The influence of micrometric alumina (low surface area-to-volume ratio) and nanometric alumina (high surface area-to-volume ratio) on microstructure, hardness and abrasive wear of a NiCrBSi hardfacing alloy coating applied to an AISI 304 substrate using flame spraying (FS) combined with surface flame melting (SFM) is studied. Remelting after spraying improved the mechanical and tribological properties of the coatings. Microstructural characterization using XRD, SEM and EDS indicated that alumina additions produced similar phases (NiSi, Ni 3 B, CrC and Ni 31 Si 12) regardless of the alumina size, but the phases differed in morphology, size distribution and relative proportions from one coating to another. The addition of 12 wt.% nanometric Al 2 O 3 increased the phases concentration more than five-to sixfold and reduced the hard phases size about four-to threefold compared with NiCrBSi + 12 wt.% micrometric Al 2 O 3. Nanoalumina led to reduced mass loss during abrasive wear compared to micrometric alumina and greater improvement in hardness.
This research aims to assess the effect of the debris particle size on the tribological performance and lubrication regime parameters of a Ni-based alloy coating. This is a key industrial problem, and its resolution can contribute to better machine endurance and proper maintenance. The debris particles are simulated by hard Al 2 O 3 particles of size ranging from nanometers to 45 μm and dispersed in an oil lubricant. The coating studied is NiCrBSi deposited by flame spraying technique followed by the Surface Flame Melting (SFM) process. The counterpart disk sample was fabricated from quenched and tempered F-5220 steel (in line with A681(O1) ASTM). This pair was tested under linear sliding contact. Our results show that the addition of alumina particles contributes to a significant increase in wear, particularly for the largest particles (micrometric size). In the case of micrometric particles, it is possible to observe the formation of higher surface roughness, numerous microgrooves, and plastic flow of NiCrBSi coating perpendicular to the sliding direction, resulting in higher loss of volume. It was found that the actual surface roughness (obtained as a function of the debris particle size) allows better identification and prediction of the lubrication regime for wear processes instead of the traditional approach that uses the initial surface roughness as a parameter.
A challenge currently facing the orthopedics sector consists in the durability problems posed by joint prosthesis based on metal‐on‐metal contacts. While the diamond‐like carbon (DLC)‐based coating solves the shortcomings of wear and friction found in the uncoated metal parts, they are generally subject to adhesion failures that may prove to be catastrophic. Our coatings were deposited with a specific multilayered composition that changes from highly metallic at the metal interface, up to a DLC at the sliding contact region. These coatings show very good wear performance results when tested in a highly humid air atmosphere as well as when they are tested in water immersion or in bovine serum. The friction coefficients of our DLC‐against‐DLC tribological pair are found to be always less than 0.1, while wear rates are extremely low, under 2.5 × 10−8 mm3/N m, and it produces highly polished surfaces. The compressive stresses of our coatings are always lower than 2.5 GPa, and when combined with good interface adhesion to the CoCrMo metal substrates, make the coatings highly resistant to delamination even after prolonged test runs. Raman analyses do not reveal any detectable changes even after very long test runs, indicating that no tribochemical reactions occur on the DLC coating.
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