Tailoring of Atomic-Scale Interphase Complexions

for Mechanism-Informed Material Design

Developing Predictive Thermodynamic Models …and

Validation ExperimentsPresented by Jian Luo

On Behalf of the MURI Team

Office of Naval Research Multidisciplinary University Research Initiative Project Review Meeting

December 18, 2012ONR Topic Chief: David Shifler

ONR-MURI Review 2

Based on the Feedbacks from DFT Calculations and STEM…

A Revised Thermodynamic Description of Bilayers?

BBimonoS

bilayergb )()( 2

2 adsorbed Bi layers are weakly bonded

CMU: Ni annealed in Bi vapor

Deep Groov

e

Atomic Steps

Reconstruction(NOT 1 on 1)

Coherent?

DFT (CMU)Bi on Ni (111)

“4 on 9” reconstructi

on

Specific Bilayer Structure ~ Orientation

Original

A “Coarse-Grained” Description

Bi LayerBi Layer

Ni LayerNi LayerNi Layer

Ni LayerNi LayerNi Layer

Coh

ere

nt

Inte

rface

Str

on

g B

i-N

i B

on

ds

Incoh

ere

nt

Inte

rface

Weak B

i-B

i B

on

ds

Bilayer Stability (The Key Idea unchanged):Strong Ni-Bi (Measured by

Ni-Bi)

Weak Bi-Bi

Experimental Evidence

Suggested by DFT (@CMU)

ONR-MURI Review 3

Segregation driving forces in metals:• Eelastic = f(RB/RA)

• H |EB-B| - |EA-A|

• EA-B - ½(EA-A + EB-B); zN

Wynblatt & Chatain Metall. Mater. Trans. A 2006

Key Parameters for Prediction?

Strong Ni-Bi

Weak Bi-Bi

Science, 333: 1730 (2011)

ONR-MURI Review 4

To Predict Bilayer Stability…

Bi doped Ni

ubiquitous

An experiment designed in Feb. 2012 (@ a MURI meeting at TMS)

observed, but in a narrow window

NOT observed

Ni-Bi = -14.8 kJ/molCu-Bi = +14.2 kJ/mol Fe-Bi = +72.3 kJ/molMiedema:

Ni-Bi = -16.4 kJ/molCu-Bi = +34.8 kJ/mol Fe-Bi = +91.6 kJ/molDFT (CMU):

Bilayers are…

Gao & Widom( 4Hmix

0.5)

Subsequently, specimens were made at Clemson and characterized at Lehigh; we observed that:

Bi Bi BiNi Cu Fe

Bi doped Cu Bi doped Fe

Reducing Bilayer Stability Predicted…

Large Eelastic

Large |EB-B| - |

EA-A|

Varying A-B EA-B - ½(EA-A +

EB-B)

ONR-MURI Review 5

Ni-Bi

Cu-Bi

Fe-Bi

Fe-Bi = 91.6 kJ/mol(DFT, Gao & Widom)

Fe

Fe

“Clean”

Cu-Bi = 34.8 kJ/mol(DFT, Gao & Widom)

Ni-Bi = -16.4 kJ/mol(DFT, Gao & Widom)

Scripta Mater. 2013

Science 2011

Clemson Updates

MURI Review: 5/17/2012 6

Wynblatt et al.’s Multilayer GB Segregation Model Wynblatt, Chatain et al. [JMS 2005; 2006, MMA 2006]

GB Core:

Inside:

Segregation Enthalpy

Same Crystal Structure

Weak Segregation Systems?

“Solid-State” Complexion Transition

Clemson Updates

MURI Review: 5/17/2012 7

The Most Recent Modeling Results using the Wynblatt Model

[See the description of the Model: Wynblatt & Chatain, Metall.

Mater. Trans. A 2006]

1E-3 0.01 0.1 1

0.0

0.5

1.0

1.5

2.0

2.5 Ni-Bi Cu-Bi Fe-Bi Ni-Bi CalPhad

(#

of

mo

no

laye

r)

X %

DFT para.(CMU)

CalPhaD

1E-4 1E-3 0.01 0.1 10.00

0.25

0.50

0.75

1.00

1.25

1.50 Ni-Bi Cu-Bi Fe-Bi Ni-Bi CalPhad

GB/

(0)

GB

X (%)

XBi(0)

(Cu-Bi)

XBi10-6 10-5 10-4 10-3 10-2

10-6 10-5 10-4 10-3 10-2 XBi

XBi(0)

(Ni-Bi)

XBi(0)

(Fe-Bi)

Approx.Solid

SolubilityLimit

XBi(0)

(Ni-Bi)

The Wynblatt Model

(111)FCC or (110)BCC high-angle (low-

symmetry) twist GBs

T/Tm =0.563

Fe-BiCu-Bi Ni-Bi

Consistent with

Experiment

In the Meta-Stable Supersaturated Region:

Effective GB 0 “Equilibrium” Grain Size

(Weissmuller, Johnson, Kirchheim, Schuh et al.)

Clemson Updates

MURI Review: 5/17/2012 8

Stabilization of Nanocrystralline Alloys via GB Segregation (a.k.a. Complexion)

Kinetic Stabilization• Solute drag• Second phase pinning• Chemical ordering• …

Thermodynamic Stabilization (reducing GB, ideally to ~ 0?)

competing

New Insight: The complexion theory argued that segregation induced interfacial

disordering can increase GB mobiles (demonstrated in Al2O3, Al-Ga etc.)

