HYDROGEN EFFECTS IN MATERIALS

HYDROGEN EFFECTS IN MATERIALS Proceedings of the Fifth International Conference

on the Effect of Hydrogen on the Behavior of Materials sponsored by the Structural Materials Division (SMD)

Mechanical Metallurgy and Corrosion & Environmental Effects Committees of The Minerals, Metals & Materials Society

held at Jackson Lake Lodge, Moran, Wyoming September 11-14, 1994

Edited by

Anthony W. Thompson Lawrence Berkeley Laboratory

Berkeley, California

and

Neville R. Moody Sandia National Laboratories

Livermore, California

A Publication of

THUS Minerals · Metals · Materials

A Publication of The Minerals, Metals & Materials Society 420 Commonwealth Drive

Warrendale, Pennsylvania 15086 (412) 776-9000

The Minerals, Metals & Materials Society is not responsible for statements or opinions and is absolved of liability due to misuse of information contained in this publication.

Printed in the United States of America Library of Congress Catalog Number 96-75439

ISBN Number 0-87339-334-1

Authorization to photocopy items for inter-nal or personal use, or the internal or per-

sonal use of specific clients, is granted by The Minerals, Metals & Materials Society for us-ers registered with the Copyright Clearance Center (CCC) Transactional Reporting Serv-ice, provided that the base fee of $3.00 per copy is paid directly to Copyright Clearance Center, 27 Congress Street, Salem, Massa-chusetts 01970. For those organizations that have been granted a photocopy license by Copyright Clearance Center, a separate sys-tem of payment has been arranged.

TMS Minerals · Metals * Materials

If you are interested in purchas ing a copy of this book, or if y o u w o u l d like to receive the latest TMS publicat ions catalog, please te lephone 1-800-759-4867.

©1996

CONTENTS

Foreword xiii

CONFERENCE KEYNOTE The Role of Hydrogen: Is The Story Any Clearer? 3

/. M. Bernstein

HYDROGEN INTERACTIONS Hydrogen-Dislocation Interactions (Keynote) 15

H. K. Birnbaum and P. Sofronis

Hydrogen Interaction with 0-, 1-, and 2- Dimensional Defects (Invited) 35 J. Gegner, G. Hörz and R. Kirchheim

Deuterium and Tritium Applications to the Quantitative Study of Hydrogen Local Concentration in Metals and Related Embrittlement (Invited) 47

J. Chêne and A. M. Brass

Hydrogen Induced Embrittlement and the Effect of the Mobility of Hydrogen Atoms (Invited) 61

J.-S. Wang

Atomistic Calculations of Hydrogen Interactions with Ni3Al Grain Boundaries and Ni/Ni3Al Interfaces (Invited) 77

/Vf. /. Baskes, J. E. Angelo, and N. R. Moody

Bonding Strengths and Anomalous Hydrogen Absorption in Some Intermetallic Systems 91

/. Jacob

The Investigation of Hydrogen Redistribution Under a Tensile Load 97 B. K. Zuev and O. K. Timonina

Characterization of Defects in Deuterium-implanted Beryllium 105 R. A. Anderl, A. B. Denison, S. Szpala, P. Asoka-Kumar, K. G. Lynn, and B. Nielsen

The Role of Traps in Determining the Resistance to Hydrogen Embrittlement 115 B. G. Pound

Hydrogen Trapping and its Correlation to the Hydrogen Embrittlement Susceptibility of Al-Li-Cu-Zr Alloys 131

5. W. Smith andj. R. Scully

The Interaction of Hydrogen with a β-Titanium Alloy 143 H. Zhang, T. Lin, and R. Chang

On the Mechanism of Hydrogen Interaction with Titanium at Temperatures from 300 to 373K and Pressures up to 150 MPa 153

Yu. I. Archakovand T. D. Aleferenko

Modeling the Segregation of Hydrogen to Lattice Defects in Nickel 161 J. E. Angelo, N. R. Moody, and M. I. Baskes

The Behavior of Impurity Hydrogen in Metallic Materials 171 C. Itoh, H. Okada, and M. Kanno

Hydrogen Absorption in Metals During Electrolytic Processes and the Physical-Mechanical Properties of Steel 181

Vu. M. Loshkaryov, A. N. Baturin, and V. I. Korobov

PERMEATION The Effect of Surface on the Measurement of Hydrogen Transport in Iron with the Electrochemical Permeation Technique (Invited) 189

A. M. Brass and J. Collet-Lacoste

Diffusion of Hydrogen in Titanium 205 O. S. Abdul-Hamid and R. M. Latanision

Hydrogen Solubility in Ti-24Al-l lNb 215 M. C. Shanabarger, S. N. Sankaran, and A. W. Thompson

