Selective laser melting of Fe–Al alloys with simultaneous gradients in composition and microstructure

Selective laser melting technique was employed to fabricate a step-wise compositionally graded Fe–Al alloy coupon using the in-situ alloying of blended powders. Microstructural characterization of the fabricated coupons shows a columnar to equiaxed grain structure transition with increasing Al content along the building direction, along which the laser scan speed is increased. In the low Al content regions, the absence of constitutional undercooling (CUC) allows columnar grain growth against the macroscopic thermal gradients, whereas dominance of CUC in high Al regions leads to fully equiaxed and refined microstructures. Nanoindentation studies show a linear increase in hardness and reduction in elastic modulus for Al content up to ~20 at.%; no significant anisotropy in these properties could be seen.