Design of a gradient elastic modulus transition layer based on film-substrate adhesion

The codeformation process of Ti6Al4V (TC4) substrate and chromium nitride (CrN) films with dense/loose CrN and gradient elastic modulus CrN/CrNx/Cr(N) (G-CrN) structures under normal impact load were simulated by changing the thicknesses of the films or the loose CrN and G layers. The dispersed distribution of interfacial tensile stresses and strains of G-CrN films improved the layers' codeformation, compared with the firm large layer of the dense/loose CrN films. The stress reduced as the loose/G layer thicknesses increased. The 4.7 mu m CrN films with various thicknesses of the G-layers, 0.2 mu m, 0.6 mu m, 0.75 mu m and 0.9 mu m, were prepared on TC4 to evaluate the film-substrate adhesions and verify the simulated deformation procedure. A G-layer between a ceramic film and its alloy substrate is needed, and the 0.83-1.08 mu m thicknesses of the G-layers were suggested for the CrN/TC4 system varied with the films' thicknesses. The dispersed distribution of the tensile stress and strain within the G-CrN film was the mechanism of the film-substrate adhesion improvement.