Hydrogen Solution and Diffusion in Ll2-Ordered (Co, Fe)3V Alloy and Their Roles in Environmental Embrittlement 223

C. Nishimura, M. Komaki, and M. Amano

Modeling of Hydrogen Transport in Cracking Metal Systems 233 j. P. Thomas and C. E. Chopin

Comparison of the High Temperature Hydrogen Transport Parameters for the Alloys Incoloy 909, Haynes 188, and Mo-7.5 Re 243

M. C Shanabarger

Deuterium Desorption from Beryllium 251 R. Bastasz, j. A. Whaley, T. J. Venhaus, and D. M. Manos

Hydrogen Transport Through Ti0 2 Film Prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) Method 261

S.-l. Pyun and Y.-G. Yoon

Measurements of Diffusion and Permeation for Protium in ß-PdHx and Modeling of Diffusion Process 271

J. C. Hamilton and W. S. Swansiger

Investigation of a Hydrogen Charging Method on an Austenitic Structure 283 C. Dagbert, M. Sehili, J. Calland, and L. Hyspecka

Thermal Desorption Analysis (TDA): Application in Quantitative Study of Hydrogen Trapping and Release Behavior 293

E. Abramov and D. Eliezer

MECHANICAL PROPERTIES The Effect of Deformation Rates on Hydrogen Embrittlement 303

W. Dietzel and M. Pfuff

Hyrdrogen Attack in Creeping Polycrystals due to Cavitation on Grain Boundaries 313

M. W. D. van der Burg and E. van der dessen

The Effect of Hydrogen on the Fracture Behavior of Aluminum Titanium Metal Matrix Composites 323

G. Solovioff and D. Eliezer

Effect of Pressure and Temperature on Hydrogen Environment Embrittlement of Incoloy® Alloy 909 331

R. K. Jacobs, A. K. Kuruvilla, T. Nguyentat, and P. Cowan

Hydrogen Effects on Cyclic Deformation Behavior of a Low Alloy Steel 343 H. J. Maier, W. Popp, and H. Kaesche

The Relationship between Strain Rate, Hydrogen Content, and the Tensile Ductility of Uranium 355

C. L Powell

Influence of Strain Rate on Tensile Properties in High-Pressure Hydrogen 363 E. J. Veselyjr., R. K. Jacobs, M. C. Watwood, and W. B. McPherson

Void Formation in Hydrogen Charged Metals Induced by Plastic Deformation as the Initial Stage of Embrittlement 375

Yu N. Jagodzinski, L. N. Larikov, and A. Yu. Smouk

CRACK GROWTH SUSCEPTIBILITY Fracture Toughness and Hydrogen assisted Crack Growth in Engineering Alloys (Keynote) 387

J. F. Knott

Modeling Hydrogen Environment-enhanced Fatigue Crack Growth in Al-Li-Cu-Zr (Keynote) 409

R. S. Piascik and R. P. Gangloff

Local Approach of Fracture in a Tempered Martensitic Steel Cathodically Hydrogenated at High pH 435

R. P. Hu, M. Habashi, G. Hu, and). Galland

Cracking of a Hydrided Zirconium Alloy in Hydrogen 445 J.-H. Huang and F.-l. Jiang

Hydrogen Induced Damage in High Strength Pearlitic Steel: Micromechanical Effects and Continuum Mechanics Approach 455

J. Toribio, A. M. Lancha, and M. Elices

The Hydrogen Embrittlement of Alloy X-750 465 D. M. Symons and A. W. Thompson

Effects of Anisotropy on the Hydrogen Diffusivity and Fatigue Crack Propagation of a Banded Ferrite-Pearlite Steel 475

L. Tau, S. L. I. Chan, and C. S. Shin

Influence of Water Vapor Pressure on Crack Growth Rate in 7017-T651 Aluminum Alloy 487

J. Ruiz and M. Elices

The Kinetics of Hydrogen Assisted Cracking of Metals 497 A. G. B. /Vf. Sasse and V. J. Gadgil

FRACTURE MECHANISMS The Role of Hydrogen in Enhancing Plastic Instability and Degrading Fracture Toughness in Steels (Keynote) 507

J. P. Hirth

Hydrogen and Moisture-Induced Embrittlement of Nickel and Iron Aluminides (Invited) 523

N. S. Stoloff

Hydrogen Induced Cracking Mechanisms -Are There Critical Experiments? (Invited) 539

W. W. Gerberich, P. G. Marsh, and). W. Hoehn

Some Contribution to the Understanding of the Mechanism of Hydrogen Induced Cracking of Intermetallic Compounds (Invited) 555

C.-M. Xiao, W.-Y. Chu, and F.-W. Zhu

A Theory for Hydrogen Embrittlement of Transition Metals and Their Alloys 569 J. A. Lee

