This dissertation proposal focuses on the development of functionally graded orthopedic implants using Ti-6Al-4V, addressing challenges in current biomedical implants related to stress and mechanical bonding. It describes proposed methodologies such as powder processing and sintering techniques, along with necessary experiments and validation of mechanical and biological properties. The goal is to enhance the performance and longevity of hip implant devices while minimizing the risk of complications such as loosening or infection.

1. Ti-6Al-4V for Functionally Graded
Orthopedic Implant Applications
PhD Dissertation Proposal
Kyle Crosby
University of Connecticut - IMS 4/2/2013

2.  Motivation
◦ Biomedical implant issues
 Ti-6Al-4V Background
◦ Properties, processing and applications
 Proposed Research Objective
◦ Functionally graded orthopedic implant
 Proposed Methodology
◦ Powder processing and sintering techniques
 Preliminary Results and What’s Left To Do
◦ Characterization of powders and sintered bodies
 Conclusion
◦ Viability as an artificial biological component
University of Connecticut - IMS 4/2/2013

3.  Biomedical implant
◦ Femoral stem, cup and ball socket
 Invasive operation
◦ Long, painfull rehab and recovery time
 Secondary surgery within 5-25 years to repair
or replace implant
◦ Fracture of metallic implants due to stress
concentration sites and contaminates (i.e. pores
and composition gradients)
◦ Implant loosening due to poor mechanical bonding
between metallic implant and native bone
University of Connecticut - IMS 4/2/2013

4.  Metallic components
◦ Stainless steel, pure titanium, titanium alloys, Co-
Cr alloys
 Surface structures
◦ Porous surface network to allow for bone ingrowth
and improved mechanical interlocking
◦ Pores act as stress amplifiers
 Bioactive coatings
◦ Hydroxyapatite ceramic mimics natural bone
because HA is composed of mainly calcium
phosphate
University of Connecticut - IMS 4/2/2013

5.  Ti-6Al-4V vitals
◦ Lightweight
 D = 4.45 g/cm3
◦ High strength
 σYS = 924 MPa
◦ Cheaper than pure Ti
◦ Corrosion resistant
◦ Biocompatible
◦ HCP @ R.T.
University of Connecticut - IMS 4/2/2013

6.  Cast
◦ Sheet, barstock, ingot from a melt
 High cost to maintain melt temperature continuously
 Contamination of gases during melting and from crucible/mold during
pouring
 Forged
◦ Better mechanical properties
◦ Additional processing step = additional cost
 Machining
◦ Difficult due to high hardness
 Powder Metallurgy (PREP)
◦ Tight geometrical tolerances
◦ Sintering process is less expensive than casting with equivalent
mechanical properties
University of Connecticut - IMS 4/2/2013

7.  Grade 5 α/β Alloy
◦ Aerospace
 Engine components
 Fasteners
◦ Marine
 Structural components
◦ Sporting goods
 Golf clubs, bicycles
◦ Jewelry
 Earrings, studs
◦ Biomedical
 Orthodontics
 Screws, pins, staples
 Total joint replacements
University of Connecticut - IMS 4/2/2013

8.  Development of improved hip implant devices Ti-6Al-4V
through functionally graded Ti-6Al-4V + rich core
Hydroxyapatite composite components.
◦ Avoid implant loosening
◦ Avoid bioceramic spallation
◦ Avoid infection and secondary surgery
 Currently, co-sintering of Ti-6Al-4V +HA leads
to formation of oxide and phosphate phases
which have poor mechanical properties and
show adverse bioactivity
 Powder metallurgy and sintering studies are HA rich
conducted to reduce sintering temperature surface
below threshold where undesirable phases
form
 Slurry preparation and co-sintering of Ti+HA
Current Ti Functionally
using solid freeform fabrication technique
hip joint graded Ti/HA
hip joint
University of Connecticut - IMS 4/2/2013

9.  Co-sintering of Ti-6Al-4V + HA components
requires the temperature to be reduced below
1000°C
◦ Thermodynamic alteration
 Diffusion mode shifted via particle size refinement and
increased defect concentration
 bulk lattice limited → grain boundary limited
◦ Kinetic alteration
 Rate of thermal energy application (°C/min)
 Tube furnace, MWS, and SPS densification methods
University of Connecticut - IMS 4/2/2013

