Materials for Extreme EnvironmentsDavid N. Seidman

Northwestern UniversityDepartment of Materials Science & Engineering

Evanston, IL 60208-3108http://arc.nucapt.northwestern.edu

d-seidman@northwestern.eduRoom 1013, Cook Hall

847.491.439119th September 2005

Subjects for Ph.D. students• NSF funded: Understanding the

temporal evolution of the microstructure of high-temperature nickel-based superalloys for turbine blades.

• ONR funded: Further development of a blast-resistant steel to replace existing steel of all surface naval ships by the year 2020.

Subjects for Ph.D. students

• DOE: In cooperation with Professor Amanda Petford-Long – informational materials. E-mail: petford.long@anl.gov

Motivation for NSF funded research

• Why this precipitation reaction (γ →γ + γ’)? – γ’-precipitates principle

strengthener in Ni-based superalloys – Very limited number of experiments on ternaries

Temporal Evolution of Ni-5.2 Al-14.2 Cr at 600ºCTurbineblade

• Why this Ni- Al- Cr alloy?- Previous work suggests that the earliest stages of precipitation are observable- Binary Ni-Al well-characterized - Small lattice parameter misfit (0.03%) - Free energy expressions exist

TurbineMicrostructure

γ’γ

High T and strength application

Commercial Ni-base Superalloys

GOALS

Detailed understanding of the thermodynamics, atomic-scale mechanisms, and kinetics of γ'-precipitation ina ternary alloy both experimentally and with lattice kinetic Monte Carlo (LKMC) simulation using state-of-the art techniques

Atom-Probe Tomography

• We are using a unique instrument to study the chemistry of nanostructures, the so-called local-electrode atom-probe (LEAP) tomograph.

• This instrument is located in room 1082 and/or 1086, Cook Hall. It is part of Northwestern University Center for Atom-Probe Tomography (NUCAPT).

Specimen wire

• Curved crystalline surface leaves circular ledges: crystallographic poles

• Inert gases are ionized from ledge sites for imaging surface

• FIM image can reveal crystallographic orientationof specimen tip

Field Ion Microscopy

FCC structure with [001] axisFIM image of W tip:BCC structure with [110] axis

Atom-probe tomographyAtom-probe tomography, with field-evaporation technique, allows atom-

by-atom reconstruction of a needle-shaped material containing features of interest

The time-of-flight (TOF) of each field-evaporated ion is measured simultaneously with the position of the impact on the 2D detector

• Time of flight Chemical nature• Impact Position Atom position on tip surface

(projection microscope)

Schematic

LEAP® TomographLocal-Electrode Atom-Probe (LEAP®) Tomograph

•Can determine spatial position of individual atoms and their chemical identities• Analyze data with NUCAPT’s APEX or Imago’s IVAS programs

•Analyze volumes of 100x100 x(at least) 100 nm• 10-10 torr Ultrahigh vacuum• Cryogenic conditions, 20 to 80 K• 200 kHz pulsing

The Strengths of Atom Probe Tomography

• Mass Analysis– Phase formation and

composition identification• Quantitative composition gradients

• Compositional Imaging– Buried interfaces

• Thin films• Precipitates• Diffusion couples

• Structural Imaging– Precipitate number density, size distribution, …– Cluster formation in devitrification,

• Element specific radial distribution function

• Qualitative composition gradients

Mass SpectrumPremium on accuracy

3D ImagePremium on precision

LEAP Pushes Detection Limits

10

10

10

10

10

10 10 10 10 10-9 -7 -5 -3 -1

-9

-7

-5

-3

-1

Lateral Spatial Resolution (m)

MDMF*EPMA

XPS & ISS

XRF

PIXE

SIMS

LAMMA

FEGAEM

AEM SAM

APFIM

LEAP

Not yet achieved

Moore’s Law

Physical Limit

*MDMF = minimum detectable mass fraction (analytical sensitivity)

After Charles LymanLehigh University

ppm

ppb

~80-100 mmDetector

The Local Electrode Atom Probe (LEAP) Microscope

• 3DAP: counter electrode mm away from specimen

• Much shorter flight path– Smaller detector– Larger solid angle

3DAP LEAP LEAP vs. 3DAP

Analysis Speed 2-6 days 10 – 60

minutes 100-1000X

Typical Mass Resolution

1:500 FWHM

1:500 FWHM Same

Specimen Type

5mm needles

Microtips and needles

Expanded capabilities

80-120mm

40mm

10-50 micron

Field of View 10nm 30-70nm 10-50X Area

~500 mm

• Local electrode within microns of specimen

Local electrode

Scanning Atom Probe & Local Electrode Atom Probe

SAP (Nishikawa et al. 1993)positionable funnel-shapedelectrode for atom probe.