Microautoradiography of Fatigue Crack Growth in Low-Carbon Steel Using Tritiated Water Vapor 581

D. L. Davidson and j. B. Campbell

Effects of Internal Hydrogen on the Toughness and Fracture of Forged JBK-75 Stainless Steel 591

B. C. Odegard Jr., S. L. Robinson, and N. R. Moody

Model for Plasticity-Enhanced Decohesion Fracture 599 C. Altstetter and D. Abraham

Advances in the Theory of Delayed Hydride Cracking in Zirconium Alloys 611 S.-Q. Shi and M. P. Puis

High Resolution Fractography of Hydrogen-Assisted Fracture in Iron-3 wt.% Silicon 623

T. J. Marrow, M. Aindow, and]. F. Knott

STRESS CORROSION CRACKING Distributions of Anodic and Cathodic Reaction Sites during Environmentally Assisted Cracking (Invited) 635

B. G. Ateya and H. W. Pickering

Calculation Model of Hydrogen-Mechanical Crack Propagation in Metals under Corrosive Environment Effects 647

O. Andreykiv and N. Tymiak

The Effect of Hydrostatic Pressure on Hydrogen Permeation and Embrittlement of Structural Steels in Seawater 657

j. Woodward, R. P. M. Procter, and R. A. Coffis

The Effect of Microstructure on Hydrogen-induced Stress-Corrosion Cracking of Quenched and Tempered Steels 669

G. Echaniz, T. E. Perez, C. Pampillo, R. C. Newman, R. P. M. Procter, and G. W. Lorimer

Influence of the Ni-Content on the Cathodic and Corrosive Hydrogen Induced Cracking Behavior of Austenitic Alloys 679

K. Mummert, H. J. Engelmann, S. Schwarz, and M. Uhlemann

Hydrogen Embrittlement During Corrosion Fatigue of Duplex Stainless Steel 689 K. N. Krishnan, J. F. Knott, and M. Strangwood

HYDROGEN IN TITANIUM ALLOYS Effect of High Temperature Hydrogen on Titanium Base Alloys (Keynote) 699

H. G. Nelson

Hydrogen Effects in Titanium (Invited) 719 F. H. Froes, D. Eliezer, and H. G. Nelson

Effect of Hydrogen on the Microstructure and Mechanical Properties of the Ti Alloy: Ti-15Mo-3Nb-3Al-0.2Si 735

D. A. Hardwick and D. G. Ulmer

Hydrogen Interactions and Embrittlement in Metastable Beta Ti-3Al-8V-6Cr-4Mo-4V 745

M. A. Gaudett, S. W. Smith, and). R. Scully

Hydrogen Effects in Titanium Aluminide Alloys 755 D. Eliezer, F. H. Froes, C. Suryanarayana, and H. G. Nelson

Effects of Hydrogen-induced Phases on Mechanical Behavior of the Ti-25Al-10Nb-3 Mo-lV Titanium Aluminide Alloy 765

X. Pierron and A. W. Thompson

Hydrogen Effects on Ti-22Al-27Nb 777 D. Eliezer, A. Ben-Guigui, N. Stern, N. Eliaz, E. Abramov, and R. G. Rowe

The Effect of High Pressure Hydrogen Charging on Microstructure and Mechanical Behavior of a Cast γ+α2 Titanium Aluminide 787

U. Habel, T. M. Pollock, and A. W. Thompson

Hydride Dissociation and Hydrogen Evolution from Cathodically Charged Gamma-Based Titanium Aluminides 799

A. Takasaki, Y. Furuya, K. Ojima, and Y. Taneda

Hydrides in High Pressure Hydrogen-charged TiAl Alloys 809 K. Li, M. De Graef, T. M. Pollock, D. B. Allen, and A. W. Thompson

Influence of Hydride Precipitation on the Ductility of Titanium Under Stress Triaxiality 819

J. Huez, A.-L. Helbert, I. Guillot, A. W. Thompson, and M. Clavel

The Effects of Hydrogen on the Stability of the Orthorhombic Phase in Ti-24Al-llNb 831

D. B. Allen, A. W. Thompson, and M. De Graef

HYDROGEN IN STAINLESS STEELS AND SUPERALLOYS Effect of Internal Hydrogen on the Mixed-Mode I/III Fracture Toughness of a Ferritic/Martensitic Stainless Steel 843

H. Li, R. H. Jones, J. P. Hirth, and D. S. Gelles

Effects of Internal Helium on Tensile Properties of Austenitic Stainless Steels and Related Alloys at 820°C 855

W. C. Mosley

Mechanical Austenite Stability of Fe-Ni-Cr-Mn Stainless Steels 865 J. M. Larsen and A. W. Thompson

Tritium and Decay Helium Effects on the Fracture Toughness Properties of Types 316L, 304L, and 21Cr-6Ni-9Mn Stainless Steels 873

