YAG-based transparent ceramics: comparison between HIP and SPS postsintering treatments

Abstract: YAG-based transparent ceramics are conventionally prepared by vacuum sintering or by a double sintering process, viz. vacuum sintering followed by Hot Isostatic Pressing (HIP). The use of a pressure-assisted process on vacuum pre-sintered ceramics favours the closure of residual porosity, and is therefore suitable for the production of highly transparent ceramics, where pores would otherwise act as light scattering centres. On the other hand, these post-sintering treatments are effective with samples exhibiting a suitable microstructure after vacuum sintering, i.e. no secondary phases and only closed pores with a size smaller that the size of the grains. As an alternative to HIP, a fast post-sintering treatment with Spark Plasma Sintering (SPS) is proposed. In this poster we present a comparison of transparent YAG-based transparent ceramics obtained by vacuum sintering followed by post sintering with HIP and with SPS. Several combinations of vacuum sintering + HIP/SPS conditions were tested on YAG and Yb:YAG samples prepared by reactive sintering of single oxides in order to modify their microstructure, especially grain size and residual porosity. Magnesium oxide (M) or magnesium oxide with TEOS (M+T) were used as sintering aids. SEM and optical microscopy analyses were used to characterise the microstructure of the samples after vacuum sintering and after post-sintering, and to identify correlations between the microstructure and optical properties of transparent YAG ceramics. Acknowledgements: F. P. gratefully acknowledges the financial support of JECS TRUST.The authors from CNR ISTEC gratefully acknowledge the support from the Italian Ministry of Defence under PNRM Contract No. 8731 of 04/12/2019 (CeMiLAP²).