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

A. Yu. Kachalov, Postgraduate Student at the Department of Casting and Materials Working, e-mail: kachalov.ltm@mail.ru
V. D. Belov, Head of the Department of Casting and Materials Working, e-mail: vdbelov@mail.ru
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.

1. Demenok A. O., Ganeev A. A., Demenok O. B. et al. Developing a resource saving technology for producing large castings out of titanium alloys. Vestnik YuUrGU. Seriya "Metallurgiya". 2015. Vol. 15, No. 2. pp. 20–25.
2. Bakerin S. V., Demenok O. B., Mukhamadeev I. R., Demenok A. O. Manufacturing of shell moulds for large precision titanium castings. Metallurgy and latest developments in casting, forming and heat treatment of light alloys: Conference proceedings. Moscow : Vserossiyskiy nauchno-issledovatelskiy institut aviatsionnykh materialov, 2016. 29 p.
3. Koldaev A. B., Yasinskiy K. K., Buttsev B. I. Analysing the surface gassaturated layers of VT5L titanium alloy castings cast in a variety of moulds. Nauchno-tekhnicheskiy sbornik. Voprosy aviatsionnoy nauki i tekhniki. 1989. No. 3. pp. 51–58.
4. Si-Young Sung, Young-Jig Kim. Alpha-case formation mechanism on titanium investment castings. Materials Science and Engineering: A. 2005. Vol. 405, Iss. 1-2. pp. 173–177.
5. Koike M., Cai Z., Fujii H., Rezner M., Okabe T. Corrosion behavior of cast titanium with reduced surface reaction layer made by a face-coating method. Biomaterials. 2003. Vol. 24, Iss. 25. pp. 4541–4549.
6. Smeacetto F., Salvo M., Ferraris M. Protective coatings for induction casting of titanium. Surface & Coatings Technology. 2007. Vol. 201, Iss. 24. pp. 9541–9548.
7. Belov V. D., Fadeev A. V., Ivashchenko A. I., Beltyukova S. O. Vacuum melting and casting: Vacuum melting and production of shaped castings from titanium and titanium alloys. Moscow : MISiS. 2013.
8. Mukhamadeev I. R., Demenok O. B., Ganeev A. A., Pavlinich S. P., Alikin P. V. Selecting water-based binders for shell moulds used in investment casting of titanium alloys. Vestnik YuUrGU. Seriya "Metallurgiya". 2015. Vol. 15, No. 3. pp. 95–104.
9. Si-Young Sung, Bong-Jae Choi, Young-Jig Kim. Alpha-Case Controlled Titanium Alloys Casting. Ti-2007 Science and Technology. 2007. Vol. 2. Pres. 74.
10. Xu Cheng, Lianjing Chai, Guoqing Wu, Hong Wang, Hai Nan. Evaluation of interfacial interactions between Ti – 6Al – 4V and mold use Ti-added backup coat in investment casting. The Minerals, Metals & Materials Society and ASM International. 2016. Vol. 47, No. 5. pp. 2313–2318.
11. Chonghe Li, Mingyang Li, Hao Zhang, Wajid Ali, Ziwei Qin, Hongbin Wang, Xionggang Lu. Fabrication of Y₂O₃ doped BaZrO₃ coating on Al₂O₃ applied to solidification of titanium alloy. Surface & Coatings Technology. Elsevier Science Publishing Company, Inc. 2017. Vol. 320. pp. 146–152.
12. Chonghe Li, Jin He, Chao Wei, Hongbin Wang, Xionggang Lu. Solidification and interface reaction of titanium alloys in the BaZrO₃ shell-mould. Materials Science Forum. Trans Tech Publications Ltd. 2015. Vol. 828–829. pp. 106–111.
13. Varfolomeev M. S., Moiseev V. S., Shcherbakova G. I. Highly heat resistant moulds designed for shaped castings made of titanium alloys. Izvestiya vysshikh uchebnykh zavedeniy. Tsvetnaya metallurgiya. 2016. No. 6. pp. 49–54.
14. Pei-Ling Lai, Wen-Cheng Chen, Jen–Chyan Wang, Ta-Ko Huang, Chun-Cheng Hung. A newly developed calcia/titanium modified magnesiabased investment mold for titanium casting. Materials Science and Engineering: C. 2011. Vol. 31, Iss. 2. pp. 144–150.
15. Ganeev A. A., Demenok A. O., Bakerin S. V., Kulakov B. A., Mukhamadeev I. R., Garipov A. R. Analysis of the physico-chemical interaction between titanium alloys and mould materials. Vestnik YuUrGU. Seriya "Metallurgiya". 2016. Vol. 16, No. 3. pp. 70–78.
16. Saha R. L., Jacob K. T. Casting of Titanium and its Alloys. Defence Science 3. 1986. Vol. 36, No. 2. pp. 121–141.
17. Limin Jia, Daming Xu, Min Li, Jingjie Guo , Hengzhi Fu. Casting Defects of Ti – 6Al – 4V Alloy in Vertical Centrifugal Casting Processes with Graphite Molds. Metals and Materials International. 2012. Vol. 18, No. 1. pp. 55–61.
18. Wu Shi Ping, Liu Dong Rong, Guo Jing Jie, Li Chang Yun, Su Yan Qing, Fu Heng Zhi. Numerical simulation of microstructure evolution of Ti – 6Al – 4V alloy in vertical centrifugal casting. Materials Science and Engineering: A. 2006. Vol. 426, Iss. 1-2. pp. 240–249.
19. Myoung-Gyun Kim, Shae. K. Kim and Young-Jig Kim. Effect of Mold Material and Binder on Metal-Mold Interfacial Reaction for Investment Castings of Titanium Alloys. Materials Transactions. 2002. Vol. 43, No. 4. pp. 745–750.
20. Barbosa J., Caetano Monteiro A., Silva Ribeiro C. Controlled Residual Surface Contamination of -TiAl, Induction Melted in Ceramic Crucibles. European Congress on Advanced Materials, Processes and Applications — Materials Week 2001. 2001. pp. 100–108.
21. Illarionov A. G., Popov A. A. Processability and performance of titanium alloys: Learner’s guide. Ed. by S. L. Demakov. Yekaterinburg : Izdatelstvo Uralskogo universiteta, 2014. 137 p.

