Phase Transformations Interface s ByeongJoo Lee POSTECH MSE

Phase Transformations Interface s Byeong-Joo Lee POSTECH - MSE calphad@postech. ac. kr Byeong-Joo Lee cmse. postech. ac. kr

Scope Fundamentals 1. 2. 3. 4. Free Surfaces vs. Grain Boundaries vs. Interphase Interfaces Concept of Surface Energy/Surface Tension Origin of Surface Energy and its Anisotropy Grain Boundary/Interfacial Energy Interface Phenomena 1. Curvature Effect 2. Multi-component system • Segregation 3. General • Grain Growth • Morphological Evolution 4. Interface Engineering Byeong-Joo Lee cmse. postech. ac. kr

Surfaces Byeong-Joo Lee cmse. postech. ac. kr

Concept of Surface Energy and Surface Tension for liquid film Generally, Byeong-Joo Lee cmse. postech. ac. kr

Estimation of Solid Surface Energy - Origin of Surface Energy Pair approximation Necessary Work for Creation of (111) surface in fcc (/atom) For fcc (111): N/A = 4/(31/2 a 2) fcc (100): N/A = 2/a 2 For Cu: a = 3. 615 Å △Hs =337. 7 J/mol γ(111) = 2460 erg/cm 2 (1700 by expt. ) For fcc ※ Origin of Anisotropy Byeong-Joo Lee cmse. postech. ac. kr

Estimation of Solid Surface Energy - Orientation dependence High Index Surface Energy Comparisons 1. W. R. Tyson and W. A. Miller, Surf. Sci. 62, 267 (1977). 2. L. Z. Mezey and J. Giber, Jpn. J. Appl. Phys. , Part 1 21, 1569 (1982). Byeong-Joo Lee cmse. postech. ac. kr

Equilibrium shape of a Crystal - Wulff construction Byeong-Joo Lee cmse. postech. ac. kr

Equilibrium shape of a Crystal - Numerical Example Byeong-Joo Lee cmse. postech. ac. kr

Note - Estimation of Surface Energy J. Park, J. Lee, Computer Coupling of Phase Diagrams and Thermochemistry 32 (2008) 135– 141 Byeong-Joo Lee cmse. postech. ac. kr

Atomistic Computation of Surface Energy Grain Boundary / Interface Byeong-Joo Lee cmse. postech. ac. kr

Grain Boundaries Byeong-Joo Lee cmse. postech. ac. kr

Grain boundaries in Solids - Misorientation vs. Inclination Byeong-Joo Lee cmse. postech. ac. kr

Grain boundaries in Solids - tilt vs. twist boundaries Byeong-Joo Lee cmse. postech. ac. kr

[100] Twist Boundary Structure in pure Cu 3 o 15 o 4 o 20 o 7 o 30 o 10 o 45 o Byeong-Joo Lee cmse. postech. ac. kr

[100] Twist Grain Boundary Energy of Copper Byeong-Joo Lee cmse. postech. ac. kr

Special High-Angle Grain Boundaries Byeong-Joo Lee cmse. postech. ac. kr

Special High-Angle Grain Boundaries · Incoherent boundary energy is insensitive to orientation. ※ Special boundaries with low energy [100] and [110] tilt Boundary energy of Al Byeong-Joo Lee cmse. postech. ac. kr

Equilibrium Microstructure - balance of GB tensions θ Byeong-Joo Lee cmse. postech. ac. kr

Normal Grain Growth - the mechanism Byeong-Joo Lee cmse. postech. ac. kr

Effect of particles on Grain Growth - Zener pinning effect Consider the balance between the dragging force (per unit area) and the pressure from the curvature effect • dragging force due to one particle of size r • number of ptl. per unit area of thickness 2 r ⇒ drive it ! • • total dragging force per unit area Maximum grain size Byeong-Joo Lee cmse. postech. ac. kr

Interphase Interfaces Byeong-Joo Lee cmse. postech. ac. kr

Interfaces in Solids – Coherent, Semi-Coherent & Incoherent Interfaces Byeong-Joo Lee cmse. postech. ac. kr

