Toward CRMs-free coatings: a comparison between HVOF and CGS AISI 304-TiC

Hard carbides based CerMets are widely used for machining tools in extreme applications against wear and corrosion occurring in several harsh environments. Their wear resistance is three to five times that of electroplated chromium HC, and their average manufacturing costs are low. To this end they are considered a viable alternative to HC prepared from Cr(VI). However, two main issues are recently affecting coatings containing some elements: raw materials shortage and association with high risk, due to the presence critical elements. Among CerMets the well-known and most commonly used WC-Co and in a less extent NiCr-C2Cr3 are in-or very close-to the black list of the CRMs. Co and WC-Co were included among the possible carcinogenic material. The actions aimed to decrease the EU dependence on critical raw materials account for the development CRMs-free coatings, although substitution or even reduction of certain elements is yet to come. In this paper one possible alternative to CerMet coatings (W, Co, Cr)-free is proposed. AISI 304-TiC deposited by High-Velocity-Oxy-Fuel and by Cold Gas Spray are compared. Powders, with a composition ratio of 25-75 % wt prepared by High Energy Mechanical Alloying have been deposited with the two techniques. Coatings were characterized and compared revealing different mechanisms taking place during the deposition processes.