From the late Dr. Rowland

Cannon (2004 GRC)

A GB transition?

Schuh & co-workers’ recent work (Science 2012)

Can we pursue a more quantitative “CalPhaD for Nanocrystalline

Alloys”

Show the importance

of simultaneously evaluating bulk and GB thermodyna

mics

This MURI revealed (for Ni-Bi)…Bi adsorption reduce GB of Ni

significantly (not yet 0)Bi inhibits Ni GG at low T, but Promote

GG at high T!

ONR-MURI Review 9

Background: Developing Design Tools for the Materials Genome Initiative

CalPhaD for “Complexions” & “Nano-Phases”2 related but different tasks

Melting T for Au

Nanoparticles

Binary

T. Tanaka et al. 2001

Premelting(Complexion)

Related, but

different phenomen

a

A Successful Example of Predictive Modeling (AFOSR Project)

To predict the stabilization of nanoscale quasi-liquid intergranular films (complexions)

ONR-MURI Review 10

Developing A New “Materials Genome” Tool for Designing Nanocrystalline Alloys?

“CalPhaD for Nanocrystalline Alloy” Diagram

GB Complexion

Model(Wynblatt model

for this case)

Bulk CalPhaD

(Computational Thermodynamics)

+

Metastable nanocrystalline alloys possible,

but probably impractical for Ni-

Bi…

Cu-BiMayr & Bedorf

Phys. Rev. B 2007

Consistent with

Experiment

ONR-MURI Review 11

A More Practical Case“CalPhaD for Nanocrystalline Alloy” Diagram for Fe-Zr

Consistent with Prior ExperimentsNo fitting/free parameters used other than the CalPhaD data obtained in

literature!

ONR-MURI Review 12

100 200 300 400 500 600 700 800 900 10001

10

100

1000

10000

100000

Lo

g10

Gra

in S

ize

(n

m)

T(oC)

Ni Ni(Bi) Ni-W Ni-W(Bi)

Grain Growth (GG): Intriguing Results

Bi inhibits GG at low T’s?

CMU High-Purity Ni (930C)

Bi promote GG (no AGG) at high T’s

Clemson High-Purity Ni (1100C)

~20 m

~40 m

Clemson Electrodeposited Ni & Ni-WIsothermally annealed w/ or w/o Bi vapor, 4 hrs

Pure Ni: 137 mNi (+ Bi liquid): 159 m

UIUC GB diffusion measurements showed the consistent trends

earlier…

? Confirmed

SEMXRD,

confirmed by SEM

STEM in progress at

UIUC & Lehigh

Current Explanation:At low T’s: Bi inhibits grain growth due to the reduction of

driving force (GB/GB(0) = ¼) and solute drag (given the large

adsorption amount)

At high T’s: Bilayers become more “liquid-like” the kinetic effect due to disorder overwhelms the thermodynamic stabilization and solute drag

ONR-MURI Review 13

Bi doped Ni W doped NiRBi = 1.78Å RNi =

1.25Å

Bi Ni

RW = 1.39Å RNi =

1.25Å

W Ni

H |EBi-Bi| - |ENi-Ni| < 0

: small negative

Eel big RB/RA = 1.42

H |EW-W| - |ENi-Ni| > 0

: small negative

Eel moderate RB/RA = 1.11

• Reduce GB moderately• Stabilize nano grain size • Good mechanical properties

Strong SegregationLimited Solubility

Weak SegregationLarge Solubility

Nanocrystalline W-Ni (Schuh et al. & others)

• Reduce GB significantly• Promote GG at high T; inhibit GG at low T• Severe embrittlement

ONR-MURI Review 14

Dangling bonds(incoherent interface)

High-energy W broken bonds W depletion at the very core?

Possible Complexion Structure in Ni-W (Following Wynblatt et al.’s Multilayer GB Segregation Model)

H = +0.3 Hel = -0.2 (eV/atom)

H = 0Hel = -0.05 (eV/atom)

• Inhibit grain growth• No severe embrittlement

Non-equilibrium W segregation possible during

electrodeposition

Ni-W (made by electrodeposition) Supersaturated with W

Heat Treatment:700C for 4 hrs + 400C for 24 hrs

To verify/disapprove this prediction:

Specimens made at Clemson

STEM Characterization current in progress at

Lehigh…

ONR-MURI Review 15

Concluding Remarks

“Simple” thermodynamic models can predict useful trends

• Predicted decreasing bilayer stability in Ni-Bi, Cu-Bi and Fe-Bi verified by experiments

• DFT (and atomistic) calculations are useful for providing thermodynamic parameters (particularly in cases where experimental data are not available)

A new “CalPhaD for Nanocrystalline Alloys” method has been developed – in the spirit of the “Materials Genome” initiative?

• Combining complexion models & bulk CalPhaD

• Initial validation with literature data & our experiments

An Intriguing New Discovery

• Bi inhibits the grain growth of Ni at low T, but promotes grain growth at high T.

ONR-MURI Review 16

Backup Slides

ONR-MURI Review 17

Electrodeposited Ni specimens, annealed at 900 C, 4 hrs

Ni

Niin Bi vapor

Grain Size Increases