Erfahrungs- und Forschungsbericht 2012 - Ensi

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Erfahrungs- und Forschungsbericht 2012 - Ensi

were taken out for subsequent FIB sample preparation.

FIB-TEM sample preparation

A Zeiss NVision 40 workstation FIB (equipped with

electron and ion beams) with an EDS system by

Oxford instruments and a Kleindiek micromanipulator

was used. The TEM sample preparation followed

the procedure described in [8].

The irradiated material deformed during the thinning

due to internal stresses, therefore the width

of the electron-transparent window had to be restricted.

In some cases more than one window

was thinned to avoid fracture and bending of the

sample. The samples were often not sufficiently

thin for the TEM analysis; thus, in the case of each

material more than one TEM lamella was needed

to analyze in detail the microstructure of the

metal-oxide interface.

TEM observations

A JEOL2010 equipped with a LaB 6 cathode and

an EDS system by Oxford Instruments is used. The

investigations were focused on the geometry of

the metal-oxide interface, the composition and

microstructure of precipitates in the metal and

the oxide, the oxide microstructure and when

possible the presence of hydrides. The EDS analyses

are performed in particular on precipitates

in the metal-side and oxide-side of the interface,

the results are based on semi-quantitative analyses.

Results

Alloy A fresh

The composition of this alloy in wt% consists of

0.58% of Sn, 0.36% of Fe, 0.26% of Cr, and

0.31% of Nb, 1550 ppm O2 and the balance of

Zr. In comparison with all the alloys studied in this

research work, it is the only alloy that contains

Cr to a level considered as an alloying element.

Furthermore, as it is for Zirlo and E635, this alloy

contains Sn (0.58 wt%), the only alloy not containing

Sn being M5.

This alloy has been irradiated to 53.4 MWd/KgU.

The material was very hard to cut and polish, it

was therefore, mounted without polishing on the

SEM sample holder for FIB sample preparation. The

sample was first polished by FIB to obtain a sufficiently

large window to prepare subsequently the

TEM lamella. The archive material of this alloy is

requested and received from Halden HRP. It has

been examined, to clarify the microstructure of the

cladding and the nature of precipitates prior to

irradiation.

In the first part of this section, the analysis of the

irradiated material will be reported. This material

had precipitates in the metal side of the interface.

These precipitates are assumed to be (Cr,Fe) 2 Zr,

intermetallics and Nb is partly replacing Zr sites.

The composition of precipitates was examined

by EDS analysis and two families of precipitates

could be described, one with a ratio of Cr to Nb

ranging between 3 and 4, and another with a

ratio of Cr to Nb between 6 and 7. In the regions

examined, close to the metal/oxide interface, no

β Nb precipitate or any Nb rich phase were observed.

This could be due to the low concentration

of Nb in the material. No Nb was observed

in the matrix, apart from a small amount close to

a

Figure 1: (A) TEM

bright field contrast of

the metal-oxide interface

of alloy a fresh,

the interface (white

arrows) is undulated.

(B) TEM dark field

contrast of the metal

side of the interface,

hydrides can be

observed.

ENSI Erfahrungs- und Forschungsbericht 2012 117

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