Study of interface reaction in the Si₃N₄/Al composite prepared by pressureless infiltration

It is significant to study the relationship between the oxidation level of the Si₃N₄ porous preform and the interface reaction for providing the base of optimizing designation of the Si₃N₄/Al composite. The preforms with different oxidation level were pressurelessly infiltrated under the same processing conditions. Oxygen content of the preforms, phase constituents, and hardness of the composites were characterized by EDS, XRD instruments and Rockwell hardness tester respectively. The XRD results showed that the Si₃N₄/Al composite contain Al, Si₃N₄, A1N and a small amount of Si, Mg₂Si, MgO, MgAl₂O₄. With the increasing oxidation level of preforms, the reaction product of A1N decreased remarkably and MgO increased. More MgAl₂O₄ were measured from the composite which preform presintered at the higher temperature of 1200°C. The hardness of composite went down with the increasing of the oxidation level of preform. It is an important reason for the reduction of the hardness of composites that the oxide over Si₃N₄ particles results in the decreasing of replacement reaction between Al-Mg melt and Si₃N₄.