CARBON IMPLANTATION INTO HARD CHROME COATINGS

Carbon ions were implanted into hard chrome coatings at an energy of 3 0 keV for various doses up to 4 x 10(17) C cm(-2) to study possible ne u phase formation and its effect on the tribological properties. The r etained doses and ion distributions were determined by ion beam analys is techniques and phase formation was monitored by grazing incidence X -ray diffraction, Indication of an amorphous phase or a nanocrystallin e structure and evidence for a new crystalline phase were revealed aft er 2 x 10(17) C cm(-2) and 4 x 10(17) C cm(-2) implantations respectiv ely. In addition, nanoindentation tests suggested an increase in the n ear-surface hardness following ion implantation. From dry sliding wear tests carried out with a ruby ball as the counterbody in a ball-on-di sc configuration, it was found that the highest dose implantation redu ced the friction coefficient significantly and the treated coatings be came 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 we ar mechanism. The correlation between new phase formation and improvem ent in the tribological properties is discussed and the results are co mpared with the more widely studied nitrogen implantation case.