Synthesis And Properties Of MoAl_0.97Si_0.03B Solid Solution

Ternary layered MoAlB has good mechanical properties and high temperature oxidation resistance,making it a preferred material for high temperature components.In order to further strengthen MoAlB,Si element was introduced to form MoAl?Si?B solid solutions.In addition,the solution of Si in MoAlB is expected to improve the oxidation resistance and crack self-healing ability of MoAlB.In present study,MoAl?Si?B solid solution materials were firstly synthesized.The influences of different raw powders,molar ratio of mixture,sintering temperature and holding time on the purity of solid solution and solution content of Si were studied.The mechanical properties including Vickers hardness,fracture toughness and flexural strength of the solid solution were measured.The high temperature oxidation resistance and crack self-healing behavior of MoAlB and MoAl?Si?B solid solution were investigated.The results showed that:?1?A dense MoAl?Si?B solid solution with high purity can be synthesized by hot-pressing of the mixtures of Mo B,Al,and Si powders with a molar ratio of 1:1.3:0.1,and Mo,Al,B and Si powders with a molar ratio of 1:1.3:1:0.1,respectively,at 1200oC under 25 MPa for 1 hour in Ar.Scanning electron microscopy and energy spectrum analysis showed that the solid solution of Si was 0.91 at%,corresponding to the formula of MoAl0.97Si0.03B.?2?Vickers hardness and flexural strength of MoAl_0.97Si_0.03B were 14.89 GPa and385 MPa,respectively,higher than 8.41 GPa and 306.8 MPa for MoAlB,while the fracture toughness was 4.77 MPam^1/2,close to 4.91 MPam^1/2 for MoAlB.?3?The mass gains of MoAl_0.97Si_0.03B were lower than those of MoAlB when oxidized for 10 h in the temperature range 1200-1400oC in air,and the thicknesses of oxide layers were also lower than MoAlB,indicating the enhanced oxidation resistance of MoAl0.97Si0.03B.?4?MoAl_0.97Si_0.03B has an attractive self-healing ability.After healing at 1200oC for 1 h,the recovery strength of 390 MPa was achieved,even exceeding the initial strength of 385 MPa.The main crack healing mechanism is the filling of cracks by the formation of Al₂O₃ and Si O₂ at 1200oC.