Low temperature pressureless sintering technology of Al_2O_3-SiC composites

6H-SiC and α-Al2O3 powders mixed as raw materials(mass ratio 7:3),adding MgO and CaO as sintering additives,Al2O3-SiC composites were prepared by pressureless sintering for 1h in hydrogen atmosphere after the green body being preoxidized for 1 h at 1 200 ℃.The effects of sintering temperature and MgO-CaO content on the sintering properties and phase composition were investigated.Result shows that when sintering temperature is 1 500 ℃,the compactness improves obviously with the increase of content of sintering addictives.With w(MgO-CaO) of 10 % added,the sample's apparent porosity is 0.1%.When the green body is preoxidized,CaAl2Si2O8 and Mg2Al4Si5O18 are generated by the reaction of MgO-CaO with α-Al2O3,SiO2.During the sintering process,CaAl2Si2O8 and MgAl2O4 form liquid glass phase which promotes sintering and deposits α-Al2O3.The sample's crystal phases are 6H-SiC and α-Al2O3 at 1 500 ℃.