Biomedical Compatibility of Ti-Al-Nb Alloys for Implant Applications

The attention given biocompatible Ti alloys has been generated by a number of important technological and economic factors. Within the last three decades a strong push has been made to replace human bone and teeth with strong, lightweight, and stiff biocompatible Ti alloys. To date the material of choice used in implants is titanium-vanadium-aluminum (Ti-V-Al) alloys because of their excellent biocompatibility and their combination of high specific strength, corrosion resistance, low density, good ductility and elastic modulus, oxidation resistance, conventional processability, fatigue strength, and fracture toughness. In particular Ti-6Al-4V(wt.%), which was initially developed as a high-temperature aerospace alloy, is a commonly used implant material due to its excellent properties and processability compared to other Ti-V-Al alloys. However, V is a potentially toxic element; therefore, other alloying elements are currently being examined. In particular substitution of niobium (Nb) for V is attractive as this does not result in degradation of several mechanical properties, and the microstructural phases present in Ti-Al-Nb alloys are similar to those in the Ti-V-Al system.

Characterization and Modeling of Deformation Induced Damage in Ti Alloys

To accelerate the insertion of new or optimized materials into applications that enhance efficient energy conversion or reduce energy consumption, sophisticated material models are needed to enable flexible and reliable simulation of material behavior in structural components. Since microstructural details such as grain orientation, grain-to-grain misorientation, and grain boundary character ultimately influence macroscopic performance, it is necessary to integrate modeling across length scales to effectively predict deformation behavior and associated deformation damage evolution in real components. The research to be performed in this newly award program combines experimental and computational efforts to study how microstructural details affect the early stages of damage nucleation that occurs due to mechanical deformation. The work will use series of Ti-based alloys with increasing microstructure complexities ranging from single phase α to a more complex α+β microstructure, as a model system for characterizing and modeling damage nucleation behavior at room and elevated temperatures. The specific materials are Commercially-Pure Ti, Ti-5Al-2.5Sn , Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-4V. A unique set of tools will be used to investigate this series of alloys in order to develop a deep quantitative and crystallographically-based understanding of how details of deformation behavior and microstructure correlate with damage nucleation mechanisms.

Development of In-Situ Electron-Microscopy Techniques

This research has three main goals. The first thrust is to develop a technique to combine in-situ deformation observations with in-situ electron backscattered diffraction observations of metallic alloy specimens inside the chamber of a scanning electron microscope. The second area is to identify phase transformations using in-situ observations of metallic alloys using a heating stage within an electron microscope. The third area would be to combine the heating capability of the stage with the loading capability of the stage to perform in-situ deformation observations of metallic alloy specimens during isothermal fatigue, thermomechanical fatigue, creep, and fatigue-creep interactions at elevated temperatures.

Elevated-Temp Grain Boundary Deformation Processes of Structural Alloys: Grain Boundary Engineering

The lifetimes of metallic alloys under imposed thermo-mechanical loads are influenced by microstructure, and in particular the grain size and the orientation of one grain with respect to its neighbor grain. Using an electron microscopy technique, called orientation imaging microscopy (OIM) or electron backscatter diffraction (EBSD), we can determine the crystallographic orientations which form between grains at the grain boundaries. These orientations have an important influence on the mechanical behavior of alloys and in particular the high-temperature deformation or creep behavior. By altering the distribution of the grain boundary orientations [also referred to as changing the grain boundary character distribution (GBCD)] in a material’s microstructure using different thermomechanical processing techniques (involving different applied pressures and temperatures or “heat-it and beat-it” metallurgy), we can improve the deformation resistance of the material. Thus it is possible to exert control over the types of grain boundaries in the microstructure and thereby engineer properties. This technique is referred to as grain boundary engineering. The understanding gained through grain boundary engineering leads to processing techniques which can be tailored to obtain the desired mechanical properties for a given material’s application.

