Available online at ScienceDirect. Procedia Engineering 183 (2017 )

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1 Aville online t ScienceDirect Procedi Engineering 183 (2017 ) th Interntionl Conference on Sheet Metl, SHEMET17 On The Microstructurl Anlysis of LFW Joints Of Ti6Al4V Components Mde Vi Electron Bem Melting Fio Scherillo *, Mricir Lierini, Antonello Astrit, Stefni Frnchitti, Crmine Pirozzi, Rosrio Borrelli, Pierluigi Cirillo c, Antonio Crviello c, Antonino Squillce, Luigi Crrino Università degli studi di Npoli Federico II, Diprtimento di Ingegneri Chimic, dei Mterili e dell Produzione Industrile, pizzle Tecchio 80, 80125, Npoli, ITA CIRA, Centro Itlino Ricerche Aerospzili, vi Miolise 1, Cpu, ITA c Sòphi HIGH TECH, Zon Industrile Csert Sud, Mrcinise, It Astrct Additive Mnufcturing (AM), pplied to metl industry, is fmily of processes tht llow complex shpe components to e relized from rw mterils in the form of powders. The compction of the powders is chieved y locl melting of ed. Electron Bem Melting (EBM) is n dditive mnufcturing process in which foclized electron em is the het source tht llows the powders to e compcted. By EBM it is possile to relize complex shpe components; this feture is of prticulr interest in titnium industry where numerous efforts re done to develop ner net shpe processes. One of the limits of EBM sed AM process is the difficulty to relize lrge dimension prts. Due to this limit the study of joining processes of different prts is of gret interest. In the present work the microstructure evolution of sheets of TI6Al4V mde y EBM nd joined y Liner Friction Welding (LFW) is nlyzed in detils. The ulk microstructure of the specimen is fine lmellr; lmelle re enclosed in lph colonies. Different types of porosities re oserved. In the joint Thermo Mechnicl Affected Zone (TMAZ) nd Weld Bed (WB) re evident. In TMAZ prtil recrystlliztion occurs nd the prent microstructure is deformed. Complete recrystlliztion occurs in WB whose structure is mrtensitic The Authors. Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license 2017 The Authors. Pulished y Elsevier Ltd. ( Peer-review Peer-review under under responsiility responsiility of the of orgnizing the orgnizing committee committee of SHEMET17 of SHEMET17. * Corresponding uthor. Tel.: ; fx: E-mil ddress: fio.scherillo@unin.it The Authors. Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of the orgnizing committee of SHEMET17 doi: /j.proeng

2 Fio Scherillo et l. / Procedi Engineering 183 ( 2017 ) Keywords: Electron Bem Melting; Liner Friction Welding; Ti6Al4V, Microstructure 1. Introduction Additive Mnufcturing is n innovtive technology tht llows relizing complex shpe components using powder s rw mteril The finl shpe of components is relized y the ddition of different lyers of powders. The powders re loclly compcted y focused het source like lser or n electron em. The compction occurs vi melting nd generlly the process is conducted under vcuum or inert tmosphere [1]. Electron Bem Melting (EBM) uses n electron em s het source nd opertes under vcuum, lens nd mgnetic fields re used to control the em. Due to the presence of electron currents EBM is not suitle for mgnetic mterils, ut it is prticulrly dvntgeous for titnium lloys tht re very difficult to e worked y trditionl sutrctive techniques. One of the limits of EBM technology is the difficulty to relize lrge components, t this im the necessity to study proper welding processes to join different prts ppers very useful. Among the welding procedures Liner Friction Welding (LFW) hs een investigte due to its opertionl flexiility nd cpility to produce sound joints when pplied to titnium lloys nd lso dissimilr joints. From opertive point of view the source of het is friction which produces plsticized zone, once plsticiztion hs reched desired level forging pressure is pplied nd so welding is relized. During the process severe plstic deformtion nd heting re experienced y mteril, which is suject to importnt microstructurl trnsformtions [2,3]. The knowledge of those trnsformtions is of crucil importnce ecuse they directly influence the mechnic ehvior nd other properties. Fig. 1. () specimen efore welding; () fter welding. 2. Mterils nd Methods EBMed specimen suitle for LFW were prepred y CIRA (Centro Itlino Ricerche Aerospzili) using n ARCAM A2X fcility. The geometry of the specimen is reported in Fig. 1. The specimen were joined using mchine designed y Sophi HIGH TECH srl, the prmeters used in welding process re: frequency 40 Hz, mplitude 1 mm nd forging force N. The contct surfce is 253 mm 2.

