Marzhan Chukmanova

This study presents the results of a study of the reaction interaction and contact angle during contact between a titanium melt and a calcium metatitanate substrate. It is shown that at temperatures slightly above the melting point, the titanium melt poorly wets the CaTiO₃ substrate surface. The contact angle and the onset temperature of active reaction vary depending on the fractional composition of the CaTiO₃ powders from which the substrates are made and their porosity. Under isothermal holding conditions below the onset temperature of active reaction, the contact angle changes insignificantly. At the onset temperature of the reaction interaction, after a short stabilization period of the contact angle, the reaction leads to rapid penetration of the molten droplet into the depth of the CaTiO₃ substrate and, in some cases, to the expulsion of a Ca-Ti-O liquid phase from the reaction zone. The interaction of titanium melt with calcium titanate is accompanied by a series of physicochemical reactions associated with the reaction interaction, which intensifies with increasing temperature and causes the restoration of calcium to a metallic state and the dissolution of oxygen in the titanium melt, as well as the formation of a liquid Ca-Ti-O layer in the transition zone.

The paper presents the study results obtained for the reactive interaction and the wetting contact angle when a titanium melt comes into contact with the surface of a calcium ti-tanate substrate. It is shown that the wetting contact angle decreases from 93 to 74° with an increase in the contact temperature of the melt with the CaTiO3 substrate from 1670 to 1728 °C. As the isothermal holding time increases at 1705°C, the wetting contact angle in-creases, and at 1720°C, the wetting contact angle gradually decreases. The processes oc-curring at the interface of the solid and liquid phases are described. It is shown that when titanium comes into contact with CaTiO3, the following processes develop: penetration of titanium melt through capillaries between CaTiO3 particles; dissolution of CaTiO3 in the melt; reduction of calcium to a metallic state and its evaporation with the formation of a vapor layer between the substrate and the melt; diffusion of oxygen into the melt and its binding into a TiO compound that forms a shell on the melt surface. Due to the dissolu-tion of CaTiO3 in the titanium boundary layer and a decrease in the concentration of Ca, a melt is formed after crystallization of which the eutectic CaTiO3+αTi(Ca,O) is formed. The most likely cause of the large wetting contact angle of the CaTiO3 surface by titanium melt is the formation of a vapor layer at the interface between the solid and liquid phases. The found features of the CaTiO3 interaction with titanium melt made it possible to recom-mend it as the basis of molding materials for casting molds intended for the production of castings from titanium alloys.

The problem to obtain casting molds for titanium alloys is not resolved in full. It is primarily due to the high reactivity of titanium alloys resulting in their interaction with refractory materials. This reduces the quality of the castings due to the formation of various defects. The interaction of VT1-0 grade titanium in the liquid state with CaO, ZrO2 and CaZrO3 were studied. The processes occurring at the contact boundary between these substances and a change in the structure and microhardness of titanium castings near this boundary were described herein. The data obtained showed the disadvantages of molding materials based on CaO and CaZrO3. The features revealed for the interaction of a titanium melt with CaZrO3, where a highly porous CaTiO3 layer has been formed in the reaction zone,made it possible to recommend this compound as a promising material to cast molds in order to produce castings from titanium alloys.

The effect of various binding agents based on aqueous solutions of nitric acid, yttrium nitrate and orthophosphoric acid and yttrium hydroxide gel on the physical and mechanical properties of casting molds based on Y2O3 has been studied. It is shown that the most promising binding agent for yttrium oxide casting molds is a phosphate bond. The data describing the curing mechanism of phosphate-bonded molding mass is presented. The influence of the concentration of binding agent solutions on the strength characteristics of molding materials after curing and heat treatment is shown. Information about the interaction of yttrium oxide powder molds with phosphate-binding with titanium melt of VT1-0 and VT6 grades is presented. The obtained data allowed us to describe the advantages and disadvantages of the developed molding compound. A method for producing casting molds based on yttrium oxide powder with a yttrium phosphate-binding agent was developed based on this research.