Pulsed E-beams to improve corrosion barriers for lead alloy cooled - - PowerPoint PPT Presentation

IHM/ KIT/ Campus Nord 1 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

• A. Weisenburger, A. Jianu W. An, M. DelGiacco, A. Heinzel, R. Fetzer, G. Müller

KIT Institute for Pulsed Power and Microwave Technology

Pulsed E-beams to improve corrosion barriers for lead alloy cooled reactors: overview and dedicated mechanical tests

Creep resistance of Al-surface alloyed T91 steel exposed to heavy liquid metals

Introduction – why do we need corrosion barriers Corrosion barrier concept Mechanical tests - Creep to Rupture Influence of liquid lead alloy Behavior of corrosion barrier Summary

IHM/ KIT/ Campus Nord 2 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Actual and planned nuclear facilities cooled with liquid lead alloys

MEGAPIE Coolant +Target: Pb, PbBi LEADER - Pb, SVBR-100 – PbBi

Future GEN IV reactors

EFIT, XT-ADS, MYRRHA Coolant + target: Pb, PbBi

Subcritical systems for transmutation Neutron source - spallation

IHM/ KIT/ Campus Nord 3 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Material compatibility of steels with lead alloys

f/m Stahl / T91 550 °C ~10000h‘s

• xide

200µm

10000 h

• strong oxide scale growth

frequent spallation inter alia growth stresses

• reduced heat removal

Dissolution of alloying elements (solubility : Ni>>Cr>Fe). Dissolution rate up to 1 µm/h

austenitic steel / 1.4970 550°C ~7000h‘s

Two main effects of corrosion: structural integrity – material loss of metal – dissolution attack, oxidation (Spinel + IOZ) heat removal - : oxidation (magnetite + spinel) > 500°C additional corrosion barriers are needed

30µm

IHM/ KIT/ Campus Nord 4 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Corrosion barrier concept against dissolution and strong oxidation: thin, protective, slow growing oxide scales

Al2 O3

Al2 O3 Fe(Cr,Al) Steel (T91)

Requirements

Corrosion resistant in HLM up to ca. 650 °C Self healing of mechanically damaged layers No negative influence on mechanical properties Irradiation stability under relevant fluxes The coating / alloying process must be of industrial relevance

Oxide map FeCrAl – Oxide at 1000°C

Thermal conductivity of Al2 O3 (400°C) = 8 – 12 W/mK (500°C) = 14 W/mK

IHM/ KIT/ Campus Nord 5 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

LPPS sprayed FeCrAlY coating on T91 steel

Al content of powder eg. around. 11 wt% Al – particle size ~ 30µm - Al content still under investigation specific LPPS process that allows spraying of 20 to 30µm thick scales Substrate temperature during spraying < 600°C Layer is porous, rough with significant variation in thickness, bonding to substrate only mechanical GESA – Re-Melting of deposed layer by pulsed electron beams – T91 has to stay < 650 °C

T91

IHM/ KIT/ Campus Nord 6 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Surface modification using Pulsed Electron Beams (GESA) (Process development in cooperation with NIIEFA, St. Petersburg)

Volumetric Heating: rate: < 109 K/s time: < 40 µs Melt layer: depth: < 100 µm cooling: < 107 K/s (heat conduction)

Surface alloyed layer

e-- beam

Magnetic- coil Anode Target

GESA facility

Electron beam Parameter: Electron Energy:125 keV Power density : ∼ 2 MW/cm² Pulse duration controllable: < 40 µs Beam diameter: ~ 4cm GESA I Treatable length ~ 30 cm GESA IV

LPPS sprayed FeCrAl layer

T91 Substrate temperature remains relatively low – no micro-structural changes in T91 observed

cathode

IHM/ KIT/ Campus Nord 7 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Al content ~ 5 - 7 wt% Al content ~ 10 wt%

T91 + FeCrAlY layer before and after surface modification

As sprayed After GESA treatment

10 20 30 40 10 20 30 40 50 60 70 80 90 100

Fe, Cr, Al content in % distance from surface in μm Fe Cr Al

5 10 15 20 25 10 20 30 40 50 60 70 80 90 100

Fe, Cr, Al contnet in % distance from surface Fe Cr Al

Surface smoothed, pores are removed, layer densified, metallic bonding to substrate surface alloyed material

IHM/ KIT/ Campus Nord 8 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Influence of temperature – “perfect” Al surface alloyed steel at optimal oxygen concentration 10-6 wt%

10000 h 10000 h 10000 h 500°C 550 °C 600°C Up to 600°C and 10000 h no corrosion attack and no visible

• xidation.

Thin alumina scales protect the surface alloyed steel.

