A Study Of Plasma Oxynitrocarburising And Duplex Plasma Treatment For AISI 1045 Steel

In this study, AISI 1045 steel is selected as the testing material,which is widely used in modern industry, such as biological field, medical field, and mechanical field, chemical field, due to its low cost and excellent combined properties. In order to further enlarge its application,surface modification is necessary to improve its properties to meet the requirements in various service environments. Plasma nitriding is one of the widely used surface modification techniques; it has some advantages in that they are environmental friendly, little deformation and stable quality. It has been proven to be one of the most effective methods to improve wear resistance, surface hardness and corrosion resistance of most metal materials. However, it generally takes a long duration, which results in its obvious shortcoming of energy consuming and low efficiency. The developed plasma nitrocarburizing, it can promote the efficiency of plasma nitriding. However, it has been found that the formation of a loose layer is unavoidable in the utmost surface, which causes side effects on surface performance. Therefore, developing a new way to overcome the disadvantages of traditional plasma nitriding and plasma nitrocarburizing is of paramount importance, and it is very important to make good use of the advantages of both plasma nitrocarburizing and plasma nitriding. All of these are very valuable to investigate.Based on this issue, gas sources of Air-N2-C3H8 was used in plasma oxynitrocarburising for AISI 1045 steel, and the effects of air flow on its microstructure and properties are investigated. A novel duplex treatment of plasma nitrocarburizing and plasma nitriding was primarily developed for AISI 1045 steel, and the microstructure and properties are investigated.Sand blasting was conducted as a pretreatment prior to plasma nitriding,and the effect of sand blasting on plasma nitriding was evaluated. The AISI 1045 steel are measured by means of optical microscopy (OM),scanning electron microscopy (SEM), X-ray diffraction (XRD),microhardness tester, electrochemical workstations, pin-on-disk tribotester, contact angle measurement and etc.The results of plasma oxynitrocarburising show that the maximum compound layer thickness of 20.1 ?m is obtained at air flow of 0.3 L/min,more than twice as high as that obtained in traditional plasma nitriding at 510 ? for 4 h. Hence, it can be concluded that plain air addition can increase the efficiency of plasma nitrocarburizing. Fe3O4 occurred after plasma oxynitrocarburising, which could effectively prevent substrate from corroding, thereby further improve the corrosion resistance for AISI 1045 steel. The possible catalysis mechanism is due to the formation of oxides on the outmost surface, which have the lower contact angle and higher SFE, and benefiting to produce more nitrogen and carbon atoms in plasma oxynitrocarburising process. Meanwhile, the formation of oxides on the outmost surface can effectively prevent substrate from corroding,thereby further improve the corrosion resistance for AISI 1045 steel.The results of duplex treatment combining plasma nitrocarburizing and plasma nitriding show that higher efficiency and better properties were obtained after the complex treatment for AISI 1045 steel. The nitrided layer thickness was increased remarkably, and the effective hardening layer increased above 35 ?m, which was more than double.Meanwhile, the frangibility of nitrided layer was decreased notably. The relative amount of ? phase in the compound layer was increased and that of y' was reduced.The results of duplex treatment of sand blasting and plasma nitriding showed that sand blasting could enhance the nitriding efficiency and bring about much thicker nitrided layer than that of the nitrided-only sample under the same plasma nitriding condition, which is over about 76%, and the optimal time is 15 min. The microhardness was enhanced to 799 HV0.05, which is increased about 125 HV0.05. Furthermore, the duplex treatment of sand blasting and plasma nitriding could increase the wear and corrosion resistance, the corrosion rate is only 1/3 of the traditional plasma nitriding.