Investigation Of Fabrication And High Temperature Oxidation Resistance Of MoAlB Alloy By Hot-pressure Sintering

MoAlB phase is a new type similar to MAX phase.Its good comprehensive mechanical properties and excellent high temperature oxidation resistance make MoAlB alloys have potential applications in high temperature structural materials and high temperature anti-oxidation materials.Therefore,investigation of fabrication and anti-oxidation mechanism of MoAlB alloys are urgent and important.In this study,the mechanical alloying method was used to prepare Mo-Al-B alloy powders with different ratios(Mo:Al:B=1:1.2 and 1.3:1,at%)and the mechanical alloying time was analyzed for the alloy powders of the law of influence.Then the vacuum hot-pressing sintering process with different temperatures(1200°C,1300°C,1400°C)was used to sinter the powder and study the effect of alloying distribution ratio and sintering temperature on the phase composition and microstructure of MoAlB alloy.The high-temperature oxidation tests at different temperatures and different time have been used to analyze the high-temperature oxidation behavior and mechanism of high-temperature oxidation resistance of MoAlB alloys.Through microstructure observation and energy spectrum analysis,the prepared MoAlB alloy is mainly composed of MoAlB phase and a small amount of Mo B phase.At the same time,the relative diffraction peak intensity and microstructure of the Mo B phase in XRD and microstructure photograph were compared.It can be concluded that MoAlB has the highest content prepared in a bulk alloy when the sintering temperature is 1300°C and the alloying ratio is Mo:Al:B=1:1.3:1.The hardness,bending strength,fracture toughness and compressive strength of MAB-1.3Al bulk alloys prepared at different sintering temperatures(1200?1400°C)were tested and found that with the increase of sintering temperature,the grain size of the alloy was increased significantly,but the strength,toughness,and hardness of the alloy tend to decrease.In the test of fracture toughness and bending strength,the fractures of the alloy show a mixed brittle fracture of transgranular and intergranular,and the MAB-1.3Al alloy sintered at 1300°C has the highest fracture toughness value.Comprehensive comparison shows that the MAB-1.3Al alloy with a sintering temperature of 1300°C has good comprehensive mechanical properties.The high temperature oxidation test of MAB-1.3Al alloy specimens sintered at 1300°C for30 h at different temperatures under constant temperature indicates that the alloy has excellent oxidation resistance.Its oxidation resistance mainly comes from the MoAlB phase,which forms a dense layer of Al₂O₃ oxide protective film at high temperature to protect the substrate from destructive oxidation,and the oxide film formed on the surface of the alloy becomes thicker as the oxidation temperature increases.The oxide film was only 1.15?m at 1100°C and8.37?m at 1300°C.And the oxidation tests at 1200?for different time show that Mo B in the alloy has an adverse effect on the formation and densification of the oxide film at the initial oxidation of the alloy.