LEAP (Kelly et al. 1994) adds post acceleration concepts with low voltage operation

xy

Vpulse z

Vex

Vaccel

Vex small, Vaccel largeImprove mass resolutionLarger field of view

Vex is small ⇒ Vpulse is smallMuch higher repetition rates

Analyze microtipsPlanar specimensMultiple tips per specimen

Analysis of atom-probe tomography data

Atom-probe Tomography:Reconstructedvolume

Isoconcentration surface

Selected Volume

Temporal Evolution10x10x25 nm3 subsets of 3DAP

reconstructions

~125,000 atoms/volumeatoms omitted for clarity

Ni-5.2 Al-14.2 Cr (at. %)

time, hours 0.1666 0.25 1 4

Aged at 600°C

9 at.% Al isoconcentration surface

in red reveals Ni3(AlxCr1-x) precipitates

time, hours 16 64 256 1024

ONR: Thermally-aged precipitated Fe-Cu steels

• Blast resistance at low temperatures• Transportation, infrastructure, and defense industries

• Naval requirements– 150 ksi (1034 MPa)– Percent elongation-to-failure > 15%– Good impact toughness at -30ºF

• 25-50 ft-lbs (34-68 J)

Advantages of AlNiCu Precipitation-Strengthened Steels

• Low carbon content, therefore can omit elements needed to obtain martensite on quenching

• Easy welding --- no brittle heat-affected zone (HAZ) next to welds

• Good to excellent fracture toughness at low temperatures, -40ºC

• Copper gives superior weatherability/ corrosion resistance

Al, Ni, Cu, and NbC Precipitation -Influence of Ni and Al Alloying Addition

Steel Compositions (wt.%)

C Mn Si Cu Ni Al Nb Ti

NUCu-60 0.03 0.53 0.52 1.29 0.52 0.05 0.07 0.10

NUCu-70-80 NUCu-100

0.03 0.49 0.49 1.36 0.84 0.05 0.07 0.03

AlNiCu-150 0.05 0.47 0.46 1.34 2.71 0.60 0.07 0.03

AlNiCu-170 0.04 0.49 0.50 2.00 2.81 0.68 0.06 0.03

Cu Ni Mn Si AlC and Nb not detected Fe not shown

Box dimensions 14 × 14 × 101 nm3

Cu-rich Precipitates in NUCu-100

1100ºC 30 min. austenitized and then aged at 490ºC for 100 min. direct aged: <R> = 1.5 nm; NV = 1.1 x 1024 m-3

NUCu100: 0.06C, 1.36Cu, 0.82Ni, 0.034Al, 0.49Mn, 0.49Si, 0.079Nb (wt.%)

1100oC + 490oC 100min direct aged

Proxigram Analysis of Cu-rich Precipitates in NUCu-100

Ppt. Coreat.%

(wt.%)

Ferriteat.%

(wt.%)

Cu 64.0 ± 1.0(67.2 ± 1.0)

0.50 ± 0.01(0.57 ± 0.01)

Fe 32.9 ± 0.9(30.3 ± 0.8)

96.94 ± 0.02(97.0 ± 0.02)

Ni 1.33 ± 0.21(1.29 ± 0.20)

1.27 ± 0.01(1.34 ± 0.01)

Mn 0.76 ± 0.16(0.69 ± 0.15)

0.55 ± 0.01(0.54 ± 0.01)

Al 0.50 ± 0.10(0.22 ± 0.05)

0.047 ± 0.003(0.023 ± 0.015)

Si 0.60 ± 0.14(0.28 ± 0.07)

0.99 ± 0.01(0.50 ± 0.05)

Nb ND ND

C ND ND

Errors based on counting statisticsProxigram wrt 10 at.% Cu Isosurface

1100oC + 490ºC 100min direct aged

NUCu100: 0.06C, 1.36Cu, 0.82Ni, 0.034Al, 0.49Mn, 0.49Si, 0.079Nb (wt.%)

Temporal Evolution of Yield Stress in AlNiCu-150 (1st heat)

0

25

50

75

100

125

150

175

200

0 20 40 60 80 100 120

Aging Time, hrs

Yie

ld S

tres

s, K

si

0

200

400

600

800

1000

1200

1400

Yie

ld S

tres

s, M

Pa

LEAP Tomography Studies

Water quenched from 900oC; aged at 500oC

AlNiCu-150: 0.05C, 1.34Cu, 2.71Ni, 0.60Al, 0.47Mn, 0.46Si, 0.07Nb (wt.%)

52 nm54 nm

52 nm

AlNiCu-150: 0.05C, 1.34Cu, 2.71Ni, 0.60Al, 0.47Mn, 0.46Si, 0.07Nb (wt.%)

23 nm

50 nm

3 h 24 h 100 hAging at 500oC

3DAP LEAP LEAP0.6 M atoms 3.3 M atoms 2.6 M atoms

Cu-rich Precipitates in AlNiCu-150

Cu Ni AlFe Si Mn C

22 nm

23 n

m

Cu-rich Precipitates, 5at.% Cu Isoconcentration SurfaceAlNiCu-150: 0.05C, 1.34Cu, 2.71Ni, 0.60Al, 0.47Mn, 0.46Si, 0.07Nb (wt.%)

52 nm

50 nm

22 nm

3DAP LEAP LEAP

3 h 24 h 100 hAging at 500ºC

Proxigrams with respect to 5at.% Cu Isoconcentration Surface

AlNiCu-150: 0.05C, 1.34Cu, 2.71Ni, 0.60Al, 0.47Mn, 0.46Si, 0.07Nb (wt.%)

3DAP LEAP LEAP

3 h 24 h 100 hAging at 500ºC

Proximity Histogram Concentration Profiles

Materials for Extreme EnvironmentsDavid N. Seidman

Northwestern UniversityDepartment of Materials Science & Engineering

Evanston, IL 60208-3108http://arc.nucapt.northwestern.edu

d-seidman@northwestern.eduRoom 1013, Cook Hall

847.491.439119th September 2005