Abstract:

Proposed in this paper is a new method to avoid the defects on titanium alloy surface formed during theEDM- induced ablation machining with functional electrode.In this method,nitrogen gas is injected into the pro-cessing area through the original processing system,and the electric spark discharge is adopted to trim the ma-chined surface. With the help of the heat due to the discharge,a reaction of nitrogen gas and titanium occurs,andthe TiN coating is thus synthesized in situ. It is found from the SEM,XRD and microhardness test results of TiNcoating that (1) the electric spark discharge process is stable and continuous in the process of coating formation andis of efficient energy utilization; (2) the coating is a dense,uniform and continuous layer dominated by TiNstrengthening phase,with a thickness of more than 400μm; (3) the microhardness of the coating reaches 1761.8,which is 4.7 times more than that of the matrix; (4) there exists a metallurgical combination with high bondingstrength and even TiN phase distribution between the coating and the matrix; and (5) the synthesis reaction has astrong reverse plating effect on the electrode,which causes a TiN strengthening phase- dominated electrode endface,effectively reduces the electrode spoilage,avoids the coating pollution caused by electrode elements,and effe-ctively maintains the purity of TiN phase in the coating.

Key words: function electrode, electrical discharge machining, in- situ synthesis, titanium alloy, TiN coating