M. J. Morgan and M. H. Tosten

Helium 3 Precipitation in Tritiated AISI 316 Stainless Steels 883 A. M. Brass, A. Chanfreau, and j. Chêne

Phase Transformations and Relaxation Phenomena in Hydrogen-Charged CrNiMn and CrNi Stable Austenitic Stainless Steels 893

V. G. Gavriljuk, H. Hänninen, S. Yu. Smouk, A. V. Tarasenko, A. S. Tereschchenko, and K. Ullakko

Hydrogen Effects on 316L Austenitic Stainless Steel: Mechanical Modeling of the Damage/Failure Process 903

J. Toribio and A. Valiente

Hydrogen Degradation Mechanisms in Single Crystal Turbine Blade Alloys 913 D. P. DeLuca and B. A. Cowles

Role of Microstructure on Hydrogen Embrittlement of Nickel Base Superalloy Single Crystals 923

D. Roux, J. Chêne, and A. M. Brass

Effect of Strain Rate on Hydrogen Embrittlement in Ni Al 933 H. Li and T. K. Chaki

Influence of the Failure Mode on Fatigue Crack Growth Behavior in Single Crystal Superalloys 943

J. Telesman, L. J. Ghosh, and D, P. DeLuca

Internal Hydrogen Embrittlement at 300°C in Nickel Base Alloys 690 and 800 953 /. Lenartova, M. Habashi, and L. Hyspecka

Temperature Effects on Hydrogen-induced Cracking in an Iron-Based Superalloy 967

N. R. Moody, 5. L. Robinson, J. E. Angelo, and M. W. Perra

Hydrogen Embrittlement in Duplex Steel Tempered Between 200°C and 1050°C and Cathodically Charged at 200°C 979

F. lacoviello, M. Habashi, M. Cavallini, and J. Galland

ENGINEERING APPLICATIONS Catastrophes of Large Diameter Pipelines: The Role of Hydrogen Fields 991

V. N. Polyakov

The Effect of Boron as a Micro-alloying Element on the Behavior of a 1038 Steel in a Hydrogen Environment 1001

P. Bruzzoni, G. Domizzi, M. I. Luppo, D. Zaicman, and}. Overjero Garcia

NASA-HR-1, A New Hydrogen-resistant Fe-Ni-Base Superalloy 1011 P. S. Chen, B. Panda, and B. N. Bhat

Hydrogénation Evolution of Steels under Friction in Synthetic Sea Water 1021 K. Bencherif, P. Manolatos, P. Ponthiaux, and J. Galland

NASA-23 for HEE Resistant Structural Applications 1029 A. K. Kuruvilla, B. Panda, W. B. McPherson, and B. N. Bhat

Preventing Degradation and Predicting Response in Fracture Toughness of Ti-6A1-4V Fan Disks Using Hydrogen Measurements 1039

M. A. Durfee

Effect of Hydrogen Exposure on a Cu-8 Cr-4 Nb Alloy for Rocket Motor Applications 1049

D. L Ellis, A. K. Misra, and R. L Dreshfield

Welding Tritium Exposed Stainless Steel 1057 W. R. Kanne Jr.

Hydrogen Test Standardization of Low Cycle Fatigue Tests 1065 W. B. McPherson and J. P. Strizak

Author Index 1073

FOREWORD

In the five years since our previous conference addressed hydrogen effects on material properties, there has been a significant amount of work that made another conference appropriate to assess progress. We chose to return to Jackson Lake Lodge, Wyoming, for the fourth time. The response was overwhelming with over 150 abstracts submitted. After a difficult selection process, the conference consisted of 118 presentations from 16 countries, divided into seven oral and three poster sessions. These sessions addressed hydrogen effects in metals and alloys, from permeation and effects on properties to crack propagation and fracture. Keynote and invited speakers provided overviews of core topics and pressing issues. These were followed by contributed papers discussing these topics in depth as well as new results. Discussions after each presentation highlighted the controversial issues and defined our understanding of hydrogen effects. In that sense, this fifth international conference on hydrogen in materials met our goals and was successful in its intentions.

The proceedings begins with an invited perspective of progress made in studying hydrogen effects over the last twenty years by I. M. Bernstein. The balance of the proceedings is then divided into ten areas that reflect the directions and issues which have been evident in hydrogen research for the past five years. The first two sections deal with the fundamental aspects of hydrogen permeation and interaction with defects in metals and alloys. These are followed by three sections addressing hydrogen effects on crack growth susceptibility, stress corrosion cracking, and fracture. This is followed by a section providing an overview of hydrogen effects on mechanical properties of metals and alloys, two sections on hydrogen effects in titanium, stainless steels and superalloys, and two sections on engineering alloys and applications. The emphasis on titanium alloys, stainless steels, and superalloys reflects the strong focus in recent years on hydrogen-resistant alloys required for aerospace applications in hydrogen environments. Comparison with previous conferences shows we have made progress in understanding hydrogen effects in these alloys as well as in all aspects of hydrogen effects on material behavior. We hope the papers in these proceedings stimulate discussion of hydrogen interactions and mechanisms that control behavior of materials, and also help to stimulate, focus, and direct future research.

