Montana Tech Library Digital Commons @ Montana Tech Graduate Theses & Non-Theses Student Scholarship Spring 2015 Thermal Processing and Mechanical Properties of Beta Phase Titanium Alloys for Biomedical Applications Ethan Wood Montana Tech of the University of Montana Follow this and additional works at: http://digitalcommons.mtech.edu/grad_rsch Part of the Metallurgy Commons Recommended Citation Wood, Ethan, "Thermal Processing and Mechanical Properties of Beta Phase Titanium Alloys for Biomedical Applications" (2015). Graduate Theses & Non-Theses. 26. http://digitalcommons.mtech.edu/grad_rsch/26 This Thesis is brought to you for free and open access by the Student Scholarship at Digital Commons @ Montana Tech. It has been accepted for inclusion in Graduate Theses & Non-Theses by an authorized administrator of Digital Commons @ Montana Tech. For more information, please contact [email protected]. THERMAL PROCESSING AND MECHANICAL PROPERTIES OF BETA PHASE TITANIUM ALLOYS FOR BIOMEDICAL APPLICATIONS By Ethan Thomas Wood A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Metallurgical Engineering Montana Tech May 2015 ii Abstract The past few decades have seen an increase in the use of beta titanium alloys as structural biomaterials. Their combination of excellent mechanical properties, corrosion resistance and biocompatibility, along with a lower Young’s modulus than stainless steel, cobalt-chromium and commercially pure titanium make the beta titanium alloys ideal biomaterials. This work evaluates the use of three beta titanium alloys for biomedical applications. Three beta titanium alloys, Ti 15-3-3-3, Ti SP-700 and Ti Beta-C, underwent thermal processing to optimize mechanical properties. The alloys were subjected to tensile testing, hardness testing, fatigue testing, optical microscopy and SEM fracture analysis in order to determine the best processing conditions for biomedical alloys. In order to understand the effects of the thermal processing, the grain structures of the beta titanium alloys were examined. The fracture surfaces of the alloys were examined to understand the fracture and failure mechanisms involved. Thermal processing yielded good properties (998 MPa and 23% elongation) in the Ti 15-3-3-3 alloy aged at 550 ºC. The annealed condition of the Ti SP-700 produced good mechanical properties for biomedical applications (1031 MPa and 27% elongation). Titanium Beta-C aged at 455 ºC yielded good mechanical properties (964 MPa and 23% elongation). However, the Ti Beta-C alloy’s mechanical properties can be improved upon still by implementing a duplex aging process. All three alloys fractured in a ductile manner, which is desired for structural alloys. All three alloys, Ti 15-3-3-3, Ti SP-700 and Ti Beta-c, can be processed to have good mechanical properties for biomedical applications, a combination of high strength (1000 MPa) and ductility (15% elongation). Keywords: beta phase titanium, biomedical alloys, mechanical properties, microstructure, fatigue, fracture iii Dedication I wish to thank my parents and family for their steadfast commitment to my education and their unconditional love. I also want to thank my church community for making my time at Montana Tech memorable and productive. Finally, I dedicate this thesis to my Lord and savior, Jesus Christ. iv Acknowledgements I would like to thank the following people, whose help has proved invaluable to my research. My advisor Dr. K. V. Sudhakar; my committee members Dr. Al Meier and Dr. Jack L. Skinner; Gary Wyss for his help with SEM fractography; Ronda Coguill for her help with the mechanical testing and sample preparation; and The Army Research Laboratory [Beta Titanium Alloys/ARL Project # B28520] for financial support. v Table of Contents ABSTRACT ................................................................................................................................................ II DEDICATION ........................................................................................................................................... III ACKNOWLEDGEMENTS ........................................................................................................................... IV LIST OF TABLES ..................................................................................................................................... VIII LIST OF FIGURES ...................................................................................................................................... IX 1. INTRODUCTION AND BACKGROUND ....................................................................................................... 1 2. LITERATURE REVIEW ........................................................................................................................... 3 2.1. Titanium and Titanium Alloys ............................................................................................ 3 2.2. Titanium 15-3-3-3, SP-700 and Beta-C ............................................................................... 5 2.3. Thermal Processing ............................................................................................................ 5 2.3.1. Annealing ............................................................................................................................. 6 2.3.2. Solutionizing and Aging ........................................................................................................ 6 2.4. Microstructure in Beta Phase Titanium Alloys ................................................................... 7 2.5. Tensile Testing .................................................................................................................... 7 2.6. Fatigue Testing ................................................................................................................... 8 2.7. Fractography ...................................................................................................................... 9 2.8. Biomedical Applications of Beta Phase Titanium Alloys................................................... 10 3. EXPERIMENTAL METHODS AND MATERIALS .......................................................................................... 11 3.1. Materials .......................................................................................................................... 11 3.2. Heat treatment ................................................................................................................ 11 3.3. Tensile Testing .................................................................................................................. 15 3.4. Fatigue Testing ................................................................................................................. 18 3.5. Hardness Measurement ................................................................................................... 21 vi 3.6. Optical Microscopy ........................................................................................................... 21 3.7. SEM Fracture Analysis ...................................................................................................... 22 3.7.1. Tensile Sample Fracture Analysis ....................................................................................... 22 3.7.2. Fatigue Sample Fracture Analysis ....................................................................................... 22 4. RESULTS AND DISCUSSION ................................................................................................................. 23 4.1. Tensile Properties ............................................................................................................. 23 4.1.1. Ti 15-3-3-3 Alloy ................................................................................................................. 23 4.1.2. Ti SP-700 Alloy .................................................................................................................... 26 4.1.3. Ti Beta-C Alloy .................................................................................................................... 29 4.1.4. Ti Sample Comparison ........................................................................................................ 31 4.2. Fatigue Analysis ............................................................................................................... 32 4.3. Hardness Measurement ................................................................................................... 35 4.4. Optical Microscopy ........................................................................................................... 38 4.4.1. Ti 15-3-3-3 Alloy ................................................................................................................. 38 4.4.2. Ti SP-700 Alloy .................................................................................................................... 41 4.4.3. Ti Beta-C Alloy .................................................................................................................... 44 4.5. Fractography .................................................................................................................... 47 4.5.1. Fracture Analysis of Beta Phase Titanium Tensile Specimens ............................................ 48 4.5.1.1. Ti 15-3-3-3 Alloy ........................................................................................................