A new type of polishing technology! Nanoscale ultra-smooth surface can be obtained

Recently, the research team of Assistant Professor Deng Hui from the Department of Mechanical and Energy Engineering, Southern University of Science and Technology published the latest research results in the International Journal of Machine Tools and Manufacture, a top journal in the field of mechanical manufacturing, and proposed a contour envelop based on electrochemical isotropic etching Principle of universal polishing technology for metal materials.

Polishing is a common surface processing technology, the main purpose is to reduce the surface roughness, remove the damaged layer, and ultimately obtain a smooth and damage-free high-quality surface. Whether it is a consumer product in daily life or a semiconductor chip with a highly integrated manufacturing technology, polishing is an indispensable technical means to ensure surface quality.

In recent years, in the field of ultra-precision machining of metal materials, the polishing of metal parts with complex shapes and internal cavities has been a technical problem faced by industry. Traditional such as chemical mechanical polishing, laser polishing and magnetorheological polishing, all have “tool interference” problems. How to obtain nano-level smooth surface with high efficiency without destroying the surface shape accuracy of metal parts is a technical problem to be solved urgently.

Inspired by the principle of tool tip trajectory envelope for single-point diamond ultra-precision turning, the research team proposed a polishing technique based on the principle of isotropic etching profile envelope: under the passivation of the polishing liquid, a metal surface generates a A layer of passivation film; under the action of an electric field, breakdown discharge occurs preferentially in the weak position of the passivation film; the relevant parameters are optimized by the Arrhenius formula, and the breakdown site can achieve a density-controlled isotropic etching reaction As the isotropic etching progresses, the etch pits continue to expand and merge with each other to complete the envelope; the original rough surface is eventually replaced by an ultra-smooth surface.

According to the above-mentioned polishing principle, the research team conducted a modeling analysis of the surface morphology change and roughness change of the material during the polishing process, and the results are as shown. At the beginning of polishing, the surface roughness gradually increased due to the formation of etch pits; as the polishing progressed, the surface etching sites merged with each other to replace the original rough surface, and the surface roughness decreased rapidly; finally, the initial surface was completely replaced, Turns into an ultra-smooth surface. It can be seen from the model that, based on the proposed envelope polishing principle, a sub-nanometer ultra-smooth surface can be obtained theoretically.

Taking the ultra-precision polishing of titanium (TA2) as an example, the research group achieved the isotropic etching of the material surface by optimizing the parameters such as electrolyte and breakdown voltage. The etch pits formed by the polishing present a regular hemisphere, the density can be controlled, and the inner surface has nano-level roughness Sa=1.13nm). The results show that this method can achieve a high efficiency removal of 15.1m/min for TA2, and the surface roughness Sa rapidly decreases from 64.1nm to 1.23nm after polishing for 3 minutes, and a nano-level surface is obtained with high efficiency.

At the same time, the research team also applied this polishing technology to other typical metal materials, such as nickel-phosphorus alloys, nickel-titanium alloys, 304 stainless steel, 6063 aluminum alloy, and Inconel718 alloy. As shown, the polished sample surfaces all have a mirror effect, and all have nano-level surface roughness. This result shows that the isotropic etching profile envelope polishing technique proposed by the research team can be applied to common metal materials as a universal polishing process, and has significant industrial application value.

Deng Hui introduced that the etching profile envelope polishing technology proposed by this research avoids the use of rigid tools that are indispensable to traditional polishing processes. Therefore, this technology does not have the problem of “tool interference” and can process complex shapes and cavities. The structured metal parts have high processing efficiency and no residual stress on the surface after processing. In addition, according to the processing principle of this technology, this technology is suitable for most metal materials and has strong versatility. In the future, this technology is expected to be applied in aerospace and automotive parts, and it can also solve the post-processing difficulties of 3D printed metal parts.

The 2019 doctoral student Yi Rong of the Deng Hui research group is the first author of the article, Deng Hui is the corresponding author of the article, and Southern University of Science and Technology is the communication unit. The research was supported by the Shenzhen Science and Technology Innovation Committee International Cooperation Project and Shenzhen Overseas High-level Talent Innovation and Entrepreneurship Project.