Advancing coating technology

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Imagine a Hong Kong manufacturer taking a mould to Singapore for coating service. Soon after he returns, he has to send the mould back because it fails to meet his requirements. Not only has he invested his time and money but his competitiveness is also greatly undermined. This scenario was true several years ago in Hong Kong. When Taiwan, Japan, Korea, Singapore, Europe and the US were investing in developing surface coating technology, Hong Kong lagged behind. But thanks to the joint efforts of scientists, and the support of both the government and industry, Hong Kong is fast catching up.

When science and engineering go hand in hand

"Coating is a very useful technique that has wide applications," said Professor Haydn Chen, Chair Professor of Materials Science and Head of the Department of Physics and Materials Science (AP). Scientists at CityU are undertaking a range of research that supports different applications, he said. While scientists from the Department of Manufacturing Engineering and Engineering Management (MEEM) focus on the tribological and engineering applications, AP scientists look at the electrical, optical, mechanical, chemical and medical aspects. As MEEM takes a more engineering approach to study the relationship between deposition conditions and the properties of coating, and to develop coatings, AP takes a materials approach to understand the relationship between coating processes, microstructure and properties.

Cooperation between the two departments in advancing coating technology and offering help to the industry can best be exemplified by the establishment of the Advanced Coatings Applied Research Laboratory (ACARL).

Establishment of ACARL

With a HK$10 million grant from the HKSAR's Innovation and Technology Commission and sponsorship from local industries in 2000, the ACARL was established in December 2001, under the directorship of Dr Lawrence Li, MEEM Associate Professor, to promote the use of advanced hard coatings to local industry. The ACARL serves as the pilot facility to adapt surface coatings technology to various materials to improve their friction, hardness, wear and scratch resistance qualities, helps boost technology transfer and develops new applications and research in surface coatings to benefit local industries. Dr Li focuses on research in lubrication, coating, surface engineering and tribology. His cooperation with AP can be traced back to 1997, when he returned from an international conference that aroused his interest in coatings. Dr Li approached Professor S T Lee, Chair Professor of Materials Science, AP, for advice, and started a joint project on diamond-like carbon (DLC) with Associate Professors Dr Igor Bello and Dr C S Lee, which was supported by a CityU grant of HK$0.27million.

The ACARL focuses mainly on two types of coating: hard coating and solid lubricant. Hard coatings that have a higher wear resistance, for example titanium nitride (TiN) and titanium aluminium nitride (TiAlN), are best for most tooling and forming applications such as cutting blades, punches and drills. Solid lubricants, such as titanium-based diamond-like carbon coating (Ti-DLC), chromium-based DLC (Graphit-IC) and MoS2/metal composite (MoST), enhance both the durability of products and their surface quality by providing a protective and lubricating layer. Solid lubricant has a low friction coefficient. The average friction coefficient of well-polished steel is 0.2, Dr Li explained, and a solid lubricant coating will further reduce its friction coefficient to 0.02, which is 10 times lower. Its lubricating property helps save the use of liquid lubricant. It is best used in plastic moulds and sliding surfaces.

The first ACARL joint project between AP and MEEM is on DLC coating, a type of hard solid lubricant. DLC coating is suitable for a wide range of engineering applications and can be applied to plastic, glass, ceramic and metal. It can also be used as a decorative coating because of its black colour.

In 2000, when the ACARL started the project, industrial application of DLC technology had already been in use for 10 years in Japan, Singapore, Taiwan, Europe, and the US. In Hong Kong, however, it was just taking off. Despite a demand from industry for coating technology and services, there was not much work done in the field, including in universities and research institutes. "What we were thinking of at that time was to make use of CityU's technology and expertise to transfer the film production technology from other countries and provide testing and characterization services that meet the specific needs of different industries," said Dr Zhou Zhifeng, MEEM Research Fellow. Through workshops and testing services, the ACARL helps enhance the industry's knowledge of the applications of coatings. In addition, the project aims to produce ready-to-market development of DLC applications which include adapting diamond coatings to metals, glasses and plastics to improve their hardness, wear and scratch resistance qualities.

