Geometrically Necessary Dislocations Research Articles

Dislocation distribution, crystallographic texture evolution, and plastic inhomogeneity of Inconel 718 fabricated by laser powder‐bed fusion

Dislocation distribution, crystallographic texture evolution, and plastic inhomogeneity of Inconel 718 fabricated by laser powder‐bed fusion

Revealing the Enhancement Mechanism of Laser Cutting on the Strength–Ductility Combination in Low Carbon Steel

The strength–ductility mechanism of the low-carbon steels processed by laser cutting is investigated in this paper. A typical gradient-phased structure can be obtained near the laser cutting surface, which consists of a laser-remelted layer (LRL, with the microstructure of lath bainite + granular bainite) and heat-affected zone (HAZ). As the distance from the laser cutting surface increases, the content of lath martensite decreases in the HAZ, which is accompanied by a rise in the content of ferrite. Considering that the microstructures of the LRL and HAZ are completely different from the base metal (BM, ferrite + pearlite), a significant strain gradient can be inevitably generated by the remarkable microhardness differences in the gradient-phased structure. The hetero-deformation-induced strengthening and hardening will be produced, which is related to the pileups of the geometrically necessary dislocations (GNDs) that are generated to accommodate the strain gradient near interfaces. Plural phases of