Fracture Toughness of FCC High Entropy Alloy

Seoul National University High Entropy Alloy <ul style="display: flex;"><li style="flex:1">Traditional alloy </li><li style="flex:1">High entropy alloy </li></ul>Minor element 3 Major element … Major element 3 Minor element 2 Major element 1 Major element Major element 2 Minor element 1 풏ꢇꢈꢉꢊꢋ 풐ꢌ ꢊ풆ꢊꢈꢊ풏ꢍꢎ ↑ ↔ 풄풐풏ꢌꢏꢐꢇꢋꢑꢍꢏ풐풏ꢑ풆 ꢊ풏ꢍꢋ풐ꢒꢓ ↑ ∆푆푐ꢀꢁꢂꢃꢄ. = 푅ꢅꢆ(ꢆ) Y.Zhang et al., Prog.Mat.Sci. 61, 1 (2014) <ul style="display: flex;"><li style="flex:1">(1) Thermodynamic : high entropy </li><li style="flex:1">(3) Kinetics : sluggish diffusion </li></ul>(2) Structure : severe lattice distortion (4) Property : cocktail effect High entropy alloy : Potential candidate material for extreme environment applications Seoul National University Mechanical properties of HEA . Ashby map Bernd Gludovatz / SCIENCE VOL 345 ISSUE 6201 There are clearly stronger materials, which is understandable given that CrMnFeCoNi is a single-phase material, but the toughness of this high-entropy alloy exceeds that of virtually all pure metals and metallic alloys. Seoul National University Fracture toughness of HEA Bernd Gludovatz / SCIENCE VOL 345 ISSUE 6201 Although the toughness of the other materials decreases with decreasing temperature, the toughness of the highentropy alloy remains unchanged. mechanical properties actually improve at cryogenic temperatures Seoul National University Fracture Toughness Testing Compact tension test & Three point bending test Pre-cracking Limitation  Destructive Fracturing  Complex testing procedure  Cannot apply to in-service Development of testing method to measure the fracture properties more easily and more economically Seoul National University Indentation Fracture Toughness . Instrumented Indentation Technique (IIT)  In-situ & In-field System, Non-destructive & Local test, Simple & fast . Indentation Cracking Method (cracking in indentation) 1 2 <ul style="display: flex;"><li style="flex:1">E</li><li style="flex:1">P</li></ul>  K = α   IC 32  H  c Only for ceramic materials (very brittle) [Vickers indenter, Macroscale] Seoul National University Indentation Fracture Toughness . In case of metallic materials (no cracking in indentation) <ul style="display: flex;"><li style="flex:1">IIT </li><li style="flex:1">Fracture test </li></ul>Indenter <ul style="display: flex;"><li style="flex:1">No crack and no fracture </li><li style="flex:1">Crack propagation and fracture </li></ul>. How to correlate flat punch indentation with crack tip behavior Virtual crack isotropic Seoul National University How to correlate flat punch indentation with crack tip behavior <ul style="display: flex;"><li style="flex:1">Contact mechanics </li><li style="flex:1">Fracture mechanics </li></ul><ul style="display: flex;"><li style="flex:1">of flat punch indentation </li><li style="flex:1">of cracked round bar specimen </li></ul>Direct calculation of J from indentation curve Determination of Fracture toughness Flat punch: regarded as a very deep cracked round bar specimen Seoul National University How to correlate flat punch indentation with crack tip behavior * Size effect <ul style="display: flex;"><li style="flex:1">* Load-depth curve </li><li style="flex:1">* Normalization </li></ul>* Crack initiation point J. H. Giovanola et al., ASTM STP 1244 (1995) In flat-punch indentation test Seoul National University How to correlate flat punch