10.  Powder processing
◦ Particle size reduction
◦ Crystallite/grain size reduction
◦ Particle morphology changes
 Green body formation
◦ Uniaxial pressure effect
◦ Uniaxial pressing of as rec, 1 hr and 4 hr SPEX powders
 Sintering conditions
◦ Heat generation method, ramp rate, holding time
◦ Crystallite/grain size after sintering
◦ Relative density after sintering
University of Connecticut - IMS 4/2/2013

11. ½” stainless steel
¼” stainless steel
Ti-6Al-4V
Stearic acid
*Not to scale
University of Connecticut - IMS 4/2/2013

12. 200 µm 250 µm 100 µm
As received PREP 1 hr SPEX milled 4 hr SPEX milled
Avg. Dia. = 110 µm Avg. Dia. = 150 µm Avg. Dia. = 25 µm
University of Connecticut - IMS 4/2/2013

13. 10000
9000
8000
Ti 6-4 as rec powder
7000
Relative Intensity (a.u.)
Ti 6-4 SPEX 2wt%/1hr
6000 Ti 6-4 SPEX 3wt%/1hr
Ti 6-4 SPEX 3wt%/4hr
5000
Ti 6-4 SPEX 4wt%/1hr
4000 Ti 6-4 SPEX 4wt%/2hr
Ti 6-4 SPEX 4wt%/3hr
3000
Ti 6-4 SPEX 4wt%/4hr
Ti 6-4 SPEX 5wt%/1hr
2000
Ti 6-4 SPEX 5wt%/4hr
1000
20 30 40 50 60 70 80 90
2 Theta (°)
University of Connecticut - IMS 4/2/2013

14. 120
(1011) c 100
Ti 6-4 (002)
Ti 6-4 (101)
(0002)
Crystallite Size (nm)
80
60
40
a2
20
0
0 1 2 3 4 5
Milling Time (hr)
a3
a1
University of Connecticut - IMS 4/2/2013

15. (1011) c 45
Ti 6-4 (002)
40
(0002) Ti 6-4 (101)
35
Crystallite Size (nm)
30
25
20
a2 15
10
5
0
2 3 4 5 6
a3 PCA Concentration (wt%)
a1
University of Connecticut - IMS 4/2/2013

16. As received Ti-6Al-4V PREP powder 4 hr SPEX milled Ti-6Al-4V powder
University of Connecticut - IMS 4/2/2013

17. 300 MPa
As received PREP powder 1 hr SPEX milled 4 hr SPEX milled
5 wt% PEG binder no binder no binder
Dtheor = 50% Dtheor = 46% Dtheor = 58%
University of Connecticut - IMS 4/2/2013

18. NO YES
Heavily oxided Light surface
throughout oxidation
Low mechanical Polishes to mirror
strength finish
Useless for load High density
bearing
University of Connecticut - IMS 4/2/2013

19.  Tube furnace sintering (RHS)
◦ Radiant heating of green body, from outside
inward, through furnace atmosphere by electrical
resistance through molybdenum heating elements
 Spark plasma sintering
◦ Electrical resistance heating at contact point
between each powder particle in the green body
 Microwave sintering
◦ Dipole interaction of particle-pores within green
body with microwave radiation
University of Connecticut - IMS 4/2/2013

20. HOT
COLD
V
University of Connecticut - IMS 4/2/2013

21.  Sintering chamber
◦ Inert atmosphere
◦ Microwave transparent crucible (good dielectric)
◦ Particle-pore dipole interaction within green body
COLD
HOT
University of Connecticut - IMS 4/2/2013

22. University of Connecticut - IMS 4/2/2013

23. As received Sintered 2 hr Sintered 2 hr
300 MPa uniaxial @ 1100°C @ 1250°C
Dtheor = 50% Dtheor = 75% Dtheor = >97%
University of Connecticut - IMS 4/2/2013

24. 15000
Ti 6-4 as rec tube - 1250C/2hr
14000
Ti 6-4 as rec tube - 1100C/2hr
13000 Ti 6-4 as rec SPS - 1000C/3min
12000 Ti 6-4 SPEX 4/4 tube - 1250C/2hr
Relative Intensity (a.u.)
11000 Ti 6-4 SPEX 4/4 tube - 1100C/2hr
10000 Ti 6-4 SPEX 4/4 SPS - 1000C/3min
9000 Ti 6-4 SPEX 4/4 SPS - 600C/5min
8000 Ti 6-4 SPEX 4/4 MWS - 1250C/30min
Ti 6-4 SPEX 4/4 MWS - 900C/1hr
7000
Ti 6-4 SPEX 4/1 tube - 1250C/2hr
6000
20 30 40 50 60 70 80 90
2 Theta (°) Ti 6-4 SPEX 4/1 tube - 1100C/2hr
University of Connecticut - IMS 4/2/2013

