Inverse Columnar-Equiaxed Transition (CET) in 304 and 316L Stainless Steels Melt by Electron Beam for Additive Manufacturing (AM)
Inverse Columnar-Equiaxed Transition (CET) in 304 and 316L Stainless Steels Melt by Electron Beam for Additive Manufacturing (AM)
复制标题
DOI：
10.3390/cryst11080856
复制
发表时间：
2021-08-01
期刊：
影响因子：
2.7
通讯作者：
Nakano, Takayoshi
中科院分区：
文献类型：
--
作者：
Miyata, Yuichiro;Okugawa, Masayuki;Nakano, Takayoshi
根据公认的Hunt柱状晶向等轴晶转变（CET）准则，凝固前沿的高温度梯度（G）比低G更有利于形成柱状晶。在这里，我们报告了在通过扫描电子束部分熔化的不锈钢的凝固微观结构中发现的相反趋势，用于粉末床熔融（PBF）型增材制造。等轴晶更频繁地观察到在高G的区域，而不是在低G的区域，与CET标准的趋势相反。计算热流体动力学（CtFD）模拟表明，在较小的熔体区域的情况下，流体速度显着较高。小熔池的凝固前沿的G趋于高，但同时沿熔池表面的温度梯度沿着也趋于高。高的熔体表面温度梯度可以促进Marangoni流动，明显地逆转等轴晶的形成趋势。
According to Hunt's columnar-to-equiaxed transition (CET) criterion, which is generally accepted, a high-temperature gradient (G) in the solidification front is preferable to a low G for forming columnar grains. Here, we report the opposite tendency found in the solidification microstructure of stainless steels partially melted by scanning electron beam for powder bed fusion (PBF)-type additive manufacturing. Equiaxed grains were observed more frequently in the region of high G rather than in the region of low G, contrary to the trend of the CET criterion. Computational thermal-fluid dynamics (CtFD) simulation has revealed that the fluid velocity is significantly higher in the case of smaller melt regions. The G on the solidification front of a small melt pool tends to be high, but at the same, the temperature gradient along the melt pool surface also tends to be high. The high melt surface temperature gradient can enhance Marangoni flow, which can apparently reverse the trend of equiaxed grain formation.