3 266 Fio Scherillo et l. / Procedi Engineering 183 ( 2017 ) The joints were cut using REMET 3000 metllogrphic cutter, then the specimen, contining the weld zone, were mounted in epoxy conductive resins. All smples were polished to mirror like finishing using conventionl techniques end etched y 0.5% HF solution [4]. Opticl imges were tken y mens of Zeiss Axiopln 2 Microscope. Scnning Electron Microscope (SEM) nlysis ws performed using An Hitchi TM 3000 electron microscope. Energy-Dispersive X-ry Spectroscopy (EDS) ws relized y mens of n Oxford Instrument Swift ED 3000 silicon drift detector t the operting condition of 15 kev 3. Results nd Discussion In Fig.2 the mcrogrph of the weld zone is reported. Prent Mteril, Thermo Mechnicl Affected Zone nd Weld Bed cn e distinguished. The joint is sound without crck or other mcroscopic defect. Fig. 2. Welding zone More in detils the PM (Fig. 3) is chrcterized y the presence of horizontl strtifiction nd elongted structures in the direction of het flux. The horizontl strtifiction corresponds to the different lyers dded during the EBM process. During the EBM process the cooling of melted Ti6Al4V genertes in first β phse, further cooling produces the typicl α+β structures. The elongted structures re the former et grins mentioned ove. They grew in epitxil wy due to the presence of sustntilly unidirectionl het flow [5]. From β grins the α-lmelle originte, the lmelle re seprted ech other y β phse. Whole α+β structure is Widmnstätten type. From the oundry of the former β grins the lph lyer origintes, it is continuous string mde entirely of α phse (Fig 3) [6].

4 Fio Scherillo et l. / Procedi Engineering 183 ( 2017 ) Fig. 3. () Opticl imge of PM; () SEM imge of PM with highlighted the α lyer Inside PM two different type of porosity cn e distinguished. The first (Fig. 4) consists of round shped pores of out 40 µm. The origin of these pores is ttriuted to the presence of gses tht evolve during the melting process. In fct the Ti6Al4V lttice contins dissolved toms of C, N, O tht t melting point re relesed forming gs molecules. Another source of gses is the sulimtion of the different component of the lloy. The second type of porosity (Fig. 4) consists of irregulr shped pores whose dimension is few microns. The presence of those pores is due to compction defect inside the powder ed during the EBM process. Fig. 4. () Round shped pore oserved in prent mteril; () Irregulr shped pore The microstructure of TMAZ is reported in Fig. 5, the former et grins re still distinguishle, ut they re deformed. In some res of TMAZ chnge in microstructure occurs. As showed in Fig. 5 sket-wve microstructure is present. The presence of this type of structure is ttriuted to phenomen of recrystlliztion tht occurs when the mteril experiences heting ove the β-trnsus followed y cooling fster to respect PM.

5 268 Fio Scherillo et l. / Procedi Engineering 183 ( 2017 ) Fig. 5. () Opticl imge of TMAZ; () Bsket wve microstructure of the Recrystlliztion Zone c Fig. 6. () Ares of TMAZ with different morphology of β phse nd reltive EDS spectrum (); (c) EDS spectrum of β phse in PM

6 Fio Scherillo et l. / Procedi Engineering 183 ( 2017 ) Agin in TMAZ some smll res chrcterized, in comprison to PM, y oth chnge in composition nd morphology of β phses cn e noticed. In Fig. 6 the results of EDS nlysis performed on forementioned res nd on β phse of PM re reported. Those differences re ttriuted to locl diffusion phenomen cused y the comined effect of deformtion nd het. In Fig. 7 the microstructure of WB is reported. It is mrtensitic type tht mens tht the mteril experienced rpid cooling from temperture ove the β-trnsus. Finlly in oth TMAZ nd WB considerle decrese of porosity is oserved. Fig. 7. () Opticl imge of WB (); SEM imge of WB 4. Conclusion On the sis of the results discussed ove the following conclusion cn e deduced: The LFW process pplied to EBMed Ti6Al4V specimen produces sound joint Both in WB nd TMAZ decrese in porosity is oserved to respect prent mteril IN TMAZ recrystlliztion nd redistriution of lloy components occurs The WB hs mrtensitic microstructure tht indictes fst cooling from temperture ove the β-trnsus References [1] L. E. Murr et l, Metl Friction y Additive Mnufcturing Using Lser nd Electron Bem Melting Technologies, J. Mter. Sci. Technol. 28(1) (2012) 1-14 [2] L. Frtini et l, Investigtions on the liner friction welding process through numericl simultions nd experiments, Mter. Design 40 (2012) [3] G. Buff et l, FEM sed prediction of phse trnsformtions during Friction Stir Welding of Ti6Al4V titnium lloy, Mt. Sci. Eng. A, 581 (2013) [4] K. Geels nd M. Ruckert: in Metllogrphic nd Mterilogrphic Specimen Preprtion, Light Microscopy, Imge Anlysis nd Hrdness Testing, Geels K, ed., ASTM interntionl, West Conshohocken, 2007, pp [5] S. S. Al-Bermni et l, The Origin of Microstructurl Diversity, Texture, nd Mechnicl Properties in Electron Bem Melted Ti-6Al-4V, Metll. Mter. Trns. A, 41A (2010) [6] G. Lutjering, J.C. Willims: Titnium, Springer, Berlin, 2003