The papers in this volume have been reproduced directly from camera-ready manuscripts submitted by the authors for post-conference publication. Although it was possible to correct many grammatical and typographical errors, the number of corrections had to be minimized in the interest of economical publication. We hope that the readers view any errors in this light. Discussion during the conference was captured by written forms given to questioners, and then to speakers. Those which were completed and returned to us are included here.

The success of this conference was due to the efforts of many people to whom we are grateful. We especially wish to thank R. H. Jones, who joined us on the program committee, and H. G. Nelson and R. O. Ritchie, who helped us obtain funding; their help was invaluable. Our appreciation is also given to R. H. Jones, D. Eliezer, N. Stoloff, H. G. Nelson, W W. Gerberich, J. F. Knott, and R. R Gangloff who served as session chairmen

xiii

and promoted lively discussions between all participants. Partial support funding was provided by grants from the National Science Foundation and from the Ames Research Center of the National Aeronautics and Space Administration, and without that support, the conference finances would have had to be much different.

We thank a number of our colleagues at Sandia National Laboratories, the Lawrence Berkeley Laboratory, and University of California at Berkeley who generously devoted their time and efforts. To Jim Angelo, Ben Odegard, and Steve Robinson from Sandia National Laboratories, we express our gratitude for their coordination and assistance with all program functions. We also extend our thanks to Tony Thompson's graduate students, David Allen, Xavier Pierron, and Kezhong Li, for their help at the conference with forms for questions posed by the audience and for answers given by the speakers, which enabled us to include the discussions for many papers in these proceedings.

To our wives, Jo Anne Moody and Mary Thompson, goes a special thanks, for they helped with registration, ensured that many activities for participants and their families ran smoothly, and provided support and'encouragement to us through all phases of preparation for the conference. We also extend our gratitude to Carmella Orham who did a myriad of secretarial and typing tasks in support of the conference. Finally, we gratefully acknowledge the provision of support, through availability of both people and resources, given generously by Sandia National Laboratories, the Lawrence Berkeley Laboratory, and University of California at Berkeley, that made this conference a success.

Anthony W. Thompson Lawrence Berkeley Laboratory Berkeley, CA

Neville R. Moody Sandia National Laboratories Livermore, CA

XIV

CONFERENCE KEYNOTE

THE ROLE OF HYDROGEN: IS THE STORY ANY CLEARER?

I.M. Bernstein

Tufts University Medford, MA

Abstract

This twentieth anniversary Keynote Lecture introduces the conference and de-scribes the landscape of prior research accomplishments as well as identifying the principal unanswered questions and puttingthem into perspective.

Hydrogen Effects in Materials Edited by A. W. Thompson and N. R. Moody

The Minerals, Metals & Materials Society, 1996

3

Introduction In any retrospective look at a set of phenomena or attempts to develop theoreti-

cal underpinnings for predicting behavior, it is usually irresistible to do so in a his-torical context. The case of hydrogen effects, in particular for structural metal and alloys, is hardly an exception. We all know that the most blatant manifestations of deleterious hydrogen-related effects - blistering and embrittlement of low, medium and high-strength ferritic, bainitic and martensitic steels - have been observed, com-mented on and studied for more than 100 years. However, I plan to stray from this ad seriatim approach, using the aggregate experiences, results and sense or lack of progress, as chronicled in the four preceding hydrogen conferences [x-z]. This ap-pears to be a more sensible approach, as in each conference there are many ex-amples of relating phenomena to quite classical, and, perhaps correct approaches.

Progress thus appears to follow two paths, which while not divergent are often independent. For example, many investigators over this 20-year period continue to stress the near-exclusivity of the occurrence and importance of hydrogen embrittlement in ferritic and martensitic steels, with attendant sensitivity increas-ing more or less monotonically with yield or ultimate strength; others speak of more universal hydrogen phenomena, controlled more by specific microstructural features than by macroscopic strength levels. Similarly, for more than 50 of these years, two widely accepted but quite disparate theoretical explanations have prevailed: the pres-sure theory and the surface energy (or cohesive energy) change theory. Some would argue that recent attempts at presenting more 'modern' explanations consists of little more than refinements of these two venerable suggestions, while others would point to a quite fundamental shift away from models dependent on normal stress to those dominated by shear stress control.

