Laser Remelting Process Simulation and Optimization for Additive Manufacturing of Nickel-Based Super Alloys

Nickel-based super alloys are popular for applications in the energy and aerospace industries due to their excellent corrosion and high-temperature resistance. Direct metal deposition (DMD) of nickel alloys has reached technology readiness for several applications, especially for the repair of turbomachinery components. However, issues related to part quality and defect formation during the DMD process still persist. Laser remelting can effectively prevent and repair defects during metal additive manufacturing (AM); however, very few studies have focused on numerical modeling and experimental process parameter optimization in this context. Therefore, the aim of this study is to investigate the effect of determining the remelting process parameters via numerical simulation and experimental analyses in order to optimize an industrial process chain for part repair by DMD. A heat conduction model analyzed 360 different process conditions, and the predicted melt geometry was compared with observations from a fluid flow model and experimental single tracks for selected reference conditions. Subsequently, the remelting process was applied to a demonstrator repair case. The results show that the models can well predict the melt pool shape and that the optimized remelting process increases the bonding quality between base and DMD materials. Therefore, DMD part fabrication and repair processes can benefit from the remelting step developed here.

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Sensitivity of Thermal Predictions to Uncertain Surface Tension Data in Laser Additive Manufacturing

Journal of Heat Transfer ◽

10.1115/1.4047916 ◽

2020 ◽

Vol 142 (12) ◽

Cited By ~ 1

Author(s):

J. Coleman ◽

A. Plotkowski ◽

B. Stump ◽

N. Raghavan ◽

A. S. Sabau ◽

...

Keyword(s):

Heat Transfer ◽

Surface Tension ◽

Fluid Flow ◽

Additive Manufacturing ◽

Current Model ◽

Surface Tension Gradient ◽

Process Conditions ◽

Conductive Heat ◽

Melt Pool ◽

Super Alloy

Abstract To understand the process-microstructure relationships in additive manufacturing (AM), it is necessary to predict the solidification characteristics in the melt pool. This study investigates the influence of Marangoni driven fluid flow on the predicted melt pool geometry and solidification conditions using a continuum finite volume model. A calibrated laser absorptivity was determined by comparing the model predictions (neglecting fluid flow) against melt pool dimensions obtained from single laser melt experiments on a nickel super alloy 625 (IN625) plate. Using this calibrated efficiency, predicted melt pool geometries agree well with experiments across a range of process conditions. When fluid mechanics is considered, a surface tension gradient recommended for IN625 tends to overpredict the influence of convective heat transfer, but the use of an intermediate value reported from experimental measurements of a similar nickel super alloy produces excellent experimental agreement. Despite its significant effect on the melt pool geometry predictions, fluid flow was found to have a small effect on the predicted solidification conditions compared to processing conditions. This result suggests that under certain circumstances, a model only considering conductive heat transfer is sufficient for approximating process-microstructure relationships in laser AM. Extending the model to multiple laser passes further showed that fluid flow also has a small effect on the solidification conditions compared to the transient variations in the process. Limitations of the current model and areas of improvement, including uncertainties associated with the phenomenological model inputs are discussed.

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Influence of Process Conditions on the Local Solidification and Microstructure During Laser Metal Deposition of an Intermetallic TiAl Alloy (GE4822)

Metallurgical and Materials Transactions A ◽

10.1007/s11661-021-06139-2 ◽

2021 ◽

Vol 52 (3) ◽

pp. 1106-1116

Author(s):

Silja-Katharina Rittinghaus ◽

Jonas Zielinski

Keyword(s):

Heat Treatment ◽

Additive Manufacturing ◽

Process Parameters ◽

Titanium Aluminides ◽

Metal Deposition ◽

Experimental Investigations ◽

Process Conditions ◽

Laser Metal Deposition ◽

Melt Pool ◽

Temperature Regimes

AbstractTemperature-time cycles are essential for the formation of microstructures and thus the mechanical properties of materials. In additive manufacturing, components undergo changing temperature regimes because of the track- and layer-wise build-up. Because of the high brittleness of titanium aluminides, preheating is used to prevent cracking. This also effects the thermal history. In the present study, local solidification conditions during the additive manufacturing process of Ti-48Al-2Cr-2Nb with laser metal deposition (LMD) are investigated by both simulation and experimental investigations. Dependencies of the build-up height, preheating temperatures, process parameters and effects on the resulting microstructure are considered, including the heat treatment. Solidification conditions are found to be dependent on the build height and thus actual preheating temperature, process parameters and location in the melt pool. Influences on both chemical composition and microstructure are observed. Resulting differences can almost be balanced through post heat treatment.

