Metallurgical and Materials Transactions A ( IF 2.8 ) Pub Date : 2021-03-24 , DOI: 10.1007/s11661-021-06227-3 Mangesh V. Pantawane , Shashank Sharma , Sriswaroop Dasari , Srinivas Aditya Mantri , Abhishek Sharma , Rajarshi Banerjee , Srikumar Banerjee , Narendra B. Dahotre
The spatial variation of thermokinetic parameters has a significant influence on solidification and microstructural aspects such as grain orientation, types and dimensions of the microstructural features, and crystallographic defects. In laser-based additive manufacturing, these factors are mainly dependent on the process parameters and have a wide implication on the microstructural aspects and, in turn, on the mechanical properties. In view of this, the current study focuses on the spatial variation on thermokinetic parameters such as cooling rate, thermal gradient (G), and solidification velocity (R) within the melt pool formed during laser processing of IN718. The continuous-wave Nd-YAG laser was employed at a laser fluence of 14.85, 19.10, and \(23.34\text { J/mm}^2\) with varying power (700, 900, 1100 W) at a constant scanning speed of 100 mm/s. The finite element method-based multiphysics heat transfer model, coupled with the dynamic fluid flow, was developed to predict these parameters. The model was correlated with microstructural aspects such as melt pool dimensions, orientation of columnar grains, and secondary dendritic arm spacing. The cumulative diffusion length of Nb obtained via thermo-diffusion calculation during multiple heating/cooling cycles was enough to dissolve the fine intragranular plate-shaped \(\delta \) precipitates in the heat-affected zone.The spatial variation of the G/R ratio recognized the transition of columnar to equiaxed solidification grains which was associated with the G/R ratio lower than \(10 \text {K s/mm}^2\) in the top region (\(\sim 25 \mu \text {m}\)) of the melt pool. In addition, the coupled solid mechanics model predicted the evolution of thermal stresses during solidification of the melt pool under a high thermal gradient, which marked the generation of high dislocation density in the solidified melt pool.
中文翻译:
激光表面工程IN718中热动力学的空间变化和相关的微结构演变:增材制造的前体
热动力学参数的空间变化对凝固和微观结构方面具有重大影响,例如晶粒取向,微观结构特征的类型和尺寸以及晶体学缺陷。在基于激光的增材制造中,这些因素主要取决于工艺参数,并且对微观结构以及机械性能具有广泛的影响。有鉴于此,当前的研究集中在热动力学参数的空间变化上,例如在IN718激光加工过程中形成的熔池内的冷却速率,热梯度(G)和凝固速度(R)。连续波Nd-YAG激光的能量密度为14.85、19.10和\(23.34 \ text {J / mm} ^ 2 \)以100 mm / s的恒定扫描速度改变功率(700、900、1100 W)。建立了基于有限元方法的多物理场传热模型,并结合动态流体流动来预测这些参数。该模型与微观结构方面相关,例如熔池尺寸,柱状晶粒的取向和次生树枝状臂间距。得到Nb的累积扩散长度经由多个加热期间的热扩散计算/冷却循环是足以溶解所述细颗粒内的板状\(\三角洲\)在的热影响zone.The空间变化沉淀ģ / ř比率识别柱状晶粒向等轴凝固晶粒的转变,这与顶部区域(\(\ sim 25 \ mu \ text )的G / R比低于\(10 \ text {K s / mm} ^ 2 \)有关。{m} \))熔池。此外,耦合固体力学模型预测了在高热梯度下熔池凝固过程中热应力的演变,这标志着凝固熔池中高位错密度的产生。