Thickness Effect of (0001) Textured Al2O3 Layer on the Optical and Mechanical Properties of MgAl2O4/Al2O3 Laminated Transparent Composite

Abstract

The effect of the thickness of (0001) textured Al2O3 layer on the optical and mechanical properties is examined in the MgAl2O4/Al2O3 transparent laminated composite. The textured Al2O3 layers with various thicknesses are formed on the MgAl2O4 polycrystals using a magnetic field alignment technique followed by one step spark‐plasma‐sintering (SPS) processing. Depending on the thickness of the textured Al2O3 layer, the transmittance efficiency of the composite sensitively changes and attains the higher in‐line transmittance of Tin,0.64 ≈ 54% at a visible range of λ = 0.64 μm for the thin Al2O3 layer with a thickness of ≈400 μm. In addition to the transparency, the hardness Hv measured on the textured Al2O3 layer surface also changes sensitively with the thickness and can attain Hv = 30.4 GPa, which is much higher than 25.5 GPa of monolithic Al2O3 polycrystals. The higher hardness can be ascribed to residual stresses formed in the textured Al2O3 layer. These results indicate that by controlling both the thickness and the texture structure of the Al2O3 layer, the MgAl2O4/Al2O3 composite simultaneously achieves excellent optical and mechanical properties.