THE ROLE OF ACTIVE ELEMENTS IN THE OXIDATION BEHAVIOUR OF

HIGH TEMPERATURE METALS AND ALLOYS

Proceedings of the European Colloquium organised by:

Commission of the European Communities Directorate General: Science, Research and Development

and held at the Institute of Advanced Materials, Joint Research Centre, Petten Establishment, Petten, (N.H.), The Netherlands, on 12-13 December 1988.

THE ROLE OF ACTIVE ELEMENTS IN THE OXIDATION BEHAVIOUR

OF HIGH TEMPERATURE METALS AND ALLOYS

Edited by

E. LANG CEC Joint Research Centre , Institute of Advanced Materials,

Petten, The Netherlands

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© 1989 ECSC, EEC, EAEC. BRUSSELS AND LUXEMBOURG Softcover reprint of the hardcover 1st edition 1989

British Library Cataloguing in Publication Data

The role of active elements in the oxidation behaviour of high temperature metals and alloys. 1. Metals. High temperature oxidation 1. Lang, E. 546'.3

ISBN-13: 978-94-010-7009-6 DOl: 10.1007/978-94-009-1147-5

e-ISBN-13: 978-94-009-1147-5

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PREFACE Metals and alloys rely for their application at high temperature on the formation and retention

of oxide scales, which act as a barrier between the metallic substrate and the reactive species in the environment such as 0, S, N, C, Cl, etc. This protection concept requires that the oxide grows slowly, develops a dense, uniform layer, is well adherent, has sufficient ductility to accom­

modate plastic deformation of the substrate and is resistant to thermal cycling. For many years it has been known that small concentrations of certain "active elements" such as

Y and the rare earths, as well as carbon and sulphur, can exercise a significant influence upon the

oxidation! corrosion behaviour of high temperature metals and alloys. An increasing number of experimental studies on this topic have been published recently. However no generally

accepted understanding with regard to the detailed mechanisms and the way in which alloy composition and structure, temperature and environmental conditions, etc., are interacting has yet been achieved, although many - often controversial - theories and ideas have been presented. It therefore seemed to be an appropriate time to bring together a group of experts to review and

evaluate the current state-of-the-art and to discuss various aspects of this important topic.

OBJECTIVES of this Colloquium were: + To provide a forum for the presentation and discussion of an up-to-date and comprehensive

evaluation of recent progress and unsolved problems regarding the role of active elements in

the oxidation and corrosion behaviour of HT-metals and alloys. + To bring together experts and other scientists with interests in this topic in order to facilitate

and encourage mutual exchange of knowledge and experiences. + To aid in the identification of research needs and the orientation of future studies.

The 11 h days Colloquium was based upon a number of keynote papers by invited speakers on the different aspects of the subject. Further short communications relevant to the respective topics were presented and poster contributions on original and unpublished material were displayed. This structure is retained in the proceedings.

PROGRAMME CoMMrrIEE: - M.l. Bennett - AM. Huntz - E. Lang - M. Merz

: UKAEA Harwell, UK : Universite de Paris-Sud, F. : CE.C JRC Petten, Establishment, Petten, NL. : CE.C JRC Petten, Establishment, Petten, NL.

The Editor.

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LIST OF CoNTENTS Preface

Opening of Colloquium:

THE MAGIC OF ACTIVE ELEMENTS

E.D. Hondros. Director of the Institute of Advanced Materials.

Joint Research Centre. Petten. NL.

Session 1: INTRODUCTION

Chairman: P. Kofstad, University of Oslo, N.

Keynote Paper:

PRINCIPLES OF GROWTI1 AND ADHESION OF OXIDE SCALES

F.H. Stott, Univ. ofManchester/UMIST, UX

Communication:

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XI

3

OXIDE ADHESION ON PERIODIC TABLE GROUP4 AND 5 METALS 23

M. Lallemant*, G. Bertrand*, D. Ciosmak*, J.P. Larpin* and A. Sanfeld**

* L.R.R.S. Univ. de Bourgogne, Dijon, F.

** U.L.B., Service de Chimie-Physique, Bruxelles, B.

Poster:

ELECTRODE POTENTIAL/TEMPERATURE DIAGRAMS AND THEIR 31

APPLICATION TO HIGH TEMPERATURE CORROSION

M. Pourbaix, CebeIcor, Brussels, B. (Abstract)

Keynote Paper:

ACTIVE ELEMENTS IN OXIDATION AND THEIR PROPERTIES

G. Beranger, F. Armanet and M. Lambertin

Universite de Technologie de Compiegne, F.

