Highly transparent LiAlON ceramic prepared by reaction sintering and post hot isostatic pressing

A highly transparent polycrystalline LiAlON ceramic with the size of Φ57 mm × 6 mm was successfully fabricated by reaction sintering (1750 °C, 20 h) and post hot isostatic pressing (HIP, 1850 °C, 3 h, 180 MPa) using AlN, Al2O3 and LiAl5O8 powders. Related mechanism on the reaction sintering and densification were studied via the analysis of phase and microstructural evolution. High transparency was resulted from full elimination of Al2O3 secondary phase and residual pores. It has excellent optical transparency from the visible to middle infrared (IR) bands with the maximum transmittance of ∼ 85.5%. The flexural strength and Vikers hardness reach ∼303 MPa and ∼15.0 GPa, respectively.