Three-dimensional reconstruction of anomalous eutectic in laser remelted Ni-30 wt.% Sn alloy

Abstract

Laser remelting has been performed on Ni-30 wt.% Sn hypoeutectic alloy. An anomalous eutectic formed at the bottom of the molten pool when the sample was remelted thoroughly. 3D morphologies of the α-Ni and Ni3Sn phases in the anomalous eutectic region were obtained and investigated using serial sectioning reconstruction technology. It is found that the Ni3Sn phase has a continuous interconnected network structure and the α-Ni phase is distributed as separate particles in the anomalous eutectic, which is consistent with the electron backscatter diffraction pattern examinations. The α-Ni particles in the anomalous eutectic are supersaturated with Sn element as compared with the equilibrium phase diagram. Meanwhile, small wavy lamella eutectics coexist with anomalous eutectics. The Trivedi–Magnin–Kurz model was used to estimate undercooling with lamellar spacing. The results suggest that the critical undercooling found in undercooling solidification is not a sufficient condition for anomalous eutectic formation. Besides, α-Ni particles in the anomalous eutectic do not exhibit a completely random misorientation and some neighboring α-Ni particles have the same orientation. It is shown that both the coupled and decoupled growth of the eutectic two phases can generate the α-Ni + Ni3Sn anomalous eutectic structure.

Effects of Doping Ni on the Microstructures and Thermoelectric Properties of Co-Excessive NbCoSn Half-Heusler Compounds

“…One possible explanation for such phenomenon is that there might be a competition between the reaction of Sn and Nb and the reaction of Sn and Ni in the Ni- x samples. According to the Ni–Sn and Nb–Sn binary phase diagrams, the formation temperature of the Ni–Sn phase (1073 K) is lower than that of the Nb 3 Sn phase (∼1200 K) . When Ni is added, it will first form the Ni–Sn phase rather than the Nb 3 Sn phase.…”

Uncoupling Growth Mechanisms of Binary Eutectics during Rapid Solidification

“…Moreover, from Figure 1, we find that only one α-square crystal can exist in each closed melt region finally, and the orientations for α-square are different in one anomalous eutectic colony because these grains are crystallized from individual nuclei. In experimental investigations, the orientations for the second phase (Ni 3 Sn) are the same for each anomalous eutectic colony, which is mainly because the discrete particles are often crystallized from one closed melt region 27 (the discrete regions are often connected in the third dimension). From this point of view, our results are still consistent with experimental observations.…”

Globular to lamellar transition during anomalous eutectic growth

“…Previous anomalous eutectic growth models were based on the remelting of lamellar eutectic or primary dendrites. In our precious paper (figure 11 in reference [16]), the schematic of the anomalous eutectic growth was also based on the partial remelting theory, which has been recently shown to be infeasible [15]. Mullis et al [15] discussed that the volume faction of anomalous fraction was around an order of magnitude greater than the calculated recalescence solid fraction.…”

“…Experimental investigations on anomalous eutectic solidified from deep undercooled melts have been continued for several decades [3][4][5][6][7][8][9][10][11][12][13][14][15]. Recently, the anomalous eutectic has also been observed during laser remelting of Ni-Sn alloy [16][17][18][19]. The typical morphologies of anomalous eutectic microstructure has been characterized as its globular pattern [20].…”