Effect of the TiSiN interlayer properties on the adhesion and mechanical properties of multilayered TiSiCN thin films

The interlayer design is crucial in optimizing the adhesion of TiSiCN thin films on tool steel. Thus, Ti/TiN/TiSiN interlayer systems were deposited varying the TiSiN interlayer bias voltages (-100 V, -150 V, -200 V) in a magnetron sputtering process to investigate the influence on the mechanical properties and adhesion of the TiSiCN top layer with different thicknesses. A higher bias voltage densifies the TiSiN interlayer structure, thereby increasing its residual stresses (0.11 GPa to 1.46 GPa) and hardness (28.1 GPa to 34.9 GPa). This occurs without affecting the columnar-like microstructure of the TiSiCN top layer and its hardness (25.9 GPa to 29.1 GPa for t = 1.0 mu m, 22.6 GPa to 24.8 GPa for t = 2.3 mu m). Adhesion classification by Rockwell C indentation of TiSiN declined from HF2 to HF4 due to increased residual stresses, impacting TiSiCN top layer adhesion with a similar deterioration. Scratch tests revealed reduced critical loads Lc2 and Lc3 for the TiSiN interlayer system and also for TiSiCN top layers. The highest critical loads were observed for TiSiCN (1.0 mu m) and TiSiCN (2.3 mu m) with TiSiN interlayer deposited at a bias voltage of -100 V, measuring (64.4 +/- 4.5) N and (73.4 +/- 8.3) N for Lc2, and (57.4 +/- 5.3) N and (71.6 +/- 4.5) N for Lc3, respectively. Increasing bias voltage decreases Lc2 and Lc3 to (23.2 +/- 4.5) N and (50.20 +/- 2.2) N for TiSiCN (1.0 mu m), and (21.4 +/- 4.5) N and (58.0 +/- 3.6) N for TiSiCN (2.3 mu m). Achieving high adhesion strength of TiSiCN multilayered system requires minimizing the residual stress differences between the layers. Therefore, when designing a complex multilayer structure for TiSiCN thin films, careful consideration of the stress state among the layers is crucial, which is achieved by adjusting the bias voltage.