ORNL is managed by UT-Battelle for the US Department of Energy

Experience with Thin-Walled High-

Temperature Components

Laboratory Materials Research at ORNL

Bruce Pint, Group LeaderCorrosion Science & Technology GroupMaterials Science & Technology Division

Oak Ridge National Laboratory

October 2015

2 2015 Akron U

Primary surface recuperators for gas turbines are a great materials science problem

Require: - creep resistance- corrosion resistance- fabricability (roll foil, fold, weld)- cost

courtesy of I. G. Wright

Annular recuperator65kW microturbine:

Solar TurbinesMercury 50 4.6MW

~80µm foil

air

exhaust

Foil not like bulk alloy:- fine grain size (creep)- limited Cr (Al) reservoir

3 2015 Akron U

Specialized techniques for creep testing of thin foils(Building on initial work of Montague at Solar

Turbines)

LVDTs for ContinuousMonitoring of Creep Strain

Extensometer

Thermocouples

Specimen

Specimenw/Tabs

Specimen

Dime

4mil ThickFoil

J.P. Shingledecker

R.W. Swindeman

B.L. Sparks

Oak Ridge National Laboratory

4 2015 Akron U

Why is testing needed?HR230 (NiCrW) is sensitive to grain size, which makes the creep resistance of foils much less than thicker plate/tube

0

5

10

15

20

25

30

35

40

0 5,000 10,000 15,000 20,000

CR

EEP

STR

AIN

(%)

TIME (hrs)

CREEP AT 750oC 100MPa

Haynes 230 Wrought (Tubing)

Haynes 230Comm. 3.2 mil Foil

(~800 hrs)

Haynes 230ORNL 4mil Foil

1382°F, 14.5ksi

5 2015 Akron U

Several alloy foils were evaluated at 700°-750°C under DOE Office of Distributed Generation

70

80

90

100

200

21,000 21,500 22,000 22,500 23,000 23,500 24,000 24,500

620 640 660 680 700 720 740

10

20

STR

ESS

(MP

a) -

Log

Scal

e

LMP (K, C=20)

TEMPERATURE FOR 10,000 HOUR RUPTURE LIFE

STR

ESS

(ksi

) - L

og S

cale

Commercial 3-5mil Foils

347

Haynes 230 HR-120

AL20/25+Nb - Phase 1

AL20/25+Nb - Phase 2

625

347: Fe-17Cr-11NiAL+Nb: Fe-20Cr-25Ni120: Fe-25Cr-35Ni230: Ni-23Cr-12W625: Ni-23Cr-9Mo-4Nb

Also 214, PM2000

Not done:617740H282

6 2015 Akron U

ORNL (Maziasz) helped improve the strength of commercial 347 and AL20/25+Nb foilby composition and processing control

0

5

10

15

20

25

30

35

40

0 200 400 600 800 1000

Commercial Sheet Creep-Rupture

CR

EEP

STR

AIN

(%)

TIME (hours)

AL20/25+Nb Phase 210 mil SheetAL20/25+Nb Phase 1

15 mil Sheet

347 10 mil Sheet

Creep Tests:

750oC, 100MPa0

5

10

15

20

25

30

35

0 500 1000 1500 2000

Commercial Foil Creep-Rupture Tests

CR

EEP

STR

AIN

(%)

TIME (hours)

HR120 3.2 mil Foil

AL20/25+Nb Phase 14 mil Foil / 5mil Foil

347 3.2 mil Foil

AL20/25+Nb Phase 23.2 mil Foil

Creep Tests:

750oC, 100MPa

1382°F, 14.5ksi

7 2015 Akron U

AL20-25+Nb optimized microstructureCoarsened grain size and fine carbides

SEM BSE images10 mil, as processed condition

20 m

AlNNbC

Phase 2 Avg. Grain Size = 18.2 mm

15 mil, as processed condition

Phase 1 AverageGrain Size = 11.4 mm

specimens crept 750ºC, 100 MPaPhase 2; 3.2 mil; tr=1702 h

500 nm

NbC

MC / M C23

6

TEM imagesPhase 1; 15 mil; tr=400 h

NbCM23C/M6C

8 2015 Akron U

Summary & Closing ThoughtsORNL has 20 years experience evaluating and optimizing

the high temperature properties of thin-walled alloys for gas turbine heat exchangers♦ International recognition for recuperator materials♦ High quality data base on creep and oxidation behavior♦ Alloy optimization and development impacted the industry

Current small project supports the deployment of ORNL alumina-forming austenitic (AFA) steel foil♦ Evaluation of current alternatives♦ 8,000h durability test in 65kW engine in progress at ORNL

ORNL expertise can assist in the development of new thin-walled heat-exchangers for supercritical CO2♦ New alloys should be evaluated♦ Current materials have improved since ~1999-2006 data