Abstract No.:
6363

 Scheduled at:
Thursday, June 11, 2020, Hall K2 1:40 PM
Tribological Coatings I


 Title:
WC-based hardmetal coatings with Co-free matrices: microstructure and properties

 Authors:
Giovanni Bolelli / Department of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Italy
Beatrice Benedetti / Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Italy
Veronica Testa*/ University of Modena and Reggio Emilia, Italy
Luca Lusvarghi/ Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Italy
Stefania Morelli/ Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Italy
Pietro Puddu/ Department of Engineering Enzo Ferrari, University of Modena and Reggio Emilia, Italy
Paolo Sassatelli/ Il Sentiero International Campus, Italy

 Abstract:

Cobalt is considered a critical raw material to many industrialized economies, due to its strategic importance coupled to supply risks. Moreover, a proposal for classification as a Cat. 1B human carcinogen and mutagen within the European CLP regulation is currently under evaluation. Therefore, partial or total replacement of cobalt as the binder phase of WC-based hardmetals, including for thermal spray applications, is desirable both for economic and workplace safety reasons. The aim of this work is to test High Velocity Oxy-Fuel (HVOF) sprayed coatings based on commercially available hardmetals with Fe- or Ni-based metal matrix, including WC-18%(Ni-16Mo-15Cr-5Fe-2Co), WC-15%(Fe-30Ni-28Cr-7Mo-1Cu) and WC-15%(Fe-20Cr-6Al) (all compositions in wt.%), comparing them to two reference WC-10%Co-4%Cr HVOF-sprayed coatings with micron- and submicron-sized carbide grains. WC-NiMoCrFeCo and WC-FeNiCrMoCu compositions were sprayed according to a fractional factorial design of experiment plan, in order to determine optimal processing conditions, whereas deposition conditions for WC-FeCrAl and WC-CoCr compositions had been previously optimized. All samples were tested for microstructure, phase composition, microhardness, dry sliding wear and dry particle abrasion resistance, and electrochemical corrosion resistance in a 3.5% (w/v) NaCl aqueous solution. The novel compositions always yielded dense coatings (porosity <1%). Hardness values in excess of 1000 HV0.3 (WC-FeNiCrMoCu, WC-FeCrAl) or 1100 HV0.3 (WC-NiMoCrFeCo) were comparable to those of corresponding WC-CoCr samples. Very mild ball-on-disc wear rates <10^(-7) mm^3/(Nm) testify to the suitability of the novel compositions for sliding conditions. Wear mechanisms involve micro-scale plastic flow on the contact surface, with minimal brittle fracture. The Ni-based matrix also resulted in better corrosion resistance than the WC-CoCr references. The WC-FeCrAl composition, on the other hand, suffered from slightly higher wear rates, because of a certain brittleness, and from higher corrosion current density values, due to selective matrix dissolution. Overall, these outcomes indicate which compositions are most promising for diverse operating conditions.



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