EMC 2005 September 18 th -21 th, Dresden Production of -TiAl-Ingots by Aluminothermic Reduction of TiO 2 and Refining by ESR Stoephasius, Jan-Christoph; Friedrich, Bernd; IME Process Metallurgy and Metal Recycling RWTH Aachen University, Germany Prof. Dr.-Ing. Bernd Friedrich
Position of TiAl in the Material World Weltproduktion / m³/a world prduction 10 10 10 10 9 7 5 3 1 steel copper zinc magnesium PVC, PP, PE aluminium, ABS polycarbonate titanium path nickel aim silver -TiAl gold 10 10 10 10 10 10 10 10-1 0 1 2 3 4 5 price Preis / US-$/kg
Conventional Route for TiAl-Alloy Production electrolysis granulation Kroll crushing ATR VIM aluminium titanium crushing prime-electrode welding compacting masteralloys VAR 1 VAR 2 VAR 3 ingots
Alternative Production of TiAl-Alloys electrolysis chipping aluminium TiO 2 Me x O y Advantage: significantly reduced process steps, few mechanical work necessary, reduced energy consumption, higher metal yield, strongly reduced investion costs. ATR-in-line-casting ingots VAR? PESR prime-electrode
ATR Reaction Front Fundamentals I Reaction Start ignition mixture Reaction Phase 1 offgas, cooled down offgas, hot offgas, cooled down TiO 2 + Me x O y + Al + agents + booster reaction front reactor
ATR Reaction Front Fundamentals II Critical Moment Reaction Phase 2 dust offgas, hot dust slag offgas, hot reaction front collapses pressure increase reaction front
ATR Reaction Front Experimental phase 1: u = 3,2 mm / s m = 3,7 kg / m²s phase 2: u = 7,5 mm / s m = 8,7 kg / m²s
ATR Process Model Thermochemical Model Target: Calculation of the thermochemical equilibria and theoretical (adiabatic) process temperature FactSage 5.3.1 (GTT Technologies, Herzogenrath, Germany) Databases: FACT 5.3, FToxid, 9329-Al-Nb-Ti Composition Model Target: Calculation of the reaction mixture from independent parameters (composition, total mass, energy density) MeTeCalc 1.0a (not yet commercial available) Heat Transfer Model Target: Calculation of the energy losses by radiation and heat conduction EpiTherm 1.0a (not yet commercial available)
ATR Ti-Al-Nb-System Metal Phase 60 12 50 10 At.-% Ti, Al 40 30 20 8 6 4 At.-% Nb, O 10 2 0 0 2 4 6 8 10 At.-% Nb, target Ti Al Nb O 0
ATR Ti-Al-Nb-System Slag Phase 6 0,12 5 0,10 At.-% Ca, Ti 4 3 2 0,08 0,06 0,04 At.-% Nb 1 0,02 0 0 2 4 6 8 10 At.-% Nb, target Ca Ti Nb 0,00
Direct Aluminothermic Electrode Production I process flow: filling of the mould with argon ignition of the aluminothermic reaction in the reactor melting of an aluminium sheet between reactor and mould filling of the mould with the metal alloy measuring of the process temperature with IR two colour quotient pyrometer removing of the electrode from the mould after cooling down small scale reactor No crushing, compacting and welding is necessary for electrode production!
Direct Aluminothermic Electrode Production II sample: 5.5 kg Ti-45Al-10Nb electrode sample: 60 kg Ti-45Al-10Nb electrode theoretical adiabatic process temperature: 2 040 C (5.5 kg electrode) theoretical process temperature: 1 930 C very good accordance! measured process temperature: 1 920 C
Principle of Electro Slag Remelting (ESR) electrode power cable current circuit Cu mould slag skin slag pool metal pool 30-45 V ~ 0,5-50 ka ingot air gap base plate
TiAl-Desoxidation during PESR Process PESR-slag: CaF 2 (Wacker S 2052) and small amounts of pure Ca. Refining Reaction (simplified) [O] TiAl [Ca] [CaO] CaF 2 CaF 2 Thermochemical Model 2.000 FactSage 5.3.1 1.800 1.600 Databases: FACT 5.3, SGTE, 9329-Al-Nb-Ti, CaO-Ca-CaF 2 -slag Ca [wt.-%] 0 5 10 0 5 10 15 20 CaO [wt.-%] 25 30 1.400 1.200 1.000 800 600 400 200 0 O [ppm]
TiAl-Desoxidation during PESR Process First experiment: Desoxidation (16 000 <500 ppm) increases slag height drastically (80 220 mm) Very thick slag skin (3 mm instead of 1 mm) leads to very poor surface quality Higher melting rate necessary to increase slag temperature and decrease slag skin thickness. PESR furnace is actually modified: 4,2 6 ka new process controll unit improvement of electrode feed motor Ingot is actually analysed
Conclusions and Further Outlook Conclusions: The in-line-production of TiAl-electrodes combined with the aluminothermic reaction is feasible. The Co-reduction of Nb 2 O 5 is possible and leads to better mechanical properties of the electrode. A reaction model of the PESR-process was made. It shows that reducing the oxygen content in metal below 500 ppm is possible. A first remelting experiment of a Ti-45Al-10Nb-electrode was successfully conducted. Next steps: replacing of TiO 2 -pigment by a high grade rutile optimizing of the sampling and analysing technology (new equipment) optimizing of the PESR-furnace due to the increased demands of TiAlremelting introduction of an online-ca-measurement system for the slag
EMC 2005 September 18 th -21 th, Dresden Thank you for your attention We like to acknowledge the AiF, DFG and BMBF for support of our research in metallothermy and electroslag technology. IME Process Metallurgy and Metal Recycling RWTH Aachen University, Germany Prof. Dr.-Ing. Bernd Friedrich
IME ESR-/ PESR Furnace electrode dimensions: max. 110 x 1340 mm moulds: mid = 90, 160, 200 mm remelting current: max. 4,2 ka ~, 50 Hz, max. 65 V working pressure PESR: pressure: max. 50 bar vacuum: < 10 mbar PESR ESR