The Effect of Boron the Creep and Fatigue Behavior of Ti-6Al-4V(wt.%)

The objectives of this program are to access the effects of B additions (0, 0.1, and 1wt.%) on the creep strain-life behavior of Ti-6Al-4V(wt.%), to understand and evaluate the creep deformation mechanisms of Ti-6Al-4VB-xB(wt.%) as a function of stress and temperature, and to evaluate the creep deformation evolution as a function of stress, temperature, time, and strain using in-situ surface observations. Constant-load creep experiments will be performed and post-experiment SEM and TEM analysis of the deformed gage sections will be evaluated. The test matrix will involve experiments performed at temperatures ranging between 400-455C and stresses ranging between 400-6500MPa. Such experiments will last up to 800 hours based on previously reported data of Ti-64 [Materials Property Handbook: Titanium Alloys, Boyer, Welsch, Collings (1994) ASM Intl., pp.530-532]. In addition, load-jump and temperature-jump experiments will be performed to evaluate the creep parameters, n and Q, for a cursory prediction of the suggested dominant secondary-creep-stage deformation mechanisms based on creep of pure metals. This type of evaluation will be supplemented by experiments performed in-situ in an SEM chamber. Such specimens will be metallographically polished prior to testing in order to image the surfaces at certain stages of creep strain using an Ernest-Fullam tensile stage. Such experiments will be performed at identical temperatures and stresses as those to be performed in the conventional creep experiments using the lever-arm creep frames. The in-situ testing will be used to accomplish the third objective. It is noted that a few of the conventional experiments will be performed in a vacuum environment (5x10-8 torr) in order to evaluate the effect of environment on the creep response.

Understanding Processing-Microstructure-Property Relationships of Structural Magnesium Alloys

Magnesium (Mg) alloys are considered to be potential materials for replacing Beryllium (Be) in structural defense-related applications due to their high specific strength and stiffness and nontoxic nature. In this light, research is being performed to identify processing-microstructure-property relationships of Mg-based alloys to improve their mechanical behavior. The alloying additions being evaluated are Y, Zn, and Zr.

Reviewed Journal Publications

J.P. Quast, C.J. Boehlert, R.M Gardner III, E. Tuegul, and T Wyen, "A Microstructure and Sonic Fatigue Investigation of Ti-TiB Functionally Graded Materials", Materials Science and Engineering A, in print.

W. Chen and C.J. Boehlert, "The Elevated-Temperature Fatigue Behavior of Boron-Modified Ti-6Al-4V(wt.%) Castings", Materials Science and Engineering A, Vol. 494 Issues 1-2 (2008) 132-138.

C.J. Boehlert, "The Creep Behavior of Powder-Metallurgy Processed Ti-6Al-4V-1B(wt.%)", Materials Science and Engineering A, 2009

C.J. Boehlert, "The Effect of Thermomechanical Processing on the Creep Behavior of Alloy 690," Materials Science and Engineering A, Vol. 473 (2008)233-237.

C.J. Boehlert, S.C. Longanbach, M. Nowell, and S. Wright, "The evolution of grain-boundary cracking evaluated through in-situ tensile creep testing of Udimet alloy 188," Journal of Materials Research, Vol. 23 No. 2 (2008) 500-506.

C.J. Cowen and C.J. Boehlert, "Microstructure, Tensile, and Creep Behavior of Boron-Modified Ti-15Al-33Nb(at.%)," Metallurgical Transactions, Vol 39A No. 2 (2008) 279-293.

Cowen, C.J.; Boehlert, C.J. "The Microstructure and Creep Behavior of a Boron-Modified Ti-15Al-33Nb(at.%) Alloy", Advanced Materials Research Vol. 15-17, 976-981, (2007).

J.P. Quast and C.J. Boehlert, "Comparison of the Microstructure, Tensile, and Creep Behavior for Ti-24Al-17Nb-0.66Mo (at%) and Ti-24Al-17Nb-2.3Mo (at.%) Alloys," Metallurgical Transactions, Vol. 38A, No. 3 (2007) 529-536.

C.J. Cowen and C.J. Boehlert, "Comparison of the Microstructure, Tensile, and Creep Behavior for Ti-22Al-26Nb (at%) and Ti-22Al-26Nb-5B (at.%)," Metallurgical Transactions, Vol. 38A, No. 1 (2007) 26-34.

