Investigation of compaction by ring rolling on thermal sprayed coatings

Abstract

Often mechanical parts have specific requirements in regard to the underlying alloy. Especially for axial symmetric parts like rings an often requested characteristic is a different requirement on the inner surface than on the outer. Therefore, different production processes exist. One strategy is to roll a basic ring e.g., via radial-axial ring rolling (RARR), and create a functional layer afterwards via thermal spraying. The temperature of the ring and the spraying particles influence the bonding behavior and compaction of the thermal sprayed layer benefits its mechanical properties. The hypothesis presented in this paper is a better performing thermal sprayed layer regarding the adhesion of the layer, reduced porosity and improved residual compressive stress through the combination of the thermal spraying process and the radial-axial ring rolling. After an introduction to the industrial processes of radial-axial ring rolling and thermal spraying, the experimental setup and the results are presented. In the first step, the approach of combining these processes includes an experimental design, in which the rolling of the basic ring, consisting of a 1.0570-steel, gets interrupted right before the target diameter is reached. The ring is then transported to the thermal spraying process where the ring gets covered with layers of 316L-Si, sprayed with a pressure of 8 bar, arc voltage of 34.0 V and a wire feedrate of 2.1 m/min. The coated rings were rolled to two different target diameters with a planned degree of deformation of 0.025 and 0.098 only in the radial direction. This deformation leads to an elongation of the outer circumference of 2.56 % and 10.26 %. Due to the rolling process, the applied coatings revealed a compacting effect and, thus, a significant reduction in the total porosity. The main goal of this study is to investigate the material pairings and parameters regarding thermal spraying and RARR to produce an intact coating with adequate adhesion to the substrate. The long term vision is to adapt thermally sprayed coating into the radial-axial ring rolling process.