Presentation File HEA - Andreas Sugiarto.pptx

introduction to high entropy alloys presentation

1. High Entropy Alloys (HEA) By: Andreas Sugiarto Image Source: [1] Pham, M. (2020)

2. General Overview Image Source: [2] Gludovatz , B. (2014)

3. Brief History of HEA 2 Source: [3] Cantor, B., et al. (2004) Source: [4] Yeh, J.W., et al. (2004) Source: [5] Ranganathan, S. (2003)

4. Definition of HEA 3 Source: [6] Yeh, J. W. (2013) Thermodynamics of HEA

5. Thermodynamics of HEA When liquid and solid solutions formed [4] Δ G mix = Δ H f mix - T Δ S mix Enthalpy  Intermetallic formed vs Entropy  Solid solution formed Mixing Entropy: Configurational is dominant over vibrational, magnetic dipole, electronic randomness [4] Consider an equi -atomic alloy in its liquid or regular solid solution state Δ S conf = R ln n (from Boltzmann equation) [4] 4 Table 1 Ideal configurational entropies in terms of R for equiatomic alloys with constituent elements up to 10 [ 6] Configurational entropy increases as the number of element increases [6] Source: [4] Yeh, J.W., et al. (2004) [6] Yeh, J.W. (2013) Example Cr-Cu: [ 6] Formation enthalpy of intermetallic = 12 kJ/mol Entropy for solid solution = 1.06 R Entropy ≥ 1.5 R (12.471), will have probability to win against enthalpy From table 1.1  at least five elements [6]

6. Definition of HEA 5 Source: [6] Yeh, J.W. (2013) [7] Gao, M.C., et al. (2015) Principle: Has High Mixing Entropy [7] Enhance the formation of solid solution Inhibit the formation of intermetallic compounds These definitions are just guidelines, not laws [7] Fitting only one of the two definitions - C lose to the lower limits of both definitions Considered HEA [7]

7. Phase Formation Rules Thermodynamics: Δ H f mix vs T Δ S mix Geometry: Atomic Size Difference Ω Parameter: Electron Concentration: VEC and e/a   Source: [8] Guo, S., et al. (2011) 6 Solid solution will form when: δ = small Δ H f mix = not negative enough to form compound Fig. 1 Phase selection diagram of HEAs and BMGs based on the enthalpy of mixing, Δ H mix , and the atomic size difference, Delta ( δ) [ 8 ] Atoms easily substitute for each other & Have similar probability to occupy lattice sites [8]

8. Phase Formation Rules Thermodynamics: Δ H f mix vs T Δ S mix Geometry: Atomic Size Difference Ω Parameter: [9] Electron Concentration: VEC and e/a   Source: [9] Yang, X. et al. (2012) [10] Zhang, Y. et al. (2014) 7 Fig. 2 Phase selection diagram of HEAs and BMGs based on Ω and δ [ 10 ] New criteria for forming solid solution phases in HEA [10] Solid solution formed: Ω ≥ 1.1 δ ≤ 6.6 %

9. Phase Formation Rules Thermodynamics: Δ H f mix vs T Δ S mix Geometry: Atomic Size Difference Ω Parameter: Electron Concentration: VEC and e/a   Source: [10] Zhang, Y. et al. (2014) 8 Fig. 3 Dependence of crystal structures on the enthalpy of mixing, Δ Hmix , and the atomic size mismatch, δ, in various HEAs [ 10 ] Atomic size difference has limited use  Controlling the formation of crystal structure FCC : Small δ BCC : Larger δ Ways to control the formation of crystal structure (common: BCC, FCC, HCC) FCC and BCC overlapping each other (middle region) However,

10. Phase Formation Rules Thermodynamics: Δ H f mix vs T Δ S mix Geometry: Atomic Size Difference Ω Parameter: Electron Concentration: VEC and e/a   Source: [42] 9 VEC  Transition Metal Alloys e/a  Noble Metal Alloys [11] e/a : average number of itinerant electrons per atom ratio (e.g. Cu = 1) VEC : number of total electron, including d in valence band (e.g. Cu = 11) Home- Rothery Rules [11] Fig. 4 Relationship between VEC and the phase stability for fcc and bcc solid solutions in various HEAs [ 12 ] Source: [11] Mizutani , U. (2011) [12] Guo, S., et al. (2011)

11. Phase Formation Rules Thermodynamics: Δ H f mix vs T Δ S mix Geometry: Atomic Size Difference Ω Parameter: Electron Concentration: VEC and e/a   Source: [42] 9 Fig. 4 Relationship between VEC and the phase stability for fcc and bcc solid solutions in various HEAs [ 12 ] Based on experimental results from cast alloys No intermetallic compounds formed Maybe disordered and ordered solid solutions BCC / FCC maybe multiphase Quantitative measurement may vary in different alloy systems BCC : Lower (6.87 ≤ VEC < 8) FCC : Higher (VEC ≥ 8) notes Source: [12] Guo, S., et al. (2011)

