0.4）,with good toughness.（2）The AISI 4140 steel appearsε-Fe2-3N andγ’-Fe4N nitride phases after low-temperature ion nitriding（LPN）and high-temperature ion nitriding（HPN）.The composite treatment samples deposited after nitriding mainly consist of W2N,CrN,TiN and AlN phases,ε-Fe2-3N andγ’-Fe4N phases were also detected.After ion nitriding,the hardness of the sample increased.Low-temperature nitrided and coating composite treatment（LPN+Coating）sample have a hardness of 1332HV0.05 and the high-temperature nitridation and coating composite treatment（HPN+Coating）sample reached a maximum of 2200 HV0.05.The bonding strength of the composite treated samples increased,and the binding capacity of HPN+Coating composite sample is 51N.After the treatment,the corrosion resistance of the samples in 3.5wt.%NaCl solution increased.After the polarization test,no corrosion phenomenon occurred on the surface of the HPN+Coating composite treatment sample,which has excellent corrosion resistance. |
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