Carbon implantation into hard chrome coatings

Carbon ions were implanted into hard chrome coatings at an energy of 30 keV for various doses up to 4 x 10(17) C cm(-2) to study possible neu phase formation and its effect on the tribological properties. The retained doses and ion distributions were determined by ion beam analysis techniques and phase formation was monitored by grazing incidence X-ray diffraction, Indication of an amorphous phase or a nanocrystalline structure and evidence for a new crystalline phase were revealed after 2 x 10(17) C cm(-2) and 4 x 10(17) C cm(-2) implantations respectively. In addition, nanoindentation tests suggested an increase in the near-surface hardness following ion implantation. From dry sliding wear tests carried out with a ruby ball as the counterbody in a ball-on-disc configuration, it was found that the highest dose implantation reduced the friction coefficient significantly and the treated coatings became markedly more resistant to spalling. Scanning electron microscopy and associated X-ray energy dispersive spectroscopy were utilized to characterize the worn surfaces in order to gain an insight into the wear mechanism. The correlation between new phase formation and improvement in the tribological properties is discussed and the results are compared with the more widely studied nitrogen implantation case.