Study On Nitriding Behavior Of Hollow Cathode Ion Source On Surface Of Cr-containing Alloy Steel

Plasma nitriding is widely used as a high-efficiency nitriding method for the surface strengthening of Cr-containing steels.However,the workpiece needs to participate in the plasma generation process during conventional ion nitriding,which is prone to surface arcing and edge effects,which affects the strengthening effect of the workpiece.The hollow cathode ion source nitriding is to generate high-activity plasma and high temperature effect through the hollow cathode device,and the workpiece is no longer used as a cathode for plasma generation,which avoids the problem of conventional nitriding and improves the nitriding efficiency.In this paper,three different types of Cr-containing alloy steels,42CrMo alloy steel,AISI 304 austenitic stainless steel and 2Cr13 martensitic stainless steel,were used for nitriding treatment.Both 42CrMo alloy steel and AISI 304 stainless steel were nitrided by conventional nitriding and hollow cathode ion source nitriding.The surface morphology and roughness,phase composition,surface hardness,corrosion resistance and tribological properties of nitrided layer were analyzed by means of scanning electron microscopy（SEM）,X-ray diffraction（XRD）,energy dispersive spectrometer（EDS）and atomic force microscopy（AFM）.The nitriding results of 42CrMo alloy steel and AISI 304 stainless steel showed that both the hollow cathode treatment and the conventional treatment have the same phase and the element distribution of the cross section was similar,the SEM and EDS results showed that the uniformity of the compound layer treated by the hollow cathode was better,the nano-roughness of hollow cathode treatment measured by AFM was higher than that of conventional nitriding,and the micro-hardness of the hollow cathode treatment was slightly lower than the conventional treatment.The XPS results showed that the hollow cathode treated 42CrMo alloy steel had more Fe_xO_y and fewer Fe_xN.The electrochemical test showed that the corrosion resistance of 42CrMo alloy steel after nitriding was better than that of untreated samples,the corrosion potential of hollow cathode treatment was increased by 0.36V compared with conventional nitriding,and the R_CTT value of EIS fitting data samples was one order higher than that of conventional treatment.The friction test showed that the AISI 304 stainless steel had improved friction performance after nitriding treatment,the wearer causes severe plastic deformation and adhesive wear to change into oxidative wear and slight abrasive wear,the friction coefficient of hollow cathode treatment was lower than that of conventional treatment.According to the nitridation results of 42CrMo alloy steel and AISI 304 stainless steel,the 2Cr13 stainless steel was treated with three potentials of cathode,anode and floating by hollow cathode ion source nitriding.The results showed that the potential treatment had great influence on surface morphology,nitride layer thickness and surface hardness;the values of the thickness of the nitride layer,the surface hardness and the macroscopic surface roughness were the largest in the cathode potential treatment,and the values of the floating potential treatment were the smallest.After the hollow cathode nitriding,the wear mechanism was accompanied by mild plastic deformation and transformed into oxidative wear,the floating potential treatment had the lowest friction coefficient and the best wear resistance.The corrosion potential of floating potential treatment was higher,and no obvious corrosion pit was found,and its corrosion resistance was better.Comparing the nitriding results of nitriding at 450℃for 5 h and 550℃for 1 h,it was found that the nitriding of the hollow cathode ion source can achieve low temperature and long-term nitriding effect in a short time at high temperature,and no CrN precipitates.Therefore,the temperature of the sample nitriding treatment was simulated by ANSYS,and it was found that the nitriding heating rate and the holding temperature of the hollow cathode ion source were higher than the conventional treatment under the same energy.When the same holding temperature is reached,the temperature uniformity of the low-energy hollow cathode sample was better,and the surface temperature difference was only 25%of the conventional treatment.