Sliding and abrasive wear behaviour of boride coatings

Polyphase boride coatings constituted by an inner layer of Fe2B and an outer layer of FeB were thermochemically grown on iron and medium carbon steel by a pack cementation process. The tribological behaviour of borided samples was investigated under both sliding and abrasion testing conditions. Considerably different values of wear rate were found in different regions of the coatings. The differences were explained on the basis of the crystallographic order of iron borides. The resistance to both types of wear was initially poor due to the presence on the coatings of a thin, friable layer constituted by disordered crystals. Then the resistance increased to a maximum value in regions constituted by compact, highly ordered crystals of Fe2B. The resistance to dry sliding of borided samples was better than that displayed by samples submitted to alternative surface treatments (e.g. gas nitriding) and lower that that measured for a WC–Co hard metal coating.