Titanium offers the advantages of being light, strong, ductile and resistant to corrosion. With high strength-to-weight ratio, excellent tensile strength and ability to withstand high temperatures, Ti and its alloys are used in aerospace and military applications and also in automotive and sporting goods. However, Ti does attack even the most resilient ceramic crucibles during the melting process, causing the metal to be contaminated with dissolved impurities or solid refractory inclusions to the detriment of its mechanical and corrosion properties. PSI eliminates these problems through ‘clean melting’ technology, utilising:
- ‘Cold-Wall’ techniques where the molten metal is contained within a thin layer of solidified metal (the skull) which, in turn, is contained within water-cooled copper containers.
The PSI-designed cold-crucible is a cylindrical, induction-heated configuration with a bottom-pouring spout enabling a stream of Ti to either a mould for castings or an die where it is atomised with jets of inert gas to make powder.
Our YouTube video shows our cold crucible in operation.
The high cost of good quality Ti powder (fine, spherical and low oxygen) continues to slow progress in Ti powder metallurgy, despite increasing market pull from a growing number of market sectors. However, significant success in addressing this issue has, and is, being achieved by companies like PSI Ltd. through the release of their latest design of Ti atomiser. Based on the established HERMIGA range of vacuum/inert gas atomisers, PSI has added a ‘skull-melting’ cold crucible incorporating the latest thinking in induction melting technology combined with an innovative water-cooled, cold wall configuration. The new design confers a higher efficiency melt process, reducing excessive waste heat losses and increasing melt stirring for improved alloy melting.
Currently, the PSI Ti atomiser operates in a batch mode with the associated costs of this type of process; however, PSI is currently optimising this technology with a view to titanium atomisation in a continuous mode. Continuous atomisation, as opposed to batch, transforms the economics of powder production as PSI has demonstrated with its production systems for aluminium, magnesium and silver.
PSI also views the replacement of standard ceramic atomisation nozzles, which can interact with molten Ti and some its alloys, as key to the production of clean powder with its resultant improved mechanical properties.
Other Reactive Materials
Although cold crucible technology is often associated with Ti, PSI systems are equally suited to other metal melts where ceramic-free melting is preferred. These include nickel superalloys and high performance steels where low inclusion size and count are essential for good fatigue properties.