25. 250
Ti 6-4 (002)
(1011) c 200 Ti 6-4 (101)
(0002)
Crystallite Size (nm)
150
100
a2
50
0
500 600 700 800 900 1000 1100 1200 1300
Sinteirng Temperature (C)
a3
a1
University of Connecticut - IMS 4/2/2013

26. Ti 6Al-4V as rec. Ti 6Al-4V as SPEX (1hr/4wt%) Ti 6Al-4V as SPEX (4hr/4wt%)
1250°C/2hr → 90% dense 1250°C/2hr → 75% dense 1250°C/2hr → 97% dense
500 µm 500 µm 500 µm
500 µm 500 µm 500 µm
Ti 6Al-4V as rec. Ti 6Al-4V as SPEX Ti 6Al-4V as SPEX (4hr/4wt%)
1100°C/2hr → 78% dense (1hr/4wt%) 1100°C/2hr → 1100°C/2hr → 83% dense
60% dense
University of Connecticut - IMS 4/2/2013

27. Ti-6Al-4V 4 hr SPEX, MWS at 900C Ti-6Al-4V 4 hr SPEX, MWS at 1250C
for 1 hr (95% center, 80% edge) for 30 min (98% center, 81% edge)
University of Connecticut - IMS 4/2/2013

28. 3
Ti 6Al-4V as Rec
2.5
Ti 6Al-4V as SPEX 1000°C
2
Displacement (mm)
1.5
1
0.5
0
0 100 200 300 400 500 600 700 800 900 1000
Temperature (°C)
Pressure Max Displacement
Displacement Density
Sample ID Decrease Onset Displacement Plateau Temp
Onset Temp (°C) (g/cm3)
Temp (°C) Temp (°C) (°C)
Ti 6Al-4V as
550 620 800 880 4.31
rec
Ti 6Al-4V as
350 350 600 750 4.27
SPEX 1000
University of Connecticut - IMS 4/2/2013

29. (a) Ti-6Al-4V as (b) Ti-6Al-4V 4 hr SPEX (c) Ti-6Al-4V 4 hr
received, SPS @ 1000C as SPS @ 1000C for 3 SPEX as SPS @ 600C
for 3 min, 99% min, 99% for 5 min, 96%
University of Connecticut - IMS 4/2/2013

30.  SPEX milled powder sinters @ lower temp than as received PREP powder
◦ Smaller particle size = shorter diffusion distance = shorter diffusion time
◦ Increase grain boundary area = rate limiting diffusion mechanism shift DL → Dg.b.
Dg.b. >> DL
 RHS to full theoretical density is possible
◦ Requires strict atmospheric control
◦ Heat penetration lag = longer sintering dwell times
 MWS offers lower temperature, faster sintering than RHS
◦ Pressureless sintering = complex geometry retention is possible
◦ Heat emination lag = porous surface regions
 SPS offers low temperature, rapid sintering
◦ Very high heating rates = rapid diffusion
◦ Uniaxial pressure from conductive die = complex geometry retention is difficult
University of Connecticut - IMS 4/2/2013

31.  Activation energy measurement
◦ Track density as a function of sintering conditions
 Grain size analysis
◦ Monitor grain size as a function of sintering temperature
 Mechanical properties
◦ Compressive and tensile strengths
◦ Rockwell C and microhardness
 Biological properties
◦ Cell attachment (# per unit area)
◦ Cell spreading (lateral area coverage as a function of time in simulated
body fluid)
 Composite Ti-HA co-sintering studies
◦ SPS parameter optimization
University of Connecticut - IMS 4/2/2013

