Due to its exceptional mechanical and tribological properties, nanocrystalline diamond (NCD) has the potential to be used for tool coatings that can enable dry machining of Al alloys. This study explores the friction response of NCD coatings in sliding contact with 319 Al. NCD coatings were grown using microwave plasma CVD with a range of growth conditions to explore key growth modulators governing the tribological response of this material. These coatings were then characterized with Raman spectroscopic analysis at three different wavelengths. Pin-on-disc friction response of these coatings with 319 Al showed that the trans-polyacetylene content as determined by the respective Raman spectrum in NCD is the critical factor controlling friction behavior. This finding can have significant implications in other similar applications where friction response of NCD is a key design factor. © 2015, Springer Science+Business Media New York.