I plan to frame the issues of how our understanding has developed, in the context of materials presented at the various Conferences. Conveniently and, in fact, appro-priately, this can be presented by themes which follow both a chronological and a progressive order: • The kinetic behavior of hydrogen and the role of strength level in ferrous alloys; • The role of metallurgical variables, particularly microstructure, in determining and controlling sensitivity to hydrogen; • Hydrogen effects on plasticity and fracture in non-ferrous alloys, with and without the companion influence of anodic stress corrosion cracki ng; and

• The roles of slip planarity and strain localization on hydrogen effects.

Role of Kinetics and Strength Level Hydrogen behavior, particularly embrittlement, had for decades been associated

almost exclusively with medium to high-strength steels. As such, most studies fo-cused on the relative importance of composition, strength level, temperature and strain rate on fracture and occasionally stress-strain behavior. A defining early set of experiments were those of Toh and Baldwin [1], Figure 1, cited by Louthan [2] in the first hydrogen conference. They clearly showed the kinetic nature of hydrogen degradation in cathodically charged mild steel, by demonstrating the competition between diffusion and plasticity, resulting in a maximum embrittlement at room temperature and for normal strain rates. Similar behaviors have been reported in all the conference proceedings, for a wide variety of those ferrous and non-ferrous alloys, suitably disposed for similar competitions between intrinsic plasticity and lattice or defect-related diffusion.

4

I00"C

Uncharged

i o C - 2 0 0

Charged

Figure 1. The effect of strain rate and temperature on the susceptibility of mild steel to hydrogen embrittlement [1,2].

Along with the unambiguous role of kinetic variables in controlling relative sus-ceptibilities, the role of strength level has been persistently cited; viz. the higher the strength level, the more susceptible a given alloy, particularly ferrous grades. This belief continues in spite of a well-developed body of evidence demonstrating the sec-ondary role of strength level. Nowhere is this more vividly demonstrated than the catalogued results of Zmudzinski, Bretin and Toitot [3], Figure 2, on low and me-dium high strength steels, cited by Thompson and Bernstein [4] in the third hydro-gen conference. While it is possible to infer a trend of increased susceptibility with strength level in Fig. 2, many data combine high strength-high ductility, or low strength-low ductility, contradicting the trend, and there clearly must be other de-termining factors that severely compromise this classical suggested dependence. The primary such factors are believed to be microstructural [4].

100

75

Z 50 ID 2 tu

25

er o S

34 steel grades

s

. . . . . . . - - v j t s i s a l y i

':mm^:-.\ ■■:■ i 250 500 750

YIELD STRENGTH ( MPa )

1000

Figure 2. Embrittlement index (RA Loss) as a function of yield strength for 34 grades of low and medium strength steels, totalling 465 data points [3,4].

5

Role of Microstructure Most investigators now agree tha t the pathway to modifying strength level the

thermo-mechanical development of varying microstructures - is the more fundamental detenninator of susceptibility. This recognition has led to a considerable body of study and supporting evidence for both ferrous and non-ferrous alloys, ranging from the more traditional alloy systems to newer generations of advanced alloys, and over a wide range of strength levels. Both in support of the controlling role of varying microstructure features to explain their role in subsequent reduced plasticity and/or enhanced brittleness, attention has focussed on the strength and extent of hydrogen trapping at heterogeneities (5).

The most compelling evidence for hydrogen trapping results from direct observa-tion using tri t ium microradiography. This work has been pioneered and perfected by Laurent, et al. [6] and Chene and co-workers [7] and is clearly illustrated by Figure 3, taken from reference [6]. The dark features provide incontrovertible evidence for preferential hydrogen partitioning a t a variety of microstructural features, includ-ing incoherent twin boundaries, and subgrain and grain boundaries. A number of investigators [8-10] have used such evidence in to attempt to integrate the comple-mentary roles of hydrogen entry, mobility, distribution and redistribution, to model any subsequent effects on plasticity and fracture. The methodology behind these is schematically illustrated in Figure 4, taken from reference [4]. Particularly in steels with a rich variety of different microstructural heterogeneities of varying strengths and capacities [5], relative partitioning can promote or prevent initiation and propa-gation events which promote cleavage, intergranular or ductile fracture. This focus on microstructure continues to dominate modelling attempts in both ferrous and non ferrous materials, (for examples, see references [11] and [12]).

Figure 3. Autoradiography of Armco Iron showing tritium segregation at incoherent, subgrain and grain boundaries [6].

