Co-Sn单相合金深过冷凝固时Co3Sn2 相生长形貌的演变机制

Evolution of Co3Sn2 Phase Growth Morphology in Under-cooled Solidification of Co-Sn Single Phase Alloy

摘要:

开展了(Co₆₀Sn₄₀)_100-xNb_x (x=0，0.4，0.6，0.8，at%)单相合金的深过冷凝固实验，研究了Co₃Sn₂相生长形貌的演变机制。结果表明，在小过冷度下，Co₃Sn₂相在x=0，0.4以海藻状的模式进行生长，随着添加的Nb含量增加至0.6at%，其生长形貌转变为树枝晶，并在x=0.8进一步转变为分形海藻晶，这主要是由于界面能各向异性和动力学各向异性的变化。随着过冷度的增加，(Co₆₀Sn₄₀)_99.4Nb_0.6合金中Co₃Sn₂相生长形貌在过冷度大于28 K时从树枝晶转变为分形海藻，当过冷度高于143 K时转变为密集海藻。少量的Nb添加在小过冷度和中间过冷度时能提高Co₃Sn₂相的生长速度，但是在大过冷度下会显著降低生长速度。Co₃Sn₂相生长速度随过冷度变化规律的转变对应其生长形貌从分形海藻向密集海藻的转变。

Abstract:

The undercooled solidification of (Co₆₀Sn₄₀)_100-xNb_x(x=0, 0.4, 0.6, 0.8, at%) single phase alloys was performed to investigate the changes of Co₃Sn₂ phase growth morphology.Results show that the Co₃Sn₂ phase grows with fractal seaweed morphology at small undercooling (x=0, 0.4), and transits to dendrite as the content of added Nb increases to 0.6at%, and then returns to fractal seaweed (x=0.8) as a response to the changes in interfacial energy anisotropy and kinetic anisotropy. With the increase in undercooling, the growth morphology of Co₃Sn₂ phase in (Co₆₀Sn₄₀)_99.4Nb_0.6 alloys returns from dendrite back to factual seaweed at undercooling larger than 28 K and then transits to compact seaweed at undercooling more than 143 K. The minor Nb addition slightly increases the growth velocity of Co₃Sn₂ phase at low and intermediate undercooling but obviously decreases the growth velocity at large undercooling. The sharp increase in the growth velocity is corresponding to the transition of Co₃Sn₂ phase growth morphology from fractal seaweed to compact seaweed.