TiC–NiCr thermal spray coatings as an alternative to WC-CoCr and Cr3C2–NiCr

• Published in: Wear Vol. 450-451; p. 203273
• Main Authors: Bolelli, Giovanni, Colella, Alberto, Lusvarghi, Luca, Morelli, Stefania, Puddu, Pietro, Righetti, Enrico, Sassatelli, Paolo, Testa, Veronica
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-06-2020; Elsevier Science Ltd
• Subjects: Abrasive wear; Aluminum oxide; Ball milling; Cermets; Corrosion resistance; Corrosive wear; Crack initiation; Fracture mechanics; Frictional wear; Fuels; Grooves; High temperature; High velocity oxyfuel spraying; Microcracks; Nonmetallic inclusions; Protective coatings; Raw materials; Reference materials; Room temperature; Sliding friction; Sliding wear; Sprayed coatings; Thermal spray coatings; Tungsten carbide; Wear rate; Wear resistance; Thermal spray coatings; Cermets; High temperature; Sliding wear
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2020.203273

TiC-based hardmetal coatings containing 25 or 40 vol% Ni-20 wt%Cr matrix (hereafter TiC–25NiCr and TiC–40NiCr) were obtained by High Velocity Oxygen-Fuel (HVOF) and High Velocity Air-Fuel (HVAF) spraying, starting from high-energy ball milled feedstock powders. These coatings are intended as critical raw materials-free solutions against wear and corrosion.
HVOF-sprayed coatings contain some more oxide inclusions than do HVAF ones, but, irrespective of the deposition conditions, TiC–40NiCr coatings are usually somewhat harder (800–900 HV0.3) than TiC–25NiCr ones. They also exhibit lower wear rates in ball-on-disc sliding tests against Al2O3 at room temperature. A hard asperity can indeed penetrate slightly deeper into TiC–25NiCr, as it deforms inelastically through microcracking. Bigger abrasive grooves are thus produced.
The wear resistance of TiC–40NiCr coatings compares favourably to that of a Cr3C2-25% (NiCr) reference, and even approaches that of WC-10 wt%Co-4wt.%Cr. TiC–40NiCr coatings are also more corrosion resistant than both reference materials when tested by electrochemical polarization in a 3.5% NaCl solution.
At 400 °C, to the contrary, TiC–25NiCr coatings exhibit better sliding wear resistance, whilst more severe abrasive grooving and adhesive tearing affect TiC–40NiCr samples. TiC–NiCr coatings are also unaffected by the transverse macro-cracking that was found to compromise the usefulness of WC-CoCr at 400 °C.
•High energy ball-milled TiC–NiCr powders are suitable as thermal spray feedstock.•HVAF TiC–25NiCr and TiC–40NiCr coatings have lower oxidation levels than HVOF ones.•Despite different oxide contents, HVOF and HVAF coatings exhibit similar performances.•TiC–25NiCr has better sliding wear resistance than Cr3C2–NiCr at 400 °C.•TiC–40NiCr can substitute WC-CoCr against wear and corrosion at room temperature.