Aluminum(cid:1)Lithium Alloys Aluminum(cid:1)Lithium Alloys Processing, Properties, and Applications N. Eswara Prasad Amol A. Gokhale R.J.H. Wanhill AMSTERDAM(cid:129)BOSTON(cid:129)HEIDELBERG(cid:129)LONDON NEWYORK(cid:129)OXFORD(cid:129)PARIS(cid:129)SANDIEGO SANFRANCISCO(cid:129)SINGAPORE(cid:129)SYDNEY(cid:129)TOKYO Butterworth-HeinemannisanimprintofElsevier AcquiringEditor:StephenMerken DevelopmentEditor:JeffreyFreeland ProjectManager:JasonMitchell Designer:MarkRogers Butterworth-HeinemannisanimprintofElsevier TheBoulevard,LangfordLane,Kidlington,Oxford,OX51GB,UK 225WymanStreet,Waltham,MA02451,USA ©2014ElsevierInc.Allrightsreserved Nopartofthispublicationmaybereproducedortransmittedinanyformorbyany means,electronicormechanical,includingphotocopying,recording,oranyinformation storageandretrievalsystem,withoutpermissioninwritingfromthepublisher.Detailson howtoseekpermission,furtherinformationaboutthePublisher’spermissionspolicies andourarrangementswithorganizationssuchastheCopyrightClearanceCenterand theCopyrightLicensingAgency,canbefoundatourwebsite:www.elsevier.com/ permissions. 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LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN:978-0-12-401698-9 ForinformationonallBHpublicationsvisitour websiteatwww.elsevierdirect.com/security Foreword The demand for lightweight structural ele- ments is perennial, particularly for aerospace applications. Lithium is the lightest metallic element, and thus offers stellar advantages as an alloying element in aluminum, the primary structural material for light-alloy based aerospace structures. Each unit addition of Li reduces the density of Al alloys by about 3% and enhances the elastic modulus by about 6%, besides contributing to enhanced tensile strength accompanied by improved high cycle fatigue as well as fatigue crack growth resistance. The strength(cid:1)fracture toughness combination at cryogenic temperatures is also superior in Al(cid:1)Li alloys. However, there are considerable challenges in practically realizing the above-stated advantages. As an alkali metal, Li is highly reactive and harms any surface with which it comes into contact. Therefore, innovative melting and casting technologies must be used to make Al(cid:1)Li alloy products. Moreover, Al(cid:1)Li alloys require stringent composition control and have narrow process windowsfor obtaining optimum properties. Intense international R&D efforts over the past two decades have addressed a whole range of issues related to making, shaping, and treating Al(cid:1)Li alloys. As a result, the following have been notably established: (i) production technologies for large scale melting and casting Al(cid:1)Li alloys with optimized chemistry, (ii) advanced processing based on process model- ing, (iii) thermal and thermomechanical treatments to achieve the desired microstructure(cid:1)mechanical property (strength and fracture toughness as well as fatigue and crack growth resistance) combinations, and (iv) fabrication technologies, including superplastic forming and friction stir welding. As a consequence, numerous patented Al(cid:1)Li alloys have been commercially pro- duced in different product forms. These alloys possess, in comparison to the traditional 2XXX and 7XXX series Al alloys, higher modulus (15(cid:1)25%) and higherspecificstrength(8(cid:1)15%),andthereforeprovideaeronauticaldesigners an opportunity to significantly reduce the weight of aeronautical and space structuresforensuringenhancedfuelefficienciesandhigherpayloads. The present volume systematically documents how a vast array of pro- blems have been overcome to enable significant progress in diverse technical xv xvi Foreword areas to realize production and deployment of Al(cid:1)Li alloys. All the authors have had long-standing experience with this relatively more