Session 2: EFFECTS OF ACTIVE ELEMENTS IN SYNTHETIC OXIDES

Chairman: P. Kofstad, University of Oslo, N.

Keynote Paper:

EFFECT OF ACTIVE ELEMENTS ON DIFfUSION PROPERTIES or SYNTHETIC OXIDES

A. Atkinson, UKAEA, Harwell, U.K.

33

55

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Keynote Paper: EFFECTS OF IMPURITIES ON MECHANICAL PROPERTIES OF OXIDES 1. Castaing, Lab. Physique des Materiaux, C.N.RS. Bellevue, Meudon, F.

Session 3: EFFECT OF ACTIVE ELEMENTS ON OXIDATION OF METh.LS AND ALLOYS

Chairman: 1.H. de Wit, TV Delft, NL.

Keynote Paper:

67

EFFECT OF ACTIVE ELEMENTS ON TI-lE OXIDATION BEHAVIOUR 81 OF Al20]-FORMERS AM. Huntz, Universite de Paris-Sud, F.

Keynote Paper: EFFECT OF ACTIVE ELEMENTS ON TI-lE OXIDATION BEHAVIOUR III OF CrpJ- FORMERS M.1. Bennett and D.P. Moon, UKAEA Harwell, U.K

Communications: TI-lE INFLUENCE OF ACTIVE ELEMENTS ON TI-lE STRESS­RELAXATION IN TI-lE SCALE AND SUBSTRATE ON ALUMINA­FORMING ALLOYS 1. Jedlinski, Institute of Materials Science, AM.M. Krakow, PL.

13l

TI-lE INFLUENCE OF FINE STRUCTURE, MORPHOLOGY AND 153 COMPOSITION OF ALLOY AND OXIDE ON TI-lE GROWTI-I OF CrpJ-SCALES M. Hirbod, R&D ABB STAL, Finspong, S. (Abstract)

Posters: TI-lE EFFECT OF YTTRIA DISPERSIONS ON TI-lE G ROWTI-I AND MORPHOLOGY OF CHROMIA AND ALUMINA SCALES w.1. Quadakkers*, H. Holzbrecher**, KG. Briefs* and H. Beske** * Institut flir Reaktorwerkstoffe ** Zentralabteilung flir Chemische Analysen, KFA liiIich, FRG.

IMPROVEMENTS IN TI-lE ADHESION AND PROTECTIVENESS OF SCALES FORMED ON IRON-CHROMIUM STEELS BYTI-IE APPLICA­TION OF BORON-COMPOUNDS S.R1. Saunders* and lA Little** * NPL Teddington, ** University of Cambridge, U.K

155

175

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EFFECTS OF Ta AND Y ADDITIONS ON THE OXIDATION AND HOT

CORROSION BEHAVIOUR OF Ay/y' ALLOY

M. Vilasi, 1. Steinmetz and P. Steinmetz, Lab. Chimie Solide Mineral,

Univ. Nancy, F. (Abstract)

Keynote Paper:

193

EFFECT OF ACTIVE ELEMENTS ON MECHANICAL PROPERTIES 195

OF SCALES J.R Nicholls and P. Hancock, Cranfield Institute of Technology, U.K.

Communication:

EFFECT OF RARE EARTH METALS ON THE OXIDATION

RESISTANCE AND CREEP STRENGTH

S. Darnfors and R Johansson, Avesta AB, Avesta, S.

Keynote Paper:

225

THE EFFECTS OF PRECIOUS METALS ON THE OXIDATION AND 231

HOT CORROSION OF COATINGS J. Schaeffer, G.M. Kim, G.H. Meier and F.S. Pettit

Pittsburgh University, U.S.A.

Session 4: INTERACTION OF SULPHUR AND CARBON IN OXIDATION

Chairman: G. Beranger, UTC Compiegne, F.

Keynote Paper:

THE ROLE OF SULPHUR IN THE GROWTH AND ADHESION OF

OXIDE SCALES J.G. Smeggil, A.J. Shuskus, N.S. Bomstein and M.A. de Crescente,

UnitedTechnologies Research Centre, East Hartford, U.S.A.

