Effect of Si content on the microstructure and mechanical properties of Mo–Al–Si–N coatings

Abstract

Mo–Al (Al/(Mo + Al) = 6.5%)–Si–N coatings with silicon content ranging from 0 to 17 at.% were fabricated using d.c. reactive unbalanced magnetron sputtering technique in an Ar–N2 mixture. Surface morphology, element and phase composition, residual stress and nanohardness of these coatings were studied by scanned electrical microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), residual stress tester, and nanoindenter, respectively.Results exhibit that the residual stress built in the coating is compressive in nature ranging between 0.6 and 1.8 GPa. Nanohardness of Mo–Al–Si–N coatings increased at first and then decreased with silicon content, reaching a maximum value of 36 GPa at 8.3 at.% Si. The optimum hardness could be ascribed to higher compressive stress and nanocomposite structure where nanocrystallite Mo–Al–Si–N embedded in amorphous Si3N4 matrix.