difficult class of Al alloys, with noteworthy original findings to their credit. Beginning with a superb outline of the historical development, the introductory part (first 2 chapters) summarizes the present status of Al(cid:1)Li alloys and describes aspects of aerostructural design in the context of their application. In the subsequent four parts, various aspects of physical metallurgy (3 chapters), processing (4 chapters), mechanical behavior (5 chapters), and applications (2 chapters) of Al(cid:1)Li alloys are dealt with. It is particularly pleasing for me to see that several contributing authors and two of the three editors are from the Indian Defence Metallurgical Research Laboratory with which I was associated three decades ago, just about when Al(cid:1)Li alloys were beginning toattract international attention. Thisthoughtfully editedbookofinformativearticlesonAl(cid:1)Liclearlypro- misestobeoneofthemostimportantreferencevolumesonthesescientifically intriguingandtechnologicallychallengingalloys. P. Rama Rao FNAE, FNA, FASc., FNASc, FREng., Foreign Associate NAE (US), FTWAS,FUAS PresentlyChairman, Governing Council, ARCI, PO Balapur, Hyderabad, India FormerDirector, DefenceMetallurgicalResearchLaboratory, DRDO, Hyderabad, India FormerSecretary,DepartmentofScience and Technology(DST), Government ofIndia,New Delhi, India FormerChairman, Atomic Energy Regulatory Body, Government ofIndia, Mumbai,India, FormerVC, University of Hyderabad (UoH), Hyderabad, India Former President ofIIM, ISCA, IAS, INAE, MRSI,ICF,IUMSand Present President, IndianNuclear Society, India Preface The history of aluminum(cid:1)lithium (Al(cid:1)Li) alloys goes back to the 1920s, but it is only since the 1990s that the fundamental understanding of these alloys has matured and enabled the development of a family of alloys with excellent combinations of engineering properties. These are the so-called third generation Al(cid:1)Li alloys, and excellent property combinations are required for them to compete in the “high-tech” field of aerospace structures with establishedconventional aluminum alloys and carbon-fibercomposites. ThisbooksurveystheknowledgeaboutAl(cid:1)Lialloysandtheirdevelopment, concentratingonthesecond-andthird-generationalloys.Thesecond-generation alloyswerelargelyunsuccessfulfromanengineeringpropertyviewpoint,butthe lessonslearnedfromtheirdevelopmentinthe1970sand1980shavebeenessen- tialindefiningandestablishingthethird-generationAl(cid:1)Lialloys. Thebook is divided into the following main parts: (cid:1) Part I: Introduction toAl(cid:1)LiAlloys (Chapters1 and 2) (cid:1) Part II: Physical Metallurgy (Chapters 3(cid:1)5) (cid:1) Part III: ProcessingTechnologies (Chapters 6(cid:1)9) (cid:1) Part IV:Mechanical Behavior(Chapters 10(cid:1)14) (cid:1) Part V: Applications (Chapters 15 and16) Each chapter discusses a specific topic, which is summarized in the last section of the chapter. References to the literature are added to each chapter rather than collectively at the end of the book. The scope is such that many authors were needed, generally more than one author for each chapter, and their contributionsare acknowledged by the editors. ThecurrentpaceofAl(cid:1)Lialloycommercialdevelopmentissuchthatthis bookwillinevitablybecomeoutdatedwithinthenextfewyears.Nevertheless, wehopeitwillprovideavaluablereferenceworkfortheforeseeablefuture. Republic ofIndia andthe Netherlands September, 2013 xvii About the Editors N.EswaraPrasadobtainedB.Tech.