Structure and properties of superhard materials based on aluminum dodecaboride α-AlB12

Abstract

The structures and mechanical properties of materials based on α-AlB12 without additives and with additions of carbon and titanium carbide sintered under high (2 GPa) pressure and by hot pressing (30 MPa) in the contact with hexagonal BN. The light materials were obtained having high hardness, fracture toughness, ultimate strengths at bending, R_bm, and compression. The addition of 17 wt % C to α-AlB₁₂ and sintering at 30 MPa makes possible to achieve fracture toughness K_Ic (49 N) = 5.9 ± 1.4 MPa·m^0.5, hardness H_V (49 N) = 23.6 ± 2.8 GPa, bending R_bm = 310 MPa and compression R_cs = 423 MPa strengths and specific weight was γ = 2.7 g/cm³. The addition of 20 wt % TiC to α-AlB₁₂ and sintering at 30 MPa resulted in the formation of AlB1₂C₂ and TiB₂, increase of the hardness H_V (49 N) = 28.9 ± 1.9 GPa, R_bm = 633 MPa, R_cs = 640 MPa and γ = 3.2 g/cm³, the K_Ic(49 N) = 5.2 ± 1.5 MPa·m^0.5.