Effects of ball milling time on microstructure evolution and optical transparency of Nd:YAG ceramics

Polycrystalline Nd:YAG ceramics were fabricated by the solid-state reaction and vacuum sintering method using Y2O3, α-Al2O3 and Nd2O3 as starting powders. These powders were mixed in ethanol doped with MgO and TEOS and ball milled for different time periods. The samples were sintered from 1500 °C to 1760 °C for 0.5–20 h. Effects of ball milling time on the particle size of powder mixtures as well as ceramics densification process, microstructure evolution and optical transparency of the as-prepared Nd:YAG ceramics were mainly investigated. It was demonstrated that coarse powders can be ground into fine particles. Porosities of Nd:YAG ceramics sintered at 1600 °C and 1760 °C decrease with the increase of ball milling time up to 12 h and are kept almost unchanged with further increasing the time. Contamination of the powders with impurities, which may not be observed in microstructures, when the ball milling time is overlong, and the very few residual micro-pores, will cause an infinitesimal decrease in transmittance. The grain growth kinetics of Nd:YAG ceramics fabricated from the optimal ball milling process was also studied in this paper. The highest in-line transmittance of 83% at 1064 nm was obtained by sintering the sample at 1760 °C/3 h from the powder mixtures ball milled for 12 h.