(in1985)and Ph.D. (in 1993) degrees in Metallurgical Engineering from Indian Institute of Technology (BHU), Varanasi, India, and joined the Indian Defence Research and Development Organisation (DRDO) in 1985. Since then, Dr. Prasad worked in the fields of Design, Development, Life Prediction, and Airworthiness Certificationleadingtotheproductionofaero-materials, namely Al and Al(cid:1)Li alloys; Mo and Ti intermetal- lics; aero Steels; Ti- and Ni-based high temperature alloys; monolithic ceramics such as structural alumina, graphite, and SiC; carbon, silica, and SiC-based Continuous Fiber-reinforced, Ceramic-matrix Composites (CFCCs).Hisresearch contributions areprincipally on thedefor- mation behavior, fatigue power-law relationships, creep(cid:1)fatigue interactions (CFI), and micromechanisms of fatigue and fracture. Dr. Prasad has authored 140peer-reviewedpublicationsandnearly200confidentialreportsandcertifi- cation documents. Dr. Prasad is the recipient of several awards and recogni- tions, including“YoungScientist” fromIndianScience CongressAssociation in 1991, “Young Metallurgist” of Indian Institute of Metals for 1994, “Humboldt Research Fellowship” from Alexander von Humboldt-Stiftung, Bonn, Germany (1998(cid:1)1999), “Visiting Scientist” at Max-Planck-Institut fuer Metallforschung, Stuttgart, Germany (1998(cid:1)1999), Binani Gold Medal of Indian Institute of Metals (2006), “Metallurgist of the Year for 2010” by the MinistryofSteel,GovernmentofIndia.Dr.PrasadisaFellowofInstitutionof Engineers (FIE (cid:1) 2009), Fellow of Indian Institute of Metals (FIIM (cid:1) 2011), and Fellow of Andhra Pradesh Akademi of Sciences (FAPASc (cid:1) 2011). Dr. Prasad is presently the Regional Director of the Regional Centre for MilitaryAirworthiness(Materials),CEMILACatHyderabad,India. Amol A. Gokhale obtained a B.Tech. in MetallurgicalEngineering,fromtheIndianInstituteof Technology, Bombay, in 1978, and M.S. and a Ph.D. in Metallurgical Engineering from the University of Pittsburgh,Pittsburgh,USA,in1980and1985,respec- tively. Since joining the Defence Metallurgical Research Laboratory (DMRL) in 1985, Dr. Gokhale led the development of second-generation Al(cid:1)Li alloys for Indian defence for about 20 years, which xix xx AbouttheEditors included collaborative efforts with VIAM and KUMZ in Russia, and ADA and HAL in India to manufacture deep formed clad sheet products. He also led the development of aluminum alloy castings for torpedoes and aluminum foams for shock absorption applications. His most recent contributions are in the development of materials and modules for hot structures of hypersonic vehicles. He is working in association with Belarus Powder Metallurgy Laboratory to develop Ni-based foams. Important awards received by Dr. Gokhale include the National Research and Development Corporation “Technology Innovation” Award (1994), the “Metallurgist of the Year Award” by the Ministry of Steel (2000), the “DRDO Scientist of the Year” award (2008), and the “GD Birla Gold Medal” from the Indian Institute of Metals (2010). He has been a Fellow of the Indian National Academy of Engineeringsince 2011.Hehaspublishedabout80technicalpapersandfiled 1 patent. Presently, Dr. Gokhale is the Director of the Defence Metallurgical ResearchLaboratory,Hyderabad,India. Russell Wanhill has a Ph.D. (1968) in Metallurgy from the University of Manchester Institute of Science and Technology, Manchester, UK, and a DoctorofTechnicalSciencedegree(1995)fromDelft University of Technology, Delft, The Netherlands. He joined the National Aerospace Laboratory (NLR) of the Netherlands in 1970 and since then has investi- gated fatigue and fracture of all classes of aerospace alloys, including many service failures. From 1978 to 1996 Russell was Head of the Materials Department of the NLR, and in 1979(cid:1)1980 adjunct Professor of materials at Delft University of Technology. He is the co-author of the book “Fracture Mechanics” (1984), which is now into a second edition, and has written more than320reportsandpublications.FromNovember2009toMay2010,Russell was a “Visiting Academic” at the Defence Science and Technology Organisation, DSTO, Melbourne, Australia. His collaboration