Titanium has a tendency to gall when in rubbing contact with itself and other surfaces. A number of techniques have been developed to engineer the titanium surface and overcome this problem:
• Ion Implantation
• Shot Peening
Lubricants reduce the co-efficient of friction between moving surfaces by keeping them apart. When heat is generated the lubricant may also serve to cool the surfaces but its viscosity and film thickness may then be reduced, possibly to the point where the surface separation is no longer maintained.
Proprietary lubricants of dip or spray-on dry film type, based on molybdenum disulphide, PTFE or graphite and the like have been developed specifically for titanium. These provide essential lubrication for severe and cold forming operations such as deep drawing, cold forming of springs, thread rolling and heading of fasteners. Some of these coatings are very stable and may be left on the titanium component until all processing is completed. Thermally unstable lubricants including oil grease and plastics must be fully removed before any immediate or final heat treatments are carried out.
Similar compositions are available for operational service, e.g. on threads or sliding surfaces. Some formulations afford a measure of protection for only a limited period and must be re-applied as required.
Lubricants for Hot Working
Oxidation on ingots and billets during sustained heating prior to forging can be reduced by the application of refractory glass based products. These also serve to lubricate tooling and maintain surface quality particularly during precision forging. Glass with an appropriate melting point is frequently used as a lubricant for extrusion. These coatings are normally removed in the course of post hot work shot blasting and pickling.