Investigation of Dendritic Arm Spacing in FeTi-Cu

Hydride-forming Intermetallic compounds like FeTi play a promising role in sustainable hydrogen storage technologies. Among them, the FeTi-Cu alloy shows significant potential due to its hydrogen-absorbing capabilities, due to the prospect of precise microstructure control, followed by consequent foam preparation by selective Cu dissolution. This study investigates suction casting as a fabrication method for FeTi-Cu. In this process where molten alloy is rapidly solidified in a water-cooled copper mold, resulting in a fine dendritic microstructure. In cast alloys, secondary dendrite arm spacing follows an empirical power law dependent on cooling rate, temperature gradient, and growth velocity. Understanding this relationship is crucial for tailoring microstructures during processing. FeTi-Cu was synthesized via suction casting, and the microstructure was characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). SEM imaging revealed dendritic structures, and a custom Fiji macro combined with a Python script was used to measure the arm spacing, yielding values between 3–6 μm. Attempts to correlate DSC-controlled cooling rates with the observed dendritic spacing were unsuccessful, as the derived scaling law underestimated the cooling rate. Additionally, results show that FeTi-Cu undergoes complex solidification involving multiple intermetallic phases, including CuTi and Fe2Ti, which complicates the extraction of a reliable power law using DSC alone. XRD and EDX analysis confirmed successful FeTi formation in suction cast samples. Notably, the absence of CuTi and Fe2Ti near the rod’s outer surface implies a critical cooling rate above which FeTi is predominantly formed. This may be due to altered phase equilibria at high solidification rates. To estimate the cooling rates during suction casting, FeNi was also cast and analyzed. As FeNi has well-characterized solidification behavior, its cell spacing measurements allowed for an approximate calculation of cooling rates across the rod crosssection, ranging from 15,000–30,000 Ks−1 at the surface to 5–70 Ks−1 at the center. Although these values cannot be directly transferred to FeTi-Cu, they provide a semiquantitative reference.