32. 2C/min 4C/min 8C/min
2C/min
700 700 700
800 800 800
150
Quench Temp (C)
Relative Density (%)
100 900 900 900
50 1000 1000 1000
0 1100 1100 1100
600 800 1000 1200
1250 1250 1250
Quench Temperature (C)
4C/min 8C/min
150
150
Relative Density (%)
Relative Density (%)
100
100
50
50
0
0
600 800 1000 1200
600 800 1000 1200
Quench Temperature (C)
Quench Temperature (C)
University of Connecticut - IMS 4/2/2013

33. 4 hr SPEX powder Sintering @ 900C Sintering @ 1250C
Grain size vs. mechanical strength ?
Grain size vs. activation energy barrier?
Grain size vs. cell attachment and spreading?
University of Connecticut - IMS 4/2/2013

34.  Compressive strength
◦ Quasi-static using cross-head speed of 1,10,100
mm/min
◦ High strain rate using Split-Hopkinson Pressure Bar at
300, 900 s-1 frequency
 Tensile strength
◦ Strain until failure
◦ σYS , σUTS , E
 Rockwell C and microhardness
◦ Compare to as received powder, commercially cast or
forged products and between each other
University of Connecticut - IMS 4/2/2013

35. (a) HA as SPS @ 1000C (b) Ti-6Al-4V 4 hr SPEX (c) Ti-6Al-4V 4 hr SPEX
for 3 min, 99% (90 vol%) + HA (10 vol%) (75 vol%) + HA (25 vol%)
as SPS @ 96% as SPS @ 1000C for 3
min, 83%
University of Connecticut - IMS 4/2/2013

36. University of Connecticut - IMS 4/2/2013

37.  Funding
◦ United States National Science Foundation contract CBET-
0930365
 Supervision
◦ Dr Leon Shaw
 Instrumentation
◦ Dr. Claude Estournes (SPS at CIRIMAT in France), Dr. Ashraf Imam
(MWS at NRL in D.C.), Jack Gromek (XRD), Roger Ristau and Lichun
Zhang (TEM/SEM), Bob Bouchard and Matt Bebee (SPEX vial and die
fabrication)
 Support
◦ Monica & Ling (HA synthesis and biostudies) and Girije Marathe
(quartz tube sealing) as well as the rest of my groupmates and
fellow grad students in MSE/IMS
University of Connecticut - IMS 4/2/2013

38.  [1] Hennig, R., Lenosky, T., Trinkle, D., Rudin, S., Wilkins, J. "Classical potential describes martensitic
phase transformations between the alpha, beta, and omega titanium phases," Physical Review B,
78,054121, 2008.
 [2] Kubaschewski O., Wainwright C., and Kirby F.J., “The Heats of Formation in the Vanadium-Titanium-
Aluminium System,” J. Inst. Met., 89, 1960, 139-144.
 [3] Honma BERES 7 Series Driver, honmagolf.com, 2010.
 [4] Solid Grade 5 Titanium, TNG Body Jewlery, 2012.
 [5] Deutsch, A., “Bike review: Merlin works CR 6/4,” Brooklyn Arches Cycling, 2012.
 [6] Titanium dental implants, Naomi Dental, 2011
 [7] Total hip replacement, defectivejoints.com, 2011
 [8] Shaw, L., “Rapid prototyping of functionally graded orthopedic implants via the slurry mixing and
dispensing process,” NSF proposal submitted 2009.
 [9] What’s SPS, “Principles and mechanism of the SPS process,” Fuji Electronic Industrial Co.
University of Connecticut - IMS 4/2/2013

39. ?
University of Connecticut - IMS 4/2/2013

40.  Armstrong starting powder
◦ Low apparent density (~5%)
◦ Sponge morphology with high SSA
 Slurry preparation
◦ Stable suspension
◦ Proper pH and viscosity
 Freeform 3D printing
◦ Tip diameter = slurry droplet size
 Lateral and layer thickness resolution
 Software development to allow for composition gradient from core to surface
◦ Must accommodate change in composition within each z-slice
 Mechanical and biological properties of functionally graded component
◦ Ti-HA composites via SPS
 Bioactivity as a function of surface roughness
◦ Cell # and lateral spreading as a function of SiC scratch width
 Surface functionalization
◦ Macropores filled with aerogel particles containing growth hormone or antibiotic
University of Connecticut - IMS 4/2/2013

41. SiC paper
vs.
Ti-6Al-4V
University of Connecticut - IMS 4/2/2013

42. Antibiotic or
pain relieving
aerogel capsules
University of Connecticut - IMS 4/2/2013