| MoSi2-RSiC composite combines the excellent high temperature mechanics and creep resistance of RSiC,and the excellent electrical conductivity,thermal conductivity and high temperature oxidation resistance of MoSi 2.It has broad application prospects in aerospace high temperature structur al materials and high temperature electric heating materials.The current preparation methods are mainly polymer impregnation?PIP?and activated infiltration?AAMI?,which have the advantages of significantly reducing the infiltration temperature,but the re are also some problems,such as the cumbersome PIP process,whether the addition of different metal elements has the same effect on the infiltration temperature of the composite,effect of Metal Elements such as Cr or Ti on the Oxidation Properties of C omposites.In this paper,the activation infiltration method?AAMI?was used to investigate the effects of preparation process on composite composition,microstructure,room temperature and high temperature mechanical properties,electrical conductivity,thermal expansion coefficient,thermal conductivity and oxidation resistance.The conductive mechanism of the composite was calculated and analyzed.The main conclusions are as follows:?1?With MoSi2-Si-Cr as the infiltrated phase,a uniform pre-melting alloy can be obtained at 1400oC,the composition of which is mainly Si,MoSi2 and?Mo,Cr?5Si3;when the activation infiltration temperature is 1900oC,it can be dense.?Mo,Cr?XSi2-RSiC composite,the phase composition is SiC,MoSi2,Mo4.8Si3C0.6 and?Mo,Cr?5Si3.Among them,interface bonding of MoSiCr-2-S2.6-1900.It is relatively excellent,with good mechanical properties,and the flexural strength and elastic modulus are 148.32MPa and 248.75 GPa,respectively.MoSiCr-5-S2.6-1900 has the lowest volume resistivity of 0.28?·cm,which is about 1/20 of the matrix.At 25-1200°C.The increase and decrease of MoSiCr-2-S2.6-1900 has the lowest thermal expansion coefficient of4.75×10-6K-1,and the overall performance is better in the composite material of the system?2?MoSi2-Si-Ti is the infiltrated phase,the pre-melting temperature is 1450oC,and when the activation infiltration temperature is 1700oC,the dense MXSi2-RSiC?M=Mo,Ti?composite material can be obtained,and the compo sition is mainly SiC,Si,TiSi2 and(Ti0.8Mo0.2)Si2.The microstructure of the composite shows that the MoSiTi-2-S2.6-1700 interface is tightly bonded and has no microcracks,and the enrichment of Mo and Ti is less.At the same time,MoSiTi-2-S2.6-1700 has the highest flexural strength and elastic modulus of 136.8MPa and 217.3GPa,respectively;it's high temperature mechanical properties increase with temperature,189.4MPa at1400oC,and 38%higher than room temperature.Among the composite materials corresponding to different infiltration,MoSiTi-5-S2.6-1700 has the lowest volume resistivity of 0.45?·cm.At 25-1200oC,the thermal expansion coefficient of MoSiTi-X-S2.6-1700 ranges from 4.51×10-6 K-1-4.97×10-6 K-1,and the composition of the infiltration phase has little effect on the CTE of the composite.At room temperature,MoSiTi-2-S2.6-1700has the highest thermal conductivity of 195.7 W·m-1 K-1.The thermal conductivity of the composite decreases with increasing temperature,and its thermal conducti vity mainly depends on the matrix.The composition of the infiltration phase has little effect on the thermal conductivity of the material.?3?Using the topological theory and mixing rules to calculate the conductivity of the composite,the calculated value of the topological method is closer to the true value of the material.The conductivity of composite materials is mainly affected by the three-dimensional interpenetrating network structure and interface bonding.The interpenetrating network structure has a great influence on the conductive behavior of the composite.When the density of the matrix is 2.6g·cm-3 and I1 is 0.64,the influence of interfacial bonding on the conductive behavior of the composite is mainly affected by the distribution of interface's(Ti0.8Mo0.2)Si2 and the volume fraction of the infiltrated phase,the influence factor increases first and then decreases.Due to the defects inside the composite material and the calculation of the simplified model,there is a gap between the calculated value of the finite element method and the true value of volume resistivity of the composite.?4?The oxidation rate of MoSiTi-2-S2.6-1700 composite is lower than that of RSiC matrix.After oxidation,the material has SiO2,TiO2 and Mo5Si3 phases.With the increase of oxidation time,the crack of the surface oxide layer of the composite material decreased first and then increased.When the oxidation time was 100h,a large number of pores and cracks appeared in the oxide layer,which showed a t wo-phase structure.Correspondingly,with the increase of oxidation time,the room temperature mechanics of the material first increased and then decreased,and the highest value was obtained after 40 h of oxidation.The flexural strength and elastic modul us were 142.3MPa and 191.1 GPa,respectively.The volume resistivity of the composite material decreased firstly with the increase of oxidation time,and after oxidation for 100 h.It was 0.285?·cm,which was 76.4%lower than before oxidation. |
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