intermetallic alloy development for ultrahigh temperature applications mufit akinc materials science...
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Intermetallic Alloy Development for Ultrahigh Temperature Applications
Mufit AkincMaterials Science and Engineering and
Ames Laboratory
But before that
Projects
• Rheology of Nanopowder suspensions
• Bioinspired Nano Materials• Ultra High Temperature
Materials: Silicides & Borides• Injection Repair of Composites• Thermal Shock Resistant
Materials• High Temperature Materials:
Aluminides
Directionally solidified Mo-Ni-Al with NiAl etched
Rheology of Nanopowder SuspensionsC. Li, K. Ament, S. Cinar
Bioinspired Nano MaterialsQ. Ge, X. Ma, X. Liu, S. Mallapragada (PI) and others
No template
Pluronic Peptide
Surface aream2/g
52.2 66.1 173.8
Solution (90-
100 )℃
Gel helices (60 )℃
Gel Solid like gel (25 )℃
Agarose helices
Agarose GEL GEL+ Zirconia Zirconia 900C
Ultra High Temperature MaterialsW. Wang, P. Ray, M. Kramer (Co-PI)
Injection Repair of CompositesM. Tunga, A. Bauer, M. Kessler (PI)
Inte
nsit
y (c
ps)
0500
1000150020002500300035004000
20 30 40 50 60 70 80
2 theta (degrees)
MgO
MgO
MgO
MgO MgOSi
Si
Si
SiSi
O
Mg
Si
Au\ Energy
(keV)
Inte
nsit
y (a
.u.)
4.096
After ReactionBefore Reaction
20 µm
0
100
200
300
400
500
600
10 30 50 702 theta (degrees)
Inte
nsity
(cps
) O
Si
AuEnergy (keV)
Inte
nsit
y (a
.u.)
\\
0.0 4.096
Processing of Bio-templated Smart MaterialsT. Kalem, S. Dudley
2Mg(g) + SiO2(s) 2MgO(s) + Si(s) )(9)()()(8)( 23222 lOHsBaTiOsTiOlOHOHBa
0
200
400
600
800
1000
1200
20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80
Series1
Thermal Shock Resistant NanocompositesMd. I. Ahmad, M. Kenney
Thermal Shock Resistant NanocompositesMd. I. Ahmad, M. Kenney
Intermetallic Alloy Development for Ultrahigh Temperature Applications
Mufit AkincMaterials Science and Engineering and
Ames Laboratory
1150°CEfficiency ~ 40-45%
The need for high temperature Materials
Ni-based superalloys are limited to 1150˚C with active cooling
• Candidate Materials:– Refractory Silicides
• High Melting Temps (>2000C)• Oxidative stability • Fracture toughness
– UHT Borides & Carbides• Melting > 3000C• Oxidative stability 1200-1600C, short
time
– Refractory Aluminides• Current technology• Oxidative stability <1150C• Better in humid atmospheres• Adequate fracture toughness
Alloy development timeline
R.C. Reed, The Superalloys: Fundamentals and Applications, Cambridge University Press, Cambridge (2006).
High temperature alloy industry celebrates a 15° rise in operating temperature!!
The FutureGen target1300oC
Current T D 1050°C
o High Tm
o Adequate strength and toughnesso Good oxidation resistance
High TmAlloy
Metal rich solid solution (strength and toughness)
Reservoir for passivating component (Al, Si, Cr)
Superalloys(Alumina scale)
Silicides(borosilicate scale)
Key Requirements
o Are there o better materials systems?o more effective ways of improving existing systems?
