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Herein, we have deposited Cr/CrN/Cr/CrAlN multilayer coatings with various modulation ratios on TC11 alloy substrate using cathodic arc system. The influence of various modulation ratios on microstructure and Al 2 O 3 sand erosion behavior of coatings is systematically studied. Results reveal that the coatings are about 200 nm per cycle and total thickness is 8 μm. Five groups of coatings exhibit high hardness (>3000 HV 0.025). The coating with modulation ratio of 12 adhesion can reaches 55 N. The residual stress increases with the decrease of the modulation ratio, but the increase is generally low (less than −2 GPa). In addition, according to sand erosion test, it is found that sand erosion resistance of multilayer coating is significantly around 5 times higher than TC11 alloy matrix. The erosion morphology shows that a large number of irregular cracks and layered spalling appear on the surface of the coating, indicating that the cracks are constantly initiated under the continuous impact of the sand and gravel，and finally gather together and then spalling. Moreover, dynamic response and stress field of the coating under the impact of single sand (Al 2 O 3) are studied by numerical simulations. It is determined that coating cracking is caused by high tensile stress under CrAlN layer. In addition, according to crack propagation morphology and influence of different interfaces between multilayered structures on crack tips, propagation/termination mechanism of cracks is analyzed in detail. Cracks are easy to initiate in hard CrAlN layer and consume a lot of energy after propagating into soft Cr layer, thereby ending at next soft and hard interfaces. These results provide experimental and theoretical support for the study of high tenacity and anti-erosion coating. [ABSTRACT FROM AUTHOR]

In this study, CrN and CrAlN coatings were deposited on the surface of aerospace titanium alloys using the arc ion plating technology to investigate the effect of the microstructure of the coatings on the mechanical and erosion resistance properties. The cross-sections of the coatings were observed by Scanning Electron Microscope(SEM), the microstructures were characterized by Transmission Electron Microscope(TEM), and the crystalline structures were tested by X-ray diffraction (XRD); furthermore, the hardness of the coatings was determined by a micro-Vickers hardness tester, the film-base bond strength was measured by a scratch tester, the change in curvature was measured by laser scanning and the residual stress was calculated. The fracture mechanism of the coating was elucidated by simulating the fracture pattern of the cross-section of the erosion crater. The results indicated that the thicknesses of the CrN and CrAlN coatings were almost the same, but the number of large particles on the surface of the CrAlN coating was higher. Both sets of coatings exhibited a nanocrystalline structure with a grain size of around 10 nm. Due to the doping of the Al element, the CrAlN coatings exhibited a hardness of 2846 HV and a higher residual stress of −1.831 GPa. Both the CrN and CrAlN coatings showed lower erosion rates than the titanium substrate at 30° and 90° angles of attack. The results of finite element simulations indicated that the more ductile CrN coating exhibited a better stress absorption capacity, and a typical brittle fracture failure mechanism was observed for both sets of coatings. • CrN and CrAlN coatings with good erosion resistance were obtained. Compared with the titanium alloy substrate, the erosion rate of the coated sample is only 1/8 of the titanium alloy substrate at 30°, and only 1/3 of the titanium alloy at 90°. • The erosion fracture process of the hard coating was explored, in which the cracks were mainly in the direction perpendicular to the film-base interface, and were easily deflected by stress concentration at the microparticles and the interface. • Both CrN and CrAlN coatings are typical brittle fracture failure mechanisms, but the tougher CrN coating has better stress absorption capacity. [ABSTRACT FROM AUTHOR]