In this study, the effects of solidification conditions on the grain refinement capacity of heterogeneous nuclei TiC in directionally solidified Ti6Al4V alloy were investigated using experimental and numerical approaches. Ti6Al4V powder with and without TiC particles in a Ti6Al4V sheath was melted and directionally solidified at various solidification rates via the floating zone melting method. In addition, by using the phase field method, the microstructural evolution of directionally solidified Ti6Al4V was simulated by varying the temperature gradient G and solidification rate V. As the solidification rate increased, the increment of the prior β grain number by TiC addition also increased. There are two reasons for this: first, the amount of residual potent heterogeneous nuclei TiC is larger. Second, the amount of TiC particles that can nucleate becomes larger. This is because increasing the constitutional undercooling ΔT_c leads to the activation of a smaller radius of heterogeneous nuclei and a higher nucleation probability from each radius. At a cooling rate R higher than that in the floating zone melting experiment (R = 3 to 1000 K/s), the maximum degree of constitutional undercooling ΔT_c,Max has a peak value, which suggests that constitutional undercooling ΔT_c has a smaller contribution at higher cooling rates, such as those that occur during electron beam melting (EBM), including laser powder bed fusion (LPBF).

在这项研究中，使用实验和数值方法研究了凝固条件对定向凝固 Ti6Al4V 合金中异质核 TiC 晶粒细化能力的影响。Ti6Al4V 粉末在 Ti6Al4V 护套中含有和不含 TiC 颗粒，通过浮区熔炼方法以不同的凝固速率进行熔融和定向凝固。此外，利用相场法，通过改变温度梯度G和凝固速率V模拟了定向凝固 Ti6Al4V 的显微组织演变。随着凝固速度的增加，先验β的增加添加 TiC 后的晶粒数也增加了。这有两个原因：第一，残留的有效异质核 TiC 的量较大。其次，可以成核的TiC颗粒量变大。这是因为增加结构过冷度 Δ T _c会导致较小半径的异质核被激活，并且每个半径的成核概率更高。在高于浮区熔化实验的冷却速率R 下（R = 3 至 1000 K/s），最大结构过冷度 Δ T _c,Max出现峰值，表明结构过冷 Δ T _c 在较高冷却速率下的贡献较小，例如在电子束熔化 (EBM) 期间发生的冷却速率，包括激光粉末床熔化 (LPBF)。