Decorative coatings provide attractive and aesthetic appearance to the products. They are applied to buildings and associated structures for decoration and protection. The market for decorative coatings is based on the rapid urbanization, increasing demand for colorful and glossy appearance and an extreme increase in investments in infrastructure are propelling the growth of the building, construction, and fashion industry in developing and developed countries. The reconstruction renovation projects in the building sector drive the global decorative coatings market during 2022 to 2030 to almost 100 billion by the end of this decade.The global decorative coating market can be segmented based on the different kinds of products, materials, coatings, technologies and importantly by application. Based on customers’ interests, the focus is given to luxury and home (product), with inorganic oxides and nitrides of metals (materials), exterior (coatings) done by Physical Vapour Deposition - termed as “PVD” (technology) for both residential and non-residential applications. For last four decades, environmental scientists have been making many alarms that the electroplating of finishes, such as hard chromium, cadmium and nickel in metal finishing have been recognized as a major source of environmental pollution in every country. Since last three decades, the development of ‘environmentally clean’ technologies in all aspects of industrial manufacturing has been an essential task required and initiated by environmental laws and restrictions tailored by several countries around the world. Electroplating of decorative and protective coatings stays one among the top sources of environmental pollution. Despite stringent government laws, electroplating is still surviving through strong lobbying court orders as hard chrome became easily and commercially available and electroplating-based industrial manufacturing has developed into a huge, well-organized, sophisticated and financially mammoth multi-billion-dollar sector. At least for last few years, strong activities are initiated with an objective to systematically replace some of the ‘environmentally dirty’ technologies (especially for cadmium, chrome and zinc) with high performance dry coating ‘clean’ methods. Among many available technologies for decorative coatings, the highest focus has been given on physical vapour deposition (PVD), chemical and plasma-assisted chemical vapour deposition (CVD, PACVD) and thermal spraying. The technologists and research managers faced the difficult problem of choosing an appropriate alternative coating technology, which would offer the production of cost-effective and quality coatings following available standards for each single case. PVD – a great alternative to electroplating Although in the earlier days, achieving the high deposition rates by PVD technology (either cathodic arc or sputtering) in par with electroplating was difficult, the modern PVD technologies with latest developments yield deposition rates as high as those typical of electroplating processes even in their batch coating process. With PVD processes a wide spectrum of thicknesses with similar physical and chemical properties can be obtained. Coatings thicker than 6 μm are deposited by the PVD techniques mainly for mechanical and chemical environments. For such purposes, new high-rate planar magnetrons and steering arc evaporators operated in in multi-cathode large batch or in-line systems. PVD technology overcomes the imitations are the size and shape of the substrate through custom equipped coating systems with an optimum configuration and number of sources, heaters and plasma etching units. Through proper designs of planetary rotation even can go up to 5-fold for the batch mode and a flexible system for in-line equipment delivers an impressive conformal thickness distribution and resulting coating properties. PVD technologies also outperform the advantage flagged by electroless coatings (for example: Nickel) they are uniform in thickness. In electroplating process, the components to be coated can therefore be plated to the requested size without any additional finishing operation. However, in PVD systems, the fixing spindles are different for each substrate. They are in general more expensive, more complicated and demand more assembling. However, in the recently released template spindle process, a special assembly procedure can be adopted to use same spindles for different 3D substrates. PVD coatings with specific functional properties must have minimal thickness (in the range of several nm to few μm) to exhibit with good adhesion and high wear and corrosion resistance. On the other hand, PVD decorative coatings also sustains abrasive wear, corrosion and ambient temperature and chemical conditions while exhibiting stable optical characteristics in terms of color and reflectivity) like those of the existed galvanic coating. The whole spectrum of colors can be obtained with various PVD techniques and processing conditions such as pressure, power, flow rate of organic compounds like acetylene or methane, reactive nitrogen gas or oxygen gas and sputter gas argon. PVD is superior to the electroplating process in terms of adhesion point of view. Owing to the fact that sputtering and ion plating PVD processes are powered with in situ plasma cleaning of the substrate (of course after wet cleaning process), the PVD tailored coatings exhibit superior adhesion with substrate. During the PVD process efficient low temperature pre-heating and plasma cleaning in the deposition reactor produces excellent adhesion to all substrates. For better adhesion, sputter power is further increased. To push sputtering power range even higher, to facilitate extreme ionization of all kinds of metal or reactive gas atoms, the power must be supplied in pulses to avoid overheating of cathode, magnet damage, and target melting. A general concept in pulsed power technology is that very high pulse power in megawatts range can be reached with rather conventional average power (in the range of kW) while the pulse duty cycle is kept much smaller than unity. Only rarely is an independent intermediate layer used to improve adhesion at the interface when the thermal expansion coefficient between the coated layer and substrate is too different (for example: coating of hard DLC over mild stainless steel). Although in earlier days, the replacement of galvanic electroplating technology by PVD coating technology seems to be challenge particularly for corrosion and porosity, the new developments in pulsed PVD technology such as (pulsed-DC, HiPIMS) deliver coatings with excellent surface quality with excellent long term corrosion resistance. The coatings made by PVD are fully dense but purely depends on deposition process parameters. Recent study reports that super smooth, pinhole free dense CrN coatings made by high frequency short pulsed cathodic arc technology exhibited excellent corrosion resistance properties. Furthermore no iron dissolution has been detected. Black PVD coatings For decorative applications of the automotive and for example for faucet parts, the black color PVD coatings are currently the most widely used for last two decades. A perfect black color is characterized by a brilliance L* with lowest possible value while preserving a metallic gloss through extremely smooth surface (thanks to sputtering technology) while maintaining the colour coordinates a* and b* values close to zero. Most current solutions to achieve dark black coatings are based purely on the Diamond-Like Carbon layers or on reactive compounds based on titanium. However, it is a well limitation that DLC coatings have a high level of internal stresses that spoils their adhesion to the substrate. On the other hand, the use of an organic gas such as methane or acetylene leads to an extreme contamination of the coating chamber, that requires frequent cleanings for adequate pumping and promoting good adhesion of the layers to the substrate. On the other hand, titanium-based coatings obtained with CO2 as reactive gas enable us to get dark black color with overcoming the difficulties through less polluting process and layers with low internal stresses. Also, such coatings provides the possibility of direct recoating of objects without the need to strip old layers and fast chemical dissolution of coatings in case of problems make these coatings particularly very interesting among the industrial experts. Today in the post covid era the use of sputtering, arc PVD technologies for decorative applications is increasing much faster than for technical or functional applications. The reasons for that are the following: PVD delivers the broad range of colours, mechanical properties, corrosion and wear resistance better than that of the galvanic coating to be substituted, the use of less expensive substrates and the ability to compete economically with traditional galvanic technologies. Above all, PVD technologies keep the environment clean.
Decorative coatings produced through Physical Vapor Deposition (PVD) are renowned for enhancing the appearance and functionality of various products and surfaces. PVD coatings involve the deposition of thin films of materials such as metals alloys,
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