Impact of the addition of AI2O3 on the stability of the lubrication regimens of thermally sprayed (OF) and flameremelted nickel-based coatings

Abstract

The aim of this work is to study the influence of 10% micrometric Al₂O₃ additions in NiCrBSi (10.1% and 15.25% Cr) and NiCrBSi/WC (60/40%, 15.25% Cr) coatings deposited by thermal spraying (OF) followed by oxyacetylene flame remelting, on the mechanical properties, tribological behavior and its effect on the lubrication regimes that form the Stribeck curve using the pin-on-disc system. A mathematical model of the exponential type that defines the lubrication regimes of the Stribeck curve has been established due to its high correlation fit between the friction coefficient and the Schipper parameter (Z). Al₂O₃ additions to NiCrBSi coatings present higher stability in the lubrication layer at high apparent pressures avoiding contacts between the asperities of the frictional pair while in NiCrBSi/WC, 60/40% coatings with 15.25% Cr and 10% Al₂O₃ improves their tribological behavior over the whole range of pressures and speeds used. This may be attributed to the surface hardening caused by the local stresses generated by adequate distribution of the particles of alumina particles on the soft Ni-Cr matrix and the formation of smaller hard precipitates (carbides and borides) which favors the development of a lubrication layer capable of isolating the two surfaces of the friction pair