Experimental Research On Flexible Electrode Electrical Discharge Surface Strengthening To Titanium Alloys

Titanium alloy has properties of small density, big specific strength, high specific stiffness, good corrosion resistance, high temperature mechanical properties, resisting fatigue and creep property. In addition, it has good properties of hydrogen absorption, superconductivity, no magnetism, shape memory, low damping. However, it has lots of disadvantages including low hardness, low thermal conductivity, poor wear resistance, adhesion when it is heated, poor flame resistance and so on. In order to improver titanium alloy's surface properties, through researching the traditional electrical discharge surface strengthening, a technology which is flexible electrode electrical discharge surface strengthening is proposed. At first, it not only has traditional electrical discharge surface strengthening's advantages, but also disadvantages which include low deposition efficiency, unsuitability of big area strengthening and destroying surface of traditional electrical discharge surface strengthening are overcome. Secondly because of good strengthening effect, surface quality and wide adaptation to profiles, it can be predicted that this technology has an extensive application prospect. It provides a new way of surface strengthening to titanium alloys.The main works are as follows:1) By researching the basic principles and existing problems of electrical discharge surface strengthening and combining with the test requirement, a test system of flexible electrode electrical discharge surface strengthening has been built2) Titanium alloy TC4's surface is electrical discharge strengthened in the air by the flexible electrode. Tissue components and mechanical properties of strengthened layer are analyzed. Its hardness, surface quality, thickness and tissue components are researched. It has been proved that by flexible electrode electrical discharge surface strengthening, when titanium alloy's surface quality can be assured, a certain thickness of strengthened layer can be obtained, which enhances titanium alloys'hardness.3) Discharge characteristics of flexible electrode electrical discharge surface strengthening to titanium alloys has been researched. It has been demonstrated that electrical discharge is arc discharge. Because contact time of wire electrode and test piece's surface is far smaller than pulse duration, during pulse duration there are many wire electrodes generated arc discharge with test piece's surface. Discharge state transforms each other between arc discharge and short circuit. Single pulse energy is dispersed to many points'discharge, which can improve strengthened surface quality.4) Factors influencing surface quality, thickness and surface's hardness of strengthened layer have been researched. Surface hardness and surface roughness will increase while the discharge energy is increased (an average of current and pulse width). Titanium alloys'surface is coated and ground by the flexible electrode, which can improve strengthened surface quality. For considering surface roughness and hardness, electrical parameters and other parameters by which high hardness, relatively thick strengthened layer and high strengthening efficiency can be obtained, is adopted at first. Then strengthened surface is refitted by small electrical parameters and other strengthening parameters for reducing surface roughness and improving surface quality and compactness. Through this process good surface quality and relatively high hardness of surface strengthened can be obtained at the same time.5) Corrosion resistance, wear resistance and influencing factors have been researched. It has been proved that corrosion resistance and wear resistance of titanium alloys'surface is obviously enhanced by flexible electrode electrical discharge surface strengthening.