Friction And Wear Performance Of Si₃N₄-based Graded Nano-composite Ceramic Tools

There are some difficulties in high speed cutting Nickel-based super alloys process, such as high cutting force, high cutting temperature, low tool life, and work hardening during machining. In this thesis, a Si3N4graded nano-composite ceramic tool was developed by the combination of the functionally graded materials (FGMs) and the nano-composites. The tribological properties and antifriction mechanism, high speed cutting performance and failure mechanism of the tools were investigated in the thesis, with homogeneous Si3N4-based ceramic tools used as competitors.The effect of the applied load and sliding speed on the friction coefficient and the wear rate of the two tool materials was investigated by single factor testing method. The results showed that the friction coefficient and the wear rate of the composites increased with the increase of applied load, decreased with the increase of sliding speed. Both the friction coefficient and the wear rate of the graded material were lower than those of the homogeneous one. The wear mechanisms of the composites were adhesion and abrasion in sliding wear tests.FEM simulation of the high speed cutting Inconel718was carried out using finite element software. The simulation results showed that the maximum Mises stress was obtained in the area of the tool rake face near the cutting edge. The maximum temperature was found in the contact area of the chip and the rake face. And under the same conditions, the stress and temperature of the gradient ceramic tool were lower than those of the homogeneous one.The high speed cutting experiments of Inconel718alloy were conducted using the three level orthogonal test method. The results showed that both the resultant cutting force and cutting temperature increased with the increase of cutting speed, feed rate and depth of cut. Tool life improved upon increasing the cutting speed from80m/min to 120m/min, and then showed a decreasing trend with the increase of cutting speed. The machined surface roughness decreased with the increment of cutting speed. The resultant cutting force, cutting temperature and machined surface roughness measured with the graded tool were lower than those with the homogeneous one, while the tool life of the former was higher than that of the later. The main failure mechanisms of the graded tools were adhesive wear and abrasive wear.