Research On Nano-modification Of Light-cured 3D Printing Silicon Oxide-based Ceramic Core

With the development of air cooling technology in aero-engine blades,the inner structures of hollow turbine blades becomes more and more complex.As the ceramic cores are employed to form the inner cavity of hollow turbine blade,their dimensional accuracy and high temperature performance directly affect the qualification rate of hollow turbine blade.Silicon based ceramic cores are widely used in the manufacture of hollow turbine blades due to the excellent thermal stability,low coefficient of thermal expansion and well demoulding performance.Compared with the traditional hot injection molding method,3D printing technology is more suitable for manufacturing this kind of complex structure parts.In this work,digital light processing stereolithography 3D printing was employed to manufacture silicon based ceramic cores,and the property investigation and mechanism analysis were carried out on the photocurable resin and ceramic cores.Different photosensitive resins were prepared by using polyurethane acrylate as oligomer,HDDA,DPGDA,TMPTA as active diluent and TPO as photoinitiator.It was shown that,the resin with DPGDA showed the lowest shrinkage of 1.72%,TMPTA system had the largest shrinkage of 4.36%,and the one with HDDA had excellent viscosity(360 m Pa·s).Through the curing thickness under different exposures,it is concluded that the critical exposure required by DPGDA system was the least.With increasing contents of oligomer,the volume shrinkage of the photosensitive resin decreasesd,the viscosity increased,and the critical exposure decreased,respectively.As the ration of diluent: oligomer being 6:4,the photosensitive resin exhibited excellent comprehensive performances.Through the influence of diluent systems on photosensitive resins,the resin formula with the best performance was obtained and used for the printing of ceramic cores,taking the conversion rate,volume shrinkage rate,viscosity,critical exposure and critical exposure as indexes.In this work,the effects of nano silica on UV curable 3D printing ceramic cores were discussed.It was shown that,with the increasing content of nano silica,the volume density of ceramic core increased,and the porosity and pore size decreased.Meanwhile,the interlayer spacing decreased,which leaded to the decrease of surface roughness,and increase of flexural strength and creep resistance of the cores.To simulate the casting process of superalloy blades,the thermal deformation behaviors of the ceramic cores were observed via the heating and cooling cycles between room temperature and 1540 °C in a thermal dilatometer.It was shown that,the total linear shrinkages of the ceramic cores decreased with increasing content of nano silica.When the content of nano silica was 2.5 wt.%,the ceramic cores showed superior properties with porosity of was 31.56%,surface roughness of 1.65 ?m,flexural strength of13.8 MPa,creep deflection of 0.25 mm,and leaching rate of 2.00 mg/min,the sintering shrinkage was 5.61%,4.74% and 5.00%,in the three dimensions,respectively,and the casting shrinkage was 1.11%,1.10% and 1.25%.The effect of nano alumina on the shrinkage rate,mechanical properties and microstructure of the 3D printed silica cores was studied.It was shown that,the sintering shrinkage and casting shrinkage of the 3D printed silica cores are successfully decreased by introducing nano alumina powders into the matrix.Nano alumina had a significant inhibition on the crystallization of the silica based ceramic core,and lowered the sintering temperature.With increasing contents of nano alumina,the flexural strength and high temperature flexural strength were reduced,and the high temperature deflection was enhanced.When the content of nano alumina was 1.0wt%,the ceramic cores showed lowest sintering shrinkages,which was 1.78%,1.66% and 1.72% in the three-dimensional direction,respectively.Furthermore,the ceramic cores showed lowest casting shrinkages,with values of 1.78%,3.45% and 6.30%,respectively.In this case,the flexrual strength of the core was 3.27 MPa,the high temperature strength was 25.05 MPa,the porosity was 34.53%,and the surface roughness was 1.950 ?m.