What Happens To The Surface Composition Of Hardmetal, When It Undergoes Corrosion? An Electrochemical And Spectroscopic Investigation

Authors:

Gian Pietro De Gaudenzi (F.I.L.M.S. S.p.A. – Gruppo OMCD, Italy),
Alessandro Alleva (Politecnico di Milano, Italy),
Elisa Emanuele (Politecnico di Milano, Italy),
Mattia Garabelli (F.I.L.M.S. S.p.A. – Gruppo OMCD, Italy),
Claudio Mele (Università del Salento, Italy),
Francesco Tavola (Politecnico di Milano, Italy),
Sandra Tedeschi (F.I.L.M.S. S.p.A. – Gruppo OMCD, Italy),
Augusto Travella (Politecnico di Milano, Italy),
Benedetto Bozzini (Politecnico di Milano, Italy)

Abstract:

Functional performance of hardmetal grades is strongly controlled by the poorly understood ambient-dependent nature and evolution of the near-surface chemistry, either in operational ambient or in metal-recovery processes.We carried out a systematic study on Co-Ni alloy grades without|with Cr|Mo additions in neutral aqueous ambient. Electrochemical investigations, based on CV, PS and EIS measurements, SEM|EDX microscopy, spectroellipsometry and ICP analysis of electrolytes, lead to the rationalization of the irreversibilities of the hardmetal surface properties. We could identify two limiting classes of behaviour: (i) controlled by binder dissolution, and (ii) controlled by pseudopassive film formation, involving both binder and WC corrosion products. By control of the binder composition and of the ambient oxidizing power, one can stir the behaviour of the grade towards one of the two regimes, in order to engineer the surface response to optimize: (i) corrosion and (ii) tribocorrosion resistance, (iii) room-temperature, green recovery of metal from scrap.

DOI:

https://doi.org/10.59499/WP225369576