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Akihiko Chiba - One of the best experts on this subject based on the ideXlab platform.
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microstructural evolution and deformation mode under high temperature tensile deformation of the ti 6al 4v alloy with the metastable α martensite starting microstructure
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Hiroaki Matsumoto, Takuro Nishihara, Yohei Iwagaki, Tohru Shiraishi, Yoshiki Ono, Akihiko ChibaAbstract:Abstract Ti-6Al-4V alloy having the metastable α′ martensite starting microstructure was investigated for microstructural changes during high-temperature-tensile-deformation at temperatures from 700 °C to 900 °C. As compared to the deformation of Ti-6Al-4V alloy with similar lamellar morphology consisting of an equilibrium (α+β) phase, the quite larger elongation to fracture and the higher strain-rate-sensitivity (m) are exhibited in the case of the α′ martensite starting microstructure. The dynamic globularization associated with an occurrence of the discontinuous dynamic recrystallization is enhanced during tensile deformation of the α′ martensite starting microstructure, resulting in the activation of grain boundary sliding at latter stage of deformation (which contributes to an increase in tensile elongation). Furthermore, dynamic β precipitation from the α′ martensite during deformation also results in contribution to an additional stress-Accommodation Mechanism. As compared to the case in the equilibrium (α+β) lamellar microstructure, the present work indicates that the metastable microstructure of the α′ martensite starting microstructure is more beneficial for an enhancement of high temperature ductility associated with enhancement of dynamic globularization and an occurrence of boundary sliding.
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flow behavior and microstructure in ti 6al 4v alloy with an ultrafine grained α single phase microstructure during low temperature high strain rate superplasticity
Materials & Design, 2015Co-Authors: Hiroaki Matsumoto, Vincent Velay, Akihiko ChibaAbstract:Grain refinement of Ti-6Al-4V alloy (hereafter designated as Ti-64 alloy) is well recognized as a method for revealing the superplasticity at lower temperature or higher strain rates. This work examines the superplastic flow behavior of the ultrafine-grained (UFG) Ti-64 alloy (d(alpha) = 0.4 mu m) consisting of single a phase in relation to microstructural evolution during deformation at 700 degrees C. Detailed microstructural evaluation reveals that the superplastic deformation mode of grain boundary sliding (tested at 700 degrees C-10(-2) s(-1)) can be reasonably explained in relation to the Ball-Hutchison model at initial stage of deformation and the Gifkins Core-Mantle model at latter stage of deformation. During superplastic deformation, the beta-precipitation occurs and contributes to Accommodation Mechanism of stress concentration at grain boundaries. This work also discusses the superplastic flow behavior in comparison with flow behaviors according to the Bird-Mukherjee-Dorn (BMD) generalized constitutive relation and the model which considers the effect of dynamic grain growth during deformation.
Λιμνοπούλου Αλίκη - One of the best experts on this subject based on the ideXlab platform.
