Multi-scale Simulation Study On The Dynamic Evolution Of Inconel 625 Alloy Dendrites By CMT Arc Additive Manufacturing

The nickel-based alloy Inconel 625 has garnered immense popularity due to its exceptional performance advantages such as remarkable resistance to high temperature,oxidation,heat and corrosion.Consequently,it has found widespread application not only in the aerospace industry but also in other domains including petrochemical and nuclear power sectors.Arc-wire additive manufacturing(AWAM)is a promising technique in additive manufacturing due to its high material utilization,good structural integrity,and relatively low production and equipment costs.Particularly,AWAM demonstrates great potential in the fabrication of large nickel-based alloy components.The solidification behavior and microstructure of the weld pool during additive manufacturing play a decisive role in determining the mechanical properties of the additively manufactured parts,which eventually translate into the performance of the entire additively manufactured structure.Thus,studying the solidification behavior of the melt pool during the additive manufacturing process and the resulting microstructure holds significant theoretical importance and practical value.This thesis aims to investigate the solidification behavior and dendritic growth mechanism of the melt pool in CMT arc additive manufacturing of Inconel 625 nickel-based alloy through a research approach combining numerical simulation,theoretical analysis,and experiments.Specifically,based on the results of numerical simulation,theoretical analysis,and experiments,this study delves into the solidification behavior and dendritic growth mechanism of the melt pool during CMT arc additive manufacturing of Inconel 625 nickelbased alloy.The main research contents and results are summarized as follows:Firstly,in order to account for the multiscale characteristics of the melt pool soli,dification process in arc additive manufacturing,this study employs a two-fold approach.First,macro-scale heat transfer and flow coupling models are established in order to analyze the behavior of the melt pool on a larger scale.Next,a micro-scale quantitative phase-field model is introduced to examine the dendritic nucleation and growth behavior of the alloy during solidification.By combining these two models,a multiscale model is constructed that enables investigation of both the macroscale heat and mass transfer behavior of the melt pool and the microscale behavior of dendrite growth.This multiscale model is then validated through experimental observation of the melt pool solidification interface,longitudinal section morphology,and primary dendrite arm spacing scaling laws with cooling rate.The results demonstrate the accuracy and reliability of the mathematical model.Overall,this approach provides a comprehensive understanding of melt pool solidification phenomena in arc additive manufacturing at both macro-and micro-scales.A quantitative phase-field model was employed to simulate and investigate the dynamic growth conditions of the melt pool solidification,providing insight into the growth behavior of dendrites.The study focused specifically on the effects of both additive manufacturing and solidification parameters on primary dendrite arm spacing.Results show that dendrite growth can be roughly divided into four stages: linear growth,interface instability,competitive growth,and relatively stable growth.Notably,the heat source power and speed play significant roles in temperature gradient G and interface propagation velocity Vs during the melt pool solidification process,affecting dendritic growth.As the heat source power increases,and the speed decreases,the cooling rate G·Vs of the melt pool decreases,leading to an increase in the primary dendrite arm spacing.Additionally,the temperature gradient continuously increases along the solid-liquid interface from the top to the bottom of the melt pool due to a corresponding decrease in interface propagation velocity and cooling rate,further increasing the primary dendrite arm spacing.Correspondingly,the experimental results demonstrate considerable agreement with trends seen in simulated dendritic morphology alterations.Finally,the distribution of Nb element during and after complete solidification in arc additive manufacturing of Inconel 625 was dynamically reproduced.The study investigated the effects of solidification parameters such as temperature gradient,solidification rate,and cooling rate on the spatial distribution of Nb elements and predicted their segregation behavior in the melt pool.Results indicate that the diffusion of Nb elements occurs from the solid phase to the liquid phase during melt pool solidification,leading to an accumulation of Nb-rich liquid phase at the front of the solid-liquid interface due to its rejection to tiny interdendritic regions caused by dendrite arm coarsening.After complete solidification,numerous small round droplets with a chain-like distribution are formed within interdendritic regions.The concentration of Nb element inside the dendrite is proportional to the temperature gradient,solidification rate,and cooling rate.Moreover,the concentration of Nb element at the dendrite tips is inversely proportional to the cooling rate and solidification rate while being directly proportional to the temperature gradient.