Mo, Nb-based refractory alloy for ultra-high temperature applications

Transcription

1 Mo, Nb-based refractory alloy for ultra-high temperature applications Sang Jun Kim

2 초내열신합금개발의필요성 원자력발전의안전문제제고 신에너지원셰일가스의등장 가스복합화력발전원리 가스복합화력발전수요증가 전세계적가스발전소신설증대 고효율의화력발전기술필요성증가 ( 복합화력발전효율 60% 이상 )

3 초내열신합금개발의필요성 주요가스터빈기술 주요가스터빈기술 Target: 가스터빈효율 > 40% 고효율고출력설계기술 초합금 초합금 + 냉각기술 초고온내열신소재 터빈발전효율 실제효율 이론효율 초고온내열신소재개발 냉각기술 초고온내열소재기술 : 터빈입구온도 > 1400 터빈온도 ( ) Ni계초합금의가용온도 (1100 ) 의한계 냉각기술로극복, but 엔진효율감소 초고온내열신소재개발 냉각기술완화및가스터빈온도상승 가스터빈발전효율상승

4 Candidates: Mo, Nb-based refractory alloy Candidate Elements for High temperature W Re Ta Mo Nb Melting point Density Tensile strength (GPa, 20 o C) Tensile strength (GPa, 1000 o C) Ni : 8.9 g/cm 3 Nb, Mo: High melting point(~2500 ), lower density than other refractory elements(ta, W, Re..) Good candidates for gas turbine application Poor oxidation resistance alloying with Si Metal-Silicide composites

5 Candidates: Mo, Nb-based refractory alloy Mo Si B Nb Si( Ti Hf Cr Al) Mo: Alloying with Si, B Mo + Mo 3 Si(A15) + Mo 5 SiB 2 (T2) 3phase composites Nb: Based on Nb-Si (Si: 12 ~ 20 at.%), alloying with Ti, Hf, Cr Nb + TM 5 Si 3 (D8 8 or β) + NbCr2 (Laves) BCC solid solution: Ductility Silicide: Oxidation resistance, Creep resistance

6 Mo-Si-B alloy Mo Si B phase diagram Mo 5 SiB 2 α-mo Mo 3 Si

7 Passive film for oxidation resistance #3 Oxdiation rate 700~1000 > 1300 MoO 3 vs passive film(silica) At low T, energy to form passive film is not enough Passive film X Passive film X MRS bulletin (2003): Passive film formation at 1300

8 Passive film for oxidation resistance Materials Science and Engineering: A (2003): Poor oxidation resistance of #30: Large Mo volume fraction Best performance #31: T2 dendrite + eutectic Silicides + Si, B % of intermetallic compounds + microstructure

9 Fracture toughness of Mo-Si-B alloy 3-point bending test 3-point bending test is used to measure fracture toughness at room temperature

10 Fracture toughness of Mo-Si-B alloy Poor ductility at room temperature attribute to poor toughness Fracture toughness is effected by morphology of alloy Large α-mo fraction, continuous α-mo is favorable to toughness Target: K > 20 MPam 0.5

11 Fracture toughness of Mo-Si-B alloy Intrinsic toughening Extrinsic toughening Crack blunting: sharp crack blunt crack Crack bridging: impede crack propagation α-mo Crack blunting Crack bridging Kruzic, J. J. et al., M. M. T. A 36.9 (2005):

12 Fracture toughness of Mo-Si-B alloy Intrinsic toughening Mo-12Si-8.5B-Zr (at.%) Schneibel, J. H., et al. M. M. T. A 36.3 (2005): K IC = 7.2 MPam 0.5 Ductility α-mo is affected by interstitial atoms, especially, C/O ratio Addition of Ti and Zr getter C and O control ductility of α-mo

13 Fracture toughness of Mo-Si-B alloy Extrinsic toughening Mo-4.2Si-1.1B (wt.%) Arc-melted HIPed with powder Choe et al., M. M. T. A 34.2 (2003): Schneibel, et al. Intermetallics 9.1 (2001): K IC = 7.2 MPam 0.5 K IC = 14.8 MPam 0.5 Mo-4.2Si-1.1B (wt.%): α-mo volume fraction: 38% Continuous α-mo increase fracture toughness extrinsically

14 Nb-Si alloy: MASC MASC(Metal And Silicide Composite) Directionally solidified Nb-25Ti-8Hf-2Cr-2Al-16Si (at%) As-cast Bewlay, B. P., M. R. Jackson, and H. A. Lipsitt. MSE A (1996): Mathieu, S., et al. Corrosion science 60 (2012): BCC + (Ti,Hf,Nb) 3 Si + (Ti,Hf,Nb) 5 Si 3 D8 8 BCC + (Ti,Hf,Nb) 5 Si 3 D8 8 Based on Nb-16Si (at%) Ti, Hf, Cr, Al were added to improve oxidation resistance High fracture toughness(k IC = 19 ~ 22MPam 0.5 ) Patented by General Electronics(US Patent , 1999)

15 Nb-Si alloy: MASC Nb:(Ti + Hf) ~ 2: creep resistance Fe, Cr: Laves Nb(CrFe) 2 : oxidation resistance Sn: oxidation resistance at low temperature Al: oxidation resistance(al 2 O 3 ) Ge: additional oxidation resistance Bewlay, B. P., et al. MRS bulletin (2003):

16 Mo-Nb-Si-B alloy Mo-Si-B (1600 ) Nb-Si-B (1600 ) B B Mo 5 SiB 2 T2 Mo-Nb-Si-B (?) Nb 5 SiB 2 T2 α-mo Mo 3 Si A15 Si Mo-Si-B: α(mo) + A15(Mo 3 Si) + T2(Mo 5 SiB 2 ) Nb-Si-B: α(nb) + T1(Nb 5 Si 3 ) + T2(Nb 5 SiB 2 ) α-nb Nb 5 Si 3 T1 α(bcc) + A15 + T2 α(bcc) + T2 α(bcc) + T1 + T2 Si

17 Mo-Nb-Si-B alloy B 1600 B Si Mo Si Nb Si Mo-32.6Nb-Si-B Mo Nb32.6% Nb N. Takata et al. (2016): Mo-32.6Nb-Si-B phase diagram α-mo + A15 + T2 3 phase region α-mo + T1 + T2 3 phase region (Mo,Nb)-Si-B: much room for further development Intermetallics 72 (2016): 1-8.

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