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Modeling of Solidification and Microstructure Evolution in the Scanning Laser Epitaxy (SLE) Process for Additive Manufacturing With Nickel-Base Superalloy Powders

Volume 2A: Advanced Manufacturing ◽

10.1115/imece2013-66807 ◽

2013 ◽

Author(s):

Ranadip Acharya ◽

Rohan Bansal ◽

Justin J. Gambone ◽

Suman Das

Keyword(s):

Additive Manufacturing ◽

Marangoni Convection ◽

Flow Analysis ◽

Scanning Laser ◽

Naval Research ◽

Nickel Base Superalloy ◽

Conduction Model ◽

Melt Pool ◽

Institute Of Technology ◽

Nickel Base

This paper investigates effects of natural and Marangoni convection on the resultant solidification microstructure in the scanning laser epitaxy (SLE) process. SLE is a laser-based additive manufacturing process that is being developed at the Georgia Institute of Technology for the additive manufacturing of nickel-base superalloys components with equiaxed, directionally-solidified or single-crystal microstructures through the laser melting of alloy powders onto superalloy substrates. A combined thermal and fluid flow model of the system simulates a heat source moving over a powder bed and dynamically adjusts the thermophysical property values. The geometrical and thermal parameters of the simulated laser melt pool are used to predict the solidification behavior of the alloy. The effects of natural and Marangoni convection on the resultant microstructure are evaluated through comparison with a pure conduction model. Inclusion of Marangoni effect produces shallower melt pools compared to a pure conduction model. A detailed flow analysis provides insights into the flow characteristics of the powder, the structure of rotational vortices created in the melt pool, and the solidification phenomena in the melt pool. The modeling results are compared with measurements and observation through real-time thermal imaging and video microscopy to understand the flow phenomenon. In contrast to the single weld-bead approach, the raster scan in SLE allows every position in melt pool to be visited twice by the solid-liquid interface as the scan source progresses. To properly address this situation, time tracking is incorporated into the model to correctly couple the microstructure prediction model. An optimization study is carried out to evaluate the critical values of the transition parameters that govern the columnar-to-equiaxed transition (CET) and the oriented-to-misoriented (OMT) transition. This work is sponsored by the Office of Naval Research through grant N00014-11-1-0670.

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Effects of Scan Strategy on Thermal Properties and Temperature Field in Selective Laser Melting

10.20944/preprints201908.0003.v1 ◽

2019 ◽

Author(s):

Elham Mirkoohi ◽

Daniel E. Sievers ◽

Hamid Garmestani ◽

Steven Y. Liang

Keyword(s):

