Nanohardness and fracture toughness of combustion chemical vapor deposition deposited yittria stabilized zirconia–alumina films

Abstract

Composite films with compositions of 100% yttria stabilized zirconia (YSZ) and YSZ with 15, 30, 45, 62.8 (eutectic composition), 80 mol% alumina and 100% alumina films were deposited onto sapphire substrates using combustion chemical vapor deposition. Precursors of yttrium 2-ethylhexanoate, zirconium 2-ethylhexanoate and Al acetylacetonate dissolved in toluene at a total metal ion concentration of 0.002 M were used to produce films up to 1 μm thick. Flame temperatures at the substrate surfaces were 1550±50 °C and deposition rates fell between of 0.76–1.7 μm/h, depending on composition. Nanohardness, determined with a Berkovich indenter, was constant at about 15 GPa for compositions less than 100% alumina. The 100% alumina films were about twice as hard as other films. The films' fracture toughness, determined with a cube corner indenter, increased with alumina content from 1.76±0.46 MPa m 0.5 with no alumina to 2.49±0.32 MPa m 0.5 at 30 mol% alumina. Further alumina increases had little effect on fracture toughness, with about 2.2 MPa m 0.5 being the fracture toughness at 100% alumina. Eutectic composition films, that were annealed for 2.5–10 h at 1500 °C, displayed coarsening of the second phase YSZ particles. Film hardness decreased by about half (∼22 to ∼11 GPa) after five or more hours of annealing, while fracture toughness reached a maximum of 3.33 MPa m 0.5 after a 5 h anneal.