Synthesis And Properties Of Ternary Layered MoAlB

New ternary nanolaminated MAB phases have attracted much attention due to their attractive properties.MoAlB is one of the most concerned materials in the MAB phase family because of its machinability,damage tolerance,high electrical conductivity and excellent oxidation resistance.However,there is little work on the thermal shock resistance and crack self-healing behavior of MoAlB.In this work,a dense MoAlB material has been obtained by hot pressing of Mo,Al and B powders with a molar ratio of 1:1.3:1 at 1200? with 25 MPa for 1 h in Ar.The mechanical properties of MoAlB have been measured.The thermal shock behavior in the temperature range 600-1400? and the isothermal oxidation behavior at tempera-tures of 1200? and 1300? for 10 h have been investigated.The self-healing behavior and mechanism of MoAlB has been studied.The main results were listed as follows:(1)The prepared dense material was composed of MoAlB with minor AI3Mo and AI2O3 as impurities.The measured flexural strength,fracture toughness,and Vickers hardness of MoAlB were 307 MPa,4.91 MPa.m1/2 and 8.4 GPa,respectively.In addition,the calculated damage tolerance of MoAlB was 0.71 m1/2.(2)The thermal shock test showed that the residual strength slowly decreases from 174 MPa to 45 MPa after quenching from 600? to 1400? in water.The result indicates that MoAlB has good thermal shock resistance.(3)MoAlB has good high temperature oxidation resistance at temperatures of 1200? and 1300? for 10 h due to the forming of a dense and adherent Al2O3 scale.At such high temperatures,the oxidation kinetics of MoAlB material is close to parabolic.(4)MoAlB has attractive self-healing ability and can heal millimeter-scale cracks after heat-treatment at 1200? for 4 h in air.The recovered strength is 294 MPa,close to the initial strength of 307 MPa.The main crack healing mechanism for MoAlB is that thermal-shock-induced cracks are filled by only Al2O3 well adherent with the matrix and bonding the crack planes strongly.