چكيده به لاتين
Cramic cores are widely used in investment casting of aeroengine parts and gas turbines. One of the most important application of these cores is in manufacturing of internal cooling passages in casted turbine vanes and blades. In this project the Effect of TiO2, SiO2, and MgO additives were studied on mechanical, chemical and microstructural properties of the Alumina ceramic core which is fabricated by gel-casting method. In order to obtain a high quality alumina core, a slurry with 45 vol.% solid loading, 0.05 M NH4Cl solution as an initiator and non-toxic silica sol as a binder were used. The gelation time and the viscosity of the obtained slurry were respectively less than 20 minutes and 1 Pa.s. The silica sol as a source of amourphous SiO2 and the rutile powder as a source of TiO2 were utilized. Also, MgTi2O5 was used as a source for adding MgO to the slurry in order to prevent MgO hydration in aqueous solution. The influence of different quantities of TiO2 and MgO on the properties of obtained bodies, which were sintered at 1400 and 1500˚C for 1 and 2 hours, was studied. The results showed that the sample contained 12.5 wt.% SiO2, 15 wt.% TiO2 and 4 wt.% MgO sintered in 1400˚C for 2 hours, represented less than 4% sintering shrinkage, more than 30% apparent porosity, flexural strength lower than 50 MPa, minimum thermal expansion coefficient (4.3×10-6/˚C) and maximum weight loss in leaching test (12.5%). Microstructal characterization and phase evaluation indicated that existing of MgAl2(1-x)Ti1+xO5 solid solution and consequently stabilization of Al2TiO5, uniform distribution of pores besides fine grains, and microcrack formation do to tialite decomposition are results of these appropriate properties.
