As time passes, the importance of durable products to decrease overall consumption and decrease waste is increasingly coming to light. However, not all materials are intrinsically tough, heat tolerant, or corrosion resistant. In this article, we’ll discuss a process that enhances the physical properties of such materials – the PVD coating process.
In PVD or Physical Vapor Deposition, you deposit vapors of one material onto another and wait for them to solidify. This process leads to the formation of a thin film that enhances the substrate’s properties.
You’ll often find PVD on nylon, plastics, metals, glass, and ceramics, as it ensures these materials do not corrode, react with chemicals, or wear out. It can introduce optical properties, improve conduction, increase strength, decrease friction, or enhance aesthetics.
PVD Coating Methods Used in Industrial Applications
You can use the following techniques for the Physical Vapor Deposition process:
1. Thermal Evaporation
Microfabrication in the computer industry often involves PVD coating through thermal evaporation. You’ll find two commonly used techniques: electron beam and pulsed laser deposition.
Both techniques use energy to evaporate a metal and make the vapors travel through the vacuum to a cool surface, where they solidify into a thin layer. However, electron beam deposition involves accelerating electrons to transfer energy to the target material. And pulsed laser deposition, you use a low voltage but high current to generate energy.
2. Sputter Deposition
You’ll find two common types of this technique: ion beam and magnetron sputtering.
In the ion beam sputtering PVD coating technique, the target material is ionized through an electric field. This causes it to ionize and hit the surface it should coat.
In magnetron sputtering, the electric field pushes positively charged ions onto the target surface.
Medical supplies and laboratory products are often coated through the sputter deposition technique.
3. Arc Vapor Deposition
In this technique, you use a low voltage to vaporize the target material and make it react with other gases in the chamber to produce the desired coating.
Arc vapor deposition is the most environmentally friendly PVD coating technique because it uses minimum chemicals. It also gives a thin coating in multiple colors, such as black, blue, purple, gold, bronze, graphite, and multiple color combinations.
A Step-By-Step Guide to PVD Coating
Here’s a step-by-step guide to help you understand the nuances of the PVD coating process.
Step 1: Cleaning the Substrate
You need to ensure your substrates are free of surface impurities so that the PVD coating sticks well to them. You can do this through mechanical cleaning with pressured air or chemical cleaning to disinfect the said substrate.
Step 2: Treating the Substrate
You can treat the substrate in particular ways to enhance the adhesion of the coating. For instance, you can make the surface of the substrate rougher through anodizing or plasma etching. This increases its surface area and allows for better deposition of the metal coating on it.
Step 3: Loading the Substrate into a Vacuum Chamber
After preparing the substrate, you load it into the PVD chamber – usually, a vacuum-sealed enclosure designed to maintain a low-pressure environment. The chamber is evacuated through a vacuum pump to ensure no additional particles can interfere with the coating process.
Step 4: Vaporizing and Transporting the Target Metal
Once the substrate is ready, the target material is vaporized through any of the methods discussed above. The resulting vapor is allowed to travel to the substrate, where it’s deposited in a controlled manner.
Step 5: Gas Reaction
The substrate can react with certain gasses to ensure that the coating bonds with it well. The reagent gasses can also let you alter the properties of the resulting coating, like its toughness, smoothness, etc.
Step 6: Coating
The target metal is then deposited onto the substrate at an atomic or molecular level. The process occurs under controlled pressure and temperature, as these parameters can alter the properties of the coating.
Step 7: Post-Coating Treatments
The coated substance is tested for qualities like uniformity, roughness, thickness, etc., to ensure the product meets the desired specifications. Then, post-coating treatments are employed.
Post-coating treatments further enhance the strength of the bonds between the substrate and coating. Some common ones include
- Annealing: Here, you heat the coated substrate in a controlled environment to improve the adhesion of the coating to the substrate and reduce residual stress in the coating.
