Processing and properties of sintered reaction-bonded silicon nitride with Y 2O 3–MgSiN 2: Effects of Si powder and Li 2O addition

Abstract

The effects of Si powder and Li 2O addition on the processing, thermal conductivity and mechanical properties of sintered reaction-bonded silicon nitride (SRBSN) with Y 2O 3–MgSiN 2 sintering aids were studied. Addition of Li 2O provides a less-viscous liquid phase that results in a more uniform and finer pore structure in RBSN with the coarser Si powders, but the pore structure plays a less important role in the densification of RBSN. The thermal conductivity of SRBSN without porosity decreases with increased Al impurity content and also decreases with the Li 2O addition regardless of the Si purity. The impurest coarse Si powder produces the lowest thermal conductivity (93 W m −1 K −1) but the highest four-point bending strength (∼700 MPa) and a higher fracture toughness (∼10 MPa m 1/2). However, the purer fine Si powder produces the highest thermal conductivity (119 W m −1 K −1) and highest toughness (∼11 MPa m 1/2) but the lowest strength (∼500 MPa).