Diffusion mechanism of silicon (up to 6.5 WT %) deposited from vapour phase on electrical steel sheets

Directorate-General For Research And Innovation European Commission

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Industrial research and development

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• Sciences et techniques

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• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION-EUROPEAN-COMMISSION
• Nombre de lectures: 8
• Langue: English
• Poids de l'ouvrage: 3 Mo

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EURO PEAN
COMMISSION
SCIENCE
RESEARCH
DEVELOPMENT
technical steel research
Properties and in-service performance
Diffusion mechanism
of silicon
(up to 6.5 WT %)
deposited from
vapour phase on
electrical steel sheets
Report
m
EUR 18561 EN STEEL RESEARCH EUROPEAN COMMISSION
Edith CRESSON, Member of the Commission
responsible for research, innovation, education, training and youth
DG XII/C.2 — RTD actions: Industrial and materials technologies —
Materials and steel
Contact: Mr H. J.-L. Martin
Address: European Commission, rue de la Loi 200 (MO 75 1/10),
B-1049 Bruxelles — Tel. [phone]; fax [phone] European Commission
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Properties and in-service performance
Diffusion mechanism of silicon
(up to 6-5 WT %) deposited from
vapour phase on electrical steel sheets
E Arezzo
Centro Sviluppo Materiali SpA
Via di Castel Romano 100-102
1-00129 Rome
Contract No 7210-MA/429
1 July 1992 to 30 June 1995
Final report
Directorate-General
Science, Research and Development
1998 EUR 18561 EN LEGAL NOTICE
Neither the European Commission nor any person acting on behalf of the Commission
is responsible for the use which might be made of the following information.
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Luxembourg: Office for Official Publications of the European Communities, 1998
ISBN 92-828-4903-1
© European Communities, 1998
Reproduction is authorised provided the source is acknowledged.
Printed in Luxembourg
PRINTED ON WHITE CHLORINE-FREE PAPER CONTENTS
Page
SUMMARY 5
FINAL SUMMARY 6
OBJECTIVES OF THE RESEARCH PROJECT 7
LIST OF TABLES 9
LIST OF FIGURES 10
1. INTRODUCTION H
2. MAGNETIC SHEET-STEELS1
2.1 General Considerations
2.2 Fe-Si sheet-steels2
3. VAPOUR PHASE DEPOSITION TECHNOLOGIES 13
3.1 Physical Vapour Deposition (PVD)
3.2 Chemicalrn (CVD)4
4. DESCRIPTION OF ACTIVITIES 1
4.1 Substrate Materials
4.2 PVD Experimentation
4.3 CVDn
4.3.1 Conventional CVD (1st group)
4.3.2 RFPACVD and Diffusion at 500°C (2nd group) 15
4.3.3D andn at 700°C (3rd) \6
4.3.4 Thermal CVD and Diffusion simultaneously (4th group) \j
4.3.5 Standard Annealing Furnace (5th group)7
4.3.5.1 Deposition and Diffusion Alternatively (subgroup 5A)... ig
4.3.5.2 Steady Thermal CVD Conditions (subgroup 5B) i8
4.4 Testing Procedures Ig
4.4.1 SEM Analysis 1
4.4.2 GDOESs8
4.4.3 Magnetic Testing ,ç
5. RESULTS AND DISCUSSION9
5.1 Substrate Materials
5.2 PVD Experimentation
5.3 CVDn
5.3.1 Conventional CVD (1st group) 21
5.3.2 RFPACVD and Diffusion at 500°C (2nd group)
5.3.3D andn at 700°C (3rd)
5.3.4 Thermal CVD and Diffusion simultaneously (4th group) 2
5.3.5 Standard Annealing Furnace (5th group)
5.3.5.1 Deposition and Diffusion Alternatively (subgroup 5 A) 22 5.3.5.2 Steady Thermal CVD Conditions (subgroup 5B) 23
5.4 Diffusion Mechanism 28
6. CONCLUSIONS 31
6.1 Suggested Applications and Future Work 32
REFERENCES3
FIGURES 34 DIFFUSION MECHANISM OF SILICON (UP TO 6.5 WT%) DEPOSITED FROM
VAPOUR PHASE ON ELECTRICAL STEEL SHEETS
Centro Sviluppo Materiali S.p. Α.
ECSC Agreement N° 7210-MA/429
Summary
This research has shown that it is possible to enrich with Si electrical sheet steels by
utilizing a combination of CVD deposition and diffusion. CVD conditions at 900 °C, utilizing
2% SiHt in Ar for 3 minutes alternated with 4 minutes of annealings (Ar only) in the
same reactor at 1050°C for a total time of 4 hours increased the Si content in the FIO electrical
sheet from the original 1.0% to over 6.0%.
Steady CVD conditions at 1100°C for 1 hour increased the Si content of the same FIO
samples to about 3.5 %. The magnetic behaviours (reduced loss) of these Si enriched samples
resulted similar to those of the upper classes of commercial materials having approximately
twice the Si content of each original sample.
The Si diffusion constant into the magnetic sheet steel was experimentally calculated
