Abstract
In this work, Al alloys with 6.6%, 10.4%, and 14.6% Si were deposited as thick coatings by Friction Surfacing (FS), resulting in grain refinement and spheroidization of needle-shaped eutectic Si phase. Lubricated sliding wear tests were performed on a pin-on-disc tribometer using Al-Si alloys in as-cast and FS processed states as pins and 42CrMo4 steel discs. The chemical composition of the worn surfaces was analyzed by X-ray photoelectron spectroscopy (XPS). The wear mechanisms were studied by scanning electron microscopy (SEM) and focused ion beam (FIB), and the wear was evaluated by measuring the weight loss of the samples. For the hypoeutectic alloys, spheroidization of the Si phase particles in particular leads to a significant improvement in wear resistance. The needle-shaped Si phase in as-cast state fractures during the wear test and small fragments easily detach from the surface. The spherical Si phase particles in the FS state also break away from the surface, but to a smaller extent. No reduction in wear due to FS was observed for the hypereutectic alloy. Here, large bulky primary Si phase particles are already present in the as-cast state and do not change significantly during FS, providing high wear resistance in both material states. This study highlights the mechanisms and limitations of improved wear resistance of Si-rich Al alloys deposited as thick coatings by Friction Surfacing.
Highlights
Friction Surfacing (FS) is generally used to apply metal-based coatings in a solid state, i.e., without bulk melting the material being deposited
We suggest a similar mechanism of enrichment as observed for the Si Phase
The changes in the microstructure induced by FS lead to an improvement in wear resistance for hypoeutectic alloys
Summary
Friction Surfacing (FS) is generally used to apply metal-based coatings in a solid state, i.e., without bulk melting the material being deposited. Phase dissolution at process temperatures is favored by the applied mechanical energy, and subsequent cooling rates are usually very high. This results in coatings containing supersaturated solid solution phases, non-equilibrium precipitates, or martensite [2,18,19]. Small amounts of other elements in Al alloys, e.g., chromium (Cr) and zinc (Zn), promote the formation of complex intermetallic hard phases resulting in a more brittle material [22,23]. The thermomechanical processing of Al-alloys with high Si content by FS is of great interest from an engineering
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