Development of a novel green coating process with laser.

Corrosion causes costs of about 3-4% of each country's gross domestic product, and due to the climate change, the corrosion rates on infrastructure are likely to increase furtherly in the future1,2. For corrosion protection, hard chrome plating (HCP) is commercially used since the early 20th3. Yet the biggest drawback concerns environmental protection, since toxic and carcinogenic hexavalent chromium Cr6+ is used. As an alternative, thermal spray (TS) is increasingly used since the last 20 years. Nevertheless, the coatings are technologically constrained in regard to high porosity, low material efficiency and poor bonding to the base material. Therefore, the demand for an environmental friendly and economical process that produces high-quality coatings is increasingly coming into the research focus. With laser, dense, metallurgically bonded and therefore well-adhering coatings with high material efficiency of > 90% can be produced from a large number of metallic alloys without the need to use environmentally harmful chemicals or noise emissions. However, the typical area coating rate of < 0.4 m2/h is significantly lower than that of TS of about 10 m2/h4,5, and is too small for coating large-scale components. In this regard, a novel coating process with laser was developed in this work. By decoupling the melding of powder from the coating speed, the coating speed of < 2 m/min in conventional laser coating can be increased to > 500 m/min. Defect-free layers that metallurgically bond to the base material with a thickness of 50-250 µm and a material efficiency of > 90% can be achieved. According to the results, an area coating rate up to 20 m2/h is achievable. The pioneer work of applications in offshore and automobile sectors show, this process is already providing beneficial for the industry.