Study On The Preparation,properties And Ultra-high Temperature Plasma Abation Mechanism Of Ternary Layered MoAlB Ceramic

Hypersonic aircraft has attracted much attention due to its advantages such as fast flight speed and strong penetration ability.However,during supersonic flight,key components such as the nose cone and the leading edge of hypersonic aircraft will be subjected to severe aerodynamic heating and air scouring.The problems of ablation,oxidation,deformation,high-temperature radiation,failure and other problems encountered by structural parts under this thermal-mechanical-oxygen coupling are extremely complex.Binary boride ceramics have received widespread attention due to their high melting point,high hardness and high modulus.Unfortunately,due to its strong covalent and ionic bonds,binary boride ceramics have difficulty in atom migration,are not easy to densify,and have inherent brittleness and poor oxidation resistance.Ternary layered MoAlB ceramic shows great application potential due to its lower preparation temperature,good mechanical properties,and excellent high temperature oxidation resistance.However,at present,the synthesis reaction mechanism and the ablation mechanism of MoAlB ceramic are still unclear,which seriously hinders scientists’in-depth understanding of MoAlB ceramic.In order to explore the synthesis reaction mechanism and ablation mechanism of MoAlB ceramic,this study uses Mo,Al and B element powders as raw materials,and explores the synthesis reaction mechanism of MoAlB ceramic through in-situ reactive spark plasma sintering;the microstructure,mechanical properties and physical properties of MoAlB ceramic prepared by spark plasma sintering were systematically proved;the oxygen-plasma ablation assessment system was used to systematically evaluate the ablation behavior and ablation mechanism of MoAlB ceramic.The results are as follows:（1）The MoAlB phase is formed by the reaction of Al₈Mo₃,MoB and B or Al₈Mo₃,Moand B at 1000℃.The MoAlB ceramic prepared at 1200℃ is nearly single-phase and have a density of 97.1%.The fracture morphology shows that the fracture mode of MoAlB ceramic is a mixed fracture mode of transgranular fracture,intergranular fracture and cleavage fracture.（2）MoAlB ceramic has good electrical conductivity,moderate thermal expansion coefficient and high thermal conductivity.The electrical conductivity,thermal expansion coefficient and thermal conductivity are 2.7×10⁶ S/m,10.1×10^-6K^-1 and 37.56 W·m^-1·K^-1,respectively.The flexural strength,fracture toughness and compressive strength are 456.8 MPa,5.45 MPa·m^1/2,and 1467.6 MPa,respectively.The high temperature Vickers hardness of MoAlB ceramic up to 700℃ still maintains an average hardness value of 12.27 GPa without any attenuation,showing outstanding high temperature rigidity.（3）During the oxygen-plasma flame ablation assessment process of MoAlB ceramic at 1670-2550℃,it is mainly accompanied by the transformation of Al₂O₃,MoO₃ and B₂O₃,that is,the volatilization of MoO₃ and B₂O₃ and the melting of Al₂O₃.After the temperature exceeds 2400℃,MoAlB ceramic will enter the rapid ablation behavior mode of oxidation-exfoliation-oxidation.The main mechanisms of MoAlB ceramic oxygen-plasma ablation are high temperature oxidation,high temperature thermal damage,chemical attack and mechanical attack.（4）This study shows that the prepared MoAlB ceramic has excellent physical and mechanical properties and excellent high temperature plasma erosion resistance,and has the potential to be used in extreme environments as ablation resistant parts of hypersonic aircraft.