New Technological Solutions in the Manufacture of Thermochemically Resistant Ceramic Molds for Casting Titanium Alloys

Abstract

The results of studies of interaction between titanium melts and silica-containing casting mold are presented. Pure silicon and compounds of titanium oxides and silicides have been detected by X-ray diffraction analysis in the contact zone. The problem of negative influence of the mold on the casting is solved by using thermochemically resistant monocorundic forms on an alumina sol binder and corundum filler. For casting according to meltable models, a composition of a refractory suspension with special additives has been developed, which will improve the wetting of models with suspension, as well as increase the strength of the mold. In the article, there are studies of sedimentation properties of suspension. A method has been developed for accelerated curing of sequentially applied layers of refractory suspension by drying in vacuum and subsequent chemical curing with a gaseous reagent. The formation time of one layer is reduced from 3–5 h to 20–30 min. Comparative studies of the kinetics of convective drying and dehydration in vacuum of alumina sol binder have been conducted. The process of removing moisture increases by 2–6 times once in a vacuum of 5–10 kPa. The method of X-ray phase analysis has made it possible to study the conversion of alumina sol during high-temperature heating. The stable phase α-Al₂O₃ in the mold shell is obtained when the calcination temperature rises to 1300–1350°C, and the strength of 9–12 MPa is also achieved when sintering additives are added to the suspension. Recommendations are given for additional protection of refractory ceramic layers after evacuation and drying: treatment of the last layer with gaseous hardeners and application of a polyvinyl acetal solution with a density of 1100–1200 kg/m³. The proposed technological solutions will make it possible to increase both the efficiency of the technological process of forming and casting of titanium alloys and the quality of castings.