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Study of the safety and efficacy of the intracorneal Refractive Inlay Flexivue TM Micro-Lens (Presbia, CA Cooperatief U. A, Netherlands) for the correction of presbyopia
'National Documentation Centre (EKT)', 2014Co-Authors: Limnopoulou Aliki, Λιμνοπούλου ΑλίκηAbstract:Presbyopia (aging of Accommodation Mechanism of the human eye) represents a common problem for people aged over 40-45 years. Many theories have been proposed during the past decades regarding explanation of the pathologic physiology of presbyopia development. The most popular theory of those, states that presbyopia is the result of a progressive reduction of lens ability to accommodate, that worsens with age, due to either lens hardening or degeneration of the ciliary body tissues.Regardless of the responsible cause, presbyopia reduces the ability of near vision affecting everyday life of individuals. American studies have reported that in 1998, over 113 millions of Americans were over 45 years old, underlining the effect of presbyopia condition. A wide variety of procedures have been investigated by ophthalmologists to correct the refractive error. Cornea laser surgery with multifocal patterns or monovision approaches were developed including LASIK, PresbyLASIK,photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK), thin-flap femto-LASIK or sub-Bowman’s keratomileusis (SBK). Conductive keratoplasty (CK), clear lens extraction or cataract surgery using multifocal, pseudo-accommodative intraocular lenses (IOLs) or monovision monofocal IOLs are also some of the techniques that have been used for the treatment of presbyopia.Cornea laser surgery and CK are minimal invasive methods, but they provoke irreversible changes at corneal anatomy, whereas scleral surgery and clear lens extraction are more invasive techniques. The necessity to develop a minimal invasive, reversible, and safe surgical technique with an easy learning curve for patients between 45 and 60 years, who could be considered too old for presbyopia corneal laser surgery and too young for lens extraction, led to the development of refractive intracorneal lenses (inlays) (Flexivue™ Micro-Lens) placed underneath cornea inside a pocket in the corneal stroma. The inlays are refractive lenses that have a central zone free of refractive power and a peripheral zone with a standard positive refractive power. The inlays are inserted inside a pocket in the corneal stroma of the non dominant eye, offering two different focal points, one for the far vision and a different for the near vision respectively. The pocket of the cornea is created using a femtosecond laser.The Flexivue™ Micro-Lens is a transparent, hydrophilic disc with 3 mm diameter andapproximately 15 μm edge thickness. The central 1.6 mm diameter of the disc is planoand the peripheral zone has an add power. The base power available range from +1.5 D to +3.50 D in 0.25 D increments. At the center of the disc there is a hole of 0.15 mm diameter that permits the transfer of oxygen and nutrients of the cornea through the lens. The lens is implanted inside a pocket of the corneal stroma in the center of the visual axes of the non dominant eye.The lens has a bifocal optical system which acts as a modified monovision (smartmonovision). During far vision the rays pass through the central zone of the inlay without refractive effect and will be sharply focused on the retina, whereas the rays which pass through the refractive peripheral zone will be not of focus in front of the retina.During near vision, the rays which pass through the central zone will be out of focusbehind the retina and the rays which pass through the lens peripheral refractive zone will be focused on the retina. As a result, only the peripheral zone of the lens provides the near vision correction, and affects far vision, whereas the central zone of the lens and the peripheral unaltered part of the cornea do not affect the far vision.CLINICAL HYPOTHESISThe