Production of CaO-Al2O3-SiO2 (CAS) based thermal spray coating powder and characterization of produced coatings

In this study, it was aimed to produce CaO-Al2O3-SiO2 (CAS) based thermal spray coating powder from natural raw materials and waste materials and to investigate mechanical and structural properties of the produced CAS-based coatings. For this purpose, eggshell, marble dust, zeolite, pumice and pure alumina were used to prepare stoichiometric CAS compositions that contain %57,5 SiO2, %27,5 CaO, and %15 Al2O3 by weight. The precisely weighed mixtures were mixed by wet ball milling at 250 rpm for 6 h and then dried at 100oC for 24 h. After drying process the powder mixtures was put into alumina crucibles and melted at 1450oC for 2,5 hours and then poured into a graphite mould. CAS-based coating powders with size of 45-125 μm obtained after crush grinding sieving processes, coated on AISI 304 steel by plasma spray technique. Because of the fact that the porosity is high in CAS-based coatings and the coating parameters can not be optimized due to coating system problems, this study has been changed to the production and characterization of sinter glass-ceramics by shaping the CAS powders (<45 m) with a uniaxial hydraulic press and then sintering at various times and temperatures. For this purpose, produced CAS compacts sintered for 1, 3 and 5 hours at 1000-1270oC using DTA results. From the XRD results, anorthite, wollastonite and pseudowollastonite phases formed in CAS-based glass-ceramic bodies. It was determined that the crystallization and viscous flow activation energies of the CAS glasses varied between 300,401 - 346,03 kJ.mol-1 and 395,69 - 436,41 kJ.mol-1, respectively. The calculated hardness values for CAS-based glass ceramics were changing between 872-1105 HV0.05 depending on sintering temperature and time. It has been found that the specific wear rate is about 10-7 mm3/Nm in wear tests and the main wear mechanism for CAS-based glass-ceramics is abrasive wear, with some local delamination wear.