Titanium

Q: Which titanium alloy is most used for medical prostheses?
Commercially pure titanium, Ti-6AL-4V and    Ti 6Al-7Nb continue to be the most frequently specified materials for prosthetic use.

Q: Is there any reaction by the body to these metals?    
Earlier concerns about release of vanadium and/or aluminium from alloys have been largely resolved. Commercially pure titanium and most alloys are effectively nickel free and will not cause nickel dermatitis.

Q: What are the most widely available grades of titanium and titanium alloys?
The two basic compositions that are widely available are:
• Commercially pure titanium (typically ASTM Grade 2)
• Ti-6AL-4V alloy (ASTM Grade 5)
The versatility of these two grades is such that they continue to satisfy the majority of applications.

Q: I would like to replace a high strength steel with something less heavy but maintain the mechanical properties.  I require a suitable material for use in a high chloride environment.    
You should consider the use of titanium alloys. The combination of high strength and low density results in extremely favourable strength to weight ratios. Densities range from 4.43 to 4.95 grm/cc and yield strengths vary from 172 to1400MPa.
Although some of the high molybdenum super austenitic stainless steels can be used in a high chloride concentration environment, we would recommend the use of titanium for this application.
Titanium is immune to corrosive attack by saltwater or other chlorides. It is essentially immune to both chloride pitting and intergranular attack and highly resistant to crevice corrosion and stress corrosion cracking.

Q: I have heard that titanium and titanium alloys are extremely difficult to machine and present a fire risk. Can you help?
When machining titanium or titanium alloys there are a few basic things to remember:
•    You must use rigid set ups
•    Correct speeds and feeds
•    Remove turnings frequently
•    Use flood lubrication
•    Use special closeable containers for turnings.
Also do not allow blunt tooling or rubbing. Do not mix combustible material with Ti fines or turnings and keep well away from open fire or welding operations.
The tooling supplier should help with the correct choice of tooling and machining parameters.

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