Search

Due to the health hazard, emanating from chromium trioxide based coating processes, the longtime approved hard chromium platings have to be replaced by alternative coating systems in future. Therefore, the development of PVD coatings, which protect mild steel substrates from both, corrosive and tribological stresses, is a key demand for the PVD coating industry. These coatings have to achieve comparable properties for wear protection and corrosion resistance like chromium platings and also must fulfill the current sustainability criteria in terms of environment protection and health. Recently, the authors developed a TiMgGdN coating system with improved corrosion properties for steel substrates. The superior corrosion properties of TiMgGdN was initially discovered for surface protection of magnesium alloys, which is the most corrosive construction metal (Hoche et al., 2014). In the present work, the TiMgGdN coating concept was applied to mild steel substrates. The coating composition and the deposition parameters were varied to optimize the coatings for steel substrates. The coatings were deposited by using both, DC and HiPIMS sputtering. The influences of the chemical composition, the deposition parameters, the substrate roughness and the sputter mode on the corrosion properties were examined. The coatings were characterized concerning their microstructural, mechanical and chemical properties. Salt spray tests as well as electrochemical measurements were carried out to examine the corrosion properties of the coated specimens. Furthermore, the electrochemical properties as well as the open circuit potentials of the coating materials themselves were determined.

PVD-TiMgGdN coatings have been successfully developed by the authors using an industrial DC-magnetron PVD unit. The coatings reveal excellent corrosion protection capabilities for mild steel substrates for at least 800 h in the neutral salt spray test (NSS). MgGd was added to the TiN matrix by using segmented (Seg.) multi-component targets, consisting of segments of pure Ti and of a Mg- 30 wt.-% Gd alloy. The Seg. targets caused an increased defect density due to droplets forming at the gaps between the segments which leads to an unsatisfactory wear performance. To overcome the low mechanical and wear properties by keeping the coatings excellent corrosion performances stable, a TiMgGd target with a specific Ti:Mg:Gd ratio was manufactured by powder metallurgy (PM) technology processed out of pure metal powders. In the present work, the properties of the corrosion and wear performance of DC-PVD-TiMgGdN coatings, which were synthesized onto corrosive mild steel substrates by using a Seg. target and a PM target of comparable Ti:Mg:Gd ratios together with identical deposition parameters, are compared with each other. The coatings were characterized regarding their microstructural, mechanical, physical and corrosion properties. Furthermore, ball on disk wear tests were conducted by reciprocal dry sling SRV III tests. It is shown that the excellent corrosion performance, could significantly be boosted by using the PM TiMgGd sputter target. Moreover, a remarkable increase in wear resistance of the TiMgGdN coatings can be examined by the use of a PM sputter target. It was found that the chemical properties of the TiMgGdN coatings as well as the nitrogen gas flow have a major influence on the mechanical coating properties and on the resulting microstructure, which directly correlates with the corrosion and wear properties.

Today, innovative coatings must ensure wear protection and corrosion resistance for engineering materials with high corrosion susceptibility, e.g. mild steels, as well as the current sustainability criteria in terms of environment protection and health. PVD technology fulfils most of these demands, but unfortunately, the corrosion protection performance is unsatisfactory due to the typically low coating thicknesses of only few micrometres. One solution to overcome the corrosion problem are TiMgREN (RE = Rare Earth) based coatings, which were developed by the authors. Even with 5 μm thick monolithic TiMgGdN coatings a corrosion resistance of at least 800 h could be achieved in the salt spray test without any macroscopic corrosion attack. In the present work, the influence of the coating composition, the substrate material and the surface roughness on the corrosion properties was examined. Besides, the application of Gd as alloying element, the influence and the effect of other rare earth metals (La, Ce) on the corrosion performance were investigated. As benchmark, the TiMgGdN coatings were compared with industrial standard PVD coatings, DLC and electroplated Cr regarding the corrosion and the wear performance. The coatings were characterized concerning their microstructural, mechanical and chemical properties. Salt spray tests as well as electrochemical measurements were carried out to examine the corrosion properties of the coated specimens. Furthermore, ball on disk wear tests were conducted by reciprocal dry sling tests by using a SRV 3 tribometer. It was shown that by variation of the deposition parameters, the coating properties could be improved concerning both, corrosion and wear performance. Furthermore, the effect of the used rare earth metal type and the rare earth metal content on the coating properties was investigated. The TiMgGdN coatings exhibit superior corrosion properties in comparison to the industrial standard coatings.

The conventional development of a coating system for cutting tools includes a variety of test series with elaborate experimental parameter studies. In particular, experimental investigations of the cutting behavior cause a significant consumption of cost, time and resources. In order to adapt the coating properties to the specific requirements of the cutting process, it is desirable to reduce the experimental effort of coating development by simulation of the machining process. Therefore, the main factors of the thermo-mechanical coating load in machining AISI 4140 were identified by means of 2D FEM chip formation simulations. In order to provide the required thermal and mechanical coating properties for the simulations, CrAlN-based coatings were deposited onto cutting inserts and extensively characterized. Within the simulations, the coating properties were varied between the physical and technological boundaries of CrAlN-based coatings. It was shown that the Young's modulus, the coating thickness and the friction coefficient significantly influence the thermomechanical load and the stress distribution within the coating. Finally, the cutting performance of the coated inserts was experimentally investigated and compared with the results of the simulations. Here, it was shown that delamination of the coating is particularly influenced by coating thickness. © 2017 The Authors.

Si–C–N based materials exhibit promising properties such as excellent oxidation resistance and thermal stability even at temperatures above 1300 °C, thus making them promising candidates for high temperature applications. The properties of SiCN based coatings strongly depend upon the synthesis method and the synthesis parameters. In the present study, SiCN coatings were deposited by RF, DC and HiPIMS sputtering. Beyond this, the target configuration was varied for DC and HiPIMS sputtering. The coatings were characterized regarding their chemical, structural, mechanical and thermal properties. Since the SiCN coatings are amorphous, FT-IR and Raman spectroscopy as well as XPS were used to gather structural information. The structural and the thermal properties show a significant dependency on the sputtering method and target configuration, while the mechanical and chemical properties are only slightly affected.

Since most conventional coatings are not stable at temperatures above 1000 °C, new coating concepts have to be introduced. Si–C–N based materials exhibit promising properties such as excellent oxidation resistance and thermal stability even at temperatures above 1300 °C. In the present study amorphous PVD–SiCN coatings were synthesized by conventional DC- and RF-magnetron sputtering as well as with a combined sputtering process using one target in the DC mode and one target in the HPPMS (High Power Pulse Magnetron Sputtering) mode. The coatings were characterized regarding their chemical, structural and mechanical properties. The coating properties strongly depend on the chemical composition and the structure of the amorphous network. Beyond that, the study includes thermal analysis of the coating materials, synthesized with the different sputtering techniques.