Hydrogen's Role in Stress Corrosion Cracking A persistent issue has been the extension of phenomenological observations,

modelling and theories developed for ferrous alloys to nonferrous systems, particu-larly those long identified with environmental embrittlement controlled by anodic stress corrosion cracking. The issue is not whether aluminum alloys, t i tanium al-loys, austenitic stainless steels, etc. can be embrittled under conditions of high-pres-sure hydrogen or strongly cathodic polarization. This evidence appears quite clear and has been well documented in a number of the conference proceedings [13,14]. Instead, a key issue is the role of hydrogen under more general electrochemical con-ditions, such as sea water, moist atmospheric conditions or solutions of various pH's, including basic solutions. While questions remain, evidence appears strong that

6

(ÍNTERGRANULAR) ( DUCTILE )

Figure 4. Summary of hydrogen processes: Sources leading to hydrogen in solution, transport by diffusion or dislocation atmospheres leading to mi-crostructural accumulations, and finally different resultant fracture pro-cesses [4].

—1~ TORSI0NALLOADING

TI-WAI-HMo-mv

-500mVvs. S.C.E.

CANTILEVER BEAM

TIME TO FAILURE, min

Figure 5. Susceptibility of lï-8 Al-1 Mo-1 V to stress-corrosion cracking in various salt solutions under both tensile and torsional loading [15].

7

hydrogen effects can and usually do dominate stress corrosion cracking under most operating conditions, particularly in the temperature ranges near ambient condi-tions.

As only one of many possible examples of supporting evidence, Figure 5 [15] shows the time dependence of stress corrosion cracking for a t i tanium based alloy in 3.5% NaCI under mode I (tensile) and mode III (torsional) loading, with and without the presence of a cathodic poison, whose presence greatly increases the hydrogen activ-ity. The resistance to cracking under torsional loading, capable of promoting crack advance resulting from anodic film rupture, coupled with the dominant effect of tensile loading and hydrogen poisoning, both of which accelerate local high concen-trations of hydrogen, strongly support a hydrogen embrittlement model. While the issue is not closed, an important conclusion is that the same type of effects resulting from microstructural controls in ferrous alloys should be transferrable to nonferrous systems. Thus there are real prospects of developing quite general ameliorative pre-scriptions to improve hydrogen embrittlement resistance for many classes of metal-lic based systems. Some of the identified characteristics to understand and accom-plish this, constitutes the last section of this brief, interpretive overview.

Slip Planarity and Strain Localization Microstructural heterogeneities play a number of primary and secondary roles in

their effect on sensitivity to hydrogen. They can reduce the apparent diffusivity through residence time and trapping effects. They can provide sites for preferential hydrogen segregation and partitioning, either reducing sensitivity through trapping to innocuous centers, or can accelerate it if the site is a preferred fracture initiation or propagation center.

Moreover, these deleterious effects can often be promoted if thermomechanical processing enhances slip planarity. This latter behavior has been observed in a wide variety of alloy systems, particularly those strengthened through precipitation hard-ening with particles of varying degrees of coherencies [16]. Examples are shown in Figures 6 and 7. The former is from the work of Taheri, et al. [16] on underaged and overaged 7075 aluminum alloy of equivalent strength levels, cited by Tien, et al. [17] in the third hydrogen conference. Planar slip promotes large scale, long range trans-port of cathodically produced hydrogen and a greater degree of ductility loss. Figure 7 is from the work of Kurvilla and Stoloff on the fatigue crack growth rate of a (FeNi)gV intermetallic [18], cited by Stoloff [19] in the fourth hydrogen conference. Cracking is accelerated in hydrogen gas only when the alloy is in the ordered state.

40

c V " 30 a.

o 20

ex.

10

10-» 10-3 10- ' 10- ' Initial strain rate (s-1)

Figure 6. Dependence of susceptibility to hydrogen embrittlement in a 7075 a luminum alloy [16].

8

lô1

ιο'-

z

Δ ORDERED. ARGON A OROERED,H tGAS-loir* O DISORDERED. ARSON • DISORDERED, M .GAS- iov "

LRO 60 Z5*C

lu"-

«r

• o

o

2

20 30 «O SO 6 0 70 80 KX)

AK(MNm_ s / í )

Figure 7. Influence of long range order and hydrogen gas on crack growth of LRO-60, an Fe-Ni-V intermetallic [18].

Planar slip provides a method of large-scale hydrogen transport in alloys with limited lattice hydrogen diffusivity. A remaining, unsettled issue is why this accel-eration can promote hydrogen degradation? In a number of systems, the ability to increase local hydrogen concentrations at critical sites for subsequent crack nucle-ation and growth appears to be the main way that embrittlement is enhanced. In addition, there are systems where a more synergistic interaction between mobile dislocations and transported or subsequently trapped hydrogen exists [20]. In these and possibly other cases, hydrogen more directly modifies dislocation character and behavior, introducing or suppressing specific slip systems and often then promoting shear localization. This localized plasticity accelerates localized fracture and depend-ing on the crystallography can mimic apparent brittle cleavage or interface fracture. To illustrate, Figure 8 [11], depicts strain-induced dislocation morphologies in the Ni based superalloy CSMX-2, with and without hydrogen, though at different plastic strains. Here, hydrogen appears to block dislocation ingress into the ordered pre-cipitate either through trapping at the interface or by increasing the misfit strain. Strain localization ensues.

