Investigation of grain boundary phase crystallisation of SIALON ceramics for super alloy machining

SiAlON ceramics have the extensive usage potential in cutting tool applications due to the superior high temperature resistance, mechanical and thermal properties. This tools have become a potential material in high speed superalloy machining because of their low wear rate, high temperature strength. However, because of lower fracture toughness and chemical wear resistance, superalloy machining performance of current SiAlON tools are not as good as Al2O3-SiCw cutting tools which are still used commercially. Chemical wear resistance of SiAlONs is controlled by microstructure, types and amounts of sintering aids, secondary reinforcement phases, intergranular phase chemistry (amorphous or crystalline) and the solid solubility (z) value. Research the grain boundary phase crystallization and solid solubility (z) value relationship which is a very effective parameter on chemical wear properties of the material is important. In previous studies effect of the z value on creep behaviour, wear behaviour, thermal shock resistance, strength, fracture toughness, hardness and density behaviour was investigated. However effect of the z value on grain boundary phase crystallisation is unstudied. For this purpose change of the z value depending on the dopant systems and grain boundary phase chemistry were investigated using with different dopant systems (Y2O3-Sm2O3-CaO, Er2O3-Sm2O3-CaO, Yb2O3-Sm2O3-CaO), different amount of sintering aids, designing with and without TiN additive compositions and having with 0.6 z value and 25?'75ß' phase ratio.After performed studies development of SiAlON material was provided having with crystalline grain boundary phase at high z values (0.6-0.9) and Yb2O3-Sm2O3-CaO dopant system was seen the most suitable system for crystallisation and material production with high z value, crystalline grain boundary phase and appropriate hardness and fracture toughness property was achieved.Key Words: Süperalloy machining, cutting tools, sintering, SiAlON-TiN composite.