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PVD and CVD coating methods

Coating method There are two coating methods commonly used in production: physical vapor deposition (PVD) and chemical vapor deposition (CVD).

PVD (Physical Vapor Deposition)—Physical Vapor Deposition: refers to the process of using physical processes to achieve material transfer, transferring atoms or molecules from the source to the surface of the substrate. Its function is to spray certain particles with special properties (high strength, wear resistance, heat dissipation, corrosion resistance, etc.) on a matrix with lower performance, so that the matrix has better performance. Basic PVD methods: vacuum evaporation, sputtering, ion plating (hollow cathode ion plating, hot cathode ion plating, arc ion plating, active reactive ion plating, radio frequency ion plating, DC discharge ion plating).

CVD SiC coating uses chemical vapor deposition (CVD) method to prepare SiC coating.

The former has a deposition temperature of 500°C and a coating thickness of 2~5µm; the latter has a deposition temperature of 900°C~1100°C and a coating thickness of 5~10µm, with simple equipment and uniform coating. Since the PVD method does not exceed the tempering temperature of high-speed steel itself, high-speed steel cutting tools generally use the PVD method, and cemented carbide mostly uses the CVD method. When cemented carbide is coated by CVD method, due to its high deposition temperature, a brittle decarburization layer (eta phase) is easily formed between the coating and the substrate, resulting in brittle fracture of the blade.

In the past decade, with the advancement of coating technology, PVD method can also be used for cemented carbide. Foreign countries have also used PVD/CVD combined technology to develop a composite coating process, called PACVD (plasma chemical vapor deposition). That is, using plasma to promote chemical reactions, the coating temperature can be lowered to below 400°C (currently the coating temperature can be reduced to 180°C~200°C), so that there will be no diffusion between the cemented carbide substrate and the coating material. , phase change or exchange reaction, which can maintain the original toughness of the blade. This method is reportedly particularly effective for coating diamond and cubic boron nitride (CBN) superhard coatings. When coating with CVD method, the cutting edge needs to be passivated in advance (the radius of the blunt circle is generally 0.02~0.08mm, and the strength of the cutting edge increases with the increase of the radius of the blunt circle), so the cutting edge is not as sharp as the uncoated blade. Therefore, the PVD method should be used for tools that produce thin chips for finishing and require sharp cutting edges.

In addition to being coated on ordinary cutting inserts, the coating can also be coated on the entire tool. It has now been developed to be coated on welded carbide tools. According to reports, a foreign company has adopted the PCVD method on welded carbide drill bits. As a result, the drill bit life when processing steel materials is 10 times longer than that of high-speed steel drill bits, and the efficiency is increased by 5 times.

What are the coating ingredients? What are the differences between them and what are their applications?

Commonly used coatings are: TiC, TiN, Ti (C.N), Gr7O3, Al2O3, etc. The above CVD hard coatings basically have low sliding friction coefficient, high anti-wear ability, high anti-contact fatigue ability, and high surface strength, ensuring that the surface has sufficient dimensional stability and a high degree of contact between the substrate and the substrate. Adhesion strength.

Comparison of PVD and CVD coating processes

Comparison of PVD and CVD coating processes
	Deposition temperature	coating thickness	Coated surface state	Main coating Material	Coating Bond strength	To the environment Influence	Main application areas
Object Reason Qi phase Shen product	500℃ or lower, Low deposition temperature Tool deformation is not possible, Hardness of matrix No reduction in strength.	2～5μm, The coating is thin , edge edge profit.	The coating is compressive stress, which is helpful to inhibit the expansion of cracks; the cutting edge does not need to be blunted; the surface is dense and has low roughness.	TiN TiCN TiA1N A1₂o₃ A1CrN MoS₂ WC/C wait.	Low	No pollution	1. High-speed steel general tools: drill bits, taps, end mills. 2. High-speed steel precision and complex cutting tools: broaches, gear cutting tools. 3. Solid carbide cutting tools. 4. Indexable threading blades, cutting blades, and grooving blades.
Chemistry Qi phase Shen product	1000℃, Deposition temperature High, base The hardness, Reduced intensity , need to be developed Specialized base body for coating.	5～20μm or thicker, Suitable for opening Hair in multiple layers Membrane coating, High wear resistance.	The coating is under tensile stress and is prone to cracks; the cutting edge must be passivated; the surface is rough.	TiN TiC TiCN A1₂o₃ ZrO₂ Diamond etc.	high	The exhaust gas is harmful to the environment There is pollution.	1. Carbide can be converted into blades: turning blades, milling blades, etc. 2. Diamond coating.

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