PowerPoint 프레젠테이션

Effect of electric current on

formability of dual-phase high entropy alloy

2017. 06. 19

Sang Jun Kim, Jeong Hye-Jin

Electrically-Assisted Manufacturing

After pulsing

Acceleration of Spheroidization [deformed pearlitic steel]

Edwin I et al., J. Mater. Res. (2010)

No current Current

0.00 0.06 0.12 0.18 0.24 0.30 0.36 -50

0 50 100 150 200 250 300

No current Pulsed current

Stress(MPa)

Strain

Penn State Univ. (2009) Decrease of Spring back Increase of Elongation

 Space saving

 Rapid heating

Advantages of EAM

 High energy efficiency

 No cost to maintain temperature of furnace/mold

 Enhancement of Formability  Microstructure control : Metal forming by applying electric current during deformation

Electrically-Assisted Manufacturing (EAM)

Dual-phase high entropy alloy: HCP + FCC

Composition ΔG(hcp-fcc) 1 Cr20Mn20Fe20Co20Ni20 1927.8 2 Cr20Mn18Fe22Co22Ni18 1494.4 3 Cr20Mn16Fe24Co24Ni16 1108.4 4 Cr20Mn14Fe26Co26Ni14 771.0 5 Cr20Mn12Fe28Co28Ni12 482.9 6 Cr20Mn10Fe30Co30Ni10 245.3 7 Cr20Mn8Fe32Co32Ni8 59.4

Dual

• G(FCC) – G(HCP) ≈ SFE(Stacking Fault Energy)

• Decreasing SFE → TWIP, TRIP

• Minimized SRE → FCC(γ) + HCP(ε) Dual-phase HEA

Mechanical properties of DP HEA DP HEA

300μm

0 10 20 30 40 50 60

0 200 400 600 800 1000

Engineering stress (MPa)

Engineering strain (%)

Cantor alloy Dual phase HEA

• Excellent strength and ductility

• HCP: intrinsic brittle phase → More plasticity by EAM?

FCC + HCP

DP HEA

(Cr₂₀Mn₂₀HEA Fe₂₀Co₂₀Ni₂₀)

Experiment

0 10 20 30 40 50 60 70 80

200 400 600 800 1000

Gauge length : 15 mm Gauge width : 3 mm Thickness : 1.5 mm Strain rate : 10^-3

Tested by ASTM E8

Tensile stress (MPa)

Tensile strain (%)

DP HEA

DP HEA + Al1%

Al Co Fe Cr Mn Ni

DP HEA 0.00 20.00 32.00 32.00 8.00 8.00 DP HEA +

Al1% 1.00 19.80 25.60 25.60 6.40 6.40

Experiment

0 10 20 30 40 50

0 50 100 150 200 250 300

Temperature (o C)

Time (sec)

 Pre strain 14% 후,

100A/mm² , 0.1s, 1pulse의 전류 인가

Max T. : 268^oC

0 50 100 150 200 250 300

0 50 100 150 200 250 300 350 400 450

Temperature (o C)

Time (sec)

 Pre strain 40% 후,

115A/mm² , 0.1s, 6pulse의 전류 인가

Max T. : 373^oC Pre strain 후, 100A/mm² , 0.1s의 pulse 전류 인가 실시 → 성형성 평가

DP HEA + Al1% DP HEA

Result: DP HEA + Al1%

0 10 20 30 40 50

0 200 400 600 800 1000

Tensile stress (MPa)

Elongation (%)

0 10 20 30 40 50

0 200 400 600 800 1000

Tensile stress (MPa)

Elongation (%) No current 100 A/m, 0.1s

1 pulse

Yield strength (MPa) 559 620

UTS (MPa) 971 950

Elongation (%) 37.3 39.9

약

증가

Without current 100A/mm2 , 0.1s, 1pulse

Result: DP HEA + Al1%

0 10 20 30 40 50 60 70 80

0 100 200 300 400 500 600 700 800

Tensile stress (MPa)

Elongation (%)

0 10 20 30 40 50 60 70 80

0 100 200 300 400 500 600 700 800

Tensile stress (MPa)

Elongation (%)

Without current 115A/mm2 , 0.1s, 6pulse

Softening

35 40

600 700

No current 115 A/m, 0.1s 6 pulse

Yield strength (MPa) 281 288

UTS (MPa) 699 691

Elongation (%) 76.5 80.1

약

증가

Effect of electric current of mechanical properties of DP HEA

Single FCC(γ) FCC(γ)

+ σ + BCC(α)

CALPHAD

계산 결과

• HCP(ε)

는

시 형성

→ 940K(670℃)

이하에서

열처리 시

형성

→ BCC or σ: brittle

→

제

상 석출 시 연신율 감소 예상

→ Electric currnet

에 의해

상변화가 발생하지 않음

• Annealing effect from electric current

→ Annihilation of dislocation

→

연신율 증가

940 K

Summary and Future work

• Objective and experimental:

- DP HEA: HCP(brittle) + FCC → Increasing plasticity by electric current

- Pre strain 후, 100A/mm2 , 0.1s의 pulse 전류 인가 실시 → 성형성 평가

• Results

- DP HEA Al1%: 연신율 2.6% 증가(38.3 → 39.9)

- DP HEA: 연신율 3.6% 증가(96.5 → 80.1)

• Discussion

- 100~115 A/mm2, 1~6 pulse로 인한 annealing은 268 373 도는 상변화를유

발하기에 충분하지 않음

- 전류 pulse로 인한 annealing(268℃, 373 ℃)으로 인한 연신율 소폭 증가

- 통전 성형을 통한성형성 증가 가능성확인

• Future work

- In-situ 통전 실험(지속적인 annealing 효과) 조건에서의 성형성 평가