- Surface polishing: This involves mechanical or chemical polishing to remove surface irregularities and roughness
- Surface finishing: This entails using methods like laser texturing and electro-polishing to modify the surface properties of the coating.
Materials Used in PVD Coating
PVD coating involves substrates, target materials, and gasses to assist the coating.
Substrates are materials that undergo coating. Various substrates, including metals, and ceramics, glass, can be used for the process, with some allowing better adhesion and compatibility with the process than others.
Plastics need to be coated at lower temperatures, and materials like copper, steel, and brass often undergo electroplating before vapor deposition for better corrosion resistance. Chrome-plated materials and stainless steels sustain PVD coatings well. The choice of substrates varies per application.
2. Target Materials
The material used for coating – the target material – depends on the properties you want your substrate to have.
For instance, TiCN coating increases an object’s hardness and is commonly used on cutting tools, whereas certain ceramic coatings are on optics to induce anti-reflective properties. These materials are large in number and not restricted to metals. Some of these target materials include:
- Titanium Nitride to enhance hardness
- Graphite-iC and MoST for low friction
- Zirconium Nitride for anti-corrosion
- Diamond-like-Carbon DLC for super strength
The physical vapor deposition process commonly involves the following gasses:
- Oxygen alters the film’s color if ion deposition is involved.
- Argon can be used to increase pressure.
- Nitrogen alters the color if ion deposition is involved and is used to increase air pressure.
Applications of PVD Coating
From everyday items to NASA’s machinery, PVD coating has found a variety of applications in many fields. We’ll discuss three industries that benefit greatly from the technology:
1. Automotive Industry
Moving parts in vehicles need to be resistant to tear, have low friction to minimize energy loss and wear and tear, and be lightweight to ensure the fuel lasts for a long. PVD coatings can introduce all such properties to the desired substrates.
For instance, the valve train system and engine bearings inside a car’s engine cause power loss due to friction. As multiple surfaces move against each other, the risk of component deterioration is also high.
Numerous PVD coatings, like DLC, MoS2, and Onyx, can increase the strength and thermal resistance of such components while reducing the friction between them without any considerable addition to weight or the need to use heavy materials.
Lighter materials, like aluminum or some alloys, can be protected against structural deformation by using PVD coatings as well, effectively reducing the vehicle’s weight. This increases the longevity of the vehicles and increases their fuel efficiency.
You can also use PVD coatings to enhance the aesthetic appeal of vehicles and customize the appearance of the finish by introducing multiple colors, reflection properties, and textures.
2. Firearms Industry
PVD coating is rapidly gaining traction in the firearm industry as it effectively enhances a firearm’s functionality while offering better customization options.
As with automobiles, hardness, abrasion resistance, and low friction are essential for the longevity of firearms. PVD coats can provide such properties. And as these coats are extremely thin, they do not alter the dimensions of firearm components perceivably, so users can get their guns coated after purchasing them.
Firearm enthusiasts can now also get their guns in multiple permanent colors and finishes through the PVD coating of nitrides, like CrN, TiCN, etc.
3. Medical Industry
Medical precision instruments are often thin and sharp, so they can be easily deformed if the right materials aren’t used. Additionally, many tools must be cut or drilled through bones, increasing their chances of wearing out. So, unsurprisingly, PVD coatings have long since established themselves firmly in the medical industry.
High-strength coatings like TiN, DLC, and AlTiN have gained widespread acceptance due to their part in increasing the longevity of equipment in a biocompatible manner. They also assist instruments in retaining their sharp edges so that incisions are precise and heal quickly. Certain coatings also have antimicrobial effects and can withstand multiple autoclave cycles, assisting the field of medicine by making equipment safer, economical, and last longer.
Advantages of PVD Coating
Just applying a thin coat of a suitable target material through PVD coating can open a plethora of applications by modifying the surface properties of materials. Advantages include the following:
- Unlike electroplating, PVD coats have high adhesion and are non-corrosive, scratch-proof, and can last a lifetime. Long-lasting products ultimately decrease consumption and are regarded as sustainable.
