CVD Coatings for Forming and Molding Tools
Explore the benefits of CVD coatings for increasing the durability and wear resistance of forming tools
Ionbond™ CVD coatings for the most demanding forming applications under harsh conditions
Chemical vapor deposition (CVD) is the oldest deposition technology for wear-resistant coatings for industrial forming applications. Modern CVD machines ensure robust and reliable operations and high yield rates. This has resulted in the popularity of CVD for certain applications, such as metal forming tools and extrusion dies. These tools are subject to harsh environmental conditions in terms of abrasive and adhesive wear as well as oxidation and corrosion, and CVD coatings provide them with extreme toughness and wear resistance.
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Forming & Molding Case Studies
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Highly desirable properties and flexibility
The advantages of CVD processes include:
- Advantageous residual stress profile which allows the deposition of thick CVD coatings (+20 µm)
- CVD coatings with extreme toughness and unrivaled impact fatigue resistance
- High adhesion of CVD coating on tools due to interdiffusion between coating and base material
- Tools to be coated do not require rotation within the retort
- The possibility to coat complex geometries, including certain inner diameters
- Excellent coating uniformity, independent of tool geometry
CVD technology enables the production of titanium (Ti) or chome (Cr) based coatings in form of nitrides (N), carbides (C) and carbonitrides (CN). In addition, high-quality aluminum oxide (Al2O3) layers can be created, both in the α and κ phase. These CVD coatings are almost always deposited as multilayers, such as TiC/TiN, TiN/TiCN/TiN, TiCN/Al2O3 or TiCN/Al2O3/TiN, where the layer combination is engineered to meet the demands of a specific forming application. Coating thickness typically ranges from 5 µm to 12 µm, but in some cases coatings can be as thick as 20 µm or more.
The various CVD Ti coating structures and their benefits
TiC
When deposited by CVD, a TiC layer provides a low coefficient of friction, high toughness and high resistance against abrasive wear. This is beneficial for forming applications, such as cold forming ferritic and austenitic stainless steel, high strength low-allow steels (HSLA), advanced high strength steels (AHSS) and steel workpieces with a thickness > 2 mm.
TiN/TiC/TiN multilayer or TiCN solid solution
The combination of individually deposited TiN or TiC coatings in a TiN/TiC/TiN multilayer structure or in a TiCN solid solution further increases the performance in forming applications. TiCN is the preferred coating solution for light to medium metal forming applications involving stainless steels, HSLA and steel workpieces with a thickness > 3 mm. The multilayer CVD coating TiN/TiC/TiN reveals extreme toughness under impact loading and superior adhesion between the coating and the tool, which makes it an excellent choice for cold forging steels and warm or hot extrusion of ceramics or non-ferrous alloys.
Al2O3
The CVD deposition of Al2O3 can provide further improvement in terms of oxidation resistance and hot hardness for aggressive conditions, such as those in high-temperature forming applications. Al2O3 can be deposited in α phase (thermodynamically stable) or κ phase (metastable), and is often deposited on TiC or TiCN in a multilayer structure. An Al2O3 layer exhibits excellent thermal stability, chemical inertness, and a high resistance against corrosion, abrasive wear and adhesive wear. That makes it the leading coating solution for hot extrusion of both ferrous and non-ferrous alloys.
Multilayer TiCN/Al2O3/TiN coating
Finally, a multilayer TiCN/Al2O3/TiN coating combines the main advantages of the individual layers. The TiCN bond coat ensures a high wear resistance and provides excellent adhesion to the tool. The Al2O3 layer exhibits excellent thermal stability, high hot hardness and extreme wear resistance. And the TiN top layer can be used for wear detection during service life of the coating forming tool.
Suitable for many tool steels with post-coating heat treatment
Thermal CVD is a heat-activated process where the tools to be coated are heated to an appropriate temperature and exposed to one or more solid or liquid precursors. For instance, the halides TiCl4, AlCl3, or CrCl3. In combination with certain reactive gases such as H2, N2 or CH4, the halide precursors react on the tool surface to produce the desired coating. The schematic you see shows a CVD process. By combining the precursors TiCl4 and CH4 at 1,000 °C, a TiC coating is created.
TiCl4 + CH4 ⇒ TiC + 4 HCl
The typical process temperature for CVD coatings is between 900 °C and 1,050 °C for high temperature (HT) CVD and between 720 °C and 900 °C for the moderate temperature (MT) CVD processes from IHI Bernex. These high process temperatures might make certain base materials unsuitable for CVD, or require a post-coating heat treatment of the tools. The necessity of a heat treatment should not, however, discourage the use of CVD processes on tool steels. The CVD coating is unaffected by the post-coating heat treatment. When the heat treatment is carried out under vacuum conditions, the CVD coating retains its mechanical properties and adhesion to the tool.
Selecting heat treatment parameters to match the base material
By carefully selecting the CVD coating and heat treatment parameters, the surface engineers from Ionbond help prevent excessive thermal distortion of the coated tools after heat treatment. This can be done for common cold and hot work tool steels and high-speed steels, see table. Austenitic stainless steel can even be processed by CVD without a need for post-coating heat treatment, since it does not undergo a phase transformation below the CVD process temperature. Another exception is heat-treated martensitic stainless steel. This can be also processed at a lower temperature, making it possible to use MT-CVD to retain the core hardness in the range of 35 to 40 HRC.
Table: Overview of base materials for forming and molding tool applications, common types of CVD coatings and required post-coating heat treatment.
Widely used Ionbond™ CVD coatings
Ionbond™ CVD 10
Ionbond™ CVD 13
Ionbond™ CVD 29
Ionbond™ CVD 62
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Discuss your challenges with Tobias Brögelmann
Tobias Brögelmann, Global Segment Manager Forming and Molding Tools, will be glad to support you.
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Dr. Ing. Tobias Brögelmann
Global Segment Manager Forming and Molding
