Introduction Characterization of subgrain boundary types ... · 5 May 2010 Ilka Weikusat -...

EGU Vienna5 May 2010

Ilka Weikusat - Characterization of subgrain boundary types inpolar ice (EPICA-DML ice core)

TS3.1 - Deformationprocesses

Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Characterization of subgrainboundary types in polar ice (EPICA-

DML ice core)

Foto

: RAD

ARSA

TAn

tarc

tic M

appi

ngM

issi

on

Ilka Weikusat1,Atsushi Miyamoto2, Martyn R. Drury3,

Sepp Kipfstuhl1, Sérgio H. Faria4,Gill M. Pennock3, and Nobuhiko Azuma5

1Alfred-Wegener-Institut für Polar- undMeeresforschung (Bremerhaven, Germany)

2Institute of Low Temperature Science (Sapporo, Japan)3Utrecht University (The Netherlands)

4University of Göttingen (Germany)5Nagaoka University of Technology (Japan)




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

MotivationSchematic Cross section through an ice sheet




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Relevance

(from Hondoh 2000)

Glide systems in ice

Glide on non-basal planes≈60x harder!

But needed for deformationcompatibility




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

subGB

EDML 2095.1m

Grain boundary

Air hydrate

Subgrain boundary

Slipband

MicrostructureMapping (µSM)

Glass plate

Grain boundary

Sublimation

Samplefigure: Kipfstuhl




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

State

modified after: De La Chapelle et al. 1998

upperfew X00m

deeperfewX00m

Literature - recrystallization regimes in ice sheets

normal graingrowth(NGG)

polygonization / rotationrecrystallization

GB migrationrecrystallization

(T>-10°C)

- with nucleation

Regular straight GB, “foam texture”

subGB

irregular GB

Expected in µSM




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

subGB density:

Weikusat et al. 2009, J. Glaciol.

!

"subGB

=LsubGB

A

L : total subGB lengthA : area

frequencybut, ice core data (EDML) do not show a

“subGB depth range”

... (and neither do other parameterssupport the three recrystallizationregimes)




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Weikusat et al. 2009, J. Glac.

subGB types (morphologic)




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Relevance

(from Hondoh 2000)

Glide systems in ice

Glide on non-basal planes≈60x harder!

But needed for deformationcompatibility

(after Montagnat and Duval, 2004)

creep test σ-range:Ice sheet σ-range:

!

˙ " = B # exp($Q /RT) #% n

T = absolute temperatureR = gas constantB, n, Q = constants

Flow law used in icesheet modelling




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary subGB types(morphologic)

EDML 655.9m

µSM




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

EBSD example

EDML 655.9m

subGB types(structural) >10°

>2°>1°>0,75°>0,5°

ice core axis incrystal reference

EBSD data




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Basal twist

EDML 655.9m


>2°>1°>0,75°>0,5°


subGB parallel to basal plane

subGB || basal plane+

Rot. Axis basal plane=

Twist boundary with setsof screw dislocations

on basal (b=a)

T

Rotation Axis is c-axis

EBSD data




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Basal tilt

EDML 655.9m


>2°>1°>0,75°>0,5°


subGB normal to basal plane

Rotation Axis is close to prism plane normal

sGB basal plane+

Rot. Axis || basal plane =

Tilt boundary withedge dislocations

on basal (b=a)

T

EBSD data




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Non-basal tiltsubGB types(structural) >10°

>2°>1°>0,75°>0,5°


subGB parallel to basal plane

Rotation Axis is close to prism plane normal

sGB || basal plane+

Rot. Axis || basal plane=

Tilt boundary with edge dislocations on non-basal (b=c or b=c+a)

a

EBSD data




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

subGB types statistics

NsGB = 165 ; [%]

basa

l pla

ne:

Non-basal tilt boundaryBurgers vector = c or c+a

X-ray Laue diffraction DataWeikusat et al. 2010, submitted to J. Glac.

Basal tilt boundaryBurgers vector = a

Basal twist boundaryBurgers vectors = a




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

Summery• Three recrystallization regimes have to be reconsidered

• Subgrain boundaries identified as– Tilt boundary comprised of

edge dislocations in basal plane (b=a)

– Twist boundary comprised of sets ofscrew dislocations in basal plane (b=a)

– Tilt boundary comprised ofedge dislocations in NON-basal plane (b=c or b=c+a)

• Surprising: Non-basal tilt boundaries are quite common




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary Thank you.

[email protected]




Introduction

subGB inice

Frequency

Types

type I

type II

type III

Statistics

Summary

References

• Hondoh, T. Hondoh, T. (ed.) Nature and behaviour ofdislocations in ice Physics of Ice Core Records, HokkaidoUniversity Press, 2000, 3-24

• Weikusat, I.; Kipfstuhl, S.; Faria, S. H.; Azuma, N. & Miyamoto,A. Subgrain boundaries and related microstructural features inEPICA-Dronning Maud Land (EDML) deep ice core J. Glaciol.,2009, 55, 461-472

• Montagnat, M. & Duval, P. Dislocations in ice and deformationmechanisms: from single crystals to polar ice Deffect andDiffusion Forum, Scitec Pub., 2004, 229, 43-54

• De La Chapelle, S.; Castelnau, O.; Lipenkov, V. & Duval, P.Dynamic recrystallization and texture development in ice asrevealed by the study of deep ice cores in Antarctica andGreenland J. Geophys. Res., 1998, 103, 5.091-5,106

• Weikusat, I., Miyamoto, A., Faria, S. H., Kipfstuhl, S., Azuma,N., Hondoh, T.(2010).Subgrain boundaries in Antarctic icequantified by X-ray Laue diffraction, J. Glaciol. [SUBMITTED]

Introduction Characterization of subgrain boundary types ... · 5 May 2010 Ilka Weikusat -...

Documents

Transcript of Introduction Characterization of subgrain boundary types ... · 5 May 2010 Ilka Weikusat -...