Skip to main content

High-speed and sustainable metal deposition process helps industry to protect machinery against corrosion and wear

Published on 10.10.2022
Tampere University
The image shows a hard coating made from recycled hard metal using the EHLA method in the NOPSA project. Photo: Tampere University
High-speed laser cladding offers a fast and environmentally sustainable way to protect alloys against corrosion and repair damaged machine parts. This is according to a study at Tampere University, which is also investigating the suitability of the coating method for 3D printing metals and protecting them against microbes. The fast-coating process will bring benefits to manufacturing and maintaining equipment and engines in industries such as mining and wood processing.

Extreme High-Speed Laser Cladding (EHLA) is a high material efficiency coating method combining the advantages of laser cladding and thermal spraying. EHLA can be used to produce thin, fully dense, fusion-bonded, high-quality metal and metal matrix composite coatings on top of a variety of alloys with high productivity. Coatings can be produced at a rate of approximately one square metre per hour.

“The method combines the high productivity of thermal spraying, high surface quality and low heat input with the excellent adhesion and corrosion resistance of the laser cladding,” says Senior Research Fellow Jari Tuominen, who leads the NOPSA - High-speed metal deposition for the benefits of industry at Tampere University.

The method was originally developed by the Fraunhofer Institute in Germany and is based on traditional laser powder cladding. Advantages of laser powder cladding are a wide range of additives, possibility to mix powders and add hard particles, solid lubricants and nucleating agents to achieve desired properties.

The main difference between EHLA and conventional laser powder cladding is higher power density (W/mm2) achieved by using a smaller focal spot (Ø1–2 mm). With high power density, a high traverse speed (~20–100 m/min) allows producing thin (0.1–0.5 mm) single layer depositions with low dilution. Small particle size (10–50 µm) of the powder used as primary material enables precise targeting of the powder jet even at a smaller focal point.

“Worldwide, the method is a substitute for environmentally hazardous and carcinogenic hard-chromium plating. It is a more environmentally sustainable choice because it is material efficient and does not cause direct emissions to the environment,” Tuominen says.

High-speed laser cladding offers several times the hardness of wear-resistant steels

In the NOPSA project, researchers are exploring the potential of the EHLA method in different types of corrosion protection and hard coatings’ production, as well as in repairing or remanufacturing damaged machine parts. The project, which started in January 2022, has so far produced, for example, nickel-based corrosion protection coatings on top of steels (S355, 42CrMo4) and cast irons.

The method’s suitability for 3D printing of metals by direct deposition will also be investigated, in addition to the study and production of coatings.

"The knowledge gained will be transferred to the manufacturing (mining & drilling, power plants, power transmission & gears) and maintenance (engines, pulp & paper),” says Tuominen.

The EHLA equipment at Tampere University consists of a CNC-controlled lathe, a continuous wave fibre laser (3kW) operating at a wavelength of about one micrometre, a powder feeder with two powder feed hoppers and a coaxial powder feeding head. For the cladding of flat parts, a kinematic parallel robot is used to move the part to be deposited. With the two powder feed hoppers and on-the-fly adjustment of powder proportions it is possible, for example, to produce different multi-material and gradient structures.

Image 1. The EHLA equipment at Tampere University can be used to deposit rotationally symmetric pieces. The University has another machine for coating flat pieces.

The image shows cross-sections of machined Inconel 625 coatings on top of ductile and grey cast iron. The coatings have a thickness of about 170–180 µm and an iron content of about 2–3 percentage of weight. The depth of the heat affected zone (HAZ) is a few tens of micrometres. The coatings’ corrosion resistance has been verified in a 750-hour salt spray test.

Image 2. EHLA coatings prepared in the NOPSA project: a) Inconel 625 on top of ductile cast iron, b) Inconel 625 on top of grey cast iron, and c) Inconel 625 on top ductile cast iron after 750 h of salt spray exposure.

In hard coating production, chromium carbide and tungsten carbide nickel matrix coatings have been prepared on top of S355 and 42CrMo4 steels (Image 3).

Image 3. Hard coatings produced in the NOPSA project using the EHLA method a) WC-NiBSi and b) Cr3C2/Cr7C3-NiCrMoNb.

The coatings have a microhardness of more than 1000 Vickers, which is 2–3 times higher than that of wear resistant steels. By adjusting the carbide content, coatings’ wear resistance has been matched to hard chromium’s wear resistance (~950 HV0.3) in a rubber wheel abrasion test.

Image 4. Abrasive wear resistance of EHLA hard coatings (#1–4) compared to hard chromium.

The NOPSA project is funded by the European Regional Development Fund REACT-EU as part of the European Union’s response to the COVID-19 pandemic.

Further information

Jari Tuominen
+358 40 849 0196
jari.tuominen [at]