In order to use high-temperature resisting thermoplastic polymers like polyetheretherketone (PEEK) as anticorrosion coating materials for bearing steel components in alternative power generation, a laser melting technique is developed. Hereby, the challenge of using PEEK with a high melting temperature of 380 °C on temperature sensitive bearing steel with a tempering temperature of 180 °C is solved.
The further arising challenge to achieve a sufficient adhesion between the steel substrate, which is 100Cr6 / 1.3505, a high carbon, chromium-containing low-alloy steel with a martensitic microstructure, and the polymeric PEEK-layer is solved by a meandering laser scanning pretreatment of the steel surface.
Such laser pretreatments may lead to various changes of the substrate steel surface in terms of re-hardening or softening effects, oxidation processes, topographical and microstructural transformations.
Varying the laser power and the scanning velocity, different deposited energies and power densities were induced. Here, these different parameter sets of the laser pretreatment were tested and valuated regarding their influence on promotion of the adhesion of the PEEK coating. The most promising candidate led to the formation of thin oxide layers, accompanied by topographical changes, and to the appearance of very hard white etching zones (WEZ), attributed to near-surface re-austenitization and rapid quenching.
The appeared changes of the substrate steel surfaces induced by different laser power and scanning velocities are characterized by automated micro-hardness testing, light microscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy and are correlated with the introduced deposited laser energy and the topographical changes.