indentation with crack tip behavior * Load criterion * Depth criterion * Evaluation 푷푲푰 = ퟐꢑ 흅ꢑ (ퟏ − 흂ퟐ)푲ퟐ푰 푨ꢒ풆 흅ꢑퟐ 푱 = 푱ꢊ + 푱ꢒ = + 휼ꢒ풆 푬Seoul National University Fracture toughness of cantor alloy Reference alloy : Cantor alloy – Cr20Mn20Fe20Co20Ni20 Bernd Gludovatz / SCIENCE VOL 345 ISSUE 6201 Process : Arc melting, copper mold drop casting, cold forging and cross rolling at RT, recrystallization <ul style="display: flex;"><li style="flex:1">KjIc </li><li style="flex:1">Ave. (Mpa·m1/2 </li></ul>~217 <ul style="display: flex;"><li style="flex:1">)</li><li style="flex:1">Grain size (μm) </li></ul>Cantor @293K Cantor @200K Cantor3 @77K ~ 6 ~ 6 ~ 6 ~221 ~219 Seoul National University Fracture toughness of cantor alloy Reference alloy : CrCoNi Bernd Gludovatz/ NATURE COMMUNICATIONS | 7:10602 | DOI: 10.1038/ncomms10602 | Process : Arc melting, copper mold drop casting, cold forging and cross rolling at RT, recrystallization <ul style="display: flex;"><li style="flex:1">KjIc </li><li style="flex:1">Ave. (Mpa·m1/2 </li></ul>~205 <ul style="display: flex;"><li style="flex:1">)</li><li style="flex:1">Grain size (μm) </li></ul>@293K @200K @77K ~ 5 ~ 5 ~ 5 ~265 ~273 Seoul National University XRD data of cantor alloy Cantor1 (As-cast) Cantor2 (24h homogenization) Cantor3 (After recrystallization) <ul style="display: flex;"><li style="flex:1">20 </li><li style="flex:1">30 </li><li style="flex:1">40 </li><li style="flex:1">50 </li><li style="flex:1">60 </li><li style="flex:1">70 </li><li style="flex:1">80 </li></ul>2 theta (deg.) XRD data shows that all specimen have FCC crystal structure Seoul National University Microstructure of Cantor alloy Cantor 1 (as-cast) Cantor 2 (24h homogenization) Cantor 3 ( + cold rolling + recrystallization) Dendritic growth Annealing twin 100μm 100μm 5μm Grain size : ~ 97 μm <ul style="display: flex;"><li style="flex:1">~ 107 μm </li><li style="flex:1">~ 4 μm </li></ul>Seoul National University Indentation test for toughness of cantor alloy . Test condition Loading rate : 0.3mm/min, Depth control : 100um, Zero index : 0.1kgf . Normalized curve <ul style="display: flex;"><li style="flex:1">Cantor 2 </li><li style="flex:1">Cantor 3 </li></ul>Cantor 1 2500 2000 1500 1000 500 2500 2000 1500 1000 500 2500 2000 1500 1000 500 Cantor 1 <ul style="display: flex;"><li style="flex:1">Cantor 2 </li><li style="flex:1">Cantor 3 </li></ul>0 0.0 0 0.0 0 0.0 <ul style="display: flex;"><li style="flex:1">0.1 </li><li style="flex:1">0.2 </li><li style="flex:1">0.3 </li><li style="flex:1">0.4 </li></ul><ul style="display: flex;"><li style="flex:1">0.1 </li><li style="flex:1">0.2 </li><li style="flex:1">0.3 </li><li style="flex:1">0.4 </li><li style="flex:1">0.1 </li><li style="flex:1">0.2 </li><li style="flex:1">0.3 </li><li style="flex:1">0.4 </li></ul>h/a <ul style="display: flex;"><li style="flex:1">h/a </li><li style="flex:1">h/a </li></ul>Seoul National University Result of indentation test This work Ref 260 240 245 217 220 200 217 Mpa·m1/2 200 180 0Cantor3 Cantor2 Cantor1 <ul style="display: flex;"><li style="flex:1">Ave. </li><li style="flex:1">Grain size </li></ul><ul style="display: flex;"><li style="flex:1">Kjc </li><li style="flex:1">Test 1 </li><li style="flex:1">Test 2 </li><li style="flex:1">Test 3 </li><li style="flex:1">Test 4 </li></ul>(Mpa·m1/2 217 <ul style="display: flex;"><li style="flex:1">)</li><li style="flex:1">(μm) </li></ul>Ref. <ul