Processing and properties of sintered reaction-bonded silicon nitride with Y2O3–MgSiN2: Effects of Si powder and Li2O addition

The effects of Si powder and Li2O addition on the processing, thermal conductivity and mechanical properties of sintered reaction-bonded silicon nitride (SRBSN) with Y2O3–MgSiN2 sintering aids were studied. Addition of Li2O 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 Li2O 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 m1/2). However, the purer fine Si powder produces the highest thermal conductivity (119 W m−1 K−1) and highest toughness (∼11 MPa m1/2) but the lowest strength (∼500 MPa).