Plasma Arc Building-up Welding Iron Based Alloy Coating On Sealing Face Of Air Outlet Valve

Air outlet valve is an important part in the engine. Since the valve always works under the inclement conditions, such as high temperature, impact load, corrosion media, etc., it is necessary to have the excellent high temperature behavior, wear resistance and corrosion resistance. In order to increase the properties of the air outlet valve sealing face, at present, a cobalt-based alloy coating is employed because of its outstanding properties. But the expensive price of the cobalt coating will enhance the valve's cost. This research aims to obtain a kind of iron-based alloy powder for strengthening the air outlet valve with a lower price.The composition of the iron-based alloy powder (Fe38) for strengthening coating has been designed and prepared using the atomization technique; the effects of the plasma arc build-up welding parameters on the Fe38 coating quality have been investigated, and the optimal technology parameters are suggested; the microstructure,the thermal and wear resistence as well as the corrosion resistence of the Fe38 coating have been tested and analysed; the comparison tests with the cobalt coating have been accepted. At last, the bench test of the valve has been made to simulate the working condition.The experimental result shows that the microstructure of iron-based alloy powder consists of theγsolid solution and the (Cr,Fe)7C3 carbide. The prepared powders have round shape, even particle size and compact structure; the plasma arc welding coating exhibits the good oxidation resistance properties at elevated temperature, wear resistance and anti-corrosive capacity. The coating can keep required hardness up to 800℃working temperature. When the temperature is higher than 800℃, the precipitation will separate from the solid solution and coarsen resulting in the hardness decreasing obviously.The iron-based alloy (Fe38) coating by plasma arc welding has similar properties below 800℃compared with cobalt-based alloy, which exhibits the economical advantage. Therefore, this issue has provided a new alloy powders for strengthening the air outlet valve. And also, the powders can be used for surface-strengthening of other machine elements requiring similar properties.