Ultra-precision machining of cerium-lanthanum alloy with atmosphere control in an auxiliary device

Abstract

Cerium–lanthanum alloys are the main component of nickel–metal hydride batteries, and they are thus an important material in the green-energy industry. However, these alloys have very strong chemical activity, and their surfaces are easily oxidized, leading to great difficulties in their application. To improve the corrosion resistance of cerium–lanthanum alloys, it is necessary to obtain a nanoscale surface with low roughness. However, these alloys can easily succumb to spontaneous combustion during machining. Currently, to inhibit the occurrence of fire, machining of this alloy in ambient air needs to be conducted at very low cutting speeds while spraying the workpiece with a large amount of cutting fluid. However, this is inefficient, and only a very limited range of parameters can be optimized at low cutting speeds; this restricts the optimization of other cutting parameters. To achieve ultraprecision machining of cerium–lanthanum alloys, in this work, an auxiliary machining device was developed, and its effectiveness was verified. The results show that the developed device can improve the cutting speed and obtain a machined surface with low roughness. The device can also improve the machining efficiency and completely prevent the occurrence of spontaneous combustion. It was found that the formation of a build-up of swarf on the cutting tool is eliminated with high-speed cutting, and the surface roughness (Sa) can reach 5.64 nm within the selected parameters. Finally, the oxidation processes of the cerium–lanthanum alloy and its swarf were studied, and the process of the generation of oxidative products in the swarf was elucidated. The results revealed that most of the intermediate oxidative products in the swarf were Ce3+, there were major oxygen vacancies in the swarf, and the final oxidative product was Ce4+.