Ni based alloys Refractory metal silicides
↑Alumina scale – excellent environmental resistance
↑Excellent mechanical properties
↓Relatively low Tm ↓Active cooling reduced efficiencies
↑High melting temperatures – potential for high Carnot efficiency
↑The protective borosilicate scale
↓Limited to dry air environments↓The complex phase fields: trade off
between mechanical properties and oxidation resistance
Ni-Based Superalloys vs. Silicides
Conceptual approach
Even for a 4-element Ni-Al based system requires 406 combinations
Exploring a vast phase space using an Edisonian approach is not practical
Number of elements
Possible combinations
2 3160
3 82160
4 1.58 х 106
o Rapid approximate methodso Less accurate but quickly
eliminate ‘dead-ends’
o Refining Stepso Higher degree of accuracy
o Identify key metrics and go no-go decision pointso Creep Strengtho Fracture Toughnesso Oxidation Resistance
oRespect the researcher’s intuition and experience
oUtilize the existing knowledge base
oCritical experiments for validation
Hierarchical Screening
o Semi-Empirical (Extended Miedema Model)o Rapid and quickly eliminates most
likely ‘dead-ends’ based on formation enthalpy
o Refining Steps (VASP software)
o Higher degree of precisiono Identify critical experimentso Site preference
o Experimental Validation (Processing and Testing)
o Final phase screening
16
Iterations include increasing levels of
accuracy or expanded lengths scales in
modeling and more targeted experiments
Screening
o Alloy architecture based on Ni-superalloys (Ni-NiAl)
o Retain NiAl for oxidation stabilityo Al2O3 is a passivating scaleo Increase Tm by alloying (s. solution)o Avoid brittle intermetallic formation
o Replace Ni phase with more refractory metal o V, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Re,
Os, Ir, Pto Should not react with or dissolve in NiAl
o How to down-select?o Enthalpy of formation correlates with Tm
Cu plate
Ni-Al-Rh
Strength and ToughnessBCC or FCC
High Tm & Creep Strength
Reservoir for passivating elementsAl, Si, Cr
NiNiAlAl
MoMo
High melting + poor oxidation
Low melting + good oxidation
Adequate oxidation and Hi Tm
The Mo-Ni-Al system
Mo-NiAl Alloy
Improving NiAl with TM additions
3 4 5 6 7 8 9 10 11
Sc-195
Ti-179
V-128
Cr-96
Mn-120
Fe-101
Co-109
Nixxx
Cu-95
Y-187
Zr-232
Nb-152
Mo-100
Tcxxx
Ru-113
Rh-146
Pd-171
Ag-94
La-181
Hf-211
Ta-152
W-96
Re-97
Osxxx
Ir-220
Pt-171
Au-96
3 4 5 6 7 8 9 10 11
Sc-195
Ti-179
V-128
Cr-96
Mn-120
Fe-101
Co-109
Nixxx
Cu-95
Y-187
Zr-232
Nb-152
Mo-100
Tcxxx
Ru-113
Rh-146
Pd-171
Ag-94
La-181
Hf-211
Ta-152
W-96
Re-97
Osxxx
Ir-220
Pt-171
Au-96
• Selecting alloying additions to improve β-NiAl using enthalpy of formation
• 1st cut using Extended Miedema Model
• Choices further refined using ab initio
Based upon Ni45Al50TM5
Validation
Experiments confirmed the predicted increase in Tm
PGM in Ni site lower ΔH of NiAlSynthesize alloy with PGM on Ni site
ab initio studies using VASP with GGA potentials
3x3x3 unit super-cell
Isothermal Oxidation
47Ni-50Al-3X*
44Ni-50Al-6X
41Ni-50Al-9X
X=Rh -1.73** -1.08 1.42
X=Ir -0.47 0.89 0.86
X=Pd -1.58 -1.54 -1.55
44Ni-50Al-6Rh -1.08
Ni-50Al-6Rh-0.05Hf 0.46
Ni-50Al-6Rh-0.10Hf 0.47
Ni-50Al-6Rh-0.25Hf 0.48
Ni-50Al-6Rh-0.50Hf 0.54
* all compositions are at% and substitutions were on the Ni site **mg/cm2
PMG addition Hf Addition
Baseline
Ni-50Al -1.75
1300°C for 24 hours in dry flowing air
Cyclic Oxidation
Ni44Al50TM6Ni44Al50TM6+Hf
1300°C for 2 hour → ambient for 0.5 hours
PGM and Grain Size
• Reduced grain size– Ir, Rh but not Pd
NiAl
NiAl w/ 6% Ir
Sintered
drop cast
Base Alloy (NiAl-20Mo) Microstructures
• Mo dispersion to improve strength and toughness– Sintered compact
• Isolated fine grain structure
(improved oxidation resistance)
– Arc-melt and drop cast• Dentritic, interconnected
(Improved fracture toughness)
– Directionally solidified
(Improved directional properties)
Mo Microstructure
Putting the Parts Together
• Mo-NiAl– Tailored Microstructure
• Strength vs. Oxidation
• PMG modified NiAl– Increased Tm but costly
• Coated alloy– Only put PGM where needed– Oxidation Barrier
o Well on the way of putting theory into practiceo Use of a multi-stage hierarchical screening
approach suggested the Mo+NiAl is a prospective base alloy system for a high temperature applications.
o PGM (Ir and Rh) were found to provide enhanced oxidation above 1200°Co Alloying additions increased Tmo Reduced grain size, as cast and at operating To 0.05 at.% Hf was found to further improve
oxidation stabilityo Pack cementation shown to form continuous
coating
Conclusions
Acknowledgments
• Matthew J. Kramer• Pratik K. Ray• Travis Brammer• Kevin Severs• Yi-ying Ye• Karen Derocher
Thank You
What questions do you have?
Mo-Ni-Al: microstructures
36
Literature Review
Bei and George, Acta Materialia 53 (2005) 69-77.
o Two major microstructures studied: aligned eutectics through DS and γ’ precipitates in Mo solid solution.
o Not too many studies focusing on relatively high Mo content alloys in the Mo + B2-NiAl phase field.
Wang et. al., Acta Materialia 56 (2008) 5544-5551.
Aligned eutecticsγ’ precipitates in Mo solid solution