Toughness of hard nanostructured ceramic thin films

This article reports on the investigation of cracking of hard, 3–5 μm thick Zr–Cu–O, Zr–Cu–C, Ti–Cu–C and Si–Me–N (Me = Ta, Zr, Mo, W) magnetron sputtered nanostructured films using microindentation measurements. Main aim of this investigation is to determine the interrelationships between the cracking of film, its structure and mechanical properties and to assess the toughness of thin film. Correlations between the formation of cracks, the mechanical properties of film and substrate, structure of film and macrostress σ generated in the film during its growth were investigated in detail. It was found that the resistance of the film to cracking increases with increasing ratio Hf3/Ef⁎2. It was found that (1) the correct assessment of toughness of the thin film requires to investigate the system thin film/substrate as one unit because mechanical properties of the substrate play a decisive role in the formation of cracks, (2) the strongest parameter influencing the formation of cracks is the film structure and its macrostress σ and (3) nanostructured films with X-ray amorphous structure and small compressive macrostress (σ ≈ − 0.1 GPa) are very stable against the cracking even at high values of the film hardness Hf exceeding 20 GPa.