C.J. Cowen and C.J. Boehlert, "The Microstructure, Creep, and Tensile Behavior for Ti-5Al-45Nb(at%) Fully- Alloy," Metallurgical Transactions, Vol. 38A No. 11 (2007) 2747-2753.

C.J. Boehlert, "The Tensile and Creep Behavior of Mg-Zn Alloys with and without Y and Zr as Ternary Elements," Journal of Materials Science, Vol. 42 No. 10 (2007) 3675-3684.

C.J. Cowen and C.J. Boehlert, "The Microstructure, Creep, and Tensile Behavior for a Ti-5Al-45Nb(at%) Fully-beta Alloy," Metallurgical Transactions, Vol. 38A No. 11 (2007) 2747-2753.

J.P. Quast and C.J. Boehlert, "The Effect of Molybdenum on the Microstructure and Creep Behavior of Ti-24Al-17Nb-xMo Alloys and Ti-24Al-17Nb-xMo/SiC-Fiber Composites", Journal of Materials Science, 43 (2008) 4411-4422 (DOI 10.1007/s10853-008-2582-5).

C.J. Boehlert, S.C. Longanbach, and T.R. Bieler, "The effect of thermomechanical processing on the creep behavior of Udimet Alloy 188", Philosophical Magazine, Vol. 88 Issue 5 (2008) 641-664.

Boehlert, C.J.; Cowen, C.J.; Tamirisakandala, S.; McEldowney, D.J.; Miracle, D.B. "In Situ Scanning Electron Microscopy Observations of Tensile Deformation in a Boron-Modified Ti-6Al-4V Alloy," Scripta Materialia 55, 465-468, (2006).

Cowen, C.J.; Boehlert, C.J. "Microstructure, Creep, and Tensile Behavior of a Ti-15Al-33Nb (at.%) Beta+Orthorhombic Alloy," Philosophical Magazine 86 issue 1, 99-124, (2006).

Cowen, C.J.; Boehlert, C.J. "Microstructure, Creep, and Tensile Behavior of a Ti-21Al-29Nb(at.%) Orthorhombic+B2 Alloy," Intermetallics 14 Issue 4, 412-422, (2006).

Boehlert, C.J.; Knittel, K. "The Microstructure, Tensile Properties, and Creep Behavior of Mg-Zn Alloys Containing 0-4.4wt.%Zn," Materials Science and Engineering A417, 315-321, (2006).

Boehlert, C.J.; Rider, K.A.; Flick, L.M. "Biocompatibility Evaluation of Ti-15Al-33Nb(at.%) and Ti-21Al-29Nb(at.%)," Materials Transactions 45(7), 1-9, (2005)

Wynick, G.L.; Boehlert, C.J. "Electron Backscattered Diffraction Characterization Technique for Analysis of a Ti-Al-Nb Orthorhombic Alloy," Journal of Microscopy, 219(Pt3), 115-121, (2005).

Li, D.; Boehlert, C.J. "Processing Effects on the Grain Boundary Character Distribution of the Orthorhombic Phase in Ti-Al-Nb Alloys," Metallurgical and Materials Transactions 36A, 2569-2584, (2005) .

Wynick, G.L.; Boehlert, C.J. "Use of Electropolishing for Enhanced Metallic Specimen Preparation for Electron Backscattered Diffraction Analysis," Materials Characterization Journal 55(3), 190-202, (2005).

Boehlert, C.J.; Cowen, C.J.; Jaeger, C.R.; Niinomi, M.; Akahori, T. "Tensile and fatigue evaluation of Ti-15Al-33Nb(at.%) and Ti-21Al-29Nb(at.%) alloys for biomedical applications," Materials Science and Engineering C: Biomimetic and Supramolecular Systems 25, 263-275, (2005).

Li, D.; Wright, S.T.; Boehlert, C.J. "The Grain Boundary Character Distribution in a Fully-Orthorhombic Ti-25Al-24Nb(at.%) Alloy," Scripta Materialia 51:6, 545-550, (2004).