from GDOES depth profiles and it was found to be 1.2xl0_11 m2/s and 0.8xlO-11 m2/s in the
Si concentration ranges 2.7-3.5 wt % and 2.5-2.7 wt %, respectively.
The results indicated that a series of CVD apparatus with increasing partial pressures of
the Si carrying gas in the vapour phase would be a much more efficient method for Si
enrichment. However, even in this case the long diffusion time does not seem to make feasible
the industrialisation of the process. DIFFUSION MECHANISM OF SILICON (UP TO 6.5 WT%) DEPOSITED FROM
VAPOUR PHASE ON ELECTRICAL STEEL SHEETS
Centro Sviluppo Materiali S:p.A
ECSC Agreement No. 7210-MA/429
FINAL SUMMARY
The Fe 6.5 wt.% Si alloys exhibit excellent magnetic properties, but have poor ductility.
Their brittlness has prevented the commercial scale production of steel materials with so high
Si contents.
This project aimed at developing a Si enrichment process by combining vacuum deposition
techniques and annealing processes.
The CVD technology, after a comparison with the PVD, was adopted because it was found
to be the most suitable for this purpose. Three types of electrical sheet steels with different
starting Si contents (FIO, 1.0 wt.% Si; F17, 1.7 wt.% Si; OG32, 3.0 wt.% Si) were selected
as substrate materials.
Si enrichment experiments, consisting in depositing a Si coating onto the steel samples
and then annealing them, were unsuccessful. Temperatures as high as 700°C were too low for
starting diffusion. Heavy delamination of the Si coatings also occurred at temperatures higher
than 500°C.
CVD conditions at 900°C (2% S1H4 in Ar) for 3 minutes alternated with 4 minutes of
annealings (Ar only) in the same reactor at 1050°C for a total time of 4 hours gave
positive results. SEM/EDS analysis results showed that the Si content in the FIO samples
from the original 1.0% went to about 6.0%, while in the Fl7 samples it went from 1.7% to
about 4.0%. The least increase was observed in the OG32 samples, where Si raised only
slightly and reached a maximum of 4.0% in the best cases.
Similar diffusion results were obtained in one half the time (2 hours) by utilizing steady CVD
conditions with the same 2% SiH» in Ar mixture at the temperature of 1050°C.
All these results indicated that a series of CVD with increasing partial pressures of the
Si carrying gas in the vapour phase would be much more efficient than an alternate sequence
of CVD depositions and diffusions. However, it was realized that even in this case the
excessive number of CVD apparatus required, due to the long diffusion time, would not
make feasible the industrialization of such a process.
Therefore, a last series of experiments was initiated, where stady CVD conditions with
a temperature of 1100°C for 1 hour were utilized.
These experiments were run on full size specimens so that it was possible to run magnetic
tests and to correlate the results with those of SEM/EDS and GDOES showing the levels of
Si enrichment. The Si contents in the FIO and Fl7 samples increased over 3.5% and 2.6%,
respectively.
The magnetic behaviours (reduced loss) of these Si enriched samples resulted similar to those
of the upper classes of commercial materials having approximately twice the Si content of
each original sample.
The Si diffusion constant into the magnetic sheet steel was experimentally determined
from GDOES depth profiles and it was found to be 1.2Ί0"" m2/s and 0.8-10~nm2/s in the Si
concentration ranges 2.7-3.5 wt.% and 2.5-2.7 wt.%, respectively. DIFFUSION MECHANISM OF SILICON (UP TO 6.5 WT%) DEPOSITED FROM
VAPOUR PHASE ON ELECTRICAL STEEL SHEETS
Centro Sviluppo Materiali S.p. Α.
ECSC Agreement N° 7210-MA/429
Objectives of the research project
It has been well known that the Fe-6.5 wt %Si alloy exhibits excellent soft magnetic
properties, but has poor ductility. This has prevented the commercial scale production of this
material. In 1988 NKK Corp. reported successful development of both a rolling process and a
chemical vapour deposition (CVD) process to produce coils of Fe-6.5 wt %Si alloy.
However, details of the CVD process are unavailable.
This project aimed at confirming the feasibility of the Si enrichment of sheet steels by
combining deposition techniques and annealing processes. In short, it was expected that the
results of this research would lead to the acquisition of the necessary know-how for the
development of a vacuum deposition process suitable for Si enrichment of electrical steel
sheets.