Interfaces in Solids – Shape of Coherent Second-Phase from Y. S. Yoo KIMS ※ Equilibrium Shape Byeong-Joo Lee cmse. postech. ac. kr

Strain Energy vs. Interfacial Energy - Mechanism of particle splitting Phase Field Method Simulation by P. R. Cha, KMU γ’ precipitates of Ni-Al alloy system, D. Y. Yoon et al. Metals and Materials Byeong-Joo Lee cmse. postech. ac. kr

Morphological Evolution - from Y. S. Yoo, KIMS Byeong-Joo Lee cmse. postech. ac. kr

Interfaces Phenomena Byeong-Joo Lee cmse. postech. ac. kr

Question Interfacial Phenomena (Interface or Surface Segregation) Thermodynamics of Surface or Grain Boundary Segregation 1. M. Guttmann, Surf. Sci. , 53 (1975) 213 -227; Metall. Trans. A, 8 A (1977) 1383 -1401. 2. T. Tanaka and T. Iida, Steel Research, 65, 21 -28 (1994). Byeong-Joo Lee cmse. postech. ac. kr

Interfacial Phenomena – Segregation (Guttmann) Assume a one atomic layer surface phase and consider equilibrium between bulk and surface where ωi is the molar surface area Assume ωi = ωj = … = ω Byeong-Joo Lee cmse. postech. ac. kr

Interfacial Phenomena – Segregation (Physical Meaning of Quantities) Byeong-Joo Lee cmse. postech. ac. kr

Interfacial Phenomena – Segregation (Butler/Tanaka) Byeong-Joo Lee cmse. postech. ac. kr

Thermodynamic Calculation of Surface Tension of Liquid Alloys on the Web-board of this Lecture Byeong-Joo Lee cmse. postech. ac. kr

Thermodynamic Calculation of Surface Segregation in Solid Alloys Byeong-Joo Lee cmse. postech. ac. kr

Key Point Surface/Interface Energy of Crystalline Solids is Anisotropic Byeong-Joo Lee cmse. postech. ac. kr

An issue for thinking - Surface Transition and Alloying Effect Pure W W + 0. 4 wt% Ni Vaccum Annealing Byeong-Joo Lee cmse. postech. ac. kr

Abnormal Grain Growth – Mechanism ? Byeong-Joo Lee cmse. postech. ac. kr

Abnormal Grain Growth – from N. M. Hwang Byeong-Joo Lee cmse. postech. ac. kr

Phase Field Simulation of γ→α transformation in steels Wetting angle : 36 o Wetting angle : 120 o Fe - 0. 5% Mn – 0. 1% C, d. T/dt = 1 o. C/s from SG Kim, Kunsan University Byeong-Joo Lee cmse. postech. ac. kr

Grain Boundary Identification Scheme H. -K. Kim et al. , Scripta Mater. (2011) two neighboring grains How to uniquely define misorientation and inclination between Byeong-Joo Lee cmse. postech. ac. kr

Grain Boundary Energy of BCC Fe H. -K. Kim et al. , Scripta Mater. (2011) Sigma (Σ) 5 3 11 9 3 7 3 9 7 5 3 5 11 7 9 5 Theta (θ) 36. 87 70. 53 50. 48 38. 94 60 38. 21 131. 81 96. 38 73. 4 180 101. 54 62. 96 135. 58 90 143. 13 (hkl) plane 100 110 111 111 210 210 211 211 221 Sigma (Σ) 11 5 7 3 9 11 5 11 7 7 9 9 11 7 5 11 Theta (θ) 144. 9 180 115. 38 146. 44 67. 11 180 95. 74 100. 48 149 180 123. 75 152. 73 82. 16 110. 92 154. 16 180 (hkl) plane 310 310 311 311 320 321 322 331 331 332 Byeong-Joo Lee cmse. postech. ac. kr

Phase field simulation of grain growth - Isotropic GBE H. -K. Kim et al. (2013) - Anisotropic GBE (realistic GBE DB) - Isotropic GB mobility - Random crystallographic orientation vs. weakly-textured orientation (LAGB = 1. 4 % vs. 4. 9 %) Byeong-Joo Lee cmse. postech. ac. kr

