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HIGH PERFORMANCE SELF-LUBRICATED MULTIFUNCTIONAL COATING FOR DEMANDING INDUSTRIAL APPLICATIONS

Final Report Summary - SEFUCO (High performance self-lubricated multifunctional coating for demanding industrial applications)

The reliability of large industrial fields such as energy plants, process industry and transport are dependent on the functioning of critical components. In particular, safety critical components in heavy engineering, such as bearings, seals, shafts, barrels, rolls, etc. face material sticking problems. Conventional lubrication oils often cannot be used due to process environment, temperature or impurities. Self-lubricating, wear resistant coatings are available, but only for specific applications. A broader solution is needed; this is why the SEFUCO project was set up. The SEFUCO consortium is made up of two research performers and six SMEs from Western and Northern Europe with the aim to improve coating performance for demanding industrial applications. The goal of the project is to enhance the safety and reliable use of critical components. It will also prevent people from being exposed to hazardous waste due to chemical leaks caused by sticking and tribology problems. Tribology is the science and technology of friction, lubrication, and wear. In addition to powder production and thermal spraying, tribology represents one of the three technology areas of the SEFUCO project.

Novel powder production techniques open possibilities for innovative powder compositions and tailored coating solutions. Meanwhile, thermal spray methods have been well established to produce wear resistant coatings for components. For instance, a space organisation has been investigating the use of thermally sprayed (TS) coatings with the addition of solid lubricants (SL). Universities, institutes, automobile and electronic manufacturers have all done specific research on the same topic. However, tailored coatings including solid lubricants are not yet commercially available. Thermal spray techniques are coating processes which involve spraying melted (or heated) materials onto a surface. The energy to heat the feedstock is supplied by either electrical (plasma or arc) or chemical means (combustion flame). Coating quality is usually assessed by measuring its porosity, oxide content, bond strength and surface roughness. Generally, the coating quality increases proportionally with particle velocities. The heated materials are typically fed through an insulated tube to the sprayer, where they may be atomised before being expelled through a nozzle.

The control starts from the coating material processing. At first the consortium discussed about their needs for their applications. Material compositions were tailored according to the application. After that started the powder manufacturing and the optimisation of powder processing parameters to get acceptable quality for the spray powders. When the powder quality was in sufficient level the products were sent to thermal spray tests. The SEFUCO consortium started optimising spray coating processes, especially high velocity oxyfuel (HVOF), for spraying powders containing solid lubricant materials, adapting them to different application environments. Furthermore, the consortium was undertaking tribological tests to determine tribological, wear and corrosion properties of the coatings containing solid lubricants. Controlling the whole manufacturing route from powder to coating allowed for the tailoring of the coating composition according to each application.

On the powder processing site one of the main achievements was the successful creation of powder for thermal spraying where three alloying elements were integrated into each powder particle. Innovative powder solutions consist of a hard carbide phase, metal matrix phase and solid lubricant additions, some of them alloyed in a nanostructured scale. Powder had good flowing properties which is beneficial for the coating process. Powder manufacturing parameters were adjusted so that it gave directly the suitable particle size for thermal spraying process. Thermal spray powders should have certain particle size otherwise coating quality will not come acceptable. Thermal spraying of these experimental powders developed in this project gave good coating quality.

Solid lubricant additions are very sensitive for thermal loads and could easily decompose or even evaporate during the coating process. It was possible to manufacture coatings were added solid lubricant did not decompose during the spraying process. Compared to same type of coatings without solid lubricant additions the successful coatings performed well under abrasive wear tests. And also compared to commercial available coatings the results from coating properties were encouraging. Still in some cases solid lubricant additions were decomposed. Therefore further research work is needed to fully understand the phenomena occurring during powder processing and thermal spraying.

After the quality of powders and coatings were approved to be sufficient, coatings were sent to tribological testing. Testing of coating was extensive: wear resistance of coatings was tested with abrasive wear tests, coefficient of friction (COF) was measured at three different temperatures (room temperature, 300 degrees Celsius and 400 degrees Celsius) and corrosion resistance was measured with two different methods. Solid lubricant additions did reduce the wear resistance of the coatings slightly. That was expected on the basis of literature survey. The friction properties of coatings were not much better compared to coatings without solid lubricants. This is mainly due to the surface roughness of the coatings which has very strong effect on friction properties.

Grinding of coatings containing solid lubricant may cause in some cases pullouts onto the coatings surface and therefore leave surface too rough. In friction tests surfaces are sliding against each other and in such tests the surface quality has very important role. Although friction tests performed during this two year project did not give clear evidence of reduction for COF, lot of knowledge was created and disseminated within the consortium. Next step would be finding out certain applications and test methods where this kind of coatings would give better results compared to traditional ones.

Modified coating materials (powders), which can be used in demanding applications against wear and friction problems at higher temperatures than room temperatures. At least 23 new exploitable compositions are created from the results created during the project. Knowledge for manufacturing these powder compositions was created during the project. Benefits of these tailored compositions are suitability to certain application and reliability of components functionality.

New, selflubricating coatings, which can be applied to substrate with acceptable properties. Parameters for spraying these coatings have been developed and evaluated during the project. These novel coatings can be applied to components of customers of thermal spray companies. This result has an impact on SCANA AS, KKP and TLB.