## 1 Introduction
Due to the aforementioned surface imperfections, the measured roughness is generally higher than the calculated value. Investigations regarding the influence of the feed \(f\) in the turning of iron-based atmospheric plasma sprayed coatings in the range of 0.025 mm to 0.15 mm showed the expected increase of \(Ra\) and \(Rz\)[11]. However, the proportion of pulled-out coating material decreased for feeds above 0.1 mm. Deformation of the surface is observed in connection with the machining of ductile materials. Such deformation often leads to smearing effects or to the storage of removed material within the porosity; finishing parameter adjustment can only partially mitigate these issues. One solution could be the surface hardening of coatings, which would reduce heterogeneous material states, arising, e.g., from oxidation during the thermal spray deposition process, and material ductility. Surface hardening has successfully been demonstrated for thermal spray steel coatings. Depending on the treatment parameters, both interstitial solid solution hardening and precipitation formation can be achieved during nitriding, nitrocarubizing, and carburizing of stainless steel coatings [12; 13; 14; 15; 16; 17; 18]. In addition, boronizing can also lead to a precipitation formation of particularly high hardness and temperature resistance [19; 20]. Mostly, AISI 316L coatings deposited by high-velocity oxygen fuel spraying (HVOF), atmospheric plasma spraying (APS), or cold gas spraying (CGS) were nitrided or nitrocar-burized by a thermochemical plasma process. The surface hardening only reaches depths of less than 50 \(\upmu\)m [13; 14; 17]. [PERSON] et al. also considered 17-4 PH and AISI 410 stainless steel coatings and detected precipitations of CrN, Fe\({}_{3}\)N, and Fe\({}_{4}\)N in the plasma-nitrided coatings [14]. A gas nitriding of AISI 316L HVOF sprayed coatings was investigated by [PERSON] et al. [16]. The precipitation layer, consisting of Fe\({}_{4}\)N and CrN, reached a depth of more than 100 \(\upmu\)m, which was explained by the penetration of the gaseous enrichment media through the coating porosity. Compared to the as-sprayed condition, a significant hardness increase, which averages 860 HV0.01, and a superior wear resistance were shown. [PERSON] et al. even reported hardness values up to 1300 HV0.01 for plasma-nitrided steel coatings [14]. A novel approach is using the surface properties of hardened coatings, particularly the increased hardness of the surface layer, for mechanical finishing. The precipitation formation should prevent smearing effects as well as provoke pulled-out coating material. In this way, the valley void volume should be increased and used for the storage of lubricants. [PERSON] et al. showed the positive effects of surface hardening via plasma-nitration of stainless steel with the intention of preparing extremely smooth surfaces with subsequent machining by single-point diamond turning [21]. The research work presented investigates the effect of thermochemical surface hardening of the wire arc sprayed 17 Cr steel coatings, comparable with EN 1.4122, on the resultant geometrical surface quality after finish turning. The aim of the process combination is an increase in proportion and volume of pulled-out coating material for use as possible oil reservoirs.