Temperature Field ◽

Additive Manufacturing ◽

Heat Affected Zone ◽

Material Properties ◽

Temperature Fields ◽

Analytical Models ◽

Temperature History ◽

Process Conditions ◽

Repeated Heating ◽

Melt Pool

Temperature field is an essential attribute of metal additive manufacturing in view of its bearings on the prediction, control, and optimization of residual stress, part distortion, fatigue, balling effect, etc. This work provides an analytical physics-based approach to investigate the effect of scan strategy parameters including time delay between two irradiations and hatching space on thermal material properties and melt pool geometry. This approach is performed through the analysis of the distribution of material properties and temperature profile in three-dimensional space. The moving point heat source approach is used to predict the temperature field. To predict the temperature field during the additive manufacturing process some important phenomena are considered. 1) Due to the high magnitude of temperature in the presence of the laser, the temperature gradient is usually high which has a crucial influence on thermal material properties. Consequently, the thermal material properties of stainless steel grade 316L are considered to be temperature-dependent. 2) Due to the repeated heating and cooling, part usually undergoes several melting and solidification cycles. This physical phenomenon is considered by modifying the heat capacity using the latent heat of melting. 3) The multi-layer aspect of metal AM process is considered by incorporating the temperature history from the previous layer since the interaction of the successive layers has an impact on heat transfer mechanisms. 4) Effect of heat affected zone on thermal material properties is considered by the superposition of material properties in regions where the temperature fields of two consecutive irradiations have an overlap since the consecutive irradiations change the behavior of the material properties. The goals are to 1) investigate the effects of temperature-sensitive material properties and constant material properties on the temperature field. 2) Study the behavior of thermal material properties under different scan strategies. 3) Study the importance of considering the effect of heat affected zone on thermal material through the prediction of melt pool geometry. 4) Investigate the effect of hatching space on melt pool geometry. This work is purely employed physics-based analytical models to predict the behavior of material properties and temperature field under different process conditions, and no finite element modeling is used.

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Thermoelectric magnetohydrodynamic control of melt pool dynamics and microstructure evolution in additive manufacturing

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2019.0249 ◽

2020 ◽

Vol 378 (2171) ◽

pp. 20190249 ◽

Cited By ~ 2

Author(s):

A. Kao ◽

T. Gan ◽

C. Tonry ◽

I. Krastins ◽

K. Pericleous

Keyword(s):

Magnetic Field ◽

Additive Manufacturing ◽

Microstructure Evolution ◽

Defect Formation ◽

Physical Phenomenon ◽

Convective Transport ◽

Great Promise ◽

Practical Implementation ◽

Field Orientation ◽

Melt Pool

Large thermal gradients in the melt pool from rapid heating followed by rapid cooling in metal additive manufacturing generate large thermoelectric currents. Applying an external magnetic field to the process introduces fluid flow through thermoelectric magnetohydrodynamics. Convective transport of heat and mass can then modify the melt pool dynamics and alter microstructural evolution. As a novel technique, this shows great promise in controlling the process to improve quality and mitigate defect formation. However, there is very little knowledge within the scientific community on the fundamental principles of this physical phenomenon to support practical implementation. To address this multi-physics problem that couples the key phenomena of melting/solidification, electromagnetism, hydrodynamics, heat and mass transport, the lattice Boltzmann method for fluid dynamics was combined with a purpose-built code addressing solidification modelling and electromagnetics. The theoretical study presented here investigates the hydrodynamic mechanisms introduced by the magnetic field. The resulting steady-state solutions of modified melt pool shapes and thermal fields are then used to predict the microstructure evolution using a cellular automata-based grain growth model. The results clearly demonstrate that the hydrodynamic mechanisms and, therefore, microstructure characteristics are strongly dependent on magnetic field orientation. This article is part of the theme issue ‘Patterns in soft and biological matters'.

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Improving surface quality in selective laser melting based tool making

Journal of Intelligent Manufacturing ◽

10.1007/s10845-021-01744-9 ◽

2021 ◽

Author(s):

Filippo Simoni ◽

Andrea Huxol ◽

Franz-Josef Villmer

Keyword(s):

Surface Roughness ◽

Additive Manufacturing ◽

Surface Quality ◽

Selective Laser Melting ◽

Melting Process ◽

Laser Remelting ◽

Laser Melting ◽

Great Cost ◽

Starting Point ◽

Processing Techniques

AbstractIn the last years, Additive Manufacturing, thanks to its capability of continuous improvements in performance and cost-efficiency, was able to partly replace and redefine well-established manufacturing processes. This research is based on the idea to achieve great cost and operational benefits especially in the field of tool making for injection molding by combining traditional and additive manufacturing in one process chain. Special attention is given to the surface quality in terms of surface roughness and its optimization directly in the Selective Laser Melting process. This article presents the possibility for a remelting process of the SLM parts as a way to optimize the surfaces of the produced parts. The influence of laser remelting on the surface roughness of the parts is analyzed while varying machine parameters like laser power and scan settings. Laser remelting with optimized parameter settings considerably improves the surface quality of SLM parts and is a great starting point for further post-processing techniques, which require a low initial value of surface roughness.

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