Effect Of Refractory Materials And Binders Used In Face Coating On Properties Of Ceramic Mould For Investment Casting Of Titanium Alloys

In this thesis refractory materials were prepared by domestic production and foreign production zirconia and domestic production and foreign production yttria, and the binder was adopted by two kinds of domestic zirconium acetate aiming titanium investment casting, which were formulated in different S/L ratio of the slurry. The rheology, thixotropic and suspension of slurry used for face coating were studied systematically, optimizing the S/L ratio. The ceramic mould was developed by different slurry, investigating the influence of firing temperature and time on the normal temperature strength and residual strength of different ceramic mould, optimizing the firing process of different ceramic mould.The baking process of zirconium acetate was discussed with the TG, DTA and XRD, finding that two kinds of zirconium acetate phase transformation temperature 880°C and 970°C when baked.The rheology and suspension of the slurry in different refractory materials, binders and different S/L ratio were examinatied, finding that the viscosity and thixotropy of yttrium oxide slurry was greater than zirconium, the domestic production yttria was the highest, the foreign production zirconia was the lowest; but the suspension of zirconium slurry was better than yttrium, the suspension rate of domestic production zirconia was the highest, the domestic production yttria was the lowest; for slurry with different binder, the greater the viscosity of the binder, the greater the viscosity and thixotropy of the slurry, and the better the suspension.The preparation process of the slurry was optimized, drawing the S/L ratio of slurry formulated by yttrium refractory and zirconium acetate adhesive for face coating 2.5:1 and for adjacent face coating 2.3:1, while the zirconia 3.0:1 and 2.7:1.The roasting process of ceramic mould was studied according to TG-DTA thermal analysis and X-ray diffraction analysis methods. The results showed that the weight loss rate of the zirconia shell mould was slower than yttrium, and zirconium shell mould generated the Ca0.15Zr0.85O1.85 phase after firing, while yttrium shell mould Y4Zr3O12 phase. Zirconia content was higher in composite shell mould, the slower the rate of weight loss, producing Zr0.82Y0.18O1.91 phase at high temperature.The research showed that the normal temperature strength and residual strength of zirconium ceramic mould was higer than that of yttrium ceramic mould, the domestic production zirconia was the highest, the domestic production yttria was lowest; the strength of ceramic mould adopted by 1#zirconium acetate binder was higher than that of 2#zirconium acetate ceramic mould; the addition of zirconium oxide content improved the normal temperature strength and residual strength of the composite shell. The increasing of the S/L ratio of slurry improved the normal temperature strength and residual strength of zirconium ceramic mould.The influence of firing temperature and time on the strength of ceramic mould was researched, the results showed that the higher the baking temperature and the longer the roasting time, the higher the strength of the shell, further determining two kinds of binder shell firing process 1050 °C×2.5h and 1200°C×2.5h.The morphology and phase composition of ceramic shell mould used for face coating after pouring were analysed. The results indicated yttrium shell mould was stabler, a small amount of titanium was oxidized, but zirconium shell mould and titanium produced [Ca, Zr, Ti]O2 phase by reaction.