Materials characterization by high energy synchrotron ... · Materials characterization by high...

Materials characterization by high energy

synchrotron radiation: welding

Ulrich Lienert (DESY)

BIR2Gain Lund, June 1, 2017

Swedish High Energy Materials Science Beamline

Ulrich Lienert | BIR2Gain, Lund | 01.06.2017 | Page 2

Outline

> Spatial & temporal heterogeneities

Solidification morphology

Crystallographic phases (& chemical composition)

Strain/stress

Precipitation microstructure

> Experimental techniques

Imaging

SAXS

WAXS (angle & energy dispersive)

Pencil beam CT

> In-situ & post mortem experiments


Imaging: in-situ radiography & post mortem tomography

> Initiation & growth kinetics of solidification cracking during welding of

steel

L. Aucott, et al., Sci. Rep. 7, 40255 (2017)

> ESRF, ID19

> Pink beam, 117 keV

> EN1A mild steel, 8x8x300mm3

> TIG welding


Imaging: in-situ radiography

> Solidification 0.18 s

> 1kHz frame rate

> Cracks initiate trailing the

electrode, at weld subsurface

where peak volumetric strain &

triaxiality are localised

> Cracks propagate towards the

free surface along solidifying

grain boundaries


Imaging: post mortem tomography (initiation)

> Initial micro-cavities 10-27 mm

> Flow of liquid metal to strain localized regions


Imaging: post mortem tomography (propagation)


HE-SAXS

> Contrast: electron density

> Particle size, shape, volume

fraction (form factor)

> Particle distribution

(structure factor)

> Combination with WAXS

> Resonant scattering

-> element specific

(Boldon et al. 2015)


SAXS: post mortem precipitate microstructure mapping

> AA2050 Al-Li-Cu in T8 state after friction stir welding

> Precipitates: T1 platelets & clusters/GP zones

> ESRF, BM02-D2AM, E = 16.128 keV

> Sample: cross sectional 15 x 60 x 0.6 mm3

> Beam size: 200 x 200 mm2, 0.5 mm raster (3600 points)

> SAXS fitting model informed by TEM samples

60 mm

15

mm

F. De Geuser et al., Phil. Mag. 94 (2014) 1451-1462


> Annealing: temperature most important parameter

> Good correlation with hardness measurements

Cluster radii

Cluster volume fraction

T1 precipitates: thickness

T1 precipitates: volume fractions

a.u

. Ǻ

SAXS: post mortem precipitate microstructure mapping


XRD-CT

> “phase” reconstruction

> Reverse analysis

w y

x

Bleuet et al., Nature Materials 2008


Pencil beam SAXS (& WAXS) CT

> J. Andersson (U. West), M. Fisk (Malmö U.), S. Haas & U. Lienert (DESY)

> Precipitation microstructure of Ni based superalloys in weldments

> Post heat treatment (at 788°C for 8h)

> APS, 1-ID, 80 keV, 200 mm resolution

> SAXS intensity at q = 0.125 nm-1

welding direction

HAZ

FZ


Residual strain/stress mapping

> Bead-on-plate weldments (carbon steel AS/NZS 3678-250)

> APS 1-ID, 76.8 keV

Paradowska et al., J. Pressure Vessel Technol. (2010)

12 mm


3D strain scanning

> Grain size variation (NiTi)

J.P. Oliveira et al., Mater. Design

2016

Base material HAZ Fusion zone


Far-field single grain diffraction

> Positions & axial strain of 1118 Cu

grains before & after uniaxial

deformation

J. Odershedde et al., Mater. Charact. (2011)


From strain to stress

> Lattice spacings

Relative to calibration powder

> Strain free lattice parameter: d0

Chemical composition, temperature

> Strain tensor

𝒏ℎ𝑘𝑙 ⋅ 𝝐 ⋅ 𝒏ℎ𝑘𝑙 =𝑑−𝑑0

𝑑0

Six independent components

Hydrostatic & deviatoric parts

> Elastic constants

4th rank tensor

anisotropy

Chemical composition, temperature

Orientation averaging (texture)

> Stress

𝜎𝑖𝑗 = 𝐶𝑖𝑗𝑘𝑙𝜀𝑘𝑙

2𝑑ℎ𝑘𝑙 sin 𝜃 = 𝜆


WAXS: In-situ phase ID & strain evolution by EDXRD

> Low transformation temperature (LTT) weld filler material: In-situ local phase

transformation kinetics & strain evolution during gas tungsten arc welding (GTAW)

> ESRF, ID15, EDXRD, 5 Hz data rate

> LTT: 10% Cr-10 % Ni

> Base metal: S690Q (fine grained)

J. Gibmeier et al., J. Mater. Proc. Technol. (2014)


Phase transformation kinetics

> Local martensite & austenite phase fractions &

transformation rates

> -peaks apparent for about 2.5 s

> Transient -peaks at high temperature & local

crystallographic textures during cooldown

> Continued martensite formation down to room

temperature: local chemical variations

> Ms increases away from weld surface:

Local demixing of LTT filler material

Local stress fields => deformation induced martensite

formation

Longitudinal

@ 3mm

From weld

surface


Strain evolution

> Initially increasing tensile strains in –phase due

to CTE mismatch

> a’-phase longitudinal in compression

(constraint); transverse reduced tension =>

delayed martensitic transformation counteracts

the tensile thermal strain

3 mm from weld surface

Local longitudinal strain in a-phase

> Initial strain state of a’-phase depends on the

distance to the weld: Tensile close to the weld

surface & compressive towards the base metal

> Martensite transformation starts away from weld

surface. Progressively more tensile strains in the

-phase may influence the a’-formation.

> Increasing compressive strain with cooling due

to thermal mismatch


FlexiStir (P07 HZG)

> In-situ friction stir welding


Summary

> Fixed orientation: 2D projection; rotation: 3D

> Imaging

Contrast: electron density

Solidification morphology, voids

Resolution > 5 mm & > 10 ms

> SAXS

Contrast: electron density

Precipitates, porosity

Resolution < 1 mm & > 100 ms

> WAXS

Orientation contrast

Crystallographic phases, strain/stress

Resolution > 1 mm / 200 mm & 10 ms


Swedish Beamline at PETRA III: Diffraction station

> TDR: petra3-extension.desy.de -> BEAMLINES -> P21

> First beam anticipated early 2018

P21.2: Ulrich Lienert, Sven Gutschmidt, Sylvio Haas, Thomas Bäcker

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