Sand erosion and crack propagation mechanism of Cr/CrN/Cr/CrAlN multilayer coating

Abstract

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.