Hardface coatings can be produced using cobalt-free materials

Kaveh's research shows how the industry can replace cobalt-based coatings and that the choice of process can make a big difference. Photo: Högskolan Väst.

Currently, cobalt-based materials are often used in various industries such as mining equipment, paper and wood industries, and cutting and milling tools, where a hard surface is required. Due to cobalt being a limited resource extracted under questionable conditions, the industry is seeking alternatives. Moreover, 70% of the world's cobalt reserves are in the Congo, where reports of child labor and health issues during extraction have surfaced.

Recently, Kaveh Torkashvand presented his doctoral thesis with new findings in this area. Kaveh has investigated how well three alternative cobalt-lean/free composites perform compared to a traditional tungsten-cobalt alloy.

Alternative materials with superior performance

“Cobalt has long been considered the best option in terms of technical performance. However, my research shows that there are other materials that provide comparable, and in some cases, superior performance in terms of wear resistance. All three composites* I have tested show promising results.”, says Kaveh.

Kaveh has also examined how two forms of thermal spraying, HVOF and HVAF**, can be used to deposit this class of coating materials. Currently, HVOF technology is almost exclusively used in the industry, while HVAF is relatively new to the industry.

“My experiments show that there are several advantages to using HVAF for processing this type of material. The technology allows the use of fine powder, resulting in denser coatings, paving the way for producing thinner coatings and, as a result, reducing material usage.”

Faster and more energy efficient process

Additional benefits include the fact that HVAF can significantly expedite the coating process while using less energy and subsequently becoming a more cost-effective technique compared to HVOF.”

Kaveh's study demonstrates how various factors can influence the properties of the resulting coating. The chemical composition and powder size are two important considerations. Moreover, there are several ways to adjust the spraying process to precisely create the properties that the surface coating needs to perform well under various wear conditions.

“Combating the wear phenomenon is a challenge that various industrial sectors are facing. Tool manufacturers, as well as the wood, paper, mining, and automotive industries, are just a few examples where coatings deposited by HVAF technology can be of interest.”

Brake disks can have a longer service life

“An example is brake disks for cars, which are currently mostly made of cast iron. Their lifespan is short, and a massive amount of debris is released into the environment. By coating brake disks with a Co-free hardface coating, using HVAF technology, dust emissions would be significantly reduced, and the lifespan can be dramatically increased.”

Kaveh emphasizes that cobalt-free composites are already available on the market, and industries can relatively easily replace the harmful tungsten-cobalt composites.

“Implementing HVAF technology in industries may take time, but they can still produce cobalt-free coatings with their existing deposition technology.”

Read more in Kaveh Torkashvand's doctoral thesis: "Towards more sustainable approaches for protecting surfaces against wear"

CONTACT: Kaveh Torkashvand, PhD in Production Engineering. Email: kaveh.torkashvand@hv.se. Phone: 076-552 48 03

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FACTS

*Kaveh has compared the three cobalt-free composites NiMoCrFeCo, FeNiCrMoCu, and FeCrAl with the traditionally used Tungsten-Cobalt composite WC-CoCr.

**HVOF (high velocity oxy-fuel) and HVAF (high velocity air-fuel) are two different techniques in thermal spraying. Powder is melted as it passes through a high-speed flame using compressed air, where the powder melts and is then propelled towards the component to be coated. In HVOF, oxygen from oxygen tanks is used, while regular air is used in HVAF. Different fuels are used in the two techniques, which means they provide different temperatures; HVOF about 1500 - 3000°C and HVAF below 1500°C."