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

2. 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

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

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

5. Byeong-Joo Lee cmse.postech.ac.kr For Cu: a = 3.615 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

6. 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

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

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

9. 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

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

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

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

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

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

15. 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 45 15 o 20 o 30 o 45 o

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

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

18. 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

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

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

21. 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

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

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

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

25. 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

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

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

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

29. 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, 8A (1977) 1383-1401. 2.T. Tanaka and T. Iida, Steel Research, 65, 21-28 (1994).

30. 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

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

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

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

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

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

36. Byeong-Joo Lee cmse.postech.ac.kr Pure W W + 0.4wt% Ni Vaccum Annealing An issue for thinking - Surface Transition and Alloying Effect

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

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

39. 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

40. 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)

41. Byeong-Joo Lee cmse.postech.ac.kr Sigma (Σ)Theta (θ)(hkl) planeSigma (Σ)Theta (θ)(hkl) plane 536.8710011144.9310 370.531105180310 1150.481107115.38310 938.941103146.44311 360111967.11311 738.2111111180311 3131.81210595.74311 996.3821011100.48320 773.42107149320 51802107180321 31802119123.75321 5101.542119152.73322 1162.962111182.16331 7135.582117110.92331 9902215154.16331 5143.1322111180332 Grain Boundary Energy of BCC Fe H.-K. Kim et al., Scripta Mater. (2011)

42. 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)

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

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

45. 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

46. 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

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

48. 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)0.3362515649 2 (016)0.3522535545 3 (116)0.3882551482 4 (012)0.31825061085 5 (136)0.29225191334 6 (112)0.27624591041 7 (034)0.33224441179 8 (134)0.31124701304 9 (234)0.3232553915 10 (334)0.3692561705 11 (110)0.27023551336 12 (166)0.33224431216 13 (122)0.3072541899 14 (233)0.29325541076 15 (111)0.30125721002

49. 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

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

51. 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)

52. Byeong-Joo Lee cmse.postech.ac.kr ElementSite 1Site 2Site 3 Pd 0.0713-0.29912-0.29091 Al 0.36780.1201-0.1370 Cr -0.28390.1188-0.0258 Y 0.59198-0.20411.01056 - 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 : 116 - 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 : 0.001 meV and 10 meV/Å, respectively

53. 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