Cracks of alumina ceramics by selective laser melting

Alumina ceramic powders have high melting point and are prone to cracking during the rapid heating and cooling process of selective laser melting (SLM). Research on the crack formation and growth mechanisms forms the basis to developing crack suppression techniques. Variable laser power experiments based on single-track, zigzag, and island scanning strategies are designed to analyse crack morphology, distribution state, formation reasons, and extension mechanisms in alumina (Al2O3) SLM specimens. Our experiments show that transverse cracks formed by internal stress and longitudinal cracks formed by solidification shrinkage exist in alumina SLM specimens. The transverse cracks continuously expand in melting tracks, while the longitudinal cracks expand along the centre or the juncture of melting tracks. With increasing laser power, the formation and extension length of cracks decrease. Crystal structures exert important influences on the fracture pattern and crack extension of specimens.