Innovative refractory and induction melting systems for titanium and titanium alloys

• Applicants: Professor Dr.-Ing. Christos G. Aneziris; Professor Dr.-Ing. Bernd Friedrich
• Subject Area: Glass, Ceramics and Derived Composites ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275028606

Vacuum induction melting (VIM) is a powerful technology allowing an efficient pyrometallurgical production, recycling as well as casting of titanium materials. The main limitation for vacuum induction melting of titanium materials is the corrosion of the used refractories, because due to their high oxygen affinity titanium based melts are extremely aggressive. Moreover, the gas atmosphere, thermomechanical stresses and the alloy composition have an important influence on the wear of the refractories. Based on the cooperation of the first phase of the DFG Research Unit 1372, the aim of this project is to investigate the melting of titanium and titanium alloys in calcium zirconate based refractories in order to allow a transfer into the industrial practice of the casting industry. Furthermore, the development of vibration and self flowing castables for large VIM furnaces combined with metallurgical process adaptions will allow the pyrometallurgical recycling and primary production of titanium materials. For that purpose the application partners provide their expertise and services regarding casting technology (Indutherm), the production and application of vibration and self flowing castables (Refratechnik) as well as the smelting of reactive and refractory metals in large VIM furnaces (VACUUMSCHMELZE). In laboratory melting experiments (0,5 - 1 l) conditions and process windows will be investigated especially to minimize the oxygen contamination of the melts and to achieve standard titanium qualities. Thereby, a special focus is Ti6Al4V and the influence of alloying elements such as aluminum, vanadium, and tin on the refractory corrosion. For that purpose the melting temperature and time as well as the super heating temperature and deoxidizing effect of additives will be investigated. For the first time an excess inert gas pressure will be applied to reduce the calcium evaporation from the refractories and from the melt, because it is known that calcium containing refractory materials tend to evaporate causing a fast oxygen pickup and hence contamination of the melt. These metallurgical investigations are of high interest for both casting as well as for the recycling of titanium materials. An important requirement for the technical feasibility of a recycling process of titanium materials by vacuum induction melting is a sufficient large size of the melting furnace. So far all promising alternative methods to produce titanium materials such as the electrochemical reduction (FFC process) failed on a large scale production. Therefore, scale up experiments in 14 l crucibles will finally investigate conditions to melt titanium materials in refractory crucibles without exceeding relevant contamination levels.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: INDUTHERM Erwärmungsanlagen GmbH; Refratechnik Steel GmbH