- There are unlimited target-substrate combinations to benefit from, as the technique isn’t limited to a certain class of substances. This can be utilized to attain various properties like low friction, increased strength, high chemical, and thermal resistance, altered optical qualities, etc.
- PVD techniques allow you to vary the film thickness and composition per your needs, allowing for superior modification.
- No toxic by-products are produced in the PVD process. This makes it much more eco-friendly than other metal coating methods that often require chemical reactions.
- Workers handling PVD processes do not have to work under hazardous conditions, as the process is safe.
- You can use multiple techniques for vapor deposition, so each manufacturer can choose the technique that’s economical for them and works with their substrate.
- Changing the surface properties of materials through PVD coating is significantly less expensive than investing in pure materials with the desired properties. For example, getting a DLC-coated drill is considerably more economical than investing in diamond-cutting tools.
Disadvantages of PVD Coating
- The cost of PVD equipment is high.
- Physical Vapor Deposition takes more time than many other coating techniques.
- The process requires skilled personnel to operate it, so labor costs are high.
- PVD coating requires cooling systems to deal with high heat generation.
Maintenance of PVD Coating
PVD coatings are simple to maintain as they are mainly designed to be smooth and corrosion-resistant. You can use a dry cloth or one dampened in a mild soap-water solution to remove dust and debris if necessary.
Avoid using harsh chemicals, abrasive cleaners or polishes, acids, and caustic agents, as you may not be aware of the degree of chemical resistance of your PVD coat. Steer clear of rougher cleaning pads, like steel mesh scourer sponges, and other scouring pads, like the ones used for dishes.
For firearms, PVD-coated parts should be kept oiled to ensure the coating lasts against corrosion for a long.
PVD Coating vs. Other Coating Technologies
Here are some alternative coating methods in comparison with physical vapor deposition:
1. CVD Coating
In Chemical Vapor Deposition coating, you have to use multiple reactive chemicals to get your substrate coated. The required film is produced through multiple reactions that deposit it on the substrate. It results in thin, abrasion-resistant layers and can be easily used to coat irregular materials. Manufacturers can expertly control the purity and thickness of the layers.
The material deposited in the CVD process adheres to the substrate through metallurgical and diffusion-type bonds, unlike PVD’s physical bonds, so it adheres better. However, CVD-coated components are more fragile than PVD-coated ones.
Whether you need CVD or PVD coating depends entirely on your intended application of the product.
It’s essential to note that CVD coating involves volatile precursor chemicals and produces many by-products, including toxic ones. Any leaks can be disastrous, and the laboratories need to be well-maintained under strict protocols. It also requires significantly higher temperatures than PVD processes.
2. ALD Coating
You can perform Atomic Layer Deposition (ALD) at a nano-metric scale, building the coat layer-by-layer with precision controlled at an atomic scale. Unlike PVD and CVD, which coat assembled objects, ALD coats simple nano-structures that are then assembled into larger objects. The process yields extremely precise, uniform, and deformity-free layers.
ALD is a very slow process, and the materials and processes involved are limited. Although invaluable, its applications are highly specific, like semiconductor fabrication in circuitry, anti-reflective coatings in optics, and making chemical or moisture barriers for sensitive devices. And unlike PVD, you can not use the technique on pre-manufactured objects.
Physical vapor deposition coating is proving to be an extremely valuable coating technique that can enhance the properties of materials. It deposits corrosion-resistant, durable, and stable thin layers that can enhance qualities like the coated object’s strength, resistance, and optical, magnetic, and conductive properties.
The PVD coating process can be conducted through multiple techniques and is compatible with many materials. It’s environmentally friendly, requires less energy than its competitors, produces no toxic by-products, and ensures a safe working space for workers.
If you want to secure PVD coating specialists for your business, you can contact us and benefit from all the properties PVD unlocks in materials.
Aluminum Powder Coating – Source: KDM