| Mo-Si-B alloy has high melting point(2000℃),excellent high temperature strength and oxidation resistance,and is a kind of high temperature structural materials with great potential.In particular,α-Mo-Mo3Si-Mo5SiB2 three-phase alloy containing ductile metals and intermetallic compounds has been widely studied for its excellent combined properties at both room temperature and high temperature.However,due to the large differences in the structure and properties of each phase in this alloy,it is difficult to control its composition and microstructure,and it is always difficult to obtain Mo-Si-B alloy with excellent comprehensive properties.Therefore,this study intends to remove the Mo3Si phase with poor comprehensive properties,develop Mo-Mo5SiB2 two-phase alloy,give full play to the respective performance advantages of Mo and Mo5SiB2 phases,and obtain Mo-Si-B alloy with simple structure and excellent comprehensive properties.In order to match the micro structure and properties of the alloy,the microstructure design was carried out in this study.Firstly,thin sheet Mo powder with large diameter to thickness ratio and fine uniform spherical Mo5SiB2 powder were prepared.Secondly,Mo-Mo5SiB2 alloy with different phase distribution was prepared by mixing the two-phase powder and hot press sintering.Finally,the microstructure,room temperature and high temperature mechanics and antioxidant properties of the prepared alloy were characterized and tested,the relationship between micro structure and properties was established,and the related strengthening and toughening and antioxidant mechanisms were revealed.Mo-Mo5SiB2 alloys with different two-phase distribution were obtained by hot pressing sintering of mixed powders of flaky Mo powder and spherical Mo5SiB2 powder,including continuous Mo distribution,non-continuous two-phase mixed distribution and continuous Mo5SiB2 distribution.These alloys are composed of micron scale Mo and submicron scale Mo5SiB2 phases.While the microstructure of the alloy changes from Mo matrix to Mo5SiB2 matrix,the microstructure of the Mo phase changes from continuous distribution to discontinuous island distribution,and the grains of both Mo and Mo5SiB2 phases are gradually refined.The test results of mechanical properties at room temperature show that Mo5SiB2 alloy with continuous Mo distribution has the best mechanical properties at room temperature,and its toughness,bending strength and compressive strength reach 17.3 MPa·m1/2,732 MPa and 3.12 GPa,respectively.The continuous distribution of Mo matrix promotes the crack trapping ability of the alloy during the fracture process,and many micro-cracks near the indentation tip,interface debonding and crack deflection during the crack growth process have good toughening effects on the alloy.At the same time,it can effectively release the stress concentration at the interface of the two phases,so that the alloy deformation is more uniform and not easy to yield and fracture prematurely,which is beneficial to give full play to the bearing capacity of the Mo5SiB2 phase and achieve the effect of strengthening the alloy.The high temperature mechanical test results show that the alloy with continuous distribution of Mo5SiB2 has excellent high temperature compression properties.The high strength Mo5SiB2 has good plastic deformation ability at high temperature,which contributes to the coordinated deformation of Mo5SiB2 and Mo.The deformation is mainly caused by work hardening and dynamic softening.The results of high temperature oxidation resistance test show that the oxidation weight loss of Mo5SiB2 alloy is negatively correlated with the content of Mo5SiB2 phase and positively correlated with temperature.The alloy exhibits continuous oxidation weight loss behavior at all temperatures and does not appear steady-state oxidation stage.Due to the large grain size or high content of Mo phase,the transverse flow distance of borosilicate film oxidized by adjacent Mo5SiB2 phase is large,and it is difficult to form a complete continuous borosilicate layer on the alloy surface,so that the Mo phase continues to be oxidized and volatilized.In order to improve the oxidation resistance of Mo-Mo5SiB2 alloy,the surface of MoSi2 alloy was treated with Si embedding,and the prepared MoSi2 anti-oxidation coating showed excellent oxidation resistance at 900-1300℃. |
