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Topics. motivation microstructures - deformation - recrystallization textures - deformation - recrystallization recrystallization kinetics texture simulations conclusions. Al. Fe. FeAl. Intermetallic compound with B2-structure low-cost raw material low density

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  1. Topics • motivation • microstructures • - deformation • - recrystallization • textures • - deformation • - recrystallization • recrystallization kinetics • texture simulations • conclusions Al Fe

  2. FeAl • Intermetallic compound with B2-structure • low-cost raw material • low density • high electrical resistance • heating elements • high corrosion and sulfidation resistance • high-temperature coating material • poor ductility at low temperatures • low strength at high temperatures > 600°C • limitations in applications To eliminate these disadvantages previous research was focussed on the influence of ternary alloying elements, oxide dispersions, hydrogen embrittlement and grain structure.

  3. Anisotropy, Fe-40Al 290 GPa [111] [100] 93 GPa [110] 190 GPa elastic modulus yield stress elastic and plastic behaviour of these materials is quite anisotropic  Texture is of major concern !

  4. Fe-Al

  5. Extrusion reduce the friction: Ingots (25 mm diameter, 35mm length) were put in a copper can with 2.5 mm wall thickness and a final diameter of 30mm. Text = 850 - 1300°C Round die: Ø 30 mm  13 mm Rectangular die: Ø 30 mm  7 mm x 13 mm vstem = 6 mm/s extruded samples were air cooled To study recrystallization and grain growth the samples were annealed for certain times in air at different temperatures and air-cooled.

  6. Extrusion microstructure Fe-10Al Fe-35Al Fe-50Al 1300°C, X = 95% 1300°C, X = 50% 1150°C, X = 99% 1000°C, X = 0 - 5% 1000°C, X = 15 - 40% 1000°C, X = 20% 200 µm extrusion direction

  7. Microstructure inhomogeneity Fe-35Al extruded at 1000°C extrusion direction 500 µm

  8. Grain size - composition 1300°C 1300°C 1150°C recryst. grain size 1000°C subgrain size

  9. Extrusion texture (round die) 1300°C 1300°C 1150°C max = 2.0 max = 7.2 max = 3.6 1000°C 1000°C 1000°C max = 7.7 max = 6.4 max = 5.3 900°C 850°C max = 6.0 max = 4.7 Fe-10Al Fe-35Al Fe-50Al

  10. Microstructure development Fe-10Al Fe-35Al Fe-50Al 1000°C 830°C 670°C 100 mm 100 mm after extrusion at 1000°C extrusion direction after annealing for 4 h normal and abnormal grain growth takes place simultaneously

  11. Microstructure of Fe-35Al after 16h annealing cross section longitudinal section 200 µm 500 µm • elongated grains • high degree of recrystallization • grain growth (normal and abnormal)

  12. EBSD, Fe-50Al, 1000°C 1000°C max = 5.3 [111] [111] [110] [110] [110] [110] [111] [100] [110] [111] [100] [110] [111] 400 µm [110] [100]

  13. Recrystallization texture (round die) Fe-10Al Fe-35Al Fe-50Al max 7.7 max 6.4 max 5.3 max 3.8 max 2.3 max 1.9 max 2.6 max 2.8 max 2.4 global texture after extrusion at 1000°C fraction dynamically recrystallized (EBSD) fraction statically recrystallized (EBSD) 1000°C 830°C 670°C

  14. Recrystallization kinetics The recrystallization kinetics is roughly characterized by a sigmoidal curve.

  15. Avrami plot Avrami exponent: n  1

  16. Recrystallization temperature recrystallization temperature [°C] aluminum [at.%]

  17. Grain growth d  tn normal grain growth (gg): n = 0.08 - 0.34 abnormal grain growth (agg): n = 0.31 - 0.43

  18. Extrusion texture (rectangular die) Fe-10Al Fe-35Al Fe-50Al 1000°C 1000°C 1000°C max = 6 max = 11 max = 6 Typical plane strain textures for body centered metals are a partial coverage of the a-fiber and a g-fiber texture.

  19. Slip systems A2 B2 approximate areas of slip system activity

  20. Homogeneous deformation Von Mises (1928): Homogeneous plastic deformation of a polycrystal requires 5 independent slip systems. Intermetallic compounds with B2 structure independent 3 2 5 Slip system {110} <100> {110} <110> {110} <111> equivalent 6 6 12

  21. Texture simulations • Taylor theory • Full constraints (FC) 5 independent slip systems • (Taylor, 1938) • Relaxed constraints (RC) • (Kocks & Canova, 1981; van Houtte, 1988) • RC1 (long grain): xz relaxed  4 independent slip systems • RC2 (flat grain): xz and yz relaxed  3 independent slip systems

  22. Extrusion (rectangular die) experiment, 1000°C Fe-35Al Fe-50Al Fe-10Al max = 11 max = 6 max = 6 simulation, RC2 Taylor <111> <100>/<110> = 1/1 max = 13 max = 17

  23. Curling [011] - fibre texture [011] - fibre texture  (tension) [011] [011] [100] sample grain fibre axis axisymmetric tension plane strain deformation „curling“ (compatibility)

  24. Extrusion (round die) max = 7.7 max = 6.4 max = 5.3 experiment, 1000°C Fe-10Al Fe-35Al Fe-50Al simulation, RC (curling) Taylor <111> <100>/<110> = 1/1 max = 11 max = 5.8

  25. Conclusions • Extrusion of Fe-Al alloys leads to specific deformation textures: • increase of Al content • Tension: • <110> fibre <100> + <110> double fibre • Plane strain • a + g fibre  g fibre • Dynamic and static recrystallization produces new weak texture components • <110>  <102> <114>  <111> <112> • Microstructure and texture depend on degree of order and deviation from • stoichiometry • Deformation textures can be simulated with the relaxed constraints Taylor model

  26. Thank you for your attention !

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