Tarnishing is a long-established challenge. Oxidation and corrosion cause discolouration of many metal surfaces, which decrease the shelf-life of products. The development of a new coating technology called "Pulsed Chemical Vapour Deposition (PCVD)" enables formation of uniform oxide thin films on articles such as watches, jewellery and coins of any shape and orientation. It provides an ultrathin and totally conformal anti-oxidation coating, which is also fully transparent. As compared to other deposition techniques such as physical vapour deposition (PVD) and chemical vapour deposition (CVD), this PCVD technique offers several advantages, including a defect-free and homogenous surface, and lower process temperature.
1. A pilot coating system based on the modified low-temperature PCVD process (less than 200°C) is fabricated and the PCVD process is suitable for large scale production. 2. The coatings are conformal and adherent to many substrates, including metals such as stainless steel, mold steel, gold, aluminium, silver alloys and copper alloys, as well as non-metals such as glass, silicon, quartz and plastics with melting points higher than 150°C. It is especially suitable for objects with irregular or non-planar, 3D surfaces. 3. The surface hardness of the oxide coatings is 13-20 GPa, 2-3 times higher than that of hardened steel. The wear and scratch resistance can be improved by 50-100% when applied on soft metals such as stainless steel and AuCu alloy. 4. The oxide coatings, such as aluminium oxide and titanium oxide, with thickness ranging from 10-100 nm, can be deposited uniformly through this PCVD process and are optically transparent in the visible light range. 5. The oxide films are chemically inert and can effectively protect the precious metals from oxidation and corrosion caused by factors such as humidity, chemicals, sea water and perspiration.
This application of hard and transparent coatings will be an ideal approach to enhance the durability and competitiveness of many products in the watch, electrical, optical, automotive, computer and biomedical manufacturing sectors. The substrate can include 3D objects with intricate non-planar surface topologies, e.g. jewellery, glasses, implantable medical devices, displays, etc.
The improvement of scratch and wear resistance by surface coating is a desirable added-value to the products. For example, for the watch industry, this new protective coating will lower down the yield loss during production for the component making and complete watch assembly factories. Furthermore, as the surface barrier, the coating can provide protection against corrosion and oxidation to improve the product quality, durability and desirability. Therefore, the application of hard and transparent coatings will be an ideal approach to enhance the competitiveness of watch products.