PVD (physical vapor deposition) coating, also known as thin-film coating, is a technique that involves vaporizing a solid material in a vacuum and depositing it onto a product’s surface. These coatings, however, aren’t just metal layers. Instead, complex materials are deposited atom by atom, resulting in a thin, bonded metal or metal-ceramic surface layer that dramatically improves a product’s appearance, durability, and/or function.
This method is extensively utilized in the aerospace, automotive, and medical industries, among others, to provide a long-lasting jewelry-like look, better long-term performance, and cleaning convenience.
But, what is the process of PVD coatings? How it is deposited on the product surface? This blog will be enough to explore this in detail. So, let’s get started.
PVD Coating process
PVD methods can be used to deposit mono-layered, multi-layered, and multi-graduated coating systems, as well as alloy compositions and structures. These strategies are always changing, and they continue to be a source of inspiration for numerous investigations.
PVD thin-film technology includes a wide range of deposition techniques like electron-beam or hot-boat evaporation, reactive evaporation, and ion plating. Processes based on sputtering, whether by plasma or an ion beam, are likewise included in PVD techniques.
PVD is also used to describe arc source deposition, which can be filtered or not. The most prevalent PVD processes for thin film deposition are sputtering (or cathodic spraying) and evaporation. Evaporation is the process of depositing a thin layer of atoms using heat in the process. Whereas, the atoms or molecules are dislodged from the solid target by the impact of gaseous ions in the sputtering mode (plasma). Both strategies have been refined into a number of distinct techniques.
Thermal Evaporation
Thermal evaporation is a well-known method for coating a thin layer in which the source material evaporates in a vacuum chamber below 1 × 10−6 torr (1.3 × 10−4 Pa) due to high-temperature heating, allowing the vapor particles to go more easily and directly to a substrate, where they solidify again. Vacuum deposition is the traditional name for the thermal evaporation process.
A charge holding boat or resistive coil in the form of a powder or solid bar is employed in this procedure. The resistive boat/coil is exposed to a huge direct current (DC) to achieve the high melting temperatures required for metals, where the high vacuum (below 10-4 Pa) aids in the evaporation of the metal and subsequent transport to the substrate. This approach is especially useful for low-melting-point materials. The figure below depicts two types of thermal evaporation processes.
Thermal evaporation process
For the deposition of thin films, resistive heating is most typically utilized. A resistively heated filament or boat, usually formed of refractory metals like W, Mo, or Ta with or without ceramic coatings, evaporates the source materials. An electron-beam deposition is used to evaporate refractory metals because simple resistive heating is incapable of evaporating high melting point materials.
Sputtering deposition
Sputtering is a PVD process in which blasting, energetic, and atomic-sized particles cause the physical vaporization of atoms from a surface. Sputter deposition allows for more control over the composition of multielement films as well as a wider range of materials to be deposited.
Sputter coating is a procedure that is used to coat a substrate with a very thin, functional coating. The procedure begins with an electrical charge applied to a sputtering cathode, which creates a plasma, which causes the material to be expelled from the target surface. Ion bombardment of source material, or target, is the basis of the process.
Illustration of Sputtering process
But, how does sputtering deposition take place? well, Sputter deposition can be used to deposit elemental material films as well as alloy films while maintaining the target material’s composition. This is possible because the material is removed layer by layer from the target, which is one of the process’s key advantages. This enables the deposition of more complicated alloys like Al-Si-Cu for semiconductor metallization and metal Cr-A-lY alloys for aircraft turbine blade coatings.
Steps of PVD Coating
PVD (physical vapor deposition) is a vaporization coating process that involves atomic-level material transfer. The following sequence of steps can be used to describe the process.
(1) The material to be deposited is transformed into a vapor using physical methods (high-temperature vacuum or gaseous plasma),
(2) the vapor is transferred from its source to a low-pressure location, and
(3) the vapor condenses on the substrate to produce a thin film.
PVD methods are typically used to deposit thin films with thicknesses ranging from a few nanometers to thousands of nanometers. Multilayer coatings, graded composition deposits, very thick deposits, and freestanding structures can all be made using them.
Substrate for PVD coating
The most important thing is which type of substrate can be used for PVD coating? Well, Most metals can be PVD coated, while some materials require a nickel and chromium base layer to improve corrosion resistance. PVD coating is a versatile method that may be applied to a wide range of materials, including thermoplastics. The LTAVD( Low-temperature arc vapor deposition) technique, which deposits metal coatings at a lower temperature than PVD, is used in these materials.
Some base materials stick to the metal deposition better than others. It’s critical to select the proper process in order to obtain the most durable and appealing metal finishing. Nickel or chrome electroplating may be required for the best results, depending on the material. Some materials absorb PVD coatings more readily than others.
- Titanium, graphite, and stainless steel are examples of materials that can be coated without the use of a base layer.
- Steel, Brass, and Copper – Typically nickel/chromium is electroplated before PVD processing for improved corrosion resistance, but can be applied directly
- Plastics, Aluminum, and Zinc Castings – Typically uses the Low-Temperature Arc Vapor Deposition (LTAVD) method for superior corrosion resistance.
The majority of the substrates were fixed in the vacuum chamber in the middle vertical position, while some were positioned at varying heights. The majority of the substrates were put in the middle of the vertical position, with a few at the bottom and top of the substrate holder.
