High-adhesion Cr inner coatings for slender steel tubes via PSVR

The interior walls of slender tubes often require protective coatings with high adhesion to withstand extreme conditions. However, achieving strong adhesion in confined geometries is challenging due to restricted access and uneven media distribution, limiting conventional methods. To address this, we developed a novel combination strategy integrating a dual-purpose cleaning-deposition system, a bottom deposition layer, and precise working pressure control to fabricate Cr coatings on 40 mm steel tubes using pulse sputtering with voltage reversal (PSVR). The cleaning-deposition system improved substrate conditions, while DFT simulations revealed that the bottom deposition layer created Fe/Cr hybrid atomic layers, significantly enhancing adhesion. As the working pressure increased from 0.75 Pa to 2.9 Pa, coating hardness decreased from 20.41 GPa to 12.58 GPa, improving plastic deformation capacity. Adhesion critical load for the first cohesive failure (LC2) peaked at 75 N at 2.2 Pa, while the critical load corresponding to complete delamination (LC3) exceeded 100 N at 0.75 Pa and 1.5 Pa. These findings establish a framework for customizing high-adhesion Cr coatings in confined geometries, advancing the durability and performance of coatings in tubular applications.