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ArticleName Understanding the effect of the mould material on the quality of investment titanium alloy castings
DOI 10.17580/tsm.2019.06.12
ArticleAuthor Kachalov A. Yu., Belov V. D., Bazhenov V. E., Fadeev A. V.

National University of Science and Technology MISiS, Moscow, Russia:

A. Yu. Kachalov, Postgraduate Student at the Department of Casting and Materials Working, e-mail:
V. D. Belov, Head of the Department of Casting and Materials Working, e-mail:
V. E. Bazhenov, Assistant prof. at the Department of Casting and Materials Working
A. V. Fadeev, Process Engineer at the Department of Casting and Materials Working


Because titanium alloys have a high chemical activity, their interaction with the material of the mould results in an alpha case forming on the surface of castings. The alpha case is quite hard, and it makes the casting surface brittle affecting performance. To minimize the alpha case, moulds made of more inert materials (such as oxide ceramics) are currently used in titanium alloy casting. Pressed graphite blocks can be used to make casting moulds designed for large thin-walled titanium alloy castings. Compared with other materials, the above contain a small amount of binders. Moreover, carbon materials are most inert to titanium alloys. Due to high heat conductivity of the material, it quickly solidifies thus shortening the interaction time between the melt and the mould. Graphite is machined on multiaxis CNC machines. Thus mould components are manufactured, which are then assembled into a mould. Thanks to such approach, castings of almost any shape can be produced. One knows from literature that the machined surfaces of graphite have low roughness, comparable to that in ceramic moulds. High quality surfaces help make the metal-mould interfacial reaction less intense. The authors analysed the surface layer of a pilot casting, which was an inner casing. Those areas were analysed that saw different amounts of the melt go through them. Those surface areas had different roughness, which should presumably indicate the degree of the melt/mould interaction. It is shown that regardless of the location of the area in view there is no alpha case present. The mechanical properties and the chemical composition of the pilot titanium casting were also studied. The resultant alloy is not contaminated with the mould material and fully complies with the TU 1-92-184–91 standard in terms of its chemical composition. No stress points were found in the casting, and it has good mechanical properties.

keywords Investment casting, graphite mould, casting of titanium alloys, alpha case, surface roughness

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