Production of -TiAl-Ingots by Aluminothermic Reduction of TiO 2 and Refining by ESR

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1 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

10 10 9 7 5 3 1 steel copper zinc magnesium

titanium path nickel aim silver -TiAl gold

2 Position of TiAl in the Material World Weltproduktion / m³/a world prduction steel copper zinc magnesium PVC, PP, PE aluminium, ABS polycarbonate titanium path nickel aim silver -TiAl gold price Preis / US-$/kg

3 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

4 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

5 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

6 ATR Reaction Front Fundamentals II Critical Moment Reaction Phase 2 dust offgas, hot dust slag offgas, hot reaction front collapses pressure increase reaction front

7 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

8 ATR Process Model Thermochemical Model Target: Calculation of the thermochemical equilibria and theoretical (adiabatic) process temperature FactSage (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)

9 ATR Ti-Al-Nb-System Metal Phase At.-% Ti, Al At.-% Nb, O At.-% Nb, target Ti Al Nb O 0

10 ATR Ti-Al-Nb-System Slag Phase 6 0,12 5 0,10 At.-% Ca, Ti ,08 0,06 0,04 At.-% Nb 1 0, 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

11 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!

12 Direct Aluminothermic Electrode Production II sample: 5.5 kg Ti-45Al-10Nb electrode sample: 60 kg Ti-45Al-10Nb electrode theoretical adiabatic process temperature: C (5.5 kg electrode) theoretical process temperature: C very good accordance! measured process temperature: C

13 Principle of Electro Slag Remelting (ESR) electrode power cable current circuit Cu mould slag skin slag pool metal pool V ~ 0,5-50 ka ingot air gap base plate

14 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 FactSage Databases: FACT 5.3, SGTE, 9329-Al-Nb-Ti, CaO-Ca-CaF 2 -slag Ca [wt.-%] CaO [wt.-%] O [ppm]

TiAl-Desoxidation during PESR Process First experiment: Desoxidation (16 000 <500 ppm) increases slag height

melting rate necessary to increase slag temperature and decrease slag skin thickness.

15 TiAl-Desoxidation during PESR Process First experiment: Desoxidation ( <500 ppm) increases slag height drastically ( 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

16 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

17 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

18 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

Non-Ferrous-Metallurgy in Aachen -Short Department Presentation B. Friedrich

Non-Ferrous-Metallurgy in Aachen -Short Department Presentation B. Friedrich IME Process Metallurgy and Metal, RWTH Aachen University Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich Our business education in non-ferrous