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Fatigue properties of Ti-6Al-4V manufactured using electron beam melting
Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Quality Technology and Management, Mechanical Engineering and Mathematics.ORCID iD: 0000-0001-5954-5898
2017 (English)In: Proceedings Euro PM 2017: International Powder Metallurgy Congress and Exhibition 2017, Brussels: EPMA European Powder Metallurgy Association , 2017Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The interest in powder bed fusion additive manufacturing methods, such as electron beam melting (EBM), is increasing constantly and main business areas driving the development are aerospace and implant manufacturers. EBM manufactured parts have a rather coarse surface roughness mainly originating from the layer thickness and the powder grains melted by the electron beam. Thus, there is an interest in understanding how the surface properties influences the fatigue performance of the material. In this study, EBM manufactured Ti-6Al-4V was investigated at high cycle fatigue using rotating beam and different types of specimens regarding geometry, as-built and hot isostatic pressing (HIP) post-processing were evaluated. The results confirm that as-built surfaces affect the fatigue limit and a small size specimen geometry for rotating beam fatigue testing is proposed as a part of material and process verification.

Place, publisher, year, edition, pages
Brussels: EPMA European Powder Metallurgy Association , 2017.
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:miun:diva-32484Scopus ID: 2-s2.0-85056550071ISBN: 978-1-899072-49-1 (electronic)OAI: oai:DiVA.org:miun-32484DiVA, id: diva2:1167424
Conference
International Powder Metallurgy Congress and Exhibition, Euro PM 2017; Milano Congressi (MiCo)Milan; Italy; 1 October 2017 through 4 October 2017
Available from: 2017-12-18 Created: 2017-12-18 Last updated: 2018-12-14Bibliographically approved
In thesis
1. Electron beam melting: Impact of part surface properties on metal fatigue and bone ingrowth
Open this publication in new window or tab >>Electron beam melting: Impact of part surface properties on metal fatigue and bone ingrowth
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Abstract

The aim of this thesis is to investigate aspects on how additive manufacturing (AM) contributes to functional bone implants with the use of the electron beam melting (EBM) technology. AM manufactures parts according to computer-aided design, and the EBM technology melts powder using an electron beam, which acts similar to a laser beam. The topics discussed in this thesis are related to surface roughness that originate from the melted metal powder, and the thesis tries to define some aspects that affect implant functionality. Process parameters steering the electron beam and biocompatibility arising from the surface texture were the initial parts of the PhD studies, and the other half focused on post-processing and fatigue, which are important for medical and industrial applications. There are six studies in this compilation thesis. They are abbreviated as P - process parameters, M - medical applications, and F - fatigue. Studies P, M2, F2, and F3 are journal articles, and M1 and F1 are conference proceedings.

Study P used design of experiments to investigate how process parameters affect the surface roughness of as-built EBM-manufactured parts and concluded that beam speed and energy (current) were the most important parameters that influence the surface roughness.

In studies M1 and M2, EBM-manufactured specimens of cobalt-chromium and titanium alloys were used to evaluate biocompatibility. The blood chamber method quantified the reactions of the human whole blood in contact with the metal surfaces, and the results showed how the as-built EBM surface roughness contributed to coagulation and bone healing.

Rotating beam fatigue equipment was used in studies F1–F3 and study F1 discussed the size effect on fatigue loaded as-built specimens and included specimens with different sizes and with or without hot isostatic pressing (HIP). Study F2 compared as-built and machined specimens and study F3 investigated how Hirtisation, which is a patented electrochemical surface treatment, and HIP affect the fatigue properties that originate from the electrochemical polishing surface topography. The studies showed that a decreased surface roughness increased the fatigue resistance while the stress concentrations (Kt) in the surface of EBM-manufactured specimens decreased.

The thesis concludes that EBM-manufactured as-built surfaces are suitable for direct contact with the bone, and that HIP does not improve the fatigue resistance of parts with as-built surfaces, where crack initiation starts at notches.

Abstract [sv]

Svensk sammanfattning

Denna avhandling behandlar frågeställningar inom tillverkning av benimplantat med additiv tillverkning (Additive Manufacturing, AM), med fokus på EBM-tekniken (Electron Beam Melting, smältning med elektronstråle). Additiv tillverkning bygger produkter utifrån datorkonstruerade modeller (Computer Aided Design, CAD), och EBM-tekniken gör detta genom att smälta ihop metallpulver med hjälp av en energirik elektronstråle likt en laserstråle. Avhandlingen fokuserar på ytstrukturen från det smälta metallpulvret och hur dess egenskaper påverkar funktionen av EBM-tillverkade produkter. Under första delen av doktorandarbetet var fokus på processparametrar som styr elektronstrålen och biokompatibilitet, och under den senare delen har arbetet riktats mot efterbearbetningsmetoder och utmattningsegenskaper, vilket är viktigt för medicinska implantat och industriell användning. Avhandlingen är skriven på engelska och studierna som sammanläggningen består av är döpta och numrerade med förkortningarna P-Processparametrar, M-Medicinska applikationer och F-Fatigue (Utmattning). Avhandlingen består av fyra tidskriftsartiklar kallade studie P, M2, F2 och F3 och två konferensbidrag studie M1 och F1.

Studie P undersökte med hjälp av försöksplanering (Design Of Experiment, DOE) hur processparametrarna påverkar ytgrovheten för EBM-tillverkade produkter och resulterade i att elektronstrålens förflyttningshastighet och energi har störst inverkan på ytgrovheten.

Studierna M1 och M2 använde kobolt-krom- respektive titanlegeringar, tillverkat med EBM-tekniken, och undersökte biokompatibiliteten med hjälp av blodkammarmodellen som kvantifierar blodets reaktioner vid kontakt med metallytan. Resultaten visade att den mycket grova ytan som EBM-tillverkade implantat har, stimulerar till koagulation och implantatinläkning.

Roterande utmattning användes för studierna F1-3, och studie F1 avhandlar hur EBM-tillverkade provstavar med olika storlekar och med eller utan tempererad tryckbehandling (Het Isostatisk Pressning, HIP) påverkar resultaten. Studie F2 jämförde hur den EBM-tillverkade ytan och en maskinbearbetad yta påverkar materialegenskaperna, och studie F3 undersökte hur Hirtisering, en patenterad elektrokempoleringsmetod, och kombinerat med HIP påverkar utmattningsegenskaperna. Studierna visar att minskad ytgrovhet med elektrokempolering ökar hållfastheten samtidigt som spänningskoncentrationerna (Kt) minskar i ytan för EBM-tillverkade ytor.

Avhandlingen visar att EBM-tillverkade ytor lämpar sig för benkontakt och att HIP inte förbättrar utmattningsegenskaperna om den råa ytan behålls.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 73
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 291
Keywords
Additive Manufacturing (AM), Electron Beam Melting (EBM), As-built surfaces, Bone Ingrowth, Metall Fatigue, Machined Surfaces, Hirtisation, Hot Isostatic Pressing (HIP)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:miun:diva-35182 (URN)978-91-88527-82-0 (ISBN)
Public defence
2019-01-15, Q221, Akademigatan 1, Östersund, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2018-12-14 Created: 2018-12-13 Last updated: 2018-12-14Bibliographically approved

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Klingvall Ek, RebeccaBäckström, MikaelRännar, Lars-Erik

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