with DSTO col- leagues has resulted in journal publications, four book chapters (including one in the present book), a monograph, and a 1-day failure analysis course. Since 1994Russellhasinvestigatedtheembrittlementofancientsilverandpublished a number of papers on this seemingly esoteric but serious problem. “In 2002 the Board of the Foundation NLR awarded Russell the first Dr. ir. B.M. Spee Prizeforoutstandingcontributionsinthefieldofaerospacematerials”.Russell is presently Emeritus Principal Research Scientist in the Aerospace Vehicles DivisionoftheNLR. A Note of Gratitude from the Editors The present monograph deals with the past, present, and future of one of the most exiting alloys to emerge in recent decades that have a vast potential for aeronautical applications—namely the aluminum(cid:1)lithium (Al(cid:1)Li) alloys— and highlights the aspects of alloy processing, mechanical behavior, and properties and aerospace applications. Such an arduous task is not easy to accomplish without the total support and whole-hearted participation of all the authors and members of book editorial offices at Hyderabad, India, and Elsevier, New York. We wish to profoundly thank each one of them— Professor Edgar A. Starke, Jr., Professor T.R. Ramachandran, Dr. K. Satya Prasad, Dr. Kumar V. Jata, Dr. Vijaya Singh, Dr. G. Jagan Reddy, Dr. S.B. Prabu, Professor K.A. Padmanabhan, Dr. G. Madhusudhan Reddy, Professor T.S. Srivatsan, Professor Enrique J. Lavernia, Professor V.V. Kutumbarao, Dr. G. Malakondaiah, Professor S.P. Lynch, Dr. Gary H. Bray, Dr. N.J. Henry Holroyd, Professor Roger C. Newman, Dr. A.K. Vasudevan, Mr. B. Saha, Mr. G. Gouda, Dr. K. Tamilmani, and Members, Hyderabad Book Secretariat Mr. Y. Balaji, Mr. Ch.V.A. Narasayya, Mrs. M. Swarna Bai, Mrs. C. Poornia, and Ms. P. Varsha. We are deeply beholden to Professor Palle Rama Rao, Distinguished Scientist, who led the Al(cid:1)Li alloy development program inIndia,for the exquisite Foreword. Most of the authors of this book had in their past authored or guided doctoral theses based on works on Al(cid:1)Li alloys, which include several years of research, development, production, and certification. Some of them have also painstakingly reviewed the book chapters. Notable in this effort are: Professor Ed Starke reviewing the book chapter on Aero-Structural Design; Dr. Kota Harinarayana and Mr. P.S. Subramanyam on Aero-Structural Design and Aero Certification; Professor David Laughlin on Phase Diagrams and Phase Reactions; Professor T.R. Ramachandran on Microstructure Evolution and Melting and Casting; Dr. Vikas Kumar on Fatigue Crack Growth, and Dr. S.V. Kamat on Fracture Toughness. We owe our profound gratitudetoall these contributingreviewers. Thescientific,technological,anddesigndataofseveralaluminum(cid:1)lithium alloys have been shared magnanimously by several authors, especially those concerned withthird generationAl(cid:1)Li alloys.Infact, there was a stage inthe book project that there could be no further progress without the inputs on third generation Al(cid:1)Li alloys. The support of Professor Ed Starke and xxi xxii ANoteofGratitudefromtheEditors Dr. Gary H. Bray at this crucial juncture proved critical as this very support alone had advanced the book project further to its completion. In this context, wealsothankalltheauthorsofcitedpublications,whohavegenerouslyallowed ustoincludetheirdataandschematicsinthepresentbook. Finally, it is a great pleasure to acknowledge the professional support by the Elsevier Team—particularly, Mr. StephenP. Merken, Acquisitions Editor (person having involved at all stages of book publication), Ms. Amorette Padersen, Vice President, Marketing, and all the members of Book Design Team,headed by Mr. JeffreyM. Freeland, Editorial Project Manager. Republic of India andthe Netherlands September, 2013