12. Physical metallurgy Image Source: [2] Gludovatz , B. (2014)

13. Four Core Effects of HEA [13] High Entropy Effect (Thermodynamics) Sluggish Diffusion Effect (Kinetics) Severe- Latice -Distortion Effect (Structure) Cocktail Effect (Properties) 10 Fig. 5 The scheme of physical metallurgy in which those areas influenced by four core effects of HEAs are indicated [ 13 ] Source: [13] Yeh, J.W. (2006)

14. 4 Core Effects High Entropy Effect Sluggish Diffusion Effect Severe Lattice Distortion Effect Cocktail Effect Source: [42] 11 Source: [ 14] Senkov , O.N., et al. (2011) High entropy tends to stabilize high-entropy phases (solid solution) rather than intermetallic compounds (0 entropy) [14] B eneficial  Avoid complex and brittle microstructure [14] Δ G mix = Δ H f mix - T Δ S mix Intermetallic Compound Solid Solution Phase

15. 4 Core Effects High Entropy Effect Sluggish Diffusion Effect Severe Lattice Distortion Effect Cocktail Effect Source: [42] 12 Source: [15] Swalin , R.A. (1972) [16] Tsai, K.Y. (2013) Slower diffusion rate compared to conventional alloys  A vacancy surrounded and competed by different element atoms  Slower phase transformation [15] Fig. 6 Temperature dependence of the diffusion coefficients for Cr, Mn, Fe, Co, and Ni in different matrices [ 16 ]

16. 4 Core Effects High Entropy Effect Sluggish Diffusion Effect Severe Lattice Distortion Effect Cocktail Effect Source: [42] 13 Slower diffusion rate compared to conventional alloys  A vacancy surrounded and competed by different element atoms  Slower phase transformation [15] Easiness to get supersaturated state Fine precipitates Slower grain growth Increase creep resistance Benefit on its Mechanical Properties [17] Source: [15] Swalin , R.A. (1972) [17] Tongi , C.J., et al. (2005)

17. 4 Core Effects High Entropy Effect Sluggish Diffusion Effect Severe Lattice Distortion Effect Cocktail Effect Source: [42] 14 Source: [18] Yeh, J.W., et al. (2004) [20] Kao, Y.F., et al. (2011) [19] Senkov , O.N., et al. (2010) In HEA, every atom is surrounded by different kinds of atom  Suffers lattice strain and stress [18] Fig. 7 Schematic diagram showing the severely distorted lattice and the various interactions with dislocations, electrons, phonons, and x-ray beam [ 17 ] Advantages: Increase Strength & Hardness [19] Disadvantages: Reduce Thermal & Electrical Conductivity [20]

18. 4 Core Effects High Entropy Effect Sluggish Diffusion Effect Severe Lattice Distortion Effect Cocktail Effect Source: [42] 15 Source: [5] Ranganathan, S. (2003) Unexpected properties can be obtained after mixing many elements [5] HEAs have many potential applications

19. Dislocations in HEAs 16 Lower dislocation energy than conventional alloys: [7] Easy Relaxation Effect Severe Lattice Distortion Effect Dislocations are harder to move in HEAs [7] Source: [7] Gao, M.C., et al. (2016)

20. Stacking Faults HEAs have low SFE : [7] Suzuki Interaction (Suitable T) Relaxation Segregation Severe Lattice Distortion Effect 17 SFE decrease as number of elements increase Fig. 8 SFE as a function of the number of composing elements from Ni to NiCoFeCrMn alloy [21] Source: [7] Gao, M.C., et al. (2016) [21] Lee, C., et al. (2013)

21. Stacking Faults Important  dislocation movement [22] Low SFE gives larger separation between partial dislocations (cross-slip or double cross-slip will be harder) Easier to twin (twin boundary is half thickness of a stacking fault) Dislocation structure will be more uniform in planar (strain hardening) 18 Low SFE in FCC HEAs is beneficial for good toughness at cryogenic temperature Fig. 9 Typical stress-strain curves CoCrFeMnNi HEA obtained by tensile testing at 77, 200, and 293 K. [1] Source: [22] Zaddach , A. J ., et al. (2013) [1] Gludovatz , B., et al. (2014)

22. Grain Boundaries 19 Lower grain boundary energy than conventional alloys: [7] Segregation layer of solute atoms along grain boundary High level of distorted matrix Atoms has low mobility  Stable grain structure at higher temperature  Good creep resistance [7] Source: [7] Gao, M.C., et al. (2016)

23. Mechanical Properties Improvement Image Source: [2] Gludovatz , B. (2014)

24. Mechanical Properties Improvements 1. Design crystal structure to obtain the desired properties - Control δ , VEC Add: Al / Cr as BCC stabilizer Ni / Co as FCC stabilitizer 20

25. Mechanical Properties Improvements 2. Choose appropriate fabrication techniques Arc melting : most common, but hard to control BST : good for microstructure control Lasser cladding : can minimize defects, resulting superior properties 20

