Fracture and deformation mechanism of Ti(C,N)/TiAlSiN multilayer coating: FE modeling and experiments

Ti(C,N)/TiAlSiN multilayer coating was deposited on GTD450 using the Cathodic Arc PVD method to protect compressor blades from erosion damage. The fracture and deformation mechanisms of coating were investigated. To better observe fracture and deformation events and thus the need to apply high loads, Vickers microhardness test was performed and imprint diagonals were measured. Then, using SEM analysis, indent surfaces were investigated to observe crack initiation and deformation patterns at different loadings. It was found that crack initiated at the coating top surface (top surface of TiAlSiN layer) at a loading range of 250-500 mN. Cross-section SEM images of indent surfaces at lower loads revealed shear sliding and radial cracking below the indenter in the coating-substrate interface (bottom surface of Ti(C,N) layer). To better understand coating fracture and deformation, a 3D FE model was used to determine stress distribution in the coating. FEM results showed that maximum Von Mises stresses occur beneath the indenter and its edges, causing shear sliding to take place. Also, maximum principal stresses at lower loads take place beneath the indenter at the coating-substrate interface. As load increases, the maximum principal stress zone changes and is transferred to the coating top surface. Maximum principal stress was produced during the unloading process at the coating top surface or median plane and may cause lateral cracking. Experimental and FEM results were in good agreement