function of chromium boride powder in the deposition process of hard coatings

Chromium boride powder (CrB ₂) plays multiple important roles in the deposition process of hard coatings.

Firstly, it can significantly enhance the hardness of the coating. Chromium boride itself has a high hardness. When used as a coating component in deposition, it can effectively enhance the overall hardness of the coating, enabling it to resist stronger mechanical effects such as wear and friction. This can greatly extend the service life of components that work in high load and high friction environments, such as cutting tools, molds, etc.

Secondly, chromium boride helps improve the wear resistance of coatings. It can form a dense and tough structure on the coating surface, preventing external particles from corroding the substrate material, reducing the generation of wear marks, and maintaining the flatness and integrity of the coating surface.

Furthermore, chromium boride can enhance the high-temperature stability of coatings. In high temperature environments, it can maintain its structural stability, prevent performance degradation of the coating due to temperature rise, and ensure that the coating can still perform well in terms of protection and mechanical properties under high temperature conditions.

In addition, chromium boride can affect the microstructure of the coating during the deposition process. It can promote the formation of a uniform, fine, and dense grain structure in the coating, which helps to improve the overall performance of the coating, including hardness, toughness, adhesion, etc.

Chromium boride also plays a positive role in the adhesion between the coating and the substrate. It can form a certain chemical bond or physical inlay with the substrate material, enhancing the adhesion strength between the coating and the substrate, making the coating less prone to detachment during use, and ensuring the long-term effectiveness of the coating.

For example, adding chromium boride powder to the tool coating can enable the tool to withstand higher cutting forces and frictional heat during high-speed cutting, while still maintaining a sharp cutting edge, significantly improving processing efficiency and quality, while reducing the frequency of tool replacement and saving production costs. In summary, chromium boride powder is one of the key materials for improving coating performance and expanding coating application fields in the deposition process of hard coatings.

At present, the mainstream deposition processes mainly include physical vapor deposition (PVD) and thermal spraying technology, among which magnetron sputtering and plasma spraying are the two most concentrated methods for research and application.

1. DC/RF Magnetron Sputtering

This is the most commonly used PVD process for preparing high-quality, dense chromium boride films, especially CrB ₂ superhard coatings.

Process principle: Fill the vacuum chamber with argon gas (Ar) and use an electric field to accelerate ion bombardment of chromium boride target or composite target (such as Cr+B ₄ C), causing target atoms to sputter and deposit on the substrate surface.

Key parameter control:

Magnetic field strength: Non uniform gradient magnetic fields can significantly affect the preferred orientation of coatings. Research has shown that when the magnetic field strength on the target surface increases from 40 mT to 80-100 mT, the (001) preferred orientation of CrB ₂ coating gradually strengthens, the grain size increases, and the hardness increases accordingly. At the optimal magnetic field strength (such as 80 mT), the coating hardness can reach over 47.75 GPa.

Substrate bias: Applying a negative bias voltage (such as -50 V) can increase the ion bombardment energy, refine the grains, reduce porosity, and improve the adhesion between the coating and the substrate. Excessive bias voltage can lead to an increase in porosity and a decrease in binding strength.

Temperature: Deposition is usually carried out at around 300 ° C to balance deposition rate and crystal quality.

Advantages: Dense coating, few defects, extremely high hardness (up to superhard standards), excellent corrosion resistance (self corrosion current density two orders of magnitude lower than the substrate). ‌‌

2. Reactive Plasma Spraying

Suitable for preparing thick large-area wear-resistant and high-temperature oxidation resistant coatings, especially suitable for complex shaped workpieces.

Process principle: The raw material powder is sent into a high-temperature plasma flame, where the powder undergoes a chemical reaction and melts at high temperature, and then collides with the substrate to cool and solidify, forming a coating.