Developing a new superhard coating

In 2002, with another grant of HK$7.3 million from the Innovation and Technology Commission, the ACARL began a project to develop superhard nanocomposite coatings (see related story on page 55) for the manufacturing industry, again drawing on the expertise of both AP and MEEM scientists. While the first joint project on diamond coating involved the transfer of well-developed and well-proven technology from other countries to Hong Kong, the nanocomposite project sees CityU joining the world in advancing the frontiers of coating technology. "We're working together in this project to produce nanocomposite coating with a hardness that exceeds 40GPa," said Professor Chen. Staff from AP are working on various types of characterization to understand the structure, texture, morphology of the surfaces in relation to the processes, and MEEM staff are investigating the deposition and fabrication of the coatings and tribological and machinery testing. "It's truly a joint effort," he said.

Welcomed by industry

In addition to producing coating and developing new coating, the ACARL also provides characterization testing services for industry. Before manufacturers can apply a coating, they need to test the feasibility and function of the coating films. Industry welcomes the provision of such kinds of services because it is not cost effective for them to inject heavy investment in such facilities, said Dr Zhou. The ACARL has an extensive line of testing equipment, including a scratch tester, a surface profilometer, a nano-indenter and an atomic force microscope which can be used to evaluate both the mechanical and structural characteristics of the film on a given substrate. "I guess no commercial company would have such a large range of equipment under one roof as we have here. It's simply not commercially viable," said Dr Li.

Since its establishment, the ACARL has served more than 100 companies. "Our research achievements and foundation give industries confidence and gain their trust," said Dr Li. Some of the coatings have been adopted by manufacturers for massive production. For example, the application of one of the DLC coatings produced by the ACARL is recognized by a US manufacturer as useful in improving the durability and usability of its hair cutters and the company will launch the product in Europe and the US this year. Steel hair cutters that have a high friction coefficient become overheated and magnetized during use, requiring the frequent application of liquid lubricant. DLC coating solves the problem of overheating and saves on the use of liquid lubricant, making the cutter more hygienic.

ACARL's future direction

"The ACARL provides benchmarks for industry by showing them what we can achieve," said Dr Li. As for the Laboratory's future development, while more focus will be placed on the development of hard and superhard coatings, it will continue to enhance the quality of solid lubricants, such as improving their adhesive properties, he said.

Dr Li is also thinking of starting up a separate business firm to maintain closer links with industry. "The advantage in being a university laboratory is that industry is confident in our expertise but the disadvantage is that they regard us as a place for research and teaching that does not understand their economic needs and interests," he said. He believes that by establishing a company, industries will regard it as being part of the trade, while the company's strong link with the University will provide research backup, a common practice in the US.

The close relationship with industry will help academics understand the actual needs and requirements of industry, Dr Li said. The importance of the pre-treatment of tools before application of coating, for example, cleaning grease and dirt, would not be appreciated if they hadn't worked in the industry. There is a great difference between doing a laboratory test and actually working in the field. It is therefore essential for academics undertaking applied research to work closely with industry by setting up companies, providing consultancies and helping in production, and at the same time lead industry by assisting it to develop new technology. If both steps are in sync, the application value of the research work will be greatly enhanced. "If we just do consultancy and production without research work, we will soon dry up, and, vice versa, if we just talk about research without application, people won't be aware of what we are doing. Both sides must be balanced and complement each other," he said. There is a growing demand for coating services in Hong Kong and China, Professor Chen said. "Hong Kong produces tonnes of materials that require coating services: moulds and dies, jewelry, watches, metal products, batteries and electronic products." And as China is now recognized as a major world manufacturing hub, Dr Li added, "it is also time for us to tap into that market."

Dr Li believes that coating research is just taking off and there is vast potential for development. The combined expertise provided by AP and MEEM gives CityU an edge in extending the frontiers of coating technology. "Physicists and engineers speak different languages but when we find a way to cooperate, we'll make a huge impact," he said.


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