Processing and properties evaluation of centrifugally cast in-situ functionally graded composites reinforced with Al3Ni and Si particles

The present investigation deals with the production of aluminium-based functionally graded composite cylinders containing targeted Ni concentrations of 3, 6 and 9 wt% using A413 alloy and Al-26wt%Ni master alloy in horizontal centrifugal casting route. Microstructure, hardness and dry sliding wear behavior of the FG composites (FGCs) were assessed in three different regions (outer, middle and inner region) along the radial thickness. In addition, the A413 alloy cylinder was also cast to compare the properties of FG composites. FGCs show distinct microstructural gradient formation in the radial thickness consisting of in-situ Al3Ni and primary Si particles. Outer region of the composites contains more amount of primary Al3Ni and lower amount of primary Si particles, inner region consists of more primary Si and very few primary Al3Ni particles, and middle region consists of approximately equal proportions of both particles. It was also observed that when Ni content increases, the gradient becomes steep. Hardness of the FG composites is increased from the inner to the outer region, in line with increasing concentration of in-situ Al3Ni reinforcements towards the outer region. A413 + 9 wt%Ni FGC showed an enhancement in hardness of 27.2% in the outer region and 4.5% in the inner region relative to the corresponding regions of the A413 alloy cylinder. The dry sliding wear behavior was characterized at room temperature along the cross-section of the cylinders to determine the effect of microstructural gradation on wear rate. Across the three regions, the wear rate of FG composites decreased as Ni content increased compared to A413 alloy. A maximum wear rate reduction was observed in the outer regions due to the higher concentration of Al3Ni particles, while presence of primary Si particles in the inner regions leads to a significant reduction in the wear rate of FGCs. SEM investigation on worn surfaces showed that abrasive wear with delamination is the dominant wear mechanism.