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 (0.14TL) and 227 K (0.16TL) 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.