Plasma Modified Carbide Surface Structure Of State

Morphologies of the surface layers of cemented carbides were studied after the plasmamodificaUon trealment. It has been known that the fine-grained layer on the cemented tungstencarbide surface can be produced using a direct current plasma jet apparatus by de-carbonizing and carbonizing. The plasma modillcation processes in the experiment including removing carbon from carbides and introducing carbon into the surface layer were canied out in the atmosphere consisting of Ar-H2 plasma and Ar-H2-CH4 plasma respectively. In order to reduce the binder content from the surface layer, a chemical pretreatment of etching the binder using 1:3 HNO3 solutionfor2OminwasincludecLAfter YG8 cemented cartides (WC + 8 wt % Co) inserts were de-carbonized by Ar-H2 plasma, the outside surface of WC was transfonned into pure W layer and the outside surface is coarser. On the other hand, the cemented carbide inserts without being chemically etched had some Co7W6 composite phase except W. When carbon was introduced again using ArHrCH4 plasma, the fine-grained WC was formed, the W2C phase was retained because of the short time of carbonizing, and the affected layer with a certain thickness was also formed in the process. According to the EDS analysis results, the Co diffusion caused the change of the porous layer thickness, and the concentration of Co was also found on the surface layer.Because Fe-Ni-Co alloy acted as the binder, WC-l3Fe-3Co-4Ni cemented carbides ~e considered to be fit to the process. Considering the influence of temperature, this kind of steelbonded carbide made some differences .The porous layer was not found if the samples ~wre not etched chemically, there was only a frail outside layer. But the chemically etched samples had the same microstnicture layers as the YG8 cemented carbides. Through the SEM observation, the fine-grained W and WC could be seen using Ar-H2 plasma and Ar-HrCH4 plasma treatment respectively. According to the analysis results of XRD, the surface layer of WC-1 3Fe-3Co-4Ni cemented carbides chemically etched consisted of W after Ar-H2 plasma de-cartonizing and WC~ W~ W2C after Ar-H2-CH4 plasma carbonizing. On the contrary, the surface layer of WC-l 3Fe-3Co-4Ni cemented carbides without being chemically etched consisted of W~ Co,W6~ Fe7W6 after Ar-H2 plasma de-carbonizing and WC~ W~ Co3 W3C~ Fe6 W6C after Ar-H2-CH4 plasma carbonizing.