Pressureless sintering of highly transparent aluminum oxynitride ceramic by precipitation-coating with sintering aid

AlON transparent ceramic is an ideal material for photoelectric windows, domes, and transparent armor. This ceramic is commonly fabricated by ball-mill mixing of AlON powder with appropriate sintering aids; however, it is difficult to homogeneously disperse trace sintering aids using this method and contamination is easily introduced, which may generate pores and flaws in the ceramic, resulting in degraded properties. To address this problem, we adopted a wet-chemical method to precipitation-coat sintering aids on the surface of AlON powder to achieve homogeneous distribution and enable nano-size sintering aids. Pressureless sintered AlON with 0.5 mass% Y2O3-coating gave in-line transmittance of 83.5% at a wavelength of 1064 nm and flexural strength of 326.3 MPa; the corresponding values for the ball-milled product were 79.3% and 304.6 MPa. Our results demonstrate that this method of sintering-aid coating has potential to fabricate AlON ceramic with excellent performance.