The Complete Guide To DLC Coating (Diamond Like Coating)

There are various surface treatment methods available for both metal and plastic parts, and DLC coating is one of the most important and commonly used techniques. In this article, we will learn together what DLC coating is, its characteristics, advantages and applications.

What is DLC Coating?

DLC coating, also known as diamond-like carbon coating, is a special surface coating (nanocomposite coating) with diamond-like properties such as hardness, wear resistance, corrosion resistance and chemical inertness. DLC coating is usually composed of carbon and hydrogen and is applied on the surface of various materials by physical evaporation deposition or chemical vapor deposition.

DLC is a metastable form of diamond-like amorphous carbon with a ratio of sp2 and sp3 bonds. It is often used to increase the hardness and wear resistance of material surfaces while reducing friction and surface adhesion. Diamond-like carbon (DLC) coating is a new technological advancement in PVD + PECVD coatings that has achieved widespread success in the commercial industry.

A Basic History of DLC Coating

In the 1970s, Sol and Ronald from Germany used ion beam deposition to deposit monovalent carbon ions onto a substrate at room temperature to produce DLC films.

In 1984, Lin Xigang et al. used low-energy ion beam deposition technology to prepare diamond-like carbon films and preliminarily tested their mechanical, optical, and electrical properties.

After the 1990s, researchers began to study doped DLC and continued to explore new types of DLC coatings and develop more advanced deposition techniques to improve their performance. DLC coatings have become a mature technology and have been widely used in various industries, including medical, aerospace, and electronic equipment.

Types of DLC Coating

• a-C = hydrogen-free amorphous carbon
• ta-C = tetrahedrally bound hydrogen-free amorphous carbon
• a-C: H = An amorphous carbon with hydrogen
• a-C:H: Me = metal-doped amorphous carbon with hydrogen(Me = W, Ti)
• ta-C:H = A tetrahedrally bound amorphous carbon with hydrogen
• a-C:H:Si = This is a Si-doped amorphous carbon with hydrogen
• a-C:Me = metal-doped hydrogen-free amorphous carbon (Me = Ti)
• a-C:H:X = A non-metal-doped amorphous carbon with hydrogen

Properties of DLC Coating

Hardness: With a diamond-like structure, DLC coating has high hardness, with a coating hardness greater than 2300HV, which is 10 times harder than graphite. This makes it very effective in enhancing the surface hardness and wear resistance of materials. This hardness allows its widespread use in mechanical parts, cutting tools, and bearings.

Low Friction Coefficient: The smooth surface of the DLC coating has a low friction coefficient (0.05-0.1), forming a self-lubricating friction layer on the product surface, which helps to reduce friction loss. This is particularly useful in environments where lubricants are limited or cannot be used, such as in aerospace, automotive, and industrial equipment.

Corrosion Resistance: DLC coatings have certain resistance to chemical corrosion, which helps to improve the corrosion resistance of materials. This leads to applications in marine environments, the chemical industry, and medical devices.

Thermal Stability: DLC coatings have good stability in high-temperature environments and can withstand temperatures up to 450°C. This allows their widespread use in high-temperature processes and automotive engine components.

Biocompatibility: Some types of DLC coatings meet medical implant standards and are biocompatible with the human body, making them widely used in the medical field, such as in artificial joints, implants, and surgical tools.

Conductivity: Some types of DLC coatings have good electrical conductivity, leading to some applications in electronic devices, sensors, and displays.

Advantages of DLC Coating

Corrosion and Wear Resistance: The protective layer provided by DLC coating helps maintain the integrity and functionality of the underlying material, even in harsh environmental conditions.

Durability: DLC coatings are known for their extreme durability. With high hardness, corrosion resistance, and wear resistance, these coatings can be used for extended periods. This durability ensures that the coated material remains resistant to wear or fading, as long as the underlying material is well-maintained.

Environmental Friendliness: DLC coatings do not use harmful chemicals and are generally safer for both the environment and the operators involved in the coating process.

Improved Appearance: DLC coatings can give objects a beautiful gray-black appearance and enhance the visual quality of products.

Versatility: By altering deposition conditions and adding dopants, the performance of DLC coatings can be tailored to meet various application needs.

Deposition of DLC Coating

There are several methods in the market available for the deposition of DLC coatings including ion beam, electron beam, PAVCD, sputtering, cathodic arc, and laser. In the market today, the use of PVD and PAVCD for DLC coatings is used because it is regarded as the most consistent and the highest quality. Below we mainly discuss PVD technology and PACVD technology:

PVD Technology

Physical vapor deposition (PVD) is a novel thin film deposition technology that involves physically transforming the target material (source material) into a gas or plasma in a vacuum environment and then depositing it onto the substrate surface. It is one of the primary surface manufacturing techniques currently used. It mainly encompasses three major categories: vacuum evaporation coating, vacuum sputtering coating, and vacuum arc ion plating.

Films deposited using PVD coating technology exhibit high hardness, high wear resistance (low friction coefficient), excellent corrosion resistance, and chemical stability, resulting in longer film life. Additionally, the film significantly enhances the decorative properties of the workpiece.

