High-Performance Boride Coatings for Extremely Durable Surfaces

Fraunhofer IST is expanding its infrastructure for high-performance boride surfaces. New facilities will enable the end-to-end development and testing of extremely durable surfaces for industrial applications.

When red-hot steel is forged or precision components with near-final contours are manufactured from high-temperature materials, tools are subjected to extreme stresses. High temperatures, wear, and aggressive media significantly determine their service life. Modern surface technologies therefore play a central role in efficient, cost-effective, and resource-conserving production processes. This is precisely where the Fraunhofer Institute for Surface Engineering and Thin Films IST comes in. With its expanded infrastructure, the institute can now map the entire process chain for the development of high-performance boride surfaces at its own facility.

For industrial project partners and clients, this means that all relevant process steps can be developed and tested in an integrated, reproducible, and application-oriented manner—from thermochemical diffusion treatments and modern coating technologies to high-temperature tests under realistic conditions.

The centerpiece is a completely refurbished PACVD system, which will be brought back online by mid-2026 with modernized process technology. In addition to being equipped with a modern process control system, the visualization and data acquisition systems have also been updated. The integrated and now expanded precursor system enables the development of new multicomponent coatings, such as nanocomposite layers based on titanium, silicon, boron, carbon, and nitrogen (Ti-Si-B-C-N). These coatings are characterized by high hardness, thermal stability, and oxidation resistance up to approximately 900 °C. The comparatively low coating temperatures of approximately 520 to 540 °C also enable the uniform coating of complex-shaped components—a clear advantage for demanding industrial geometries.

To further improve mechanical stability, coating processes can be combined with upstream treatment steps, e.g., in so-called duplex processes. In this process, a diffusion zone created beforehand in the edge region ensures a stable interface between the substrate and the coating.

In addition, a completely newly developed gas boriding system is available at the site. It enables the development and optimization of boron diffusion processes from the gas phase using boron trichloride (BCl₃) at temperatures up to 1050 °C. Unlike solid- or paste-based methods, gas-phase boriding offers decisive advantages: Boron activity and layer growth can be precisely controlled via the gas composition through the defined addition of hydrogen and nitrogen. This enables highly precise process control and increases reproducibility. At the same time, the process does not require plasma excitation, which simplifies the equipment design and reduces investment costs. The resulting diffusion layers are also characterized by good adhesion to the base material and outstanding tribological properties at high temperatures, which can reduce wear in many technical applications, thereby extending maintenance intervals or reducing the frequency of tool changes.

Following the boriding process, for steel materials, the mechanical properties of the base material are optimally adjusted through hardening and tempering, and further increases in hardness are achieved through phase transformations. For nickel-based materials, heat treatment steps for precipitation hardening can also be integrated into the treatment process; post-hardening is not required. Other material classes, such as CoCrMo or Mo alloys, can also be gas-boronized without any problems.

For a high-gloss polish or to precisely adjust the surface topography, the process chain can also be supplemented with dry electropolishing. The process is suitable both for polishing complex geometries in preparation for subsequent surface treatment and for finishing applied coatings. It enables the reproducible achievement of very high surface quality, reaching values as low as Rz ≤ 0.5 µm depending on the material and initial condition. A dry electrolyte granulate with only a low acid content is used; as a result, the process stands out from conventional wet-chemical methods due to its ease of automation, ability to meet high surface quality requirements, low material removal, and more environmentally friendly process operation.

An additional component of the expanded process chain is a new high-temperature vacuum furnace. It enables testing at temperatures up to 1600 °C and pressures below 10⁻⁵ mbar, as well as in defined atmospheres, such as hydrogen or inert gas mixtures. In addition, a high-temperature tribometer is available, which can be used to specifically investigate the tribological behavior of materials, coatings, and diffusion layers to determine coefficients of friction and wear patterns at temperatures up to 1000 °C. This enables customers and project partners to evaluate the performance of materials, coatings, and diffusion layers under realistic operating conditions even before components enter production.

The improved surface properties can contribute to efficiency gains in numerous industrial applications. For example, forging tools can be used significantly longer in hot solid forming, or material adhesion and scrap rates can be reduced during the extrusion of copper. Other applications include the manufacture of high-quality aluminum components, the bending of stainless steel, and the production of precision fittings and valves.

In addition, the Fraunhofer IST is opening up new areas of research and development with its new infrastructure. New gaseous starting materials enable the development of additional nanocomposite layers in carbon-free quaternary systems such as Ti-Si-B-N. In addition, the institute is expanding its expertise in electrochemical characterization to enable the early evaluation and targeted optimization of the corrosion behavior of surfaces. With its expanded infrastructure, Fraunhofer IST offers an integrated development platform—from the initial idea through process development to validation under realistic conditions. This shortens development times and accelerates the transfer of highly durable surfaces to industrial applications. (OM-8/26)