Spark Surface Local Strengthening And Alloying

In this investigation, by utilizing a self-made electrical discharge surface hardening equipment, some samples are surface hardened by several positive electrodes made of different materials such as WC and Cr12MoV. In addition, the forming mechanism and the characters of the surface-hardening layer are systemically researched as well as the layer's construction and element distribution are studied. In order to improve the hardening productiveness and the layer's quality, the layer's hardness, wearing resistance and hardening depth are inspected under different technological parameters such as the electrical capacity, the voltage, the pulse energy and the hardening time, and an optimum technology is put forward. According to the analyses of the x-ray diffraction and line scan, the hardened layer is consisted of carbides, nitrides and the elements of positive electrodes and specimen's. The electrical discharge hardening is not only a progress of the positive electrodes?overlaying on the matrix materials, but also a complicate alloying and metallurgy progress of the elements coming from the positive electrodes and specimen, and the ions coming from the ionized air. The metallograph analysis of the layer's surface and section appearance demonstrates that the hardening period is the key factor to forming a successive, well-distributed layer with a certain depth. If the hardening period is too short, the layer will be too thin and has less effect. On the other hand, if the hardening period is too long, the layer will break and come off, and the surface quality as well as the hardening productiveness will decreases. Tests show that the hardness and wearing resistance of the hardened layer are much higher than that of the matrix materials. The hardness is very high in the white- bright area, then decreases in the combining area and lowers to the minimum in the over-heated area. If the specimen is hardened by a stiff and highly wearing resistant positive electrode for a appropriate hardening period, its surface hardness and wearing resistance will be greatly improved. The optimum technology of electrical discharge surface hardening is that: to meet the requirement of a certain layer depth and improve the hardening 5productiveness, a lager electrical parameter should be adoPted first, and then a smallerelectric parameter is selected to improve the layer's smoothing and compactness.