Functionally graded aluminum reinforced with quasicrystal approximant phases – Improving the wear resistance at high temperatures

Abstract

Functionally graded aluminum was produced and displayed two well-defined metallurgically bonded layers (A and B). Layer A exhibited a ductile Al-matrix (70 HV0.01) reinforced by 53.4 vol% of hard quasicrystal approximant α-Al12(Fe,Mn,Cr)3Si phase (909 HV0.01) distributed homogeneously. Layer B presented the typical structure of a hypoeutectic Al–Si alloy. The tribological behavior of both layers was evaluated in sphere-on-plate configuration at different temperatures: room-temperature, 100, 200, and 300 °C. At room temperature, layer A ensured low coefficient of friction values around 0.2. These values were comparable to those of fully quasicrystalline coatings under dry-sliding testing conditions. The specific wear rate at room temperature of the layer A was about one order of magnitude lower than that of the layer B (1.2 × 10-4versus 2.7 × 10-3 mm3/Nm, respectively), and three orders of magnitude lower at 300 °C (2.3 × 10-5versus 2.8 × 10-2 mm3/Nm, respectively). Improved wear resistance and low friction of layer A were achieved through the formation of a protective and compacted Al-rich oxide layer, where the quasicrystal approximant phase played a critical role. The present results and the discussed wear mechanisms provide significant insights into the development of novel alloys for service in critical components.