working clinical hypothesis for this study is that implantation of the Flexivue™Micro-Lens into a pocket created by femtosecond laser in the cornea, if correctly placed in the center of the cornea corresponding to the visual axes, will enable the study patients to obtain functional near vision without further correction while maintaining their distance.PURPOSE OF THE STUDY The purpose of this study is to evaluate the safety and efficacy of the Flexivue™ Micro- Lens for the treatment of presbyopia with enhanced medication regimen.STUDY POPULATIONFor the study, approximately 10 patients in each group will be enrolled at one location.To qualify for enrollment in this study, each candidate will be thoroughly evaluated toensure that they meet all inclusion criteria and that they do not exhibit any of theexclusion criteria specified in the study protocol.METHODSThis prospective, interventional clinical study comprised 47 emmetropic, presbyopes with a mean age of 51.55 years± 4.11 (range 45 to 60 years). The inlay was implanted, centred on the line of sight, inside a corneal pocket created in the non-dominant eye of the patients, using a femtosecond laser. Follow-up time was 12 months. Visual acuity, topography, wavefront aberrometry, contrast sensitivity, structural corneal alterations and questionnaires were evaluated.STUDY PARAMETERSEfficacy Measures: Uncorrected near visual acuity.Safety Measures: Best Corrected near visual acuity, BiomicroscopySatisfaction Measures: Patient satisfaction questionnaireRESULTS Twelve months after surgery, uncorrected near visual acuity (UNVA) was 20/32 or better in 75% of the operated eyes, whereas mean uncorrected distance visual acuity (UDVA) of the operated eyes was statistically significantly reduced (p
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Study of the safety and efficacy of the intracorneal refractive inlay "flexivue TM micro-lens (Presbia, CA Cooperatief U. A, Netherlands)" for the correction of presbyopia
2014Co-Authors: Λιμνοπούλου ΑλίκηAbstract:Η πρεσβυωπία (φυσιολογική γήρανση του μηχανισμού της προσαρμογής) αποτελεί ένα κοινό πρόβλημα για τα άτομα ηλικίας άνω των 40 με 45 ετών. Αρκετές πιθανές θεωρίες έχουν προταθεί σχετικά με την παθολογική φυσιολογία για την ανάπτυξη της πρεσβυωπίας. Η πιο αποδεκτή είναι η σχετιζόμενη με την ηλικία μείωση της ικανότητας του κρυσταλλοειδούς φακού να προσαρμόσει, η οποία επιδεινώνεται προοδευτικά με την αύξηση της ηλικίας 1. Το γεγονός αυτό θα μπορούσε να προκληθεί είτε από την ηλικιακή σκλήρυνση του κρυσταλλοειδούς φακού, είτε από μεταβολές στον περιφακικό σάκο και το ακτινωτό σώμα σχετιζόμενες με ηλικιακές εκφυλίσεις των ιστών. Ανεξάρτητα τον μηχανισμό, η πρεσβυωπία μειώνει την κοντινή όραση. Όταν δε διορθωθεί μπορεί να επηρεάσει την ικανότητα του ατόμου για διάβασμα, τη συμμετοχή του σε διάφορες δραστηριότητες και τελικά την παραγωγικότητα του στην καθημερινή του ζωή 2. Είναι σημαντικό να τονισθεί η σημασία του φαινόμενου της πρεσβυωπίας και το πόσο αυτή επιδρά στην καθημερινή μας ζωή. Σε μελέτες που έγιναν στην Αμερική βρέθηκε ότι το 1998, περίπου 113 εκατομμύρια Αμερικανοί πολίτες ήταν σε ηλικία άνω των 45 ετών, ηλικία που αρχίζει να εμφανίζεται η πρεσβυωπία. Η θεραπεία της πρεσβυωπίας, παρόλο που είναι αποτελεσματική με την χρήση των θετικών διορθωτικών φακών για κοντινή όραση, έχει προκαλέσει το ενδιαφέρον των ερευνητών που έχουν προτείνει μια σειρά από χειρουργικές θεραπευτικές παρεμβάσεις. Η τοποθέτηση σκληρικών ενθεμάτων επέκτασης συνιστά μία χειρουργική τεχνική επιδίωξης αναστροφής της πρεσβυωπίας μέσω αύξησης της απόστασης της ακτινωτής απόφυσης από το σκληρό χιτώνα, με επακόλουθο την ανάκτηση μέρους της ελαστικότητας των ινών της ζιννείου ζώνης 3. Εναλλακτικά, αξιοποιείται η τεχνική της ‘μονο-όρασης’ (monovision), κατά την οποία ο κυρίαρχος οφθαλμός διορθώνεται με laser ή με τοποθέτηση μονοεστιακού ενδοφακού για την εξυπηρέτηση της μακρινής όρασης, ενώ ο έτερος για εκείνη της κοντινής. Ωστόσο, ο ασθενής συχνά αντιμετωπίζει σημαντικά προβλήματα στη