Summary I hope it is clear that, as catalogued in the previous four conference proceedings,

the past 20 years has seen considerable progress in our understanding of how hydro-gen can modify plasticity and fracture in a wide range of metallic-based alloys. While the scope of such considerations now extends well beyond ferrous alloys, the com-mon elements remain, many still elusive, as researchers pursue answers to a quite resistant and resilient set of issues. In particular, questions continue on the mecha-nistic generality of hydrogen effects in different systems, particularly of different crystal structures and bonding states. The specific area receiving attention currently

9

0.040, no hydrogen, (b) ε = 0.012, hydrogen charged [11].

is shear localization and whether this provides a unifying characteristic for a wide range of hydrogen-induced degradation phenomena The interplay between anodic and cathodic events remains to be resolved, as does the role of trapping as a amelio-rative approach. Questions and issues have been raised before, but the prospects of improved understanding are brighter, and I expect this will be borne out from the results and discussions of this fifth conference proceedings .

References 1. T. Toh and W.M.Baldwin, Stress Corrosion Cracking and Embrittlement. ed. W.D.

Robertson (Wiley, New York, 1956) 176. 2. M. R. Louthan, in Hydrogen in Metals, eds. I. M. Bernstein and A.W. Thompson

(ASM, Metals Park OH, 1974) 53. 3. C. Zmudzinski, L. Bretin and M. Toitot, in Hydrogen in Metals (Paris) vol. 3,

(Pergamon Press, New York, 1977) paper 6A-2. 4. A.W. Thompson and I.M. Bernstein, in Hydrogen Effects in Metals, eds. I. M.

Bernstein and A.W. Thompson (TMS, Warrendale PA., 1981) 291. 5. G.M. Pressouyre, ibid., 27. 6. J.P. Laurent, G. Lapasset, M. Aucouturier and P. Lacombe, in Hydrogen in Met-

als, eds. I. M. Bernstein and A.W. Thompson (ASM, Metals Park OH, 1974) 559. 7. J. Chene, M. Aucouturier, R. Arnold-Laurent, P. Tison and J.-P. Fidelle, in Hy-

drogen Effects in Metals, eds. I.M. Bernstein and A.W. Thompson (TMS, Warrendale PA., 1981) 583.

8. M. F. Stevens, I.M. Bernstein and W. A. Mclnteer, ibid., 341. 9. R. P. Wei and M. Gao, inHydrogen Effects on Material Behavior, eds. N.R. Moody

and A.W. Thompson (TMS, Warrendale PA., 1990) 789. 10. J. R. Rice, in Effect of Hydrogen on the Behavior of Materials, eds. A.W. Thomp-

son and I. M. Bernstein (TMS, Warrendale PA. 1976), 455. 11. I. M. Bernstein and M. Dollar, in Hydrogen Effects on Material Behavior, eds.

N.R. Moody and A.W. Thompson (TMS, Warrendale PA., 1990) 703. 12. N. R. Moody, M. W. Perra and S. L. Robinson, ibid., 625. 13. R. J. Walter and W.T. Chandler, in Hydrogen in Metals, eds. I. M. Bernstein and

A.W. Thompson (ASM, Metals Park OH, 1974) 515.

10

Figure 8. Deformation structures in H-free and H-charged CMSX-2. (a) ? =

14. R. E. Stoltz and A.J. West, in Hydrogen Effects in Metals, eds. I.M. Bernstein and A.W. Thompson (TMS, Warrendale PA., 1981) 541.

15. J.A.S. Green, H.W. Hayden and W.G. Montague, in Effect of Hydrogen on Behav-ior of Materials, eds. A.W. Thompson and I. M. Bernstein (TMS, Warrendale PA., 1976) 200.

16. M. Taheri, J. Albrecht, I.M. Bernstein and A.W.Thompson, Scripta Metall. 13, (1979) 871.

17. J.K. Tien, S.V. Nair and R.R. Jensen, in Hydrogen Effects in Metals, eds. I. M. Bernstein and A.W. Thompson (TMS, Warrendale PA., 1981), 37.

18. A.K. Kuruvilla and N.S. Stoloff, Metall. Trans. A, 16A (1985) 815. 19. N. S. Stolon", in Hydrogen Effects on Material Behavior, eds. N.R. Moody and

A.W. Thompson (TMS, Warrendale PA., 1990) 483. 20. J. P. Hirth, ibid., 677.

11

HYDROGEN INTERACTIONS