PVD coating technology is an environmentally friendly surface treatment method that can truly achieve micron-level coatings without pollution. It can be used to prepare various single-metal films (such as aluminum, titanium, zirconium, chromium, etc.), nitride films (TiN, ZrN, CrN, TiAlN), and carbide films (TiC, TiCN), as well as oxide films (such as TiO).

The thickness of the PVD coating film is in the micron range, with a relatively thin thickness, generally 0.3μm to 5μm. The thickness of decorative coating films is typically 0.3μm to 1μm. Therefore, it can enhance various physical and chemical properties of the workpiece surface without significantly affecting its original dimensions, eliminating the need for post-processing.

Advantages of PVD

Wear Resistance: PVD coatings are very hard and wear-resistant, making them ideal for surfaces that experience frequent use and wear.

Corrosion Resistance: PVD coatings can provide an additional layer of protection against corrosion, making them a good choice for outdoor or marine environments.

Enhanced Aesthetics: PVD coatings can be applied in various colors, providing a wide range of aesthetic options.

Environmentally Friendly: PVD coating processes do not release harmful chemicals, making them more environmentally friendly than other coating processes.

PACVD Technology

PACVD is the short form for Plasma Assisted Chemical Vapor Deposition. This method of deposition is widely used to deposit Diamond-Like Carbon coatings. This process is vacuum-based and all educts of the PACVD process occur in a gaseous state. In contrast with PVD, the gaseous depositing process makes it suitable for 3D coating with no need for rotation. PACVD coatings contain around 70% sp3 bonding and are amorphous. The sp3 bonding accounts for the ultra-high hardness (10-40GPa) property of the coating. Attemperature below 200℃, the PACVD can deposit coatings for a wide range of non-conductive and conductive substrate materials.

Advantages of PACVD

• Post-treatment is not required
• Can deposit on a broad range of substrate
• No occurrence of distortion in a high precision substrate
• Uses a gaseous process that allows for uniform coating

Tips to Improve The Bonding of DLC Coating and Substrate Material

Optimizing Surface Treatment: Cleaning and roughening the substrate surface, methods such as using sandpaper, sandblasting, and acid etching can be employed to increase the surface energy and contact area between the coating and the substrate, thereby enhancing the adhesion.

Heat Treatment: Adjusting the thermal expansion coefficient of the coating and substrate material to match can reduce stress caused by temperature changes.

Using Coupling Agents: Applying or immersing a coupling agent between the coating and the substrate can enable organic molecules to chemically react with the substrate surface, forming strong chemical bonds that improve adhesion.

Ion Implantation: Introducing metal elements into the substrate surface through ion implantation can create an intermediate layer with good adhesion to the coating material, thereby enhancing the bonding strength.

Alloying Treatment: Adding alloying elements to the substrate material can make it more compatible and stronger in bonding with the coating material.

Using Composite Coatings: Adding one or more intermediate layers with high adhesion between the coating and the substrate, such as metals, ceramics, or other polymer materials, can improve the adhesion between the coating and the substrate.

Applications of DLC Coating

DLC coating can improve the performance of materials, extend the service life, and improve the corrosion resistance of materials. It is widely used in molds, medical, automobiles, and cutting tools.

Mold

DLC coating has the characteristics of smooth surface, low friction coefficient, easy demoulding, wear resistance, and good thermal conductivity. The coating has extremely high hardness, and it is difficult for the high-pressure scouring and particles of the material to damage it, which can increase the service life of the mold. Therefore, it is often used to make various molds, including: stamping molds, injection molding molds, and semiconductor molds. For example: punches, concave molds, precision blanking, and embossing parts.

Medical

DLC coating has good biocompatibility, which can make biological tissues and implanted artificial materials coexist peacefully without rejection reaction. It can be used as surface coating for artificial joint materials, dental materials, artificial bones, artificial heart valve materials, surgical needles and medical catheters.

Automotive

DLC coating can play a good role in lubrication and wear resistance under dry friction conditions without lubricating oil, and is a good choice for automobile engine parts. The piston ring in the automobile engine reciprocates up and down in the cylinder, and the ring surface constantly scrapes the inner wall of the cylinder, resulting in a large friction power loss, which greatly affects the energy consumption and service life of the engine.

Tool

DLC coating has a low friction coefficient and strong wear resistance. It can effectively improve the service life of cutting tools and enable tools to obtain excellent comprehensive mechanical properties, thereby greatly improving machining efficiency. DLC coating has become an ideal coating material for high-speed steel and carbide tools.

FAQs

What Are DLC Coating Colors?

The color of DLC coating is affected by thickness, structure, and dopants, and there is no fixed color. It will show different colors according to different preparation processes and material components, ranging from colorless and transparent to gray-black, and even brown or yellow. The most common one is black-gray coating.

What Are the Limitations of DLC Coating？

DLC coatings generate internal stresses during the deposition process, which can lead to deformation of the substrate or even cause the coating to flake off. Excessive stress can also reduce the abrasion and impact resistance of the coating. If the coating is not homogeneous, the performance of certain areas will be reduced. Higher cost compared to other coatings.

Conclusion

After reading this blog, I believe you must have a clearer understanding of DLC coating. In recent years, DLC coating has been used more and more in various fields, from automotive parts to machine tool tools, both precision medical devices and ordinary springs.

DEK is a global custom parts manufacturer. If you choose DEK as your partner, you can experience the top DLC coating technology. Contact us now to start your project!