Wear and corrosion of niobium carbide coated AISI 52100 bearing steel

Bearing steels must have high hardness, good wear resistance and dimensional stability. In the present work, the AISI 52100 bearing steel was selected as the substrate for a niobium carbide coating produced by a salt-bath thermo-reactive deposition process. The present work addresses the effect of niobium carbide coating on the wear and corrosion resistance of the abovementioned steel. A homogeneous layer composed solely by the cubic niobium carbide (NbC) was produced. The carbide coating yielded average hardness and elastic modulus of 26 GPa and 361 GPa, respectively. No significant decarburization was detected beneath the case by means of hardness fluctuations. Dry wear tests resulted in worn volumes 10 times smaller for the NbC coated steel, comparatively to the untreated substrate, at three different applied loads. Corrosion tests in NaCl solution indicated an improved behavior for the carbide coated bearing steel at applied potentials inferior than 250 mV. At higher potentials, the electrolyte appears to penetrate trough the layer yielding wide corrosion caps.