Influence of Cr/Al ratio on Cr1-xAlxN coatings produced by dynamic glancing angle dcMS
Conjugated systems combining metallic substrates and ceramic hard coatings, such as transition metal nitrides are one of the main solutions developed by surface science and engineering in the last decades in order to address applications that require abrasion resistance, low coefficient of friction and high thermal and oxidation resistance. CrN is one of the most important transition metal nitrides for these applications since it has excellent thermal stability and corrosion resistance. The addition of Al in solid solution improves its hardness and oxidation resistance even further, allowing it to be used as coating for engine parts and cutting tools. Physical Vapor Deposition (PVD) is a film deposition technique based on the formation of coatings by vaporizing of a precursor target, transport of the forming elements, such as atoms or ions, and its condensation on the surface of the substrate. Dynamic angle glancing deposition (DGLAD) is a recent development in sputtering, in which the substrate is let to oscillate continuously over a fixed angular range in a determined frequency. This motion changes the angle of arriving of the sputtered species on the substrate’s surface and may influence in the growth texture, chemical composition, microstructure and performance of the coating. This study aimed to understand the effects of the Cr/Al ratio on the growth and on mechanical properties of coatings of Cr1-xAlxN deposited on 304 stainless steel substrates prepared by dynamic glancing angle direct current magnetron by fixing a high N2 flow rate in the reaction chamber and changing the precursor target Cr/Al content (100 % at Cr; 50 % at Cr/50 % at Al; 30 % at Cr/70 % at Al). Chemical analysis by means of EDS and GDOES depth profiling revealed a condition of increasing N content when Al was added. Although still sub stoichiometric, the samples prepared using targets of nominal 30 % at Cr/70 % at Al have shown twice the amount of Al than the ones produced with targets of 50 % at Cr/50 % at Al. An expressive change in texture was observed in coatings with Al when compared to the CrN pure sample, with strong (200) growth preference. Mechanical performance dependency with Al content was once more observed, with the Al richer sample presenting hardness of up to 27 GPa.