Li, D; Boehlert, C.J. "The Grain Boundary Character Distribution of the Orthorhombic Phase in Ti2AlNb Intermetallic Alloys," TMS Letters 1:7, 159-160, (2004).

Dickmann, D.S.; Eisinger, N.C.; Boehlert, C.J. "The Effect of Cold Rolling Deformation on the Creep Backstress of INCONELâ alloy 718", TMS Letters 1:5, 99-100, (2004).

Mitchell, J.N.; Stan, M.; Schwartz, D.S.; Boehlert, C.J. "Phase Stability and Phase Transformations in Plutonium and Plutonium-Gallium Alloys," Metallurgical and Materials Transactions 35A:8, 2267-2278, (2004).

Boehlert, C.J.; Zocco, T.G.; Schulze, R.K.; Mitchell, J.N.; Pereyra, R.A. "Electron Backscatter Diffraction (EBSD) of a Plutonium-Gallium Alloy," Journal of Nuclear Materials 312, 67-75, (2003).

Boehlert, C.J.; Farr, J.D.; Schulze, R.K.; Pereyra, R.A.; Archuleta, J.C. "Initial Electron Backscattered Diffraction Observations of Cerium," Philosophical Magazine 83:14, 1735-1744, (2003).

Boehlert, C.J.; Dimiduk, D.M.; Hemker, K.J. "The Phase Evolution, Mechanical Behavior, and Microstructural Instability of a Fully-Lamellar Ti-46Al(at.%) Alloy", Scripta Materialia, Vol 46/4 (2002) 259-267.

Boehlert, C.J.; Schulze, R.K.; Mitchell, J.N.; Zocco, T.G.; Pereyra, R.A. "Initial Electron Backscattered Diffraction (EBSD) Observations of a Plutonium Alloy," Scripta Materialia 45/9, 1107-1115, (2001).

Boehlert, C.J.; Schulze, R.K.; Mitchell, J.N.; Zocco, T.G.; Pereyra, R.A. "Initial Electron Backscattered Diffraction (EBSD) Observations of a Plutonium-Gallium Alloy," Scanning 23:2, 66-67, (2001).

Boehlert, C.J. "Part III. The Tensile Behavior of Ti-Al-Nb O+BCC Orthorhombic Alloys," Metallurgical and Materials Transactions 32A, 1977-1988, (2001).

Boehlert, C.J.; Bingert, J.F. "Microstructure, Tensile, and Creep Behavior of O+BCC Ti2AlNb Alloys Processed Using Induction-Float-Zone Melting," Journal of Materials Processing Technology 117, 401-408, (2001).

Boehlert, C.J.; Majumdar, B.S.; Miracle, D.B. "Application of the Cruciform Specimen Geometry to Obtain Transverse Interface Property Data in a High Fiber-Volume-Fraction SiC/Titanium Alloy Composite," Metallurgical and Materials Transactions 32A:12, 3143-3155, (2001).

Zupan, M.; Hayden, M.J.; Boehlert, C.J.; Hemker, K.J. "Development of High Temperature Microsample Testing," Experimental Mechanics 41:3, 242-247. (2001).

Boehlert, C.J. "The Effects of Forging and Rolling on Microstructure in O+BCC Ti-Al-Nb Alloys," Materials Science and Engineering A279:1-2, 118-129, (2000).

Boehlert, C.J.; Majumdar, B.S.; Seetharaman, V.; Miracle, D.B. "Part I: The Microstructural Evolution in Ti-Al-Nb O+BCC Orthorhombic Alloys," Metallurgical and Materials Transactions 30A, 2305-2323 (1999).

Boehlert, C.J.; D.B. Miracle, D.B. "Part II: The Creep Behavior of Ti-Al-Nb O+BCC Orthorhombic Alloys", Metallurgical and Materials Transactions 30A, 2349-2367, (1999).

Boehlert, C.J. "The Phase Evolution and Microstructural Stability of an Orthorhombic Ti-23Al-27Nb Alloy," Journal of Phase Equilibria 20:2, 101-108, (1999).

Boehlert, C.J. "Microstructure, Creep, and Tensile Behavior of a Ti-12Al-38Nb(at.%) Beta + Orthorhombic Alloy," Materials Science and Engineering A267, 82-98, (1999).

