Effects of trace Si addition on the microstructure evolution and mechanical properties of MoAlB ceramic

To simultaneously improve the toughness and strength, MoAlB ceramics have been prepared by adding different Si contents. The effects of Si addition on the microstructure and mechanical properties have been systematically investigated and the corresponding mechanism has been discussed in the present study. Si element cannot only dissolve into MoAlB crystal grain but also contribute to the phase composition transformation from MoAlB+Al₈Mo₃ +Al₂O₃ to MoAlB+ Mo(Si, Al)₂ +Al₂O₃. Additionally, MoAlB crystal grains can be effectively refined after Si addition. Accordingly, the Vickers hardness (10 N) can be greatly improved, reaching about 14 GPa. Flexural and compressive strengths increase firstly and then decrease, acquiring the highest values of 783.2 and 2760 MPa, respectively. Likely, fracture toughness of MoAlB can be improved to 7.46 MPa·m^1/2 with Si addition of 0.05 mol. Si dissolution, grain refinement and phase composition transformation synergistically affect the mechanical properties of MoAlB ceramics.