Porous silicon nitride from starting powder with addition of coarse grain

Porous silicon nitride was sintered from mixture of fine and coarse powders, of which the grain sizes were 0.1 and 10 mum, respectively. The amount of the coarse powder was varied from 0 to 30%, which resulted porosity up to 13%. The strength and elastic modulus decreased with porosity, whereas the fracture toughness was increased. The fracture strain remained almost constant with the porosity, whereas the estimated critical flaw size with the porosity of 10% was 3 times that of the dense body, suggesting that the porosity enhanced the defect tolerance of the material.