διόφθαλμη όραση (όπως η μείωση του βάθους πεδίου και η απώλεια στερέοψης) 4-7. Ένας άλλος τρόπος διόρθωσης αυτού του περιοριστικού παράγοντα είναι με τη χρήση προσαρμοστικών ενδοφακών οι οποίοι ακολουθούν τις κινήσεις της προσαρμογής που υπόκειται ο σάκος του περιφακίου (στον οποίο είναι τοποθετημένοι) από το ακτινωτό σώμα. Αυτοί οι φακοί μπορούν να παρέχουν 0,5-1 διοπτρίες ‘ψευδο-προσαρμογής’8. Συγκριτικές μελέτες απέδειξαν ότι οι προσαρμοστικοί ενδοφακοί παρέχουν την ίδια, άνευ διόρθωσης, μακρινή οπτική οξύτητα, όμως χάνεται η δυνατότητα για κοντινή όραση μετά τους πρώτους έξι μήνες, εξαιτίας μείωσης της ελαστικότητας του περιφακίου (ανάπτυξη μετεγχειρητικών συμφύσεων) 9. Η χρήση πολυεστιακών ενδοφακών τελευταία έχει γνωρίσει ιδιαίτερη αποδοχή τόσο από τους ασθενείς όσο και από τους οφθαλμιάτρους. Ωστόσο και με αυτή τη μέθοδο παρατηρήθηκε μία σχετική μείωση των ποιοτικών χαρακτηριστικών της μακρινής και κοντινής οπτικής οξύτητας με (best spectacles corrected visual acuity-BSCVA)/χωρίς (uncorrected visual acuity-UCVA) διόρθωση καθώς και της ευαισθησίας στην φωτεινή αντίθεση 10, 11. 5 Οι χειρουργικές τεχνικές με τη χρήση laser στο επίπεδο του κερατοειδούς είναι μη αναστρέψιμες, καθώς μεταβάλλουν τη δομή του ιστού μέσω φωτοδιάσπασης, ενώ ο ασθενής ενδεχομένως να υποστεί μελλοντικά επιπλέον επέμβαση στους οφθαλμούς του για την αποκατάσταση του καταρράκτη. Οι χειρουργικές τεχνικές που αφορούν το σκληρό και τον κρυσταλλοειδή φακό, είναι πιο επεμβατικές και ακρωτηριαστικές για τους νέους πρεσβύωπες μέχρι 50 ετών στους οποίους ο φακός διατηρεί κάποιες εφεδρείες προσαρμογής. Έτσι, η επιστημονική κοινότητα αναζητά μία ελάχιστα επεμβατική και δυνητικά αναστρέψιμη χειρουργική τεχνική για τη διόρθωση της πρεσβυωπίας σε ασθενείς 45-55 ετών. Με βάση τα παραπάνω, η έρευνα για την διόρθωση της πρεσβυωπίας έστρεψε το ενδιαφέρον της εκ νέου στο επίπεδο του κερατοειδούς. Το τελευταίο, πολλά υποσχόμενο, επίτευγμα της επιστημονικής αυτής αναζήτησης είναι η κατασκευή ενδοκερατοειδικών διαθλαστικών ενθεμάτων 12. Το "FlexivueTM system" είναι μία τεχνική σχεδιασμένη να εισάγει ένα μικρού μεγέθους οπτικό φακό με θετική διαθλαστική δύναμη στο στρώμα του κερατοειδούς σε ένα σημείο ακριβώς απέναντι από το κέντρο της κόρης. Πρόκειται στην πραγματικότητα για ένα διπλοεστιακό φακό πάχους 15 μm και διαμέτρου 3 mm που τοποθετείται στον μη-επικρατούντα οφθαλμό. Λόγω της διπλοεστιακότητας του φακού η μακρινή όραση στο χειρουργημένο οφθαλμό επηρεάζεται πολύ λιγότερο από ότι με ένα κλασικό monovision. Με το φακό FlexivueTM τοποθετημένο, ο κερατοειδής γίνεται διπλοεστιακός. Το κεντρικό αναλλοίωτο τμήμα του κερατοειδούς οπού ο φακός είναι τοποθετημένος, προσφέρει ευκρινή μακρινή όραση και το περιφερικό τμήμα παρέχει ευκρινή κοντινή όραση. Κατά τη μακρινή όραση, οι φωτεινές ακτίνες του αντικειμένου που διέρχονται από την κεντρική plano ζώνη του ενθέματος και εκείνες που διέρχονται από την περιοχή του κερατοειδούς εξωτερικά του ενθέματος θα εστιαστούν στον αμφιβληστροειδή, ενώ οι ακτίνες του μακρινού αντικειμένου που διέρχονται από την περιφερική ζώνη του ενθέματος με τη διαθλαστική δύναμη θα εστιαστούν μπροστά από τον αμφιβληστροειδή και η θολή εικόνα που δημιουργούν θα απορριφθεί από το οπτικό σύστημα. Εστιάζοντας σε ένα κοντινό αντικείμενο, η κόρη φυσιολογικά συστέλλεται, οπότε διέρχονται μόνο οι κεντρικές φωτεινές ακτινοβολίες, αφού όμως διαπεράσουν πρώτα το ένθεμα. Οι φωτεινές ακτίνες του κοντινού αντικειμένου που διέρχονται από την κεντρική ζώνη του ενθέματος θα εστιάζονται πίσω από τον αμφιβληστροειδή και η θολή εικόνα που δημιουργούν απορρίπτεται από το οπτικό σύστημα. Οι φωτεινές ακτίνες του κοντινού αντικειμένου που διέρχονται από την περιφερική ζώνη του ενδοκερατοειδικού ενθέματος θα εστιάζονται στον αμφιβληστροειδή. Σαν αποτέλεσμα, μόνο η περιφερική ζώνη του ενθέματος παρέχει κοντινή διόρθωση και επηρεάζει τη μακρινή όραση, ενώ το κεντρικό τμήμα του ενδοκερατοειδικού φακού και η εκτός του ενθέματος ζώνη του κερατοειδούς δεν επηρεάζουν τη μακρινή όραση του ασθενούς.INTRODUCTION