Boehlert, C.J.; Majumdar, B.S.; Krishnamurthy, S.; Miracle, D.B. "Role of Matrix Microstructure on RT Tensile Properties and Fiber-Strength Utilization of an Orthorhombic Ti-alloy Based Composite," Metallurgical and Materials Transactions 28A, 309-323, (1997).

Boehlert, C.J.; Majumdar, B.S.; Eylon, D. "Properties and Damage Mechanisms in Three Classes of Titanium Composite Matrices," Key Engineering Materials 127-131:Part I, 843-850, (1997).

Russ, S.M.; Boehlert, C.J., Eylon, D. "Out-of-phase thermomechanical fatigue of titanium composite matrices", Materials Science and Engineering A192/193, 483-489, (1995).

Books, Chapters, Monographs

Boehlert, C.J.; Civelekoglu, S.; Gundakaram, R.; Bingert, J.F. The Grain Boundary Character Distribution in BCC and O+BCC Ti-Al-Nb Alloy Microstructures. In Ti-2003 Science and Technology G. Luetjering; J. Albrecht, Eds., Wiley-VCH Verlag GmbH & CoKGaA:Weinheim, Germany, 2004, Vol. IV, 2145-2152.

Boehlert, C.J.; Civelekoglu, S.; Eisinger, N.C.; Smith, G.D.; Crum, J.R. The Effect of Cold Rolling on the Grain Boundary Character and Creep Rupture Properties of INCONEL alloy 718. In Materials Forum T. Chandra; J.M. Torralba; T. Sakai , Eds., Trans Tech Publications Ltd: Enfield, NH, USA, 2003, Part 1 Vol. 426-432, 761-766.

Conference Proceedings

C.J. Boehlert, "A Scanning Electron Microscopy Outreach Program", Proceedings of Outreach Programs in Materials Science and Engineering Symposium at the TMS Annual Meeting, editors: D. Thoma and K. Chen (The Minerals, Metals & Materials Society), Warrendale, PA, 2007, pp 1-10.

S.C. Longanbach, K. Knittel, A. Lee, and C.J. Boehlert, "Processing -Microstructure-Property Relationships of Magnesium Alloys Containing Zr and/or B," Proceedings of Magnesium Technology 2007 Symposium at the TMS Annual Meeting, Edited by R.S. Beals, A.A. Luo, N.R. Neelameggham, M.O. Pekguleryuz (The Minerals, Metals & Materials Society), Warrendale, PA, 2007, pp.313-316.

C.J. Cowen and C.J. Boehlert, "In-Situ SEM Observations of Grain Boundary Cracking during Creep for a Ti-15Al-33Nb(at.%) Alloy," Advanced Intermetallic-Based Alloys, Eds. C.L. Fu, H. Clemens, J. Wiezorek, M. Takeyama, D. Morris, MRS Fall 2006 proceedings, Materials Research Society (2007) Vol. 980, Paper #: 0980-II05-05.

C.J. Boehlert, "Electron Backscattered Diffraction Observations of Grain Boundary Cracking for a Udimet 188 Alloy during In-Situ Creep Deformation," Proceedings Microscopy and Microanalysis 2007, eds. M. Marko, J.H. Scott, E. Vicenzi, S. Dekanich, J. Frafjord, P. Kotula, S. McKernan, and J. Shields, (Cambridge University Press, Cambridge, UK) Vol. 13, Supplement 2, p. 916CD.

C.J. Boehlert, "Materials Engineering Education through Service Learning Involving Scanning Electron Microscopy Education," ASEE North Central Conference held at Ohio Northern University, Ada, Oho, April 7-8, EV-3 service learning section of conference, ASEE: Chantilly, Virginia, (2005).

Cowen, C.J.; Li, D; Boehlert, C.J. "Microstructure-Property Relationships of Two Ti2AlNb-based Intermetallic Alloys: Ti-15Al-33Nb(at.%) and Ti-22Al-28Nb(at%)," MRS Fall 2004 proceedings, Materials Research Society 842, S7.9.1-S7.9.6., (2005).

