Enhanced comprehensive properties of stereolithography 3D printed alumina ceramic cores with high porosities by a powder gradation design

Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines. Compared to traditional methods, additive manufacturing (AM) presents great advantages in forming complex ceramic cores, but how to balance the porosity and strength is an enormous challenge. In this work, alumina ceramic cores with high porosity, moderate strength, and low high-temperature deflection were prepared using stereolithography (SLA) 3D printing by a novel powder gradation design strategy. The contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse, medium, and fine particles is 2:1:1 and the sintering temperature is 1600 °C. The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder system. The sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain size. On this basis, a "non-skeleton" microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and properties. As a result, high porosity (36.4%), appropriate strength (50.1 MPa), and low high-temperature deflection (2.27 mm) were achieved by optimizing particle size gradation and sintering process, which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.