Improvement of CrMoN/SiNx coatings on mechanical and high temperature Tribological properties through biomimetic laminated structure design

Abstract

CrMoN/SiNx multilayered coatings were fabricated by controlling the shutter-open time of two sputtering guns in a radio frequency magnetron sputtering system. Employing the structure of nacreous shells from nature, nano-crystalline and amorphous monolayers were periodically stacked. CrMoN/SiNx thin films with different bi-layer periods were deposited on Si-wafer and Inconel-718 substrates. The phases of the coatings were examined using a grazing incidence X-ray diffraction (XRD) technique. Information of chemical composition was obtained by field emission electron probe micro-analyzer (FE-EPMA). The confirmation of multilayer structure was observed by transmission electron microscope (TEM). The wear tracks were revealed by scanning electron microscope (SEM). Mechanical and high-temperature tribological properties were evaluated using a nano-indenter and a high-temperature tribometer, respectively.Grain refinement phenomenon was verified using XRD peak broadening at high angles, indicating inhibition in the column structure and the formation of an amorphous phase. CrMoN/SiNx exhibited higher high-temperature wear resistance for a specific bi-layer period, which was attributed to the multilayer strengthening mechanism. Multilayered structure provided tremendous benefit to COF improvement, which was reduced by 50% of the value of CrMoN. Simultaneously, the toughening effect of the biomimetic structure design improved the wear resistance ability of the coating. Especially, the slight amount of SiNx unpredictably enhanced the wearing properties of the system, which is in consistent with the role of chitin in nacre. Moreover, an optimal bi-layer period was identified, resulting in optimal mechanical properties that were consistent with the high-temperature tribological properties. Furthermore, the wear tracks on the specimens were analyzed through field-emission scanning electron microscopy, which support the wearing behavior alteration. Finally, a CrMoN/SiNx multilayer coating with optimal high-temperature characteristics was demonstrated in this study.