Rapid growth kinetics of β-Fe₃Ge₂ intermetallic compound within undercooled liquid Fe-Ge alloys

The rapid dendrite growth of the β-Fe₃Ge₂ intermetallic compound within two liquid Fe-Ge alloys was investigated using the bulk undercooling technique. The liquid undercooling was achieved up to 202 K (0.14T_L) and 227 K (0.16T_L) for hypereutectic Fe₇₀Ge₃₀ and Fe₆₇Ge₃₃ alloys, respectively, where the primary β-Fe₃Ge₂ phase always exhibited non-faceted growth characteristics. Within the Fe₇₀Ge₃₀ alloy, the β-Fe₃Ge₂ phase morphology transformed from columnar to equiaxed dendrites with increasing undercooling, where the maximum growth velocity was measured as 1.44 m/s at 141 K undercooling. Beyond this undercooling threshold, the (β-Fe₃Ge₂ + α₁-Fe₁₇Ge₃) anomalous eutectic grew directly from the undercooled liquid, which may be attributed to the remarkably enhanced nucleation rate of the α₁-Fe₁₇Ge₃ phase. For the Fe₆₇Ge₃₃ alloy, the primary β-Fe₃Ge₂ dendrites achieved a high growth velocity of 3.53 m/s at the maximum 227 K undercooling. Furthermore, the Vickers hardness of the β-Fe₃Ge₂ compound in these two alloys was improved significantly, which resulted mainly from microstructure refinement.