Densification of Sr-Mg doped SiAlONs with GPS and SPS

Abstract

At temperature above 1200 degrees C, the thermal stability of alpha-SiAlON phases has been debated since 1992; however, it has been discussed if any alpha-SiAlON phase can be formed in Ce, La, Eu and Sr-doped SiAlON systems. In our previous studies it was shown that the use of Mg-Ce and Mg-Sr elements as dopants SiAlON compositions, in which all elements just have very low or no stability in the (alpha-SiAlON structure, would promote the stability of Mg-Ce elements in the (alpha-SiAlON phase [1, 2]. However, in Mg-Sr systems, it was obtained that Mg2+ is predominantly incorporated in a-SiAlON structure whereas Sr2+ mainly remains in the grain boundaries [2]. In this study, by applying spark plasma sintering (SPS) (at 1400-1700 degrees C) and post-sintering thermal heat treatment (at 1500 degrees C for 5 hrs and 1700 degrees C for 2hrs) Mg or Mg-Sr doped SiAlON (50:50 mole ratios) ceramics were prepared. The results were compared with GPS sintered samples data. The effect of sintering temperature on densification process, phase transformation, microstructure and mechanical properties of samples were investigated. The results showed that by using SPS, Sr-Mg doped samples can be sintered at lower temperature (at 1600 degrees C) than at GPS (at 1800 degrees C) and it has no Sr-doped grain boundary phases.