Study Of Mould Materials And Preparation Technology Of Titanium Alloy Investment Casting

Titanium alloy is a kind of metal material with outstanding property. But it has high activity in the great heat,consequently, it can almost react with every refractory. Investment casting is a common method for titanium alloy forming, however, the casting performance would be degraded by the oxygen-rich alpha-case formation reaction between molten titanium and mold material. Base on the real production condition and moulding material, compound additive was added and the refractory was improved by means of bipeak grainsize distribution in this study. The final foundry method scheme was determined after a series of experiments, and the improvement effects were also evaluated.Bipeak grainsize distribution of zirconia particles in 47 and 10 micro scale were used in the paper for the zirconia particle has stable properties of CaO. Ludox was choosed to be the binder, which was popularly used in industrial application. And compound additive was 1 percent of total volume consisting of 30% PVA and 70% emulsion. Then all the raw materials were mixed together to make the shell with 40×20×6 (±0.5) mm. Next, the improved samples were contrasted with common technical samples(only one size distribution refractory and the slurry without compound additive)according to the surface morphology observation, bending strength test, drying rate, breathability, thermochemical stability and so on. The two optimized methods were combined to manufacture invested blade mould and then vacuum smelting and vacuum pouring were carried out. Finally, the casting improvement result should be analysed and assessed.According to the bending strength test, it could be indicated that:room temperature strength and residual strength of the shell can be improved by Bipeak grainsize distribution. Room temperature strength can be further improved while residual strength shall be decreased by the addition of compound additive. And the entirely drying time of sample could be shorten significantly because of the addition of compound additive. The breathability of shell is improved because of the diffuse tiny cavities due to super polymer ignition lost by baking. The surface of shell is smooth and compact, and the liquid titanium has higher thermochemistry stability owing to Bipeak grainsize distribution. After observation and analysis of castings:Castings macroscopic surface is smooth without obvious defects or haircuts. It is diverse for the degree of interface reaction in different area. The light color titanium-silicon compounds are the mainly reaction products distributing in the interface grain boundary, which mainly influenced by ludox of invested mould materials. A certain amount of oxygen element can be found in the contact interface between castings and mold shell without distinct "alpha layer". So it can be inferred that the oxygen atom is just in the interval titanium lattice instead and insufficient to form the "alpha layer", which is harmful to the casting properties. Therefore, the degree of interface reaction between titanium alloy and invested mould can be reduced effectively by Bipeak grainsize distribution and the addition of compound additive, consequently, the surface quality of casting and mold shell is enhanced.