In-situ preparation and mechanical properties of (ZrB₂+ZrC)/ Zr₃[Al(Si)]₄C₆ composites

Fully dense (ZrB₂+ZrC)/Zr₃[Al(Si)]₄C ₆ composites with ZrB₂ content varying from 0 to 15 vol.% and fixed ZrC content of 10 vol.% were successfully prepared by in situ hot-pressing in Ar atmosphere using ZrH₂, Al, Si, C and B ₄C as raw materials. With the increase of ZrB₂ content, both the bending strength and fracture toughness of the composites increase and then decrease. The synergistic action of ZrB₂ and ZrC as reinforcements shows significant strengthening and toughing effect to the Zr₃[Al(Si)]₄C₆ matrix. The composite with 10 vol.% ZrB₂ shows the optimal mechanical properties: 516 MPa for bending strength and 6.52 MPa·m^1/2 for fracture toughness. With the increase of ZrB₂ content, the Vickers' hardness of the composites shows a near-linear increase from 15.3 GPa to 16.7 GPa. The strengthening and toughening effect can be ascribed to the unique mechanical properties of ZrB₂ and ZrC reinforcements, the differences in coefficient of thermal expansion and modulus between them and Zr ₃[Al(Si)]₄C₆ matrix, fine grain strengthening and uniform microstructure derived by the in situ synthesis reaction.