Poster: THE INFLUENCE OF SULPHUR AND ITS INTERACTION WITH

YTTRIUM ON THE COMPOSITION, GROWfH AND ADHERENCE OF OXIDE SCALES ON ALUMINA-FORMING ALLOYS A.S. Khanna, WJ. Quadakkers and C. Wasserfuhr Institut fUr Reaktorwerkstoffe, KF\ Jillich, FRG.

Keynote Paper:

THE ROLE OF CARBON ON THE GROWfH AND ADHESION OF

OXIDE SCALES

H.1. Grabke, Max-Planck-Institut fUr Eisenforschung Dilsseldorf, FRG.

271

282

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Communication: EFFECT OF CeO, COATINGS AND INTERFACIAL SEGREGATIONS 315 OF SAND C ON THE OXIDATION BEHAVIOUR OF Fe-Cr ALLOYS IN 0, P. Papaiacovou, R.J. Hussey, D.F. Mitchell and M.l. Graham National Research Council of Canada, Ottawa, CDN. (Abstract)

Posters: PREOXIDATION FOR SULPHIDATION PROTECTION OF Fe-Ni-Cr- 317

ALLOYS R. Lobnig, P. Papaiacovou, H.P. Schmidt and H.l. Grabke Max-Planck-Institut fUr Eisenforschung, DUsseldorf, FRG.

EFFECTS OF HYDROGEN CHLORIDE AND OF NITROGEN IN THE 335 OXIDATION OF Fe-20Cr D. Bramhoff, H.l. Grabke and H.P. Schmidt, Max-Planck-Institut fUr Eisenforschung, DUsseldorf, FRG.

Session 5: PRACTICAL IMPLICATIONS AND OUTLOOK

Chairman: G. Beranger, UTC Compiegne, F.

Keynote Papers:

APPLICABILITY OF ACTIVE ELEMENTS IN INDUSTRIAL PRACTICE 353 1.H. Davidson, Imphy S.A., Imphy, F.

APPRAISAL KEYNOTE: FUTURE TRENDS AND DEVELOPMENTS 367 P. Kofstad, University of Oslo, N.

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Opening of Colloquium

THE MAGIC OF ACTIVE ELEMENTS

by E.D. HONDROS

Institute of Advanced Materials

Commission of the European Communities

It is a pleasure to welcome you to the Institute of Advanced Materials of the Joint Research Centre and to this Colloquium on a well targetted and fascinating subject area.

It is indeed an intriguing theme with ramifications throughout the materials sciences and technologies. In fact, as early as 1781, Bergman a Swedish metallurgist observed closely the dramatic effects of small additions of carbon on the properti es of iron. These observa t ions, now fundamental knowledge in modern ferrous metallurgy, rather perplexed him. He described the phenomenon in terms of astonishment, as "the mystery of mysteries".

I mention this historical anecdote in order to illustrate a class of phenomena encountered in metallurgical practice in which the presence of a minor amount of an elemental constituent can induce changes in properties physical, mechanical, chemical - quite out of proportion to the amount added. Today we know that various residual elements, or deliberate additives, or dopants may procure such effects, changing significantly the materials properties. This is seen most spectacularly in connection with electronic properties of semiconductors. To those whose knowl edge of metallurgy was in its infancy, such phenomena might well have represented truly magical effects, of the type sought after by alchemists of the middle ages.

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This phenomenon is being looked at today in the context of alloys which must perform at high temperatures in agressive operational conditions of service and which depend on their performance on the formation and the retention of a highly

adherent oxide scale. The "active element effect", which is the subject of our business today, is concerned with how certain additives, in particular yttrium, help to retain the scale that is developed and prevent early spalling or breakaway oxidation.

To digress for a moment into other fields, the effects of trace elements have now been well documented and studied in a number of branches of modern materials sciences. The effects can be both negative or positive, that is, deleterious or beneficial. In fact, some of the best known phenomena involving residual trace elements or impurities produce clearly unwanted effects, for example, in the classical phenomenon of temper embrittlement which had catastrophic results in the manufacturing of large guns during the First World War (perhaps from another point of view a beneficial effect). As a result of the growing understanding of microchemical processes at grain boundaries and surfaces, we now have a good understanding of the deleterious effects of naturally occuring residuals in metallurgical phenomena such as temper embrittlement or creep embrittlement.

