Fracture Origin and Strength in Advanced Pressureless‐Sintered Alumina

Advanced raw materials and shaping approaches enable the production of pressureless‐sintered alumina parts where, in bending, the average maximum stress at the fracture origin is as high as 800 MPa. In individual specimens that fracture at lower stresses (450–600 MPa), failure often originates at volume flaws, as known for hot‐pressed alumina with a similar strength. Also, transgranular and intergranular fracture modes along the crack path are the same as those observed in hot‐pressed alumina. If the size and the frequency of volume flaws are reduced, fracture initiates at smaller defects in the ground surfaces and bodies with a bending strength of >800 MPa are produced without hot pressing. The grain‐size dependence of grinding‐induced surface damage contributes to a grain‐size effect for the strength.