Effect of addition of Cu into ZrOx film on its properties

The article reports on the effect of addition of Cu into the ZrO2 film on its structure, physical and mechanical properties. The ZrO2 and Zr–Cu–O films were reactively sputtered using a dc unbalanced magnetron from Zr (99.9) and ZrCu (90/10 at.%) targets in Ar + O2 mixture at the substrate temperature Ts = 300, 400 and 550 °C and total sputtering gas pressure pT = 1 Pa on steel, Si(100) and glass substrates. The structure of films was characterized by an X-ray diffraction (XRD) and mechanical properties, i.e. microhardness H, effective Youngʹs modulus E* = E / (1 − ν2) and elastic recovery We, were measured using a microhardness tester; E and ν are the Youngʹs modulus and the Poisson ratio, respectively. The film brittleness was characterized by the formation of cracks during the diamond indenter impression into it. 5 μm thick ZrO2 films prepared in the oxide mode of sputtering are crystalline (m-ZrO2) and exhibit relatively (i) high hardness H≈16 GPa and (ii) low ratio H3 / E*2≈0.11 GPa. The Zr–Cu–O films with low (≤ 2 at.%) Cu content exhibit (i) crystalline structure, (ii) higher H, (iii) lower (− 1.5 GPa) macrostress σ and (iv) higher ratio H3 / E*2≈0.14 GPa. On the contrary, the Zr–Cu–O films with high (24 to 44 at.%) Cu content exhibit (i) X-ray amorphous structure, (ii) lower H≈11 GPa and lower ratio H3 / E*2≈0.075 GPa. A special attention was devoted to the investigation of cracking of Zr–Cu–O films under high (0.5 and 1 N) loads of the diamond indenter. The relations between the film cracking and properties of the film and the substrate were used to assess the toughness of the Zr–Cu–O film. It was found that the film toughness increase with increasing H3 / E*2 ratio. It was shown that the addition of Cu to ZrO2 film can improve its toughness.