Plasma Nitriding Assisted By Hollow Cathode

Plasma nitriding, as a nitriding technique, is getting more and more attention, because it has some advantages, such as high nitriding speed and thermal efficiency, good quality of compound layer and mechanics performance. Plasma nitriding processing can not only be controlled easily, realizing local hardening and avoiding forming brittle phase in the nitrided layer, but also get compact compound layer which has better wear resistance, corrosion resistance. However, there still exist some problems unsolved, for example, arc discharge which will destroy the finish of surface, gas pollution and so on. By researching on flow field in the furnace, a hollow cathode assisted plasma nitriding device was designed, and 40Cr, 42CrMo, 45 steel were nitrided with this technique.The specimen was insulated, then processed by plasma nitriding assisted by hollow cathode discharge. Whereafter, the specimen was plasma nitrided and aginged alternately. In order to improve the surface hardness of the material, the specimen was plasma nitrided by applied negative voltage. The surface hardness and hardness gradient was measured, phase of the surface and optical microscope images of the nitriding layer were analysed. After comparing the research results of the samples in different conditions, the following conclusions were gotten.The plasma nitriding assisted by hollow cathode discharge nitrided effectively specimen, which can avoid generating arc and destroying the finish of surface; it can be carried out under low pressure, therefore, the expending of ammonia and tail gas emission was reduced. As a result, energy source was saved and pollution was reduced.The optimum condition of plasma nitriding assisted by hollow cathode discharge is 6 hours treatment under 500℃. After treatment, the thickness of the compound layer and the diffusion layer is 3μm and 250μm. Surface hardness is about three times as the substrate when the specimen is insulated; and is about four times as the substrate when the negative voltage is applied on the specimen. The plasma nitriding assisted by hollow...