Question:
There has been a lot of talk on powder metal injection moulding of titanium but there seems to be very few parts being produced by this technology.  Why?

Answer:
Conventional powder metallurgy, the press and sinter technology, is a very accepted technology today and is used every day to produce hundreds of tons of parts.  We need to look into the history of powder metallurgy and go back about fifty years.  While powder metallurgy was know to be a viable technology, quality powders as we know today, specifications and the availability of different alloying elements were not so readily available and the industry was dependant on people with special qualifications and experience.  The powder metal injection moulding (MIM) technology is in a similar position today.  It is no longer a laboratory curiosity but an accepted technology for low alloy and stainless steels, while other “exotic” materials are making slow progress.

Titanium, because of its reactivity, has always been a difficult material to sinter, because once it reacts with carbon, nitrogen or oxygen it can not be reduced during the sintering process.  It also forms a stable hydride in hydrogen, which is difficult to reduce.  In case of MIM the finer powder used (d50 of about 22μm) adds to these problems.  The challenges are:

• Obtaining a powder with a sufficiently low oxygen content and maintaining the low oxygen level during processing.
• Using a secondary binder that dissociates without leaving carbon residues during the secondary debinding stage.
• Maintaining a clean furnace from which carbon and oxygen are not reabsorbed.
• The lack of specifications and the expectations that for all applications the specifications for wrought materials have to be met.
• The availability and cost of titanium powders.

Today there are a number of manufacturers that produce titanium alloy powders with low oxygen levels, including one that uses a plasma processing technology resulting in oxygen levels of around 100 ppm for MIM grade powders.  The cost is still an issue, but the use of novel technology for powder production to reduce costs is also making headway.

There are a number of binder systems available that leave almost no carbon residue and one major feedstock manufacturer is making CP titanium and Ti-6Al-4V feedstock.  Elnik Systems makes the only MIM furnace that allows for complete binder removal and sintering without adding oxygen or carbon using a partial pressure of argon for titanium based alloys.

Most manufacturers making MIM titanium parts are acting on their own.  When they come together to create new specifications for MIM titanium based alloys, the industry will grow faster.