Aluminum Die-CastingCVD Diamond as a Protective Layer in Aluminum Casting from dsfsdf's blog

Crystalline diamond layers applied by chemical vapor deposition (CVD) prevent direct contact between molten aluminum and the steel tool. The Chair of Materials Science and Technology of Metals at the Friedrich-Alexander University Erlangen-Nuremberg has achieved a first-time adhesive coating of various steel alloys with crystalline diamond as part of a project called "Newaluminum die casting parts in Bavaria."

Metal Die Casting Facility

When an aluminum melt comes into direct contact with a steel mold, due to the high reactivity of aluminum with iron and other metals, alloying of aluminum to the tool surface occurs. This has a negative impact on the dimensional accuracy of the castings, as well as the demoldability and service life of the mold. Extensive countermeasures, such as spray treatments to increase demoldability or geometry restrictions, are currently required, both technically and economically. Crystalline diamond layers applied by chemical vapour deposition (CVD) prevent direct contact between the molten aluminum and the steel tool. At the normal casting temperatures, the crystalline diamond does not react with the aluminum.

The Die Casting Process Step By Step

Coatings of Crystalline Diamonds
Crystalline diamond coatings are produced by hot wire activated chemical vapour deposition (HF-CVD) under vacuum from an activated hydrogen-methane atmosphere. Because of the high affinity of iron and carbon, it is not possible to apply a diamond coating directly to steel substrates. At the current deposition conditions (hydrocarbon-containing atmosphere and temperatures ranging from 750 °C to 950 °C), metastable iron carbide would first form on the steel surface, after which it would decompose into graphite and iron. In order to avoid this, a barrier layer must be applied before the diamond coating is applied.

Boron-doped titanium nitride (TiNB) as a barrier layer performs admirably, as it significantly reduces both carbon diffusion into the steel substrate and iron diffusion out of the workpiece. Due to its rough and plate-like morphology, the interlayer system also provides excellent mechanical anchoring for the diamond layer. Boron doping enhances chemical bonding by providing carbon with free bonding sites. Hot-wall CVD (HW-CVD) is used to create the high-temperature TiNB coating, which can reach temperatures of over 1000 degrees Celsius. As an alternative, chromium carbide or tantalum based intermediate layers can be used as barrier layers for a CVD diamond coating.