Study On Gelcasting Forming Process Of Fe-Al/Al₂O₃ Composite

Fe-Al/Al2O3 composite is a material which is compounded by Al2O3 as matrix and iron-aluminized as toughnessing and strengthening phase. Ceramic strengthened and toughnessed by iron-aluminized don't have the disadvantage of which by fiber, whisker and metallic grain. It shows the advantage of iron-aluminized as semi-ceramic material that it has good consistence with alumina.Now the major method of the preparation of Fe-Al/Al2O3 composite is mechanical alloying and pressing sintering. First of all, the Fe-Al inter-metallic compounds powder is prepared by mechanical alloying. And it is mixed with alumina. The mixed powder is formed by pressing sintering. This forming method is easy , but it can't be used in complex formation. The sintering parts need later machining and this increases production cost.The forming process of gel-casting of Fe-Al/Al2O3 composite was provided, wherein, slurry of composite powder in good dispersion was casted in a mould with the organic system,which could be caused the polymerization and made the slurry in-situ formation. This process can promise the uniformity of the powder dispersion,which also gave the green body in high strength. Further, the process is optimized by decreasing the amount of organic substances so that a large amount of time was saving for giving away the organics.The Fe-Al inter-metallic compounds powder is prepared by mechanical alloying and sintering. The best techniques are the ball milling time is 40h and the holding time is 2h at 750℃.For the requirement of in-situ forming and machining process, the solid content of slurry more than 50%(by volume)is needed. Otherwise, the critical point is to obtain thick suspension in good fluidity. The effect of solid content,dispersant and pH to the fluidity were discussed in the present thesis. The study showed that Fe-Al/Al2O3 composite slurry of 58%(by volume)in solid content with viscosity 800mPa.s was obtained by adding the dispersant of MN with pH7, which gave the green body with good performance by casting, for example, the three point bending strength was more than 89MPa.By scanning on the broken surface,the SEM picture showed that the inner of the green body was well dispersed without co-aggregation. The effects of initiator and temperature on the gelation time were also discussed in the present study. The experiment showed after adding initiator 10%(by volume), the gelation time is suitable. The study also included the process of dryness and discussing how to reduce time and remove shortage.