22. Belov V. D., Kachalov A. Yu., Pavlinich S. P., Alikin P. V. Understanding the effect of the casting parameters on the surface roughness of large thinwalled investment castings made of the titanium alloy VT20L. Liteyshchik Rossii. 2016. No. 7. pp. 10–16.
23. Karwiski A., Leniewski W., Pysz S., Wieliczko P. The technology of precision casting of titanium alloys by centrifugal process. Archives of foundry engineering. 2011. Vol. 11, No. 3. pp. 73–80.
24. TU 48-4802-86–97. Shaped castings made of different grades of graphite. Introduced: 13.07.1997.
25. TU 1915-086-00200851–2007. Shaped castings made of different grades of graphite. Introduced by Niigrafit, Moscow.
26. TU 1-92-184–91. Titanium casting alloys. Grades. Introduced: 01.01.1992.
27. GOST 9454–78. Metals. Method for testing the impact strength at low, room and high temperature. Introduced: 01.01.1979.
28. GOST 1497–84. Metals. Methods of tension test. Introduced: 01.01.1986.
29. Kopeliovich B. A. High-temperature gas-static treatment as a new technology for enhanced quality and properties of parts. Tekhnologiya legkikh splavov. 1990. No. 2. pp. 5–9.
30. Kamenskaya N. I., Nochovnaya N. A., Zvereva M. I. Investigating the structure and properties of the casting alloy VT20L based on the concentration of impurities. Electronic papers of the Russian National Conference „Student Research Spring 2016 : Technology of Mechanical Engineering“. Moscow : 5–8 April 2016.