Effect of Anisotropic GBE and Precipitates on Abnormal GG C. -S. Park et al. , Scripta Mater. (2012) Byeong-Joo Lee cmse. postech. ac. kr

Interface Engineering Case Study Byeong-Joo Lee cmse. postech. ac. kr

{100} textured steel sheets Widely used electrical steel: {110}<001> Goss texture • <001> is a “soft” magnetic direction ⇒ reduction of energy loss Why {100} textured steel sheets? • Much improved magnetic properties (magnetic induction and core loss) are expected in {100}<001> cube textured electrical steels • Twenty-times high price compared to Goss texture Byeong-Joo Lee cmse. postech. ac. kr

Atomistic Approach - surf segregation vs surf energy Change of Surface Energy Anisotropy due to Surface Segregation Ave. Concentration Surface E, J/m 2 0. 01% 30% 0. 80 (110) 0. 01% 12% 1. 61 (111) 0. 01% 27% 1. 43 Surface Bulk Concentration (100) within a unit cell distance from surface Esurf of pure Fe = 2. 50, 2. 35, 2. 56 for (100), (111) (100) 0. 1% 34% 0. 65 (110) 0. 1% 17% 1. 34 (111) 0. 1% 30% 1. 00 Byeong-Joo Lee cmse. postech. ac. kr

Phase Field Modeling - surface segregation & grain growth Byeong-Joo Lee cmse. postech. ac. kr

Construction of Surface Energy Database Isotropic grain boundaries (energy and segregation) is assumed to save computation time. • average phosphorus concentration on grain boundaries: 4. 1 at% for a bulk concentration of 0. 1 at% • the resultant average grain boundary energy: 0. 666 J/m 2 vs. for pure bcc Fe: 1. 2 J/m 2 Byeong-Joo Lee cmse. postech. ac. kr

Phase Field Simulation of Grain Growth – steel sheet Byeong-Joo Lee cmse. postech. ac. kr

Experimental Verification – {100} texture on Steel Sheet Future work: Generation of {100}<001> cube texture Byeong-Joo Lee cmse. postech. ac. kr

Design of Sustainable Hydrogen Membranes Degradation of permeability due to interdiffusion V Catalytic coating layer of Pd (~150 nm) Hydrogen flux through a palladium-coated vanadium composite-metal membrane as a function of operating time. D. J. Edlund, J. Mc. Carthy, J. Membrane Sci. 107, 147 (1995) Pinhole -> V layer exposed -> oxidation Experimental information on Y effect S. I. Jeon, J. H. Park, E. Magnone, Y. T. Lee, E. Fleury, Current Applied Microstructure of V alloys after 10 hours of H permeation test at 400ºC Physics 12, 394 (2012) Eric Fleury (Center for High Temperature Energy Materials, KIST) Byeong-Joo Lee cmse. postech. ac. kr

Segregation Tendency of Y on GBs of bcc V First-Principles Calculation of GB binding energy Atomistic GCMC simulation of Y segregation on GB of vanadium {110} tilt 71°(Σ 3) V Y - Interatomic potential : 2 NN MEAM (ternary V-Pd-Y) W. -S Ko and B. -J. Lee, MSMSE (2013) W. -S. Ko et al, Int. J. Hydro. Energy (2014) - Temperature : 1100 K - Bulk concentration of Y : 0. 07 at% - Number of MCS : 20, 000 steps Byeong-Joo Lee cmse. postech. ac. kr

Experimental Verification – Effect of GB segregated Y Perform a pre-annealing before Pd coating to maximize GB segregation of Y Pre-annealing vs. Grain Growth ? V 84. 8 Ni 15 Y 0. 2 : pre-annealing(X) - Gas : H 2 Temperature : 753 K Time : 12 days Annealing Temp: 1473 K Annealing Time : 1 day V 84. 8 Ni 15 Y 0. 2 : pre-annealing(O) V 84. 8 Ni 15 : pre-annealing (O) J. -H. Shim et al. , KIST Pre-annealing > Reduction of GB Byeong-Joo Lee cmse. postech. ac. kr

Further Readings Byeong-Joo Lee cmse. postech. ac. kr