20µm 20µm 20µm 5000 h at 600 °C in flowing LBE (10-6 wt%) GESA treated FeCrAlY

IHM/ KIT/ Campus Nord 9 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Exposed to PbBi having 10-6 wt% oxygen 2000h at 10-6 wt Oxide scale formation at different temperatures (Alpowder 7wt%)

480 °C 550 °C 600 °C Large areas showed unexpected

• xidation especially at 480 and 550°C

Al content (~4 wt%) before and after exposure Optimisation of coating and post treatment process to increase Al content Al content required for selective Al-oxide formation –preliminary results At 476°C Al > ~6.2 wt% At 490°C Al > ~5.6 wt% At 550°C Al > ~5.2 wt%

IHM/ KIT/ Campus Nord 10 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Creep to rupture of T91 in PbBi and air

T91 with and without GESA modified FeCrAl layer

Material:

T91 : normalized [1050°C (30 min)] – air quenched followed by tempering [770°C (1h)] Specimens: cylindrical test-length 70 mm – diameter 6 mm GESA surface modified specimens are heat treated to release possible residual stresses Temperature of heat treatment : 400°C in air– Duration : 2 h T91 original After FeCrAlY deposition After GESA treatment

Test environment: Air at 550 and 600°C LBE at 500, 550°C and 600°C LBE contains 10-6wt% oxygen Stress levels: in air: 140 to 220 MPa in LBE: 60 to 220 MPa

IHM/ KIT/ Campus Nord 11 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Test – setup of creep rupture experiments examined at Prometey St. Petersburg (gratitude A. D. Kasthanov, V. G. Markov)

PbBi 500

∅

48 (60) Capture Bellows Body Specimen Capture

Specimens 100h in test section prior to stress initiation Measurement of strain outside at capture Using calibration curve from air experiments strain at specimen is calculated PbBi: 10-6 wt% oxygen Flow velocity : 0.5 m/s

IHM/ KIT/ Campus Nord 12 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Influence of PbBi on time to rupture of T91 orig at 550°C

Journal of Nuclear Materials 394 (2009) 102–108

Significant reduction in time to rupture

• f T91 due to contact with PbBi

Oxide scale cracks PbBi penetrates and reduces the surface energy – Rebinder effect – stress corrosion cracking

IHM/ KIT/ Campus Nord 13 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Comparison of secondary creep rates of T91 in air and PbBi at 550 °C

Stress [MPa] Ratio of 2nd creep rates, LBE/air 140 27 160 35 180 44 200 53

Influence

• f PbBi

Creep rate in PbBi up to 50 times higher than in air Ratio of creep rate in PbBi and air is stress dependant At low stresses – no cracking of oxide scale ?? – no direct contact with PbBi – no influence on creep strength - threshold stress ??

IHM/ KIT/ Campus Nord 14 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Creep tests at low stresses at 550°C – Threshold stress ??

200 400 600 800 1000 1200 1400 1600 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4

60 MPa - PbBi 80 MPa - PbBi 100 MPa - PbBi 120 MPa - PbBi 140 MPa - Air 140 MPa - PbBi

strain in % Duration in hour's

60 to 120 MPa no change - as long as oxide scale intact no influence cracks at 60 and 80 MPa reduction in strength Any deterioration of the oxide scale results in reduced creep strength 60Mpa Cracks PbBi can penetrate 120 MPa No cracks No PbBi No influence

IHM/ KIT/ Campus Nord 15 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Creep tests at lower Temperature of 500°C – reduced diffusion and sliding reduced strain

Reduction of temperature to 500°C lead to significant differences Reduced strain no cracks in oxide scale neglect able influence of PbBi 180 MPa Slow strain <0.4% No cracks in

• xide scale

220 MPa

IHM/ KIT/ Campus Nord 16 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Creep to rupture test of T91 orig. and GESA surface modified T91 in air at 550°C

Significant longer rupture times of GESA modified T91 Surface alloyed layer improves creep strength Thin Al2 O3 scale formed at surface

IHM/ KIT/ Campus Nord 17 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Stress: 200 and 220 MPa

500 1000 1500 2000 2500 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 160 MPa 180 MPa T91 orig air GESA inPbBi

Strain in % Time in h

160 MPa 180 MPa

Stress 160 and 180 MPa

Comparison of creep of GESA surface modified T91 in PbBi and T91 orig. in air at 550°C

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 2 4 6 8 10 12 14 16 18 20 22 200 MPa 220 MPa

strain in% time in h

200 MPa 220 MPa T91 orig air GESA inPbBi

T91 with GESA modified FeCrAl layer also shows an influence of LBE. However, this deterioration is significantly reduced compared to the T91 original. At 200MPa still a reduction in time to rupture from 3500 auf 2500h is observed. At a strain

• f about 3.5% influence of PbBi becomes visible.

