Study On Process Of Double Cathode Glow Plasma Nitriding

A new method of plasma nitriding was introduced in this paper,The double cathode glow plasma nitriding.The furnace body service as the anode,the porous iron cylinder service as the first cathode and the cathode plate as the second cathode.,plasma is generated to nitride the steels in the enhanced electric field.The purpose of this technology is to overcome the insufficient and shortages in ion nitriding at present,such as difficulties in maintaining a uniform temperature,the hollow-cathode effects was caused by little holes,arcing surface and so on.Moreover,The structure,the principle of nitriding,working process and the advantages of the equipment was studied sysemtically.Cr12Mo V steels had been nitrided by the double cathode of glow plasma nitriding equipment.The results of the experiment show that double cathode glow plasma nitriding is an effective way,and can achieve the similar nitriding effects as DC plasma nitriding.The nitrided layers were consituted of compoud layer and diffusion layer.X-ray diffraction analysis indicated that the compoud layer was composted of ? and ?' phases,Cr N phase was separaed out.In this thesis,Q235 steels also had been nitrided,Some testing and analysis instruments were used,such as X-ray diffractormeter,scanning electron miroscope,Vikers microhardness texter and metallurgical microsope to study the thickness,phase composition,metallurgical structure,microhardness of the nitrided layers.Nitriding parameters such as nitriding temperature,time,pressure,voltage were investigated to clear their influence on the properties and microstrcture of the nitrided layer in this paper.The results of the experiment show that nitriding temperature plays an important role on the qualities of nitrided layers.As treatment temperature increasing,the thickness of the nitriding layers increase,when temperature was550?,the compactness of white layers was falling.diffusion layers were on the rise with the elevated temperature.Surface microhardness increases at first and then decrease;and the micohardness gradients are gradually gentle.The relationship of nitriding layers thickness and time is parabolic.Extending the nitriding time,the thickness of the nitrided layers increase remarkably.When the time exceed 10 h,the growth rate droped.The microhardness of samples rising with the increase of layers thickness.The nitriding pressure affects the thickness and the surface micohardness of the nitrided layer.As the nitriding pressure nicreasing,the thickness and surface microhardness of the nitrided layers increase;and the micohardness gradients are gradually gentle.The nitriding voltage affects the decomposition, ionization of NH3, and the interface reaction.Improving the nitriding voltage the thickness and the surface microhardness of the nitrided layers increase.Decrease the voltage of cathode plate and increasing nitriding time can decrease theedging effects during the nitriding process.Comprehensive analysis,the preferable processing parameters of the double cathode glow plasma nitriding are nitriding at the temperature of500?,at the pressure of 350 Pa,with the cathode plate voltage of 650 V for 12 h.