Preparation And Properties Of MoSi₂Alloyed With Nb And Composited With SiC

MoSi2has been regarded as a candidate of high temperature structure materialwith most development potential, which has high melting point and good hightemperature oxidation resistance and other advantages. However, there are somedefects of MoSi2, such as brittleness at room temperature and creep at hightemperature. In view of the low temperature brittleness,(Mo,Nb)Si2alloy wasprepared by the combustion synthesis based on the single alloying Nb and Nballoying synergy SiC composite MoSi2. Meanwhile, feature of combustion synthesisand the phases constitute of products were analyzed. To study the effect of vacuumhot pressing process on alloy organization performance, vacuum hot-pressingsintering technology was used to make (Mo,Nb)Si2alloys densification. Theorganizations and performance of MoSi2alloy, which was prepared with singlealloying Nb and Nb alloying synergy SiC composite, was also studied.(Mo1-x,Nbx)Si2alloys was prepared through the combustion synthesis technologywith Mo, Nb, Si element powder as raw material. Combustion synthesis mode showedthat Mo-Nb-Si system of combustion mode was unsteady combustion, propagating inthe way of spiral and oscillation downward. Nb alloying promoted exothermicreaction of combustion synthesis MoSi2. With the increase of Nb content, combustiontemperature showed a rising trend, whole combustion wave spread with graduallydecrease trend. XRD spectrum results showed that when the amount of Nb x≤0.07,combustion synthesis product would be C11bphase with solid solution Nb. while, thecontent of Nb was0.09, there were very small amounts of NbSi2, and supersaturatedsolid solution was also founded.Research on vacuum hot pressing process showed that with the increase ofsintering temperature (Mo0.97Nb0.03)Si2alloy density increased, the hardness andfracture toughness decreased, bending strength increased slowly before a sharpdecrease appeared in the condition of the heat preservation time as to be90min.Under the sintering temperature of1400℃extending heat preservation time wouldmake hardness, bending strength and fracture toughness of (Mo1-x,Nbx)Si2alloyfollow a trend of increase before decrease. while the heat preservation time showed nosignificant effect on density. Therefore, the best vacuum hot pressing processparameters should be that the sintering temperature is1400℃, holding time for90min.By combustion synthesis product as raw material, dense (Mo1-x,Nbx)Si2alloy and 10%SiC/(Mo1-x,Nbx)Si2composite materials were prepared with the vacuum hotpressing optimum process parameters. systematic research on mechanical propertiesof hot-pressing materials at room temperature was carried out, the results showed thatwith the increase of Nb content,(Mo1-x,Nbx)Si2alloys hardness decreased slowlyincreased bending strength first plunged, after the first increase in fracture toughnessdrop in component (Mo0.99, Nb0.01)Si2performance best, bending strength and fracturetoughness were357MPa and3.48MPa·m1/2;10%SiC added significantly improved(Mo1-x,Nbx)Si2strength and toughness,10%SiC/(Mo0.93,Nb0.07)Si2also has the highestbending strength (559MPa) and maximum temperature toughness (7.46MPa·m1/2),respectively, than the increase of49.9%MoSi2and124.7%. A small amount of Nballoying MoSi2can improve fracture toughness at room temperature, and Nb alloyingcollaborative SiC composite can significantly improve the mechanical properties ofMoSi2at room temperature, the toughening mechanism mainly: grain refinement, Nballoyed solid solution softening effect and SiC dispersion strengthening effect.