Effect of sintering conditions on optical and mechanical properties of MgAl2O4/Al2O3 laminated transparent composite fabricated by spark-plasma-sintering (SPS) processing

To realize a high hardness in transparent MgAl2O4, the MgAl2O4/Al2O3 laminated composite was fabricated by a one-step spark-plasma-sintering (SPS) method. By sintering at a temperature of 1225 °C for 10 min and at a heating rate of ≤ 10 °C/min under a pressure of 300 MPa, the MgAl2O4/Al2O3 laminated composites can attain a high hardness with maintaining the wide band transparency. The in-line and IR transmission were ∼50 % at the visible wavelength of 500 nm and >77 % at the wavelength of 4 μm, respectively. The Vickers hardness measured on the surface of the Al2O3 layer perpendicular to the MgAl2O4/Al2O3 stacking exhibited 29 GPa, which is higher than those of the monolithic Al2O3 (26.6 GPa) and MgAl2O4 (17.2 GPa). The wide band transparency and mechanical properties can be realized by simultaneously attaining smaller grain sizes and higher densities of both the MgAl2O4 and Al2O3 phases in the laminated composite by optimizing the SPS conditions.