INFLUENCE OF NICKEL ON THE MICROSTRUCTURAL EVOLUTION AND MECHANICAL PROPERTIES OF LM6-ALLOY-BASED FUNCTIONALLY GRADED COMPOSITE TUBES

Abstract

Despite the growing demand for new materials, we used the horizontal centrifugal casting technique to synthesize functionally graded composite (FGC) tubes using an LM6 alloy containing (3, 6 and 9) w/% nickel. All the fabricated tubes were evaluated for variations in microstructure, hardness and tensile properties along the radial cross-section in three distinct zones (inner, transition and outer). X-Ray diffraction (XRD) results indicated the formation of in-situ Al3Ni in all FGC tubes, and these in-situ tri-aluminides increased further with the addition of Ni. A comprehensive microstructural analysis across the tubes utilising scanning electron microscopy (SEM) images showed that gathering in-situ Al3Ni particles keeps growing nearer the outer zone, and primary Si cuboids increase in the inner zone. This accumulation of particles improved the mechanical properties at all three zones of the FGC tubes compared to the LM6 tube having no nickel. The results of the hardness investigation showed that precipitated Al3Ni in FGCs has a beneficial impact on the enhancement of hardness. Furthermore, the observed UTS improvement in the FGC tubes was clearly associated with the precipitation and strengthening action of Al3Ni intermetallic phases, while a significant reduction in elongation has been noted. Due to the influence of centrifugal force and density variation, the tube containing 9 w/% of Ni demonstrated good gradation among composite alloy-fabricated FGC tubes, with in-situ Al3Ni particles settling largely in the outer zone and primary Si particles settling primarily in the inner zone across the radial thickness.