Preparation And Properties Of Magnesium Based Ceramic Cores

Near-net shape investment casting is an effective method for producing high-precision and complex-shape castings,and it is also the main method for producing high-temperature alloy hollow blades for aerospace engines.For narrow or complex casting cavities,ceramic cores must be used to ensure the dimensional requirements of the casting for complex cavities.The magnesium oxide-based ceramic core has excellent high-temperature mechanical properties,and it can be easily dissolved in a weak acid solution and not react with alloying elements at high temperatures.It is a prospect in the field of aero engines.Therefore,the study of magnesium oxide based ceramic cores is of great significance for the production of high temperature alloy hollow vanes.This paper focuses on the shrinkage,flexural strength and thermal shock resistance of magnesium oxide based ceramic cores,and the apparent porosity and core removal performance of the core were also investigated as the mainly performances.The ceramic core samples were prepared by hot press molding with magnesium oxide as the matrix material.The effects of final firing temperature,alumina and zirconia on the properties of ceramic cores were studied.The main results are as follows:The study on the final firing temperature showed that when the final firing temperature was increased from 1350? to 1500?,the corresponding shrinkage rate increased from 6.82%to 14.76%,and the flexural strength increased from 10.11 MPa to 25.81 MPa,the number of thermal shock cycles decreases from 7.5 to 4 times.From the viewpoint of the flexural strength and the shrinkage,1450? was selected as the final firing temperature of the experiment.The results of the research on the amount of alumina additive show that the ceramic core has reduced shrinkage,improved flexural strength,good core removal performance and improved thermal shock resistance after the addition of alumina.The highest performance of the ceramic core was obtained when the alumina dosage was 12%,under the above condition,the flexural strength was increased to 54.13 MPa,the shrinkage rate was 7.48%,the number of thermal shock cycles was increased to 13 times.Relative mass loss rate reached 78.86%after a 25 min corrosion.The results of zirconia dosage showed that thermal shock resistance and removal performance of the magnesium-based ceramic core.Moreover,the core has a small shrinkage rate,and the flexural strength also meets the demanding requirements of the core.The overall performance was best when the zirconia mass fraction was 10%.Under this condition,the shrinkage rate was reduced to 5.87%,the flexural strength was 30.34 MPa,and the number of thermal shock cycles was 37.After corrosion of 20 min in the core removal solution,the relative corrosion rate was increased to 91.33%.In summary,the optimal dosage of alumina and zirconia were 12%and 10%,respectively.Under the optimal condition,a magnesium-based ceramic core with enhanced properties can be prepared.