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CVD

What is CVD?

Chemical Vapor Deposition (CVD) is a technique in which chemical compounds are formed on the surface of a substrate from gaseous precursors. This process typically takes place at high temperatures, ranging from 700–1050 °C, and is based on chemical reactions occurring on the substrate surface.

Properties of CVD Coatings

CVD coatings are characterized by high wear resistance and excellent adhesion to carbide. The first CVD coatings included a titanium carbide layer (TiC), but nowadays aluminum oxide (Al2O3) and titanium nitride (TiN) coatings are also used. Modern coatings, such as MT-Ti(C,N) (modern titanium carbonitride), offer improved protection and enhance the wear resistance of products.

Common CVD Coatings

  • MT-Ti(C,N): Provides hardness and enhances resistance to abrasive wear, reducing flank wear.
  • CVD-Al2O3: A chemically inert material that acts as a thermal barrier and improves resistance to crater wear and plastic deformation.
  • CVD-TiN: Improves wear resistance and makes wear tracking easier.
    Post-treatments increase edge toughness and reduce chipping tendency, making them very useful in interrupted cutting operations.

Steps in the CVD Coating Process

The CVD process consists of several steps:

  • Precursor Feed: In this phase, the substrate is exposed to gaseous precursors, which decompose or react on the substrate surface to form the desired film.
  • Surface Reactions: Under the influence of heat, reactions form the coating on the substrate surface.
  • Removal of Reaction Products: The reaction products and carrier gases formed during the process are flushed out with a gas stream.
  • To activate reactions in the gas phase, heat, photons, electrons, ions, or plasma can be used. The temperature for these reactions typically ranges from 800–1100 °C.

Applications for CVD Coatings

CVD-coated grades are primarily used in applications that require high wear resistance. These include:

  • General and internal turning of steel: Especially suitable for resisting crater wear.
  • General turning of stainless steels
  • Milling of ISO P, ISO M, and ISO K materials
  • Drilling: CVD grades are often used as cutting edges.

Chemical Precursors and Coating Materials

The precursors used in the CVD process can be various compounds such as fluorides, chlorides, bromides, iodides, organometallics, hydrocarbons, phosphorous trifluorides, and ammonium complexes. Materials that can be coated include:

  • Metals and metal alloys
  • Metal compounds such as boron, silicon, and carbon
  • Borides, silicides, carbides, oxides, and sulfides

Safety and Environmental Impacts of CVD Coating

Many of the gases used in the CVD process are toxic, which requires careful handling and proper disposal of waste gases. Therefore, process safety and environmental friendliness are key concerns.

Summary

CVD coating is a versatile and effective process based on chemical reactions at high temperatures. CVD coatings provide excellent wear resistance and adhesion, making them suitable for various industrial applications, especially in the machining and manufacturing industries. Their versatility and high performance make this technique an important tool in the production of various carbide tools and components.