PVD coatings are becoming increasingly popular for metal finishing because they may be applied to a wide range of substrates or base materials. Different colors can be achieved depending on the gases introduced during the PVD process. When you use PVD coatings to polish your metal, you don’t have to stick to metallic colors, which are popular in many industries.
The samples were degreased and cleaned in an industrial-sized automated ultrasonic cleaning line prior to deposition.
Sample preparation for PVD coating
The sample preparation for PVD coating is very essential. But, How a sample should be prepared for PVD coating? What steps should be taken?
In mass production facilities, the substrate is cleaned using ultrasonic before the PVD coating is placed. Cleaning is a multi-step procedure that is followed by rinsing and drying.
Burrs were prepared for PVD using the ultrasonic cleaning technique. Oils, lubricants, cooling emulsion, and particles must be removed from the parts as much as possible before coating.
The first stage was ultrasonic degreasing with a degreaser (pH~11) in deionized water to eliminate surface contaminants (cleaning duration 15 minutes), followed by ultrasonic rinsing in deionized water and drying in pure hot air.
Advantages of PVD coating
PVD coating is being used due to its several advantages, including:
(i) coatings formed by PVD may have better properties than the substrate material;
(ii) all types of inorganic and some types of organic materials can be used;
(iii) the process is more environmentally friendly than many other processes, such as electroplating.
But, How does PVD coating increases the product’s mechanical properties? Let’s discuss this in detail.
Enhanced Durability
A medical or surgical tool that has been PVD plated will survive 10 times longer than one that has not been. PVD plating adds a thin yet robust covering of material that takes longer to corrode.
Performance and Strength
The added plating makes the material tougher, therefore PVD coating medical items help with durability. Because there is less danger of denting or chipping, a more robust surgical instrument will improve the device’s function.
PVD coating medical devices improve lubrication and make them more water-resistant. PVD coating medical tools create a more biocompatible tool that is nonreactive to the bone, biological fluids, or tissue, depending on the material coated onto the device.
Sharpening
PVD coating can assist a surgical tool to keep its blade or edge sharper for longer by enhancing edge retention.
Variation
Various colored PVD coating materials can be used to plate a medical tool. This can be used to distinguish between similar tools or to categorize specific supplies.
Lubrication of parts in mechanical components in motion is a concern in the automotive industry. Gears, pistons, cams, and bearings are examples of these parts. PVD coatings have provided a fantastic solution to this challenge. They alter the treated parts’ surface properties, lowering friction coefficients and increasing wear resistance
.
PVD, on the other hand, has some drawbacks, including
(i) issues with coating complex forms;
(ii) high process cost and low output; and
(iii) process complexity.
PVD Coating’s Industrial applications
PVD methods are used to coat materials in a variety of industries applications, including
- Cutting tooling, milling tooling, drilling tooling, molding tooling, engine parts, and bearings.
- In the vehicle business, household appliances, writing tools, electronics sector, and toy industry,
- The decorative coating creates a metallic impression on plastics.
- Lenses, optics, glasses, touch screens, and mirrors are all coated with an optical coating.
- Medical devices, such as implants, pacemakers, and surgical equipment, are coated with a wear-resistant coating.
- Solar cell glass wear-resistant coating and metallization coating for crystalline silicon solar cells.
- Packaging material with a metallization layer.
Thin PVD (Physical Vapour Deposition) coatings have become increasingly common for all types of cutting instruments in recent years. These technologies are currently widely employed in the production of drill bits, milling cutters, and boring bits, among other items.
TiN PVD coatings were recognized as an improvement for metal working with high strength and abrasive steels as well as nonferrous metals after ten years of successful application in cutting, punching, cold forming, injection molding of plastics, and die casting of some metal alloys. The high thermal stability of TiAlN coating (up to 700 °C) appeared to be the deciding factor, indicating that this coating should be utilized when superior oxidation resistance is required.
Photo by Chris Yates on Unsplash
CrN (PVD) coatings are finding their way into an ever-widening but the still-selective range of mass-produced goods. They can be made as single CrN coatings at moderate and high temperatures, as well as double TiN+CrN coatings. At high temperatures, a low voltage thermionic arc in a BAI 730M apparatus was used to deposit CrN, whereas, at low temperatures (below 250 °C), a plasma-beam sputtering method in a SPUTRON apparatus was used.
The conditions for a successful joint arthroplasty are very strict; a well-balanced mix of mechanical qualities and good biocompatibility is required. Because of their relative inertness, outstanding load-bearing qualities, and excellent wear resistance, Co-Cr-based alloys have been utilized for many years.
However, there is a risk that a slow accumulation of metal ions like cobalt and chromium could lead to negative clinical outcomes. Thus, the question is raised; what should be the possible solution to this?
Afterward, a thin layer of TiN was placed using Physical Vapor Deposition to decrease the discharge of potentially hazardous metal ions from Co-Cr-Mo based surgical implants (PVD). Electrochemical techniques and atomic absorption analysis were used to examine in vitro corrosion performance.
Conclusion
PVD Coating is also known as the thin-film coating. This is a technique to deposit single and multi-layer coatings on samples. There are a lot of techniques to deposit PVD coating but the most commonly applied methods are evaporation and sputtering. In these methods, we can utilize low and high melting point materials. PVD coating can be applied to a wide range of materials including thermoplastics. The sample should be prepared and cleaned in an ultrasonic degreaser before PVD coating. There is a broad range of industrial applications that include automotive, medical implants, aerospace, etc. Still, do you have any questions about PVD coating? Don’t hesitate just let us know by commenting below.