Presbyopia (aging of Accommodation Mechanism of the human eye) represents a common problem for people aged over 40-45 years. Many theories have been proposed during the past decades regarding explanation of the pathologic physiology of presbyopia development. The most popular theory of those, states that presbyopia is the result of a progressive reduction of lens ability to accommodate, that worsens with age, due to either lens hardening or degeneration of the ciliary body tissues. Regardless of the responsible cause, presbyopia reduces the ability of near vision affecting everyday life of individuals. American studies have reported that in 1998, over 113 millions of Americans were over 45 years old, underlining the effect of presbyopia condition. A wide variety of procedures have been investigated by ophthalmologists to correct the refractive error. Cornea laser surgery with multifocal patterns or monovision approaches were developed including LASIK, PresbyLASIK, photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK), thin-flap femto-LASIK or sub-Bowman’s keratomileusis (SBK). Conductive keratoplasty (CK), clear lens extraction or cataract surgery using multifocal, pseudo-accommodative intraocular lenses (IOLs) or monovision monofocal IOLs are also some of the techniques that have been used for the treatment of presbyopia. Cornea laser surgery and CK are minimal invasive methods, but they provoke irreversible changes at corneal anatomy, whereas scleral surgery and clear lens extraction are more invasive techniques. The necessity to develop a minimal invasive, reversible, and safe surgical technique with an easy learning curve for patients between 45 and 60 years, who could be considered too old for presbyopia corneal laser surgery and too young for lens extraction, led to the development of refractive intracorneal lenses (inlays) (Flexivue™ Micro-Lens) placed underneath cornea inside a pocket in the corneal stroma. The inlays are refractive lenses that have a central zone free of refractive power and a peripheral zone with a standard positive refractive power. The inlays are inserted inside a pocket in the corneal stroma of the non dominant eye, offering two different focal points, one for the far vision and a different for the near vision respectively. The pocket of the cornea is created using a femtosecond laser. The Flexivue™ Micro-Lens is a transparent, hydrophilic disc with 3 mm diameter and approximately 15 μm edge thickness. The central 1.6 mm diameter of the disc is plano and the peripheral zone has an add power. The base power available range from +1.5 D to +3.50 D in 0.25 D increments. At the center of the disc there is a hole of 0.15 mm diameter that permits the transfer of oxygen and nutrients of the cornea through the lens. The lens is implanted inside a pocket of the corneal stroma in the center of the visual axes of the non dominant eye. The lens has a bifocal optical system which acts as a modified monovision (smart 10 monovision). During far vision the rays pass through the central zone of the inlay without refractive effect and will be sharply focused on the retina, whereas the rays which pass through the refractive peripheral zone will be not of focus in front of the retina. During near vision, the rays which pass through the central zone will be out of focus behind the retina and the rays which pass through the lens peripheral refractive zone will be focused on the retina. As a result, only the peripheral zone of the lens provides the near vision correction, and affects far vision, whereas the central zone of the lens and the peripheral unaltered part of the cornea do not affect the far vision. CLINICAL HYPOTHESIS The working clinical hypothesis for this study is that implantation of the Flexivue™ Micro-Lens into a pocket created by femtosecond laser in the cornea, if correctly placed in the center of the cornea corresponding to the visual axes, will enable the study patients to obtain functional near vision without further correction while maintaining their distance. PURPOSE OF THE STUDY The purpose of this study is to evaluate the safety and efficacy of the Flexivue™ Micro- Lens for the treatment of presbyopia with enhanced medication regimen. STUDY POPULATION For the study, approximately 10 patients in each group will be enrolled at one location. To qualify for enrollment in this study, each candidate will be thoroughly evaluated to ensure that they meet all inclusion criteria and that they do not exhibit any of the exclusion criteria specified in the study protocol. METHODS This prospective, interventional clinical study comprised 47 emmetropic, presbyopes with a mean age of 51.55 years± 4.11 (range 45 to 60 years). The inlay was implanted, centred on the line of sight, inside a corneal pocket created in the non-dominant eye of the patients, using a femtosecond laser. Follow-up time was 12 months. Visual acuity, topography, wavefront aberrometry, contrast sensitivity, structural corneal alterations and questionnaires were evaluated. STUDY PARAMETERS Efficacy Measures: Uncorrected near visual acuity. Safety Measures: Best Corrected near visual acuity, Biomicroscopy Satisfaction Measures: Patient satisfaction questionnaire RESULTS Twelve months after surgery, uncorrected near visual acuity (UNVA) was 20/32 or better in 75% of the operated eyes, whereas mean uncorrected distance visual acuity (UDVA) of the operated eyes was statistically significantly reduced (p&λτ0.001) and mean 11 uncorrected distance visual acuity (UDVA) binocularly was not significantly altered (p=0.516).Seventeen patients lost one line of corrected distance visual acuity (CDVA) in the operated eye. Overall higher order aberrations were increased and contrast sensitivity was decreased in the operated eyes. No tissue alterations were found using corneal confocal microscopy. No intra or late-operative complications occurred. CONCLUSIONS Intracorneal refractive inlay for presbyopia FlexivueTM Micro-Lens using the femtosecond laser seems to represent an effective and safe method for the corneal compensation of presbyopia in emmetropic presbyopes aged between 45 and 60 years old, twelve months after the implantation
Hiroaki Matsumoto - One of the best experts on this subject based on the ideXlab platform.
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microstructural evolution and deformation mode under high temperature tensile deformation of the ti 6al 4v alloy with the metastable α martensite starting microstructure
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016Co-Authors: Hiroaki Matsumoto, Takuro Nishihara, Yohei Iwagaki, Tohru Shiraishi, Yoshiki Ono, Akihiko ChibaAbstract:Abstract Ti-6Al-4V alloy having the metastable α′ martensite starting microstructure was investigated for microstructural changes during high-temperature-tensile-deformation at temperatures from 700 °C to 900 °C. As compared to the deformation of Ti-6Al-4V alloy with similar lamellar morphology consisting of an equilibrium (α+β) phase, the quite larger elongation to fracture and the higher strain-rate-sensitivity (m) are exhibited in the case of the α′ martensite starting microstructure. The dynamic globularization associated with an occurrence of the discontinuous dynamic recrystallization is enhanced during tensile deformation of the α′ martensite starting microstructure, resulting in the activation of grain boundary sliding at latter stage of deformation (which contributes to an increase in tensile elongation). Furthermore, dynamic β precipitation from the α′ martensite during deformation also results in contribution to an additional stress-Accommodation Mechanism. As compared to the case in the equilibrium (α+β) lamellar microstructure, the present work indicates that the metastable microstructure of the α′ martensite starting microstructure is more beneficial for an enhancement of high temperature ductility associated with enhancement of dynamic globularization and an occurrence of boundary sliding.
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flow behavior and microstructure in ti 6al 4v alloy with an ultrafine grained α single phase microstructure during low temperature high strain rate superplasticity
Materials & Design, 2015Co-Authors: Hiroaki Matsumoto, Vincent Velay, Akihiko ChibaAbstract:Grain refinement of Ti-6Al-4V alloy (hereafter designated as Ti-64 alloy) is well recognized as a method for revealing the superplasticity at lower temperature or higher strain rates. This work examines the superplastic flow behavior of the ultrafine-grained (UFG) Ti-64 alloy (d(alpha) = 0.4 mu m) consisting of single a phase in relation to microstructural evolution during deformation at 700 degrees C. Detailed microstructural evaluation reveals that the superplastic deformation mode of grain boundary sliding (tested at 700 degrees C-10(-2) s(-1)) can be reasonably explained in relation to the Ball-Hutchison model at initial stage of deformation and the Gifkins Core-Mantle model at latter stage of deformation. During superplastic deformation, the beta-precipitation occurs and contributes to Accommodation Mechanism of stress concentration at grain boundaries. This work also discusses the superplastic flow behavior in comparison with flow behaviors according to the Bird-Mukherjee-Dorn (BMD) generalized constitutive relation and the model which considers the effect of dynamic grain growth during deformation.
Marie Loyer-prost - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamic model for lattice point defect-mediated semi-coherent precipitation in alloys
Communications Materials, 2021Co-Authors: Maylise Nastar, Lisa T. Belkacemi, Estelle Meslin, Marie Loyer-prostAbstract:The formation of precipitates with an atomic volume different from their parent phase eventually leads to a loss of the lattice continuity at the matrix–precipitate interface. Here, we show the creation or removal of lattice sites mediated by lattice point defects is an Accommodation Mechanism of the coherency loss and even a precipitation driving force. We introduce a thermodynamic approach that rationalizes the selection of phases resulting from chemical and crystallographic constraints in relation to point defect properties. The resulting semi-coherent phase diagram and the precipitation kinetic model depend on the equilibrium phase diagram, the eigenstrain of the precipitating phase, and the chemical potential of point defects. From a joint experimental and modeling study, we uncover the prominent role of excess point defects in unforeseen phase transformations of the Fe–Ni metallic system under irradiation. By addressing the fundamental role of lattice point defects in the Accommodation Mechanisms of precipitation, we provide a step torwards the understanding of semi-coherent phase transformations occurring in solid materials upon synthesis and in use. Precipitation of secondary phases in a crystalline matrix often leads to the loss of coherency at the phase boundary. Here, a thermodynamic model for precipitation is presented that takes into account the role of lattice point defects on the Accommodation Mechanism of coherency loss.
Yu V Matviychuk - One of the best experts on this subject based on the ideXlab platform.
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Deformation behavior of beta-titanium alloys
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: O.p. Karasevskaya, O M Ivasishin, S L Semiatin, Yu V MatviychukAbstract:The cold workability of four solution-treated beta-titanium alloys was determined and related to the initial substructure. Two alloys (TIMETAL-LCB and Ti-15-3), which retained a well-developed subgrain structure after solution treatment, exhibited excellent workability, while those alloys which did not (VT22 and TC6) exhibited inferior ductility. The difference in workability was explained in terms of the variation in strain-Accommodation Mechanism. Other factors that exacerbated the observed low ductility of the latter two alloys were also identified. These included the occurrence of deformation-induced martensite formation and the development of multi-component textures, both of which may lead to localization of deformation at interphase or grain boundaries and subsequent failure.
