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Near-Net Forging of Titanium and Titanium Alloys with Low Friction and Low Work Hardening by Using Carbon-Supersaturated SKD11 Dies

A new near-net forging procedure of titanium and titanium alloys was proposed by using a carbon-supersaturated punch and die. Due to the in situ formation of carbon-based tribofilm on the contact interface between the dies and work materials, a low frictional state was sustained through the forging process even in a high reduction in thickness. The work hardening was suppressed during forging; an additional annealing process was unnecessary through the whole process of near-net forging. Pure titanium and β-phase titanium alloy wires were utilized to describe their galling-free forging behavior when increasing the reduction in thickness. Wires with a diameter of 3 mm were upset in a single-shot forging. The reduction in thickness reached 58% when upsetting the pure titanium wire and 45% when upsetting the β-phase titanium alloys, without lubricating materials or oils at room temperature. The friction coefficient on the contact interface was estimated to be 0.05 by inverse analysis. The work-hardening behavior was described by the hardness mapping on the work cross section. The formation of carbon tribofilms was explained by microstructural analysis, element mapping, and Raman spectroscopy. This tribofilm was formed from the isolated carbon solute from the carbon-supersaturated punch and die to sustain the in situ solid lubrication on the contact interface.