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A hybrid magnetron sputtering process (dcMS/HiPIMS) was developed to manufacture nanostructured CrN/Cr1-xAlxN multilayers, motivated by improving the low-emission efficiency when applied on gas-nitrided diesel piston rings of a next-generation of combustion engines. In order to improve the mechanical, tribological, and corrosion behavior of the multilayers, the hybrid dcMS/HiPIMS process was designed by selecting the optimal sputtering procedure applied to AISI 440 base steel. The effect of substrate bias and carousel rotational speed on the phase composition, crystallographic texture, residual stresses, surface roughness, coating periodicity and densification, instrumented hardness, elastic modulus, as well as wear and corrosion resistance was determined. The results have demonstrated that hybrid magnetron sputtering produces multilayers with a superlattice structure, which outperforms commercial PVD coatings of CrN for diesel piston rings manufactured by cathodic arc evaporation. Also, multilayer periodicities in the range of 5 to 10 nm yield the best tribological performance under bench tests for the piston ring/cylinder liner system.

Hard coatings are a suitable solution for increasing the lifetime of tools and components employed in different industrial applications. Coatings of transition metal nitrides have great use for tribological applications due to due to their unique mechanical properties. Although widely employed, current deposition methods such as cathodic arc evaporation produce coatings with many defects, which in turn reduce the resistance to wear, especially under severe conditions. High Power Impulse Magnetron Sputtering is a novel physical vapor deposition technique that produces homogeneous coatings. In this study, CrN and CrAlN monolayer coatings were deposited on AISI 304 stainless steel substrates using HiPIMS. X-Ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy were used to evaluate the microstructure, phase composition, morphology and chemical composition of the coating. Results showed that HiPIMS is a promising technique to deposit CrN and CrAlN homogeneous coatings with high hardness and good adhesion to the substrate.

The mechanical and wear behavior of CrN/CrAlN multilayers were improved by tailoring the experimental conditions of a hybrid magnetron sputtering process based on a high-power impulse (HiPIMS) and two direct current magnetron sputtering (dcMS) power supplies. To this end, the influence of the base layer and of the combination of Cr and CrAl targets, which were switched to the dcMS and HiPIMS power supplies in different configurations, were investigated with respect to the growth of ceramic CrN/CrAlN multilayers onto commercial gas-nitrided diesel piston rings. The microstructure, grain morphology, and mechanical properties were evaluated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and instrumented nanoindentation. Bench wear tests simulating the operation of a combustion engine were conducted against a gray cast iron cylinder liner under reciprocating conditions using 0W20 oil as a lubricating agent enriched with Al2O3 particles. The results revealed a significant increase in hardness, resistance to plastic strain, and wear resistance when two CrAl targets were switched to a HiPIMS and a dcMS power supply, and a Cr target was powered by another dcMS power supply. The compressive coating stresses were slightly reduced due to the soft Cr base layer that enabled stress relief within the multilayer. The proposed concept of hybrid magnetron sputtering outperformed the commercial PVD coatings of CrN for diesel piston rings manufactured by cathodic arc evaporation.

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CASTILHO, B.C.N.M. Development and characterization of CrN/CrAlN multilayer coatings deposited by hybrid magnetron sputtering process. 2018. 106p. Dissertation