Optimization of Machining Operations of the metastablebeta alloy Ti 15Mo for Medical Applicationsbeta‐alloy Ti 15Mo for Medical Applications

F. Depentori, W. Fürbethe‐mail: depentori@dechema.de

Funded by: BMWi via AiFPeriod: 01.02.2012 – 30.09.2014

Background and problem

• Ti15Mo is a promising alloy for biomedical implants

Approach

• Influence of drilling and cutting is investigatedTi15Mo is a promising alloy for biomedical implants

• Ti15Mo is a metastable beta‐alloy

• Ti15Mo can suffer embrittlement from the formation of omega‐phase1

• Omega‐phase formation can happen during machining processes like

drilling,cutting or grinding

• Influence of omega‐phase formation on corrosion behaviour is

unknown as well2,3

• Influence of drilling and cutting is investigated

• Monitoring of temperatures near cutting and drilling zones by thermoelements

• Microstructural cross section analysis of machined parts to determine depth of

omega‐phase formation

• Integral electrochemical analysis of corrosion properties in different media

• Influence of fluoride containing solutions is investigated

Corrosion investigationsCorrosion investigations

• Electrochemical techniques used: Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization

• different heat treatments used for samples in this investigation:

850 °C for 0.5 h, air cooled, pure βmicrostructure (beta)

850 °C for 0.5 h, air cooled + 16 h at 600 °C, α+βmicrostructure (alpha)

850 °C for 0.5 h, air cooled + 5 min at 250 °C, β+ωmicrostructure (omega), , β ( g )

TiGr1 used for comparison (TiGr1)

Fig. 1: SEM images of Ti15Mo with α+βmicrostructure (left) and β‐microstructure (right). Left image shows elemental contrast in BSE due to different Mo content in α‐ and β‐phase.

Fig. 2: Polarisation curves of Ti Gr1 andTi15Mo with β‐, α+β‐ and β+ω‐microstructure in NaCl and HCl solution.

Fig. 3: Polarisation curves of Ti Gr1 and Ti15Mo with β‐, α+β‐ and β+ω‐microstructure in 1.5 wt% NaCl + 2.2 g/l NaF solution.

Fig. 4: SEM image of Ti15Mo with α+β‐microstructure after polarization in 1.5 wt% NaCl + 4.4 g/l NaF. Strong corrosive attack.

Fig. 4: SEM image of Ti grade 1 after polarization in 1.5 wt% NaCl + 4.4 g/l NaF. Mainly intact surface.

Fig. 6: EIS curves of Ti Gr1 and Ti15Mo with β‐, α+β and β+ω microstructure after 72 hours in

Fig. 7 EIS curves of Ti15Mo with β‐, α+β‐ and β+ω‐microstructure after 72 hours in 16wt% HCl TiGr1

Fig. 8: EIS curves of Ti Gr1 and Ti15Mo with β‐, α+β and β+ω microstructure after 72 hours in

Fig. 9: EIS curves of Ti Gr1 and Ti15Mo withβ α+β and β+ω microstructure after 72α+β‐ and β+ω‐microstructure after 72 hours in 

1.5 wt% NaCl.microstructure after 72 hours in 16wt% HCl. TiGr1 was not used due to violent corrosion reaction.

α+β‐ and β+ω‐microstructure after 72 hours in 1.5 wt% NaCl + 2.2 g/l NaF.

β‐, α+β‐ and β+ω‐microstructure after 72 hours in 1.5 wt% NaCl + 4.4 g/l NaF

• β+ω‐microstructure shows same corrosion properties as pure β

• α+β–microstructure susceptible to corrosion from fluoride solutions and HCl

• Titanium grade 1 superior to all Ti15Mo microstructures in fluoride solution

• No harmful effect of ω‐phase in terms of corrosion properties detected

Summary of results Acknowledgements

• This project is a cooperation with Florian Brunke and Carsten Siemers 

from Technische Universität Braunschweig

• ω‐phase (13 % Mo) is chemically very similar to β (15% Mo)

• α‐phase with 6 – 12 % Mo content is chemically different from β‐phase!

1) W. F. Ho, „Effect of Omega‐Phase on Mechanical Properties of Ti‐Mo Alloys for Biomedical Applications“, Journal of Medical and Biological Engineering, 28 (1), 47 ‐51 2) N. T. C. Oliveira et al., „ Development of Ti–Mo alloys for biomedical applications: Microstructure and electrochemical characterization“, Materials Science and Engineering A, 452 ‐453 (2007), 727 ‐731 3) N. T. C.. Oliveira, A. C. Gustaldi, „ Electrochemical stability and corrosion resistance of Ti–Mo alloys for biomedical applications“, Acta Biomaterialica 5 (2009), 399 ‐405