Byeong-Joo Lee cmse.postech.ac.kr

Byeong-Joo Lee cmse.postech.ac.kr Scope Fundamentals 1.Free Surfaces vs. Grain Boundaries vs. Interphase Interfaces 2.Concept of Surface Energy/Surface Tension 3.Origin of Surface Energy and its Anisotropy 4.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 For Cu: a = Å △ Hs =337.7J/mol γ (111) = 2460 erg/cm 2 (1700 by expt.) For fcc ※ Origin of Anisotropy Pair approximation Necessary Work for Creation of (111) surface in fcc (/atom) For fcc (111): N/A = 4/(3 1/2 a 2 ) fcc (100): N/A = 2/a 2 Estimation of Solid Surface Energy - Origin of Surface Energy

Byeong-Joo Lee cmse.postech.ac.kr Comparisons High Index Surface Energy 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). Estimation of Solid Surface Energy - Orientation dependence

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 Grain Boundary / Interface Atomistic Computation of Surface Energy

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

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

Byeong-Joo Lee cmse.postech.ac.kr Grain boundaries in Solids - Misorientation Misorientationvs.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 4 o 7 o 3 o 4 o 7 o 10 o 15 o 20 o 30 o o 20 o 30 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 · Incoherent boundary energy is insensitive to orientation. ※ Special boundaries with low energy [100] and [110] tilt Boundary energy of Al Special High-Angle Grain Boundaries

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 2r ⇒ drive it ! total dragging force per unit area Maximum grain size

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

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

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

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

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

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

Byeong-Joo Lee cmse.postech.ac.kr Interfaces Phenomena 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) ; Metall. Trans. A, 8A (1977) T. Tanaka and T. Iida, Steel Research, 65, (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 ω i is the molar surface area Assume ω i = ω j = … = 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 Pure W W + 0.4wt% Ni Vaccum Annealing An issue for thinking - Surface Transition and Alloying Effect

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 Wetting angle : 36 o Wetting angle : 120 o Fe - 0.5% Mn – 0.1% C, dT/dt = 1 o C/s from SG Kim, Kunsan University Phase Field Simulation of γ→α transformation in steels

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

Byeong-Joo Lee cmse.postech.ac.kr Sigma (Σ)Theta (θ)(hkl) planeSigma (Σ)Theta (θ)(hkl) plane Grain Boundary Energy of BCC Fe H.-K. Kim et al., Scripta Mater. (2011)

Byeong-Joo Lee cmse.postech.ac.kr Phase field simulation of grain growth - Isotropic GB mobility - Random crystallographic orientation vs. weakly-textured orientation (LAGB = 1.4 % vs. 4.9 %) - Isotropic GBE - Anisotropic GBE (realistic GBE DB) H.-K. Kim et al. (2013)

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 Interface Engineering Case Study

Byeong-Joo Lee cmse.postech.ac.kr {100} textured steel sheets Widely used electrical steel: {110} Goss texture 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} cube textured electrical steels Twenty-times high price compared to Goss texture

Byeong-Joo Lee cmse.postech.ac.kr SurfaceBulk Concentration Ave. Concentration within a unit cell distance from surface Surface E, J/m 2 (100)0.01%30%0.80 (110)0.01%12%1.61 (111)0.01%27%1.43 E surf of pure Fe = 2.50, 2.35, 2.56 for (100), (110), (111) (100)0.1%34%0.65 (110)0.1%17%1.34 (111)0.1%30%1.00 Change of Surface Energy Anisotropy due to Surface Segregation Atomistic Approach Atomistic Approach - surf segregation vs surf energy

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

Byeong-Joo Lee cmse.postech.ac.kr Construction of Surface Energy Database Surface Surface concentration of phosphorus (1100 K) Surface energy of pure bcc Fe (0 K) Surface energy for bcc Fe-P alloy (0 K) 1 (100) (016) (116) (012) (136) (112) (034) (134) (234) (334) (110) (166) (122) (233) (111)

Byeong-Joo Lee cmse.postech.ac.kr Red Yellow 8,000steps (0.75sec)Initial sample assuming that impurity atoms were segregated before the grain growth Phase Field Simulation of Grain Growth Phase Field Simulation of Grain Growth – modified How to realize the simulation condition in experiments at 1173 K

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

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

Byeong-Joo Lee cmse.postech.ac.kr ElementSite 1Site 2Site 3 Pd Al Cr Y Interatomic potential : 2NN MEAM (ternary V-Pd-Y) W.-S Ko and B.-J. Lee, MSMSE (2013) - Temperature : 1100K - Bulk concentration of Y : 0.07at% - Number of MCS : 20,000 steps V Y Segregation Tendency of Y on GBs of bcc V Atomistic GCMC simulation of Y segregation on GB of vanadium Atomistic GCMC simulation of Y segregation on GB of vanadium {110} tilt 71°(Σ3) unit : eV First-Principles Calculation of GB binding energy First-Principles Calculation of GB binding energy - Code : VASP - Pseudo potential : PAW method, GGA - Number of atoms in a cell : K-point : 4×1×3 - Cutoff energy for P-W basis : 300 eV - Vacuum region : 11Å for-y direction - Cell dimension : Fixed - Atomic relaxation : Allowed - Convergence criteria for energy and force : meV and 10 meV/Å, respectively

Byeong-Joo Lee cmse.postech.ac.kr V 84.8 Ni 15 Y 0.2 : pre-annealing(X) V 84.8 Ni 15 Y 0.2 : pre-annealing(O) V 84.8 Ni 15 : pre-annealing (O) Pre-annealing vs. Grain Growth ? Pre-annealing > Reduction of GB - Gas : H 2 - Temperature : 753 K - Time : 12 days - Annealing Temp: 1473 K - Annealing Time : 1 day Experimental Verification – Effect of GB segregated Y J.-H. Shim et al., KIST Perform a pre-annealing before Pd coating to maximize GB segregation of Y