IHM/ KIT/ Campus Nord 18 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5 10 15 20

strain in % time in h

T91 orig PbBi T91 orig Air GESA PbBi GESA Air

Comparison of creep to rupture (200 MPa) of GESA surface modified T91 and T91 orig. in air and PbBi at 550°C

Negative influence of LBE on creep strength of T91 is strongly reduced by the surface alloyed layer

IHM/ KIT/ Campus Nord 19 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Stress: 200 and 220 MPa

500 1000 1500 2000 2500 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 160 MPa 180 MPa T91 orig air GESA inPbBi

Strain in % Time in h

160 MPa 180 MPa

Stress 160 and 180 MPa

Comparison of creep of GESA surface modified T91 in PbBi and T91 orig. in air at 550°C

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 2 4 6 8 10 12 14 16 18 20 22 200 MPa 220 MPa

strain in% time in h

200 MPa 220 MPa T91 orig air GESA inPbBi

T91 with GESA modified FeCrAl layer also shows an influence of LBE. However, this deterioration is significantly reduced compared to the T91 original. At 200MPa still a reduction in time to rupture from 3500 auf 2500h is observed. At a strain

• f about 3.5% influence of PbBi becomes visible.

IHM/ KIT/ Campus Nord 20 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

180 MPa 2.2% strain

• nly minor cracks

GESA Specimens after creep to rupture experiments in PbBi 180 and 220 MPa 550°C

Al-content sufficiently high Alumina Al-content < 4wt% Spinel und Magnetite Cracks in magnetite and spinel Up to now no PbBi penetrated At the border to the necking region cracks but no PbBi Cracks in magnetite und spinel PbBi penetrated

IHM/ KIT/ Campus Nord 21 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Comparing 2nd creep rate of T91 original at 550 °C in air and PbBi and T91 GESA in PbBi

T91 GESA:

• 2nd creep rate in PbBi similar that of T91 original

in air GESA modified FeCrAlY reduces the negative influence of PbBi at 550°C Specimens not entirely protected by thin alumina scale with optimized specimens an even better result to be expected

80 120 160 200 1E-6 1E-5 1E-4 1E-3 0,01 0,1

secondary creep rate, hour

• 1

applied stress, MPa

Original LBE Original air GESA LBE T91 orig and GESA 癈 tested at 550

IHM/ KIT/ Campus Nord 22 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Creep to rupture of T91 with and without GESA in PbBi and air at 550°C

Oxide scale cracks PbBi penetrates the crack PbBi reduces surface energy of steel dissolute steel elements and penetrates the grain boundaries crack propagation Stress over time to rupture of T91 original and T91 GESA GESA modified FeCrAlY layer reduces the negative influence of PbBi No cracking of oxide scale no influence of PbBi

10 100 1000 10000 100 150 200 250 300 GESA 600 PbBi GESA 600 Air T91 orig 600 air (spire) GESA 550 PbBi GESA 550 Air T91 orig Luft (spire) T91 orig 550 PbBi

Stress (MPa) time to rupture (h)

IHM/ KIT/ Campus Nord 23 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

Summary

Concept of strong oxide formers improves significantly the compatibility between steel and PbBi Al content has to be high enough to ensure the formation of slow growing thin and stable scales Process optimization towards Al-content, homogeneity and reproducibility is ongoing Negative influence of PbBi on creep strength of T91 f/m steel tested at high stress at 550°C At 550°C low stress and at 500 °C significant reduced influence – Oxide scale stays intact – no cracks – no direct contact Surface alloyed layers improve significantly the creep behaviour in liquid PbBi At 550°C very similar to T91 orig. in air Acknowledgement: V.G. Markov, A.D. Kashtanov Central Research Institute of Structural Materials – ‘‘Prometey”, 49 Shpalernaja, St. Petersburg, 191015, Russia

IHM/ KIT/ Campus Nord 24 | A. Weisenburger et al.| IWSMT-10 Bejing October 2010

T91 surface modified specimens after 2000h of exposure 600 °C

Outer scale of Al oxide followed by chromium Al precipitations at boundary layer (Fe3 Al) No diffusion of Al into the bulk Thin stable oxide layer protects the T91 cladding

5 10 15 20 25 30 35 40 100 200 300

μm

Cr 5 10 15 20 25 30 35 40 100 200

μm

Al 5 10 15 20 25 30 35 40 100 200

μm

O 5 10 15 20 25 30 35 4 100 200 300 400 500

μm

Fe

69 70 71 72 73 74 75 76 77 78 79 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Binding Energy (eV) Normalized Intensity

Al 2p

Al3+-O Al0 XPS Measurement