Phase transformation-induced crack closure and evolution of high-temperature flexural strength in DLP-printed silica ceramic cores during cooling

Hollow turbine blades are critical components of aircraft engines, and their performance strongly depends on the dimensional stability and mechanical reliability of ceramic cores during casting. Although most previous studies have focused on the behavior of ceramic cores during the heating and holding stages at casting temperatures, cracks and deformation may also develop during cooling, during which phase transformations can significantly affect the quality of blade castings. In this study, silica ceramic cores with a commercial composition were fabricated by DLP 3D printing, and their phase transformation behavior and evolution of high-temperature mechanical properties during cooling were systematically investigated. SEM and XRD results showed that β-cristobalite gradually transformed into tridymite during cooling. This transformation was accompanied by volume expansion, which compressed cracks and promoted their closure. Correspondingly, the high-temperature flexural strength increased with decreasing temperature and eventually stabilized at 36 ± 0.4   MPa, while the tridymite content exhibited a similar trend and reached 6.5   wt.%. In addition, approximately 0.7–0.9   wt.% of zircon decomposed into zirconia and silica phases at high temperature. These findings demonstrate that the phase transformation and associated microstructural evolution during cooling are closely related to the enhancement of the high-temperature flexural strength of silica ceramic cores.