style="display: flex;"><li style="flex:1">-</li><li style="flex:1">-</li><li style="flex:1">-</li><li style="flex:1">-</li></ul>~ 6 ~ 97 ~ 107 ~ 4 Cantor1 Cantor2 Cantor3 229.913 195.559 230.931 225.478 203.835 241.726 204.192 198.548 254.396 208.74 203.291 252.385 217.0808 200.3083 244.8595 Ref. and cantor3 which are similar processing condition show 12% deviation Seoul National University Strength of Ni-Fe-Cr systems H.S.Oh / ph.D graduation paper 1100 1000 900 800 700 600 500 400 300 200 100 0V36.8Ni63.2 Ni Fe Cr (at%) 40 30 30 add V5 add V10 1200 1000 800 600 400 200 0~8.3 μm CrCoNi (Acta Mater., 2017) CrMnFeCoNi (Science, 2014) ~6.5 μm ~6 μm avg. grain size : 5.75 μm (111) V5 (311) (220) (200) FCC phase 10 1.00 1.25 1.50 1.75 2.00 2.25 d-spacing (A) <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">5</li><li style="flex:1">15 </li><li style="flex:1">20 </li><li style="flex:1">25 </li><li style="flex:1">30 </li><li style="flex:1">35 </li><li style="flex:1">40 </li><li style="flex:1">45 </li><li style="flex:1">50 </li></ul><ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">10 </li><li style="flex:1">20 </li><li style="flex:1">30 </li><li style="flex:1">40 </li><li style="flex:1">50 </li><li style="flex:1">60 </li></ul>strain (%) Engineering strain (%) <ul style="display: flex;"><li style="flex:1">at% </li><li style="flex:1">Y.S (MPa) </li><li style="flex:1">U.T.S (MPa) </li><li style="flex:1">Elongation (%) </li><li style="flex:1">Grain size (μm) </li></ul>Cantor CoCrNi NiV 331.96 452.9 693.49 927.36 1174.05 736.8 41.3 45.21 44.53 28.3 ~ 6 ~ 6.5 ~ 8.3 ~ 3.65 743.49 470.2 Ni40Fe30Cr30 Ni40Fe30Cr25V5 Ni40Fe30Cr20V10 476.4 682.7 785.7 954.7 28.6 19.4 ~ 4.18 ~ 5.75 Seoul National University Heat treatment of specimen 1 2 3<ul style="display: flex;"><li style="flex:1">Heat treatment </li><li style="flex:1">Phase </li><li style="flex:1">Grain size (μm) </li></ul>1234 Ni40Fe30Cr30 _1 Ni40Fe30Cr30 _3 <ul style="display: flex;"><li style="flex:1">FCC </li><li style="flex:1">-</li></ul>As-cast homogenization + Cold rolling + Recrystallization FCC FCC FCC ~ 3.7 -Ni40Fe30Cr20+V10 _1 Ni40Fe30Cr20+V10 _3 As-cast homogenization + Cold rolling + Recrystallization ~ 4 Seoul National University Fracture toughness and tensile property <ul style="display: flex;"><li style="flex:1">. Yield Strength vs Fracture toughness </li><li style="flex:1">. Ductility vs Fracture toughness </li></ul>800 50 40 30 20 10 V36.8Ni63.2 700 Ni40Fe30Cr20V10 CoCrNi V36.8Ni63.2 600 Cantor 500 Ni40Fe30Cr25V5 CoCrNi Ni40Fe30Cr25V5 Ni40Fe30Cr30 Ni40Fe30Cr30 400 Ni40Fe30Cr20V10 Cantor 300 <ul style="display: flex;"><li style="flex:1">200 </li><li style="flex:1">250 </li><li style="flex:1">300 </li><li style="flex:1">350 </li><li style="flex:1">400 </li></ul><ul style="display: flex;"><li style="flex:1">250 </li><li style="flex:1">300 </li><li style="flex:1">350 </li><li style="flex:1">400 </li></ul>Fracture toughness Fracture toughness Fracture toughness through IIT yield strength에 의한 영향이 더 큰 것으로 보임. Grain size effect on fracture toughness 260 This work 250 240 230 220 210 200 190 <ul style="display: flex;"><li style="flex:1">0.0 </li><li style="flex:1">0.1 </li><li style="flex:1">0.2 </li><li style="flex:1">0.3 </li></ul>1 / Grain size(um) Grain size 가 작아질 수록 Fracture toughness 가 증가하는 것으로 보임.

Fracture Toughness of FCC High Entropy Alloy

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