Research On Chip Deformation And Tool Wear Mechanism In Turning Nickel Based Superalloy

The nickel-base superalloy, which has high strength under high temperature, good heat resistance and high corrosion resistance, is a very important structural material used in aviation, aerospace and shipbuilding industries. However, because of its low thermo capacity, the adiabatic shearing phenomenon and the serrated chip may occur during the machining process, and the high-frequency fluctuation of the cutting force may be discovered which will make the cutting process unsteady. Meanwhile, because of the high strain strengthening coefficient of the nickel based superalloy, tool wear is very serious during the cutting process and notch wear will be generated on the rake face obviously. Therefore, studying of the serrated chip’s deformation mechanism and tool wear condition, especially the reason of two sides’ notch wear on the rake face, are significant for expansion and application of nickel based superalloy. In this article, main contents are as follows:First of all, the effects of cutting parameters on serrated degree, serrated frequency and serrated pace were researched based on the metallographic morphology and Digimizer software. The results show that the serrated degree, serrated frequency and serrated pace are increasing with cutting speed. Serrated degree and serrated pace appeare to enhance with feed rate, whereas feed rate has little impact on serrated frequency.Second, a new method to evaluate chip deformation by measuring slip angle was presented in this paper, and compared with the method of measuring slippage to evaluate chip deformation. It is indicated that with the increase of cutting speed and feed rate, the slippage is increasing and the slip angle is decreasing. If the size of sawtooth is uniform and the chip side flow is slight, both the slippage and the slip angle can evaluate the chip serrated degree well. But if the size of sawtooth is uneven and the chip side flow is serious, slip angle is more credible to evaluate the chip serrated degree.Finally, the wear location of the rake face, rear face and the bottom of the chips were analyzed by SEM and spectrums. It is shown that the main failure mode of rake face is the notch wear, the wear of the notch position is very serious and caused by three kinds of wear modes:oxidation, adhesion and mechanical scratch, the wear in the middle position is mainly caused by adhesion but it is very slight; the main wear modes of rear face are mechanical wearing and micro-chipping; the bottom of the chips is divided into three bands, the middle one is smooth, wide and uniform, the other two sides are rough, narrow and uneven, and the width of the smooth band is basically equal to the width of the slight wear position in the middle of the rake face.