26. Mechanical Properties Improvements 3. Use Surface Modification Technique Induce TWIP to improve its properties on RT 20 Listyawan , T.A., et al. (2020) [23] Used UNSM technique Source: [23] Listyawan , T.A., et al. (2020) Fig. 10 Vickers microhardness of UNSM treated specimens measured from the top surface down to the middle of the specimens. [23] Hardness increased with increasing static load  Deformation twinning increase

27. References Pham , M., Dovgyy , B ., Hooper , P.A., Gourlay , C.M., and Piglione , A . (2020). The role of side-branching in microstructure development in laser powder-bed fusion . Nature Communications , 11 (749), p . 6. Gludovatz , B., Hohenwarter , A., Catoor , D., Chang, E.H., George, E.P., and Ritchie, R.O. (2014). A fracture-resistant high-entropy alloy for cryogenic applications. Science, 345 , p. 1156. Cantor, B., Chang, I.T.H., Knight, P., and Vincent, A.J.B. (2004). Microstructural Development in Equiatomic Multicomponent Alloys. Mater Sci Eng A, 375–377, pp . 213–218. Yeh, J.W., Chen, S.K., Lin, S.J., Gan, J.Y., Chin, T.S., Shun, T.T., Tsau , C.H., and Chang, S.Y. (2004). Nanostructured high-entropy alloys with multiple principal elements: novel alloy design concepts and outcomes. Adv Eng Mater , 6, pp. 299–303. Ranganathan, S. (2003). Alloyed pleasures: multimetallic cocktails. Curr Sci , 85 , pp. 1404–1406. Yeh, J.W. (2013) Alloy design strategies and future trends in high-entropy alloys. JOM, 65, pp. 1759–1771. Gao, M.C., Yeh, J.W., Liaw , P.K., and Zhang, Y. (2016). High-entropy alloys . Cham: Springer International Publishing. Guo, S. and Liu, C.T. (2011). Phase stability in high entropy alloys: formation of solid-solution phase or amorphous phase. Prog Nat Sci:Mater Int , 21 (6), pp. 433–446. Yang, X. and Zhang, Y. (2012). Prediction of high-entropy stabilized solid-solution in multi-component alloys. Mater Chem Phys, 132 (2–3), pp. 233-238. Zhang, Y., Lu, Z.P., Ma, S.G., Liaw , P.K., Tang, Z., Cheng, Y.Q., and Gao, M.C. (2014). Guidelines in predicting phase formation of high-entropy alloys. MRS Commun , 4 (2), pp. 57–62. 21

28. References Mizutani , U . (2011). Hume-Rothery rules for structurally complex alloy phases . CRC Press : Boca Raton . Guo , S ., Ng , C., Lu, J ., and Liu, C.T. (2011). Effect of valence electron concentration on stability of fcc or bcc phase in high entropy alloys . J Appl Phys , 109 (10), p . 103505 Yeh JW (2013) Alloy design strategies and future trends in high-entropy alloys . JOM 65:1759–1771 Senkov ON, Scott JM, Senkova SV, Miracle DB, Woodward CF (2011) Microstructure and room temperature properties of a high-entropy TaNbHfZrTi alloy . J Alloys Compd 509:6043–6048 Swalin RA (1972) Thermodynamics of solid, 2nd edn . Wiley , New York , pp 263–266 Tsai KY, Tsai MH, Yeh JW (2013) Sluggish diffusion in Co-Cr- Fe -Mn-Ni high-entropy alloys . Acta Mater 61:4887–4898 Tong CJ, Chen YL, Chen SK, Yeh JW, Shun TT, Tsau CH, Lin SJ, Chang SY (2005) Microstructure characterization of AlxCoCrCuFeNi high-entropy alloy system with multi - principal elements . Metall Mater Trans A 36A:881–893 Yeh JW, Chen SK, Gan JY, Lin SJ, Chin TS, Shun TT, Tsau CH, Chang SY (2004) Formation of simple crystal structures in solid- solution alloys with multi-principal metallic elements . Metall Mater Trans A 35A:2533–2536 Senkov ON, Wilks GB, Miracle DB, Chuang CP, Liaw PK (2010) Refractory high-entropy alloys . Intermetallics 18:1758–1765 Kao YF, Chen SK, Chen TJ, Chu PC, Yeh JW, Lin SJ (2011) Electrical , magnetic , and hall properties of AlxCoCrFeNi high-entropy alloys . J Alloys Compd 509:1607–1614 Lee C, Yeh JW (2013) Study on deformation behaviors of equimolar alloys from Ini to CoCrFeMnNi . Master’s thesis , National Tsing Hua University 22

29. References Zaddach AJ, Niu C, Kock CC, Irving DL (2013) Mechanical properties and stacking fault energies of NiFeCrCoMn high-entropy alloy . J Appl Meteorol 65:1780–1789 Listyawan , T.A., Lee, H ., Park, N ., and Lee, U . (2020). Microstructure and mechanical properties of CoCrFeMnNi high entropy alloy with ultrasonic nanocrystal surface modification process . Materials Science & Technology , 57 , pp . 121-130. 23