Let us mention some of the positive effects of minor constituents. Here I do not have to mention the most famous example of all, namely carbon in iron. It is known for instance that boron in steel can procure a distinct toughening effect as can for example, the addition of rare earth elements. The latter, it is suspected, may procure the effect through a sort of gettering action. For example, additions of lanthanum and cerium will scavenge phosphorus or sulphur in embrittled steel. More recently, it has been discovered that boron has a beneficial effect on intermetallics, producing an improvement in toughness through the segregation of the boron at the grain boundary where the adhesion of the grains is increased. It has been said that this recent observation of the boron ductilising effect may have triggered off the present day re-examination of the whole field of inter-metallics.

The effect of active elements such as yttrium on the stability and the integrity of oxide scales represents another important example of the positive effects of additi ves. Thi s meeting aims to examine how this effect is procured. What is the mechanism of this remarkable phenomenon?

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There have been many speculations and publ ications in the past two decades and a variety of mechanisms has been proposed. These will be examined in detail during this meeting. They may be divided into two broad classes: that in which it is supposed that the effect comes via the metal/oxide interface, and secondly, that where it is supposed that the mechanism is due to the yttrium acting on the bulk scale itself. Interfacial effects may include the elimination of porosity between the metal and the oxide scale. Other ideas relate to the possibility of formation of intrusions at the interface, the "oxide pegging" effect which may produce a better mechanical bond at the interface. Another possibility is that the yttrium may reside at the metal/oxide interface and improve the intrinsic adhesion between metal and oxide. Indeed, some time ago some colleagues and I observed experimentally that yttrium does concentrate at metal/oxide interfaces in certain super-alloys. Considering the second type of possibil ity, the active element may affect the plastic properties of the scale, or it may affect the growth mechanism by provoking short circuit diffusion especially along the grain boundaries. In a more recent hypothesis, it is supposed that the active element or trace element acts as a sort of getter for the presence of sulphur impurities, which reduce the intrinsically high bond strength of the metal/oxide interface. Indeed, one may have sympathy for this idea, through analogies with other metallurgical phenomena already alluded to, in which the role of the additive is to scavenge the noxious impurities. The deleterious effects of sulphur on bulk properties of steels are well known and over the years this effect has been controlled by metallurgists through a calculated balance with manganese which "fixes" chemically the sulphur.

All these points will be taken up and discussed in detail by the specialists among us and we are looking forward to considering the latest information.

Taking this opportunity~ I would like to mention a few words in connection with the Joint Research Centre. It is timely to announce that at the present time the various Establishments of the Joint Research Centre, which have been in existence for some 20 to 30 years, are being restructured (in common with many other similar institutions). The Joint Research Centre, which is one of the instruments used by the European Community to implement its policies in the industrial, social, scientific and technological sphere, is now being transformed into a number of autonomous Institutes. Organisationally, these Institutes operate differently from the cost-shared action type of activity with which you are probably familiar, in which the Community shares in the cost of research projects. The Institutes will

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cover a number of important technological orientations, ir particular Environment, Nuclear Safety, Safety Engineering and in recognition of the importance of materials for the industrial competivity of Europe, there will be one large Institute devotee to Materials. Here, the materials activities in two Centres, Petten in the Netherlands and Ispra in Italy, will be combined in one Institute where programmes will be highly coordinated in a broad range of materials subject areas. The Institute will be based on a total coherence and coordination in the various facilities and special isms in the regional Centres. In turn, these various resources and activities will be made available to the industry of Europe either on a research contract basis or in the form of closely linked or shared programmes. In this way, we are optimistic in being able to make our contribution to the materials challenge in Europe.

I have taken the opportunity to inform you at thi s early stage of the planned structure of our organisation. Among other materials themes, the subject matter of the present meeting will be important for the future work of our Institute. I would like to add how we would in the future like to reach out to you, not only in this present Conference, which is a very enjoyable form of dialogue between scientists, but by other means such as the exchange of staff as well as the joining of allied projects in cooperative networks. Cooperation is the keynote of the future: carrying out projects cooperatively will enhance the totality and effectiveness of the European effort.

With these words I reiterate: welcome to this Institute in the fervent expectation that our deliberations on this very interesting theme will be fruitful.