Study On Fabrication And Properties Of High-porosity Alumina-based Ceramic Core

Alumina-based ceramic core has good chemical stability,high temperature strength and creep resistance,and it can be widely used in the manufacture of aviation turbine blades.However,alumina-based ceramic core has a problem of core removal after casting,and increasing porosity of the core can increase the contact area between core solution and alumina-based ceramic core,thereby increase the core removal rate.To solve the above problems,this paper conducts a study of high porosity alumina-based ceramic cores,which has great theoretical and practical significance.In this paper,the effects of particle size gradation of white corundum powder on the properties of alumina-based ceramic core were studied.The results show that when the mass ratio of three kinds of white corundum powder is 180 mesh:250 mesh:325 mesh=6:3:1,the ceramic core has better comprehensive properties.At this time,the room-temperature flexural strength is 32.3MPa,the apparent porosity is 37.26%,the solubility is 1.35g·h^-1,the line shrinkage is 2.84%and the bulk density is 2.52g·cm^-3.Based on the results of particle size gradation of white corundum powder,the effects of the addition of mineralizer?SiO₂ and MgO?on the properties of alumina-based ceramic core were studied.The results show that when the addition amount of SiO₂ is 10%?accounting for white corundum powder wt.%?and the amount of MgO is 1.0%?accounting for white corundum powder wt.%?,the ceramic core has better comprehensive properties.And the room-temperature flexural strength is 38.5MPa,the apparent porosity is 41.98%,the solubility is 1.51g·h^-1,the line shrinkage is 0.34%and the bulk density is 1.85g·cm^-3.In order to fabricate high-porosity alumina-based ceramic core,the effects of pore forming agent?starch?on the properties of alumina-based ceramic core were studied.The results show that with the increase of starch addition,the room-temperature flexural strength,line shrinkage and bulk density of the alumina-based ceramic core are reduced,apparent porosity and solubility are increased.And the addition of starch did not change the thermal expansion coefficient of the core.When the starch addition is 8%?accounting for white corundum powder wt.%?,the alumina-based ceramic core has good comprehensive properties.And the room-temperature flexural strength is 24.8MPa,the apparent porosity is 47.98%,the solubility is 1.92g·h^-1,the line shrinkage is 2.86%,the bulk density is 1.88g·cm^-3 and the thermal expansion coefficient is 10×10^-6K^-1.Using the developed material optimized formulation of high-porosity alumina-based ceramic core in this paper,the effects of mold preheating temperature on the forming properties of complex alumina-based ceramic core were studied.The results show that low mold preheating temperature will lead to be difficult to complete filling;High mold preheating temperature will lead to a large number of flash and it is difficult to mold.When the mold preheating temperature is 60?,the complex alumina-based ceramic core can be fully formed.