Evaluating mechanical properties and crack resistance of CrN, CrTiN, CrAlN and CrTiAlN coatings by nanoindentation and scratch tests

CrN, CrTiN, CrAlN and CrTiAlN coatings were deposited on Si (100) wafers, and their microstructure, mechanical properties, fracture toughness and adhesive strength were investigated via X-ray diffraction (XRD), nanoindentation and micro-scratch tests. Besides an F.C.C. crystal structure, TiN_0.3 (004) and AlN (222) phases were found in the CrTiN and CrAlN coatings while the crystallinity of the CrTiAlN coating decreased. The hardness of the CrN (14.5GPa), CrTiN (13.9GPa) and CrAlN (17.7GPa) coatings was determined by their grain sizes while the CrTiAlN coating with the most compact morphology exhibited the highest hardness of 22.0GPa. In addition, CrTiN (K_Ic=2.73MPa·m), CrAlN (K_Ic=2.70MPa·m) and CrTiAlN coatings showed a stronger crack resistance than the CrN coating (K_Ic=1.06MPa·m), especially the CrTiAlN coating without any radial cracks. However, the CrTiAlN coating encountered circumferential cracks and premature delamination (Adhesive energy G_c=70J/m²) because of its highest compressive stress (4.64GPa). Based on the results here, it is concluded that a decent compressive stress of 3.0GPa is expected to help thin films prevent from radial and circumferential cracks simultaneously.