Introduction
Traditional coatings refer to a group of materials that are applied to surfaces to improve their appearance, durability, and functionality – from infrastructure and the built environment, to industrial tools, to everyday consumer goods. These coatings have been used for centuries, and they include a variety of natural and synthetic materials such as paints, varnishes, enamels, and lacquers.
Paints are made of pigments, binders, and solvents that provide color, protection, and adhesion to a surface. They are the most common type of traditional coating used in everyday life. Varnishes and lacquers are transparent or translucent coatings that are used to enhance the natural beauty of wood, metal, or other materials while providing protection against moisture, sunlight, and abrasion. Enamels are highly durable, resistant to chemicals and abrasion, and provide a glossy finish. They are used for high-performance applications, such as industrial and automotive environments. In general, traditional coatings have been widely used for hundreds of years, and they continue to play an important role in various industries today.
Physical vapor deposition (PVD) coatings
On the other hand, PVD coatings are formed by vaporizing solid materials in a vacuum environment and then allowing the vaporized particles to condense onto the substrate, creating a thin film. The main difference between traditional coatings and physical vapor deposition (PVD) coatings is in the way they are applied and the properties they offer.
Traditional coatings are typically deposited by brushing, spraying, or dipping the material into a liquid or semi-liquid coating material. PVD coatings are applied in special coating equipment using a vacuum deposition process. This involves vaporizing the coating material in a vacuum chamber, and then depositing it onto the surface of the object to be coated. PVD coatings are typically much thinner than traditional coatings, and are often used for their unique properties such as high hardness, wear resistance, and low friction. They are also highly customizable, allowing for the preparation of unique and complex coatings with highly specific properties tailored to the individual application. A wide range of industries and applications include cutting tools, automotive industry, aerospace industry, medical devices, decorative applications, tooling and molds, electronics and optics.
Durability of coatings
PVD coatings are characterized by exceptional durability, which is one of the key reasons they are widely used in a variety of industries. Their durability is associated with exceptional hardness, wear resistance, and corrosion resistance, making them ideal for challenging applications and demanding operating conditions.
Durability of coatings can be tested in several ways using different types of loads and stressors. The most common methods used to test the durability are:
– adhesion testing, which measures the bond strength between the coating and the substrate. Methods such as scratch test, cross-cut tape test, pull-off test, or scrape adhesion test show the coating’s ability to adhere to the surface and resist delamination.
– wear and friction tests measure how well the coating performs under sliding, fretting, or rubbing conditions. Testing methods include ball-on-disc, pin-on-disk, pin-on-plate or reciprocating wear testers evaluate the coating’s resistance to wear, and friction properties.
– abrasion resistance testing evaluates the coating’s resistance to wear and abrasion. Taber Abrasion Test, or falling sand tests are used to simulate abrasive conditions and determine the coating’s ability to withstand abrasion.
– impact resistance testing assesses how well the coating can withstand impact or deformation. Instruments like falling dart impact testers or impact pendulum testers are used.
– chemical and corrosion resistance testing examines the coating’s resistance to various chemicals and environmental conditions. The samples are exposed to a highly corrosive salt fog environment, and the time until the appearance of corrosion is measured.
– weathering and UV resistance tests simulate long-term exposure to environmental factors such as sunlight, moisture, and temperature fluctuations. Resistance to UV degradation, fading, cracking, or loss of gloss are evaluated.
– flexibility and bend tests measure the coating’s ability to withstand deformation or elongation without cracking or detachment. Mandrel bend tests or conical mandrel tests are commonly used to evaluate the coating’s flexibility and adhesion under bending or forming conditions.
Testing standards set by organizations such as ISO, ASTM International, or industry-specific guidelines are often followed to ensure consistent, repeatable and reliable results.
The cost of traditional and PVD coatings
The cost of traditional coatings and PVD coatings can vary depending on several factors, including the type of coating, the size and complexity of the object being coated, and the specific requirements of the application. However, in general, PVD coatings tend to be more expensive than traditional coatings. Here are the main reasons:
– process complexity: PVD coating processes is much more complicated and more time-consuming compared to traditional coating methods. The preparation, cleaning, and deposition steps involved in processes require precise control and longer processing times, which can contribute to increased labor costs.
– equipment: specialized vacuum chambers, vacuum system, measuring units, deposition equipment, and skilled operators are required. The investment and maintenance costs associated with PVD coating equipment are typically higher compared to the equipment used for traditional coating methods.
– material costs: expensive high-purity metals or metal compounds and high-purity working and reactive gasses are necessary for PVD process. Additionally, PVD coatings often require multiple layers or complex compositions to achieve desired properties, further increasing material costs.
– performance and durability: the superior properties of PVD coatings, such as hardness, durability, enhanced performance, wear resistance, and corrosion resistance, come at a higher cost due to the advanced materials and processes involved in their production.
It is important to note that while PVD coatings may have a higher cost, they can provide very significant short-term and long-term benefits, including extended service life, reduced maintenance, and improved performance, which can definitely outweigh the initial investment. The cost-effectiveness of PVD coatings depends on the specific application and the value that the enhanced properties bring to the coated object.
In contrast, traditional coatings are generally more accessible and cost-effective options for many applications. They offer a wide range of colors, finishes, and protective properties at relatively lower costs. Wide availability, easy application, and less specialized equipment and expertise result in lower overall costs.
To conclude, the choice between PVD coatings and traditional coatings depends on the specific requirements, desired properties, and budget constraints of the application at hand.
Resources
P.J. Kelly, R.D. Arnell, Magnetron sputtering: a review of recent developments and applications
Veprek, The search for novel, superhard materials
J.E. Greene, Review Article: Tracing the recorded history of thin-film sputter deposition: From the 1800s to 2017
J.E. Greene, Tracing the 5000-year recorded history of inorganic thin films from 3000 BC to the early 1900s AD
Inspector, P.A. Salvador, Architecture of PVD coatings for metalcutting applications: A review
A. Matthews, S. Franklin, K. Holmberg, Tribological coatings: contact mechanisms and selection