Boehlert, C.J.; Dickmann, D.S.; Eisinger, N.C. "The Effect of Cold Rolling on the Creep Behavior of INCONELâ alloy 718.," Proceedings of the Sixth International Special Emphasis Symposium on Superalloys 718, 625, 706 and Derivatives, Loria, E.A., Eds., The Materials Society: Warrendale, PA, 311-320, (2005).

Boehlert, C.J.; Zupan, M.; Dimiduk, D.M.; Hemker, K.J. Microsample Tension and Tension-Creep Testing of Fully-lamellar TiAl Single Crystals. In Gamma Titanium Aluminides 1999, Y-W. Kim, D.M. Dimiduk, M.H. Loretto, Eds.; The Minerals Metals and Materials Society: Warrendale, PA, USA, 1999, 669-677.

Boehlert, C.J.; Majumdar, B.S.; Seetharaman, V.; Miracle, D.B.; Wheeler, R. Phase Evolution, Stability, and Microstructure-Creep Relations in an Orthorhombic Ti-23AL-27Nb Alloy. In Structural Intermetallics R. Darolia; J.J. Lewandowski; C.T. Liu; P.L. Martin; D.B. Miracle; M.V. Nathal, Eds.; The Metallurgical Society: Warrendale, PA, USA, 1997, 795-804.

Boehlert, C.J.; Majumdar, B.S.; Seetharaman, V.; Miracle, D.B. The Phase Evolution, Tensile, and Creep Behavior of Near Stoichiometric Ti2AlNb Orthorhombic Alloys. In Orthorhombic Titanium Matrix Composites II P.R. Smith, Ed.; Wright-Patterson Air Force Base, OH, USA, AF TR# WL-TR-97-4082, 1997, 212-227.

Boehlert, C.J.; Majumdar, B.S.; Seetharaman, V. Processing and Heat Treatment Effects on the Phase Evolution, Tensile, and Creep Behavior of an Orthorhombic Ti-25Al-25Nb Alloy. In Deformation and Fracture of Ordered Intermetallic Materials W.O. Soboyejo; H.L. Fraser; T.S. Srivatsan, Eds.; The Metallurgical Society: Warrendale, PA, USA, 1997, 565-582.

Majumdar, B.S.; Boehlert, C.J.; Rai, A.K.; Miracle, D.B. Structure-Property Relationships and Deformation Mechanisms in an Orthorhombic Based Ti-25Al-17Nb Alloy. In High Temperature Ordered Intermetallic Alloys-VI J. Horton; I. Baker; S. Hanada; R.D. Noebe; D.S. Schwartz, Eds.; Materials Research Society:Pittsburgh, PA, USA, 1995, Vol. 364, 1259-1265.

Majumdar, B.S.; Boehlert, C.J.; Miracle, D.B., Deformation Mechanisms and Structure-Property Relations in O-Alloys and MMCs (Ti-25Al-17Nb System). In Orthorhombic Titanium Matrix Composites, Proceedings of the Orthorhombic Titanium Matrix Composites Workshop, Wright-Patterson Air Force Base, OH, USA, AF TR# WL-TR-95-4068, 1995, 65-83.

Boehlert, C.J.; Majumdar, B.S.; Miracle, D.B., Effect of Microstructure on the Tensile, Fatigue Crack Growth, and Creep Behavior of a Ti-25Al-17Nb Orthorhombic Alloy. In Fatigue and Fracture of Ordered Intermetallics II W.O. Soboyejo, T.S. Srivatsan, R.O. Ritchie, Eds., The Metallurgical Society: Warrendale, PA, USA, 1995, 135-153.

Other Works

Boehlert, C.J. "The Grain Boundary Character Distribution of the Orthorhombic Phase in Intermetallic Ti2AlNb Alloys," A Collection of OIM ApplicationsTM, catalog compiled by EDAX-TSL, Inc. 87-91, (2005).

Boehlert, C.J. "Ti, Al, and Nb Alloys for Biomedical Applications," US Provisional Patent Application submitted on 10/19/05.