Tribology and Surface Mechanical Properties of Excimer Laser Nitrided Titanium

Abstract

AbstractWe have nitrided Ti-6A1-4V alloys using excimer laser pulses at 1.2 J-cm−2 in high purity N2 at approximately one atmosphere. Substantial nitrogen and oxygen incorporation resulted from multiple pulse processing. The surface microstructure that results is of fine grained precipitates in the Ti alloy matrix. Formation of a TiN surface film was not observed. We have examined the tribological and mechanical properties of these surfaces using pin-on-disk and nanoindenter techniques respectively. Nitrogen alloying results in a period of reduced friction and torque noise in the pin-on-disk measurements. At higher N concentrations, abrasive wear of the pin is observed, but with little deterioration of the disk surface. This is consistent with the formation of a transfer film at the sliding interface. Nanoindenter measurements of the surfaces show increasing hardness proportional to nitrogen incorporation. The tribological properties can therefore be understood to result from a combination of tribochemical effects and increased surface hardness.