An Advanced Perspective on Twin Growth and Slip in NiTi Huseyin - PowerPoint PPT Presentation

University of Illinois at Urbana Champaign An Advanced Perspective on Twin Growth and Slip in NiTi Huseyin Sehitoglu, Tawhid Ezaz, H.J.Maier Department of Mechanical Science & Engineering University of Illinois, Urbana University of Paderborn, Germany ICOMAT-2011, September 6, 2011 Funded by NSF- Division of Materials Research 1 ¡ 1 ¡

University of Illinois at Urbana Champaign Presentation Outline • Detwinning mechanism of Type II-1 twin in Martensitic NiTi • Compound twinning in Martensite (001), (201) (100) and Modes • Twinning in Austenite (112) and (114) Modes • Slip in B2 NiTi 2 ¡

University of Illinois at Urbana Champaign Fault Energy Measurement: Example with FCC b/2 b 1.5b 2b A A B C C A B B C FCC is the A A B C C A Simplest! B B C A A B C C A B B B A A A C C [111] C B B B A A Perfect fcc Unstable Stable γ Unstable Twin fault 2 layer twin [211] stacking fault UT γ is the energy us GPFE barrier to γ GSFE UT is linked to overcome γ us Dislocation during Twin Nucleation Nucleation γ mJ γ ( ) γ TM 2 m TM is the barrier γ to overcome 2 layertwin γ during Twin isf growth u u x x a ⎡ a ⎡ ⎤ ⎤ 211 211 ⎣ ⎦ ⎣ ⎦ 3 ¡ 6 6

University of Illinois at Urbana Champaign Detwinning and Twinning of NiTi Martensite Adapted from Ishida et al ., 2006 4 ¡

University of Illinois at Urbana Champaign Type II-1 twins Phenomenological Theory provides twinning plane to be irrational (0.7205 1 1) Experimentally evidence of rational (1 1 1) ledges and steps Liu, ¡Van ¡Humbeeck, ¡46, ¡1998, ¡Acta ¡Mat. ¡ 5 ¡ Xie,Liu,84,3497,2004, ¡Acta ¡Mat . ¡

University of Illinois at Urbana Champaign Fault Energy in Type II twin γ τ = π TM th b Ezaz -Sehitoglu., APL, 6 ¡ 2011

University of Illinois at Urbana Champaign Outline • Detwinning mechanism of Type II-1 twin in Martensitic NiTi • Compound twinning in Martensite (001), (100) and (201) • Twinning in Austenite, (112) and (114) • VASP-PAW-GGA • 9x9x9 k-point mesh with 273.2 eV energy cutoff. • Convergence assessed with increasing L

University of Illinois at Urbana Champaign (001) Compound Twin (001) Twin boundary (001) Twin boundary Twin formation due to glide of twinning partial a/2 [100] 8 ¡

University of Illinois at Urbana Champaign (001) Compound Twin-GSFE and GPFE Generalized planar fault energy (GPFE) Generalized stacking γ = 20 mJ m / 2 fault energy (GSFE) γ UT = 24mJ / m 2 us ! " mJ # ! " mJ # $ % $ % 2 & m ' 2 & m ' γ 2 TM = 7.6mJ / m u u a a x & x = a 2.884 A a[100] = [100]+ [100] a a 2 2 Ezaz, Sehitoglu, Acta. Mat, 2011 9 ¡

University of Illinois at Urbana Champaign (100) Compound Twin [ ] 100 Generalized stacking fault energy (GSFE) [ ] 001 [ ] 010 Ti ¡ Ni ¡ γ ⎛ ⎞ mJ ⎜ ⎟ 2 ⎝ m ⎠ Onda ¡et ¡al., ¡33,354,1992, ¡JIM, ¡ Mats. ¡Trans. ¡ No Metastable Position, u & = x c 4.66 A Barrier too high c 10 ¡

University of Illinois at Urbana Champaign Energy Barrier of (100) Twin Shear Direction ¡ a 3. [001] 9 γ ⎛ mJ ⎞ ⎜ ⎟ 2 ⎝ m ⎠ mJ γ = 41 TME 2 m Generalized 3 ¡layer ¡twin ¡aMer ¡ ¡only ¡shear ¡ 3 ¡layer ¡twin ¡aMer ¡shuffle ¡ planar fault B19 ’ ¡ following ¡shear ¡ energy [ ] 100 (GPFE) 0.46 ¡A ¡Shuffle ¡ 0.23 ¡A ¡Shuffle ¡ [ ] Ti ¡ Ni ¡ 001 u in ¡Ti ¡ in ¡Ni ¡ x [ ] 010 c c [ ] = c 001 13.5 M 11 ¡

University of Illinois at Urbana Champaign Two different Twin growth mechanism Matrix Aided by Ledge Ledge twinning partial Fault Energy Twin (001] Matrix [100] a a → + a [100] [100] [100] 2 2 Displacement Shear No twinning Fault Energy partial, combined shear Without shuffle and shuffle Shuffle With shuffle (100] [001] Displacement Displacement

University of Illinois at Urbana Champaign Compound Twin (201) [201] [102] Fault Energy (mJ/m 2 ) (201) Generalized Stacking Fault Energy (GSFE) u x | 102 |

University of Illinois at Urbana Champaign Energy Barrier of Twin (201) 4 layer twin 0,1 1,1 1 st Energy 2 nd Energy Barrier Barrier Fault Energy (mJ/m 2 ) Metastable position Shuffle. h 2 nd Energy Barrier Metastable position 1 st Energy Barrier 0,0 0.5,1 0.5,0 3 layer twin Reaction path along MEP Shear, e Gives the exact coupling of Shear and shuffle Computationally extensive! 14 ¡

University of Illinois at Urbana Champaign (001), (100), Compound Twins (201) Twin Migration Energy g TM (mJ/m 2 ) (001)[100] (100)[001 ] (201)[102] u x /b 3 layer 4 layer 5 layer Ishida et al., 2005 Twin Twin Twin ( ) { } η 1 K 1 τ = π γ ( τ shear ) ideal = δγ / b (MPa) TMideal TM twin (MPa) δ u x max Twin growth stress is proportional to the twin (001) [100] 277 165 migration energy (100) [001] 4530 1790 107060 3900 (201) [102] 15 ¡

University of Illinois at Urbana Champaign Digital Image Correlation Results displaying Multiple Twin Modes During Deformation of Martensite 16 ¡

University of Illinois at Urbana Champaign Outline • Introduction to NiTi – Applications – Shape Memory Behavior • Detwinning mechanism of Type II twin in Martensitic NiTi • Compound twinning in Martensite (001), (100) and (201) • Twinning in Austenite, (112) and (114)

University of Illinois at Urbana Champaign (112) and (114) Twin in Austenite (112) And (114) are the mostly observed twin systems (114) Twin (112) Twin Nishida et al., 2003 18 ¡

University of Illinois at Urbana Champaign (112) Pseudotwinning in B2 NiTi No metastable position, and 4 b 3 b labeled as ‘ impossible ’ . γ ⎛ ⎞ mJ ⎜ ⎟ 2 ⎝ m ⎠ u x ⎡ ⎤ 211 a ⎣ ⎦ [ ] 111 6 1 Shear ¡Magnitude ¡ s = Ni – In Plane ¡ Ni – Out of Plane ¡ 2 [ ] [ ] 111 = Ti – In Plane ¡ b a / 6 111 Shear ¡Direc0on ¡ Ti – Out of Plane ¡

University of Illinois at Urbana Champaign Coupled shear and shuffle mechanism during (112) twin growth s Ortho structure ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ¡ ⎡ ⎤ 211 ⎣ ⎦ Application of only 4 layer twin 5 layer twin shear [ ] 111 a 1 [ ] b = s = 1 1 1 6 2

University of Illinois at Urbana Champaign PES and MEP of (112) Twin 5 layer Twin Pseudotwin 4 layer Twin γ ⎛ mJ ⎞ ⎜ ⎟ 2 ⎝ m ⎠ 4 layer 5 layer Twin Reaction coordinate along MEP Twin

University of Illinois at Urbana Champaign (114) Deformation Twin (B2)- The ‘elusive’ one

University of Illinois at Urbana Champaign Different Shuffle Possibilities

University of Illinois at Urbana Champaign PES and MEP in (114) twinning Fault Energy (mJ/m 2 ) Normalized displacement u / a | 221 | x Fault Energy (mJ/m 2 ) • No Energy well at = b a /18[221] • Twinning combines shear and shuffle. • Barrier energy of 148 mJ/m 2 Reaction Coordinate along MEP

University of Illinois at Urbana Champaign Sharp Boundaries Further Lower the Energy Barriers ! 25 ¡

University of Illinois at Urbana Champaign Presentation Outline • Detwinning mechanism of Type II-1 twin in Martensitic NiTi • Compound twinning in Martensite (001), (201) (100) and Modes • Twinning in Austenite (112) and (114) Modes • Slip in B2 NiTi 26 ¡

University of Illinois at Urbana Champaign Consequence of Slip in Shape Memory 27 ¡

University of Illinois at Urbana Champaign Slip Systems in B2 NiTi (011)[100] (011)[111] γ ⎛ mJ ⎞ ⎜ ⎟ ⎝ 2 ⎠ m u a [100] u a [111] x x Not presented in early work, lower barrier energy in Most observed slip system in B2 NiTi, Chumlyakov, 2004, Norfleet et al., 2010, Delville et al. , 2010 (1-11) direction

University of Illinois at Urbana Champaign Experimental observation of novel [111](011) system systems (011)[100] (011)[111]

University of Illinois at Urbana Champaign Summary of Slip Systems Slip Slip δγ τ = ( ) (MPa) shear ideal Plane Direction δ u x max (011) [100] 1034 (011) 726 [111] [111] 7430 ( 211 ) (100) [010] 9320 30 ¡

University of Illinois at Urbana Champaign Summary 31 ¡

University of Illinois at Urbana Champaign Conclusions • Twinning is favored over slip in the case B19 ’ martensite (a key reason why shape memory works). • Shuffles play a significant role in Type II-1, (100), (201) twinning in martensite. • (112) and (114) twinning in B2 NiTi has to overcome much lower barrier with shear and shuffle with comparable • [111](011) slip has been shown to be significant in B2 NiTi along with [100](011) slip both with experiments and simulations. 32 ¡

University of Illinois at Urbana Champaign Thank You 33 ¡