Experimental Research On Deteriorative Layer Of Nickel-based Superalloy By Pulsed Arc Processing

Nickel-based superalloy GH4169, which has good oxidation resistance at high temperatures, high yield strength, tests show that at 600 ℃, the oxidation rate of GH4169 is only 0.0176g/m2?h. The yield strength σp0.2 reached to 550 MPa at ordinary temperatures, GH4169 also have good weldability, it can be welding, electron beam welding and other welding methods, so it is widely used in aviation, petroleum fields. But during the machining existence of large cutting force and tool wear too fast and so on, which greatly reduces the processing efficiency, limit the application of the material. Pulsed arc machining use of electric heat to the workpiece, intense heat is created in the localized area of the arc impact, high transient temperature at the local site caused by discharging can erode the materials, processing quality is not affected by material hardness, strength, impact toughness, and high processing efficiency, so it is especially suitable for difficult to machining materials such as superalloy. The workpiece fits and starts, affected layer formed on the surface of the workpiece, the roughness, thickness of the recast layer, crack, hardness influenced by the electric parameters, in order to improve the machining quality, this paper studied the following aspects:(1) Study on the mechanism of pulsed arc processing, analysis of the factors affecting the quality of the affected layer, mainly including electrical parameters, electrode materials, processing medium.(2) Determine the test purpose, design orthogonal experiment, factors is voltage, pulse frequency, duty cycle, test indices is the surface roughness, thickness of affected layer, identify the impact of the test results of the primary and secondary factors by the range analysis method. The biggest influence on the test results is the voltage, followed by pulse frequency and duty cycle, the latter two factors affect the level is closer, in order to find the best combination of electrical parameters, increase the pulse frequency and duty cycle of the single-factor test. Finally found the optimal processing quality occurs the best combination is voltage 16 V, pulse frequency at 400 HZ, duty cycle is 55%.(3) The microstructure of surface topography were observed, combined with the waveform of processing, analysis shows that, voltage at 16 V, frequency less than 200 HZ, and the duty ratio lower than 20%, the discharge gap is shortened, the tool and the workpiece is easy to contact, causing a short-circuited, the change of waveform irregularly, causing the surface roughness and thickness of affected layer increase, affected layer thickness increase. Voltage at 35 V, the frequency is more than 800 HZ and duty ratio higher than 80%, this long time discharge between electrodes produced a stable electric arc, the formation of stable electric arc between the electrodes, the product of erosion excluding unfavorable, then reduce the processing quality.