Microstructure and mechanical properties of biomedical alloys

192 Pages·2010·8.65 MB·English

by  Luca Facchini

Doctoral School in Materials Engineering – XXII cycle

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January 2010

Doctoral thesis

Microstructure and mechanical properties
of biomedical alloys produced
by Rapid Manufacturing technologies

Luca Facchini

Tutor: Prof. Ing. Alberto Molinari

Doctoral Committee:
Prof. Alberto Molinari, Università degli Studi di Trento, Italy (President)
Prof. Marjorie Olivier, Faculté Polytechnique de Mons, Belgium
Prof. Nikolaos E. Zafeiropoulos, University of Ioannina, Greece

Date of dissertation: January 21st, 2010

to the memory of Giulia

Index
Introduction
Chapter 1: Rapid Manufacturing technologies
1.1 The technologies: an overview……………………………………………….. 3
1.2 Going to a fully dense material: the process parameters……………………… 6
1.3 Incomplete homologous wetting and balling…………………………………. 6
1.4 Vaporization and volatilization……………………………………………….. 8
1.5 Epitaxial solidification………………………………………………………... 12
1.6 Fine grains…………………………………………………………………… 13
1.7 Scanning strategy…………………………………………………………….. 14
1.8 Selective Laser Melting……………………………………………………….. 15
1.9 Electron Beam Melting………………………………………………………. 17
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Chapter 2: The materials
2.1 Metallic powder for Rapid Manufacturing……………………………………. 21
2.2 Ti-6Al-4V alloy………………………………………………………………. 22
2.2.1 Ti-6Al-4V alloy: microstructure……………………………………………. 23
2.2.2 Ti-6Al-4V alloy: mechanical properties……………………………………… 27
2.2.3 Ti-6Al-4V alloy: application and corresponding required properties……………... 30
2.3 ASTM F75 alloy………………………………………………..…………….. 30
2.3.1 ASTM F75 alloy: microstructure…………………………………………… 31
2.3.2 ASTM F75 alloy: mechanical properties……………………………………... 33
2.3.3 ASTM F75 alloy: application and corresponding required properties…………….. 36
2.4 17-4 PH Stainless Steel……………………………………………………….. 37
2.4.1 17-4 PH Stainless Steel: microstructure…………………………………. 38
2.4.2 17-4 PH Stainless Steel: mechanical properties………………………….. 39
2.4.3 17-4 PH Stainless Steel: application and corresponding required properties……….. 45
Chapter 3: Requirements for the application
3.1 The biomedical standards…………………………………………………….. 48
3.2 Requirements on chemical composition……………………………………… 49
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3.3. Requirements on mechanical properties……………………………………... 50
3.3.1 ISO 5832-3 standard for Ti-6Al-4V alloy………………………………….. 50
3.3.2 ISO 5832-4 standard for ASTM F75 alloy…………………………………. 51
3.3.3 ASTM A564-02 standard for 17-4 PH Stainless Steel………………………. 52
3.4 Microstructure……………………………………………………………….. 52
3.5 Density of the alloys produced by Rapid Manufacturing techniques………….. 54
Chapter 4: Materials and experimental procedures
4.1 Powders……………………………………………………………………… 55
4.2 Process parameters…………………………………………………………... 57
4.3 Microhardness and hardness…………………………………………………. 58
4.4 Light Optical Microscopy (LOM) …………………………………………… 58
4.5 Scanning Electron Microscopy (SEM) and Transmission Electron
Microscopy (TEM) ……………………………………………………………… 59
4.6 Differential Scanning Calorimetry (DSC) ……………………………………. 60
4.7 Dilatometry…………………………………………………………………... 60
4.8 Heat treatments……………………………………………………………… 61
4.9 X-Ray Diffraction (XRD) and neutron diffraction spectroscopy
(SMARTS) ………………………………………………………………………. 61
4.10 Tensile testing………………………………………………………………. 63
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4.11 Fatigue testing………………………………………………………………. 64
4.12 Density……………………………………………………………………... 65

Chapter 5: Ti-6Al-4V in Rapid Manufacturing
5.1 Microstructures………………………………………………………………. 67
5.2 Mechanical properties of the as-built material………………………………... 74
5.2.1 Tensile properties………………………………………………………….. 74
5.2.2 Fatigue behaviour of the as-built materials……………………………………. 83
5.3 Thermal stability of the microstructures……………………………………… 84
5.3.1 Microstructural thermal stability of Ti-6Al-4V produced by Selective Laser Melting. 85
5.3.2 Microstructural thermal stability of Ti-6Al-4V produced by Electron Beam Melting. 93
5.4 Final remarks………………………………………………………………… 104
Chapter 6: ASTM F75 alloy produced by Electron Beam Melting
6.1 Microstructures………………………………………………………………. 106
6.2 Mechanical properties of the as-built and hipped materials…………………... 113
6.2.1 Tensile properties………………………………………………………….. 114
6.2.2 Fatigue properties………………………………………………………….. 117
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