Thermal Spray

Thermal spraying (other common names are metallization, sputtering, spraying) is a group of technological processes whose common denominator is the application of coatings of additional materials previously heated, plasticised or melted and fired at high speed towards the surface to be coated. It often competes with cladding methods and is rightly compared to them. The basic coating materials used also have similar chemical and phase compositions.

Thermal sprayed coatings are adhesively bonded to the substrate (exceptions are remelted coatings, where there is a metallurgical bond). Depending on the method and coating material, the range of adhesion to the substrate tested by the pull-off method is from 7 MPa (zinc, arc method) to +80MPa (carbide coatings, supersonic spraying, no adhesion higher than 80 MPa – breaking the punch in the adhesive).

The hardness of thermally sprayed coatings is up to 1600 HV for carbide coatings sprayed by supersonic method, up to 1000 HV for metallic amorphous coatings after heat treatment, sprayed by arc method. The optimum thickness range for carbide coatings is 80-350 μm, while for metallic coatings it is up to 1 mm.

The thermal spraying process has no heat effect on the substrate material, does not change its structure and does not cause distortion. The coating weighs very little due to its thickness and can be easily and frequently regenerated. The substrate material is much less important than in welding processes (spraying is possible on non-weldable metals, grey cast iron and hard surfaces e.g. after hardening is problematic). The waviness characteristic of surfacing does not occur. Coatings can be machined (grinding and polishing recommended).

In relation to hardfacing, our erosion tests show that thermal sprayed coatings have a many times longer service life than hardfaced coatings of the same thickness. This is dictated by the faster (or lack of) crystallisation, which translates into a finer coating grain size, and the strong plastic deformation resulting from the high kinetic energy of the particles on impact with the substrate and the effect of “pressing down” through successive layers.

Recently, spraying methods for thermoplastics such as polyamide or polyethylene have been gaining popularity. These layers provide barrier corrosion protection for the material, protecting it from the most corrosive environmental conditions. When combined with zinc or ZnAl alloy metallization, they provide a Duplex system with a durability that exceeds market standards. Plastic coatings can be easily and quickly applied to workpieces of any size, including at the customer’s site and in open spaces. Any damage to the coating can be easily repaired by heating. 

With thermal spraying, it is not only the choice of the right method that plays an important role, but also the quality of the material and the skill of the operator. It is therefore worth paying attention to the experience of the company offering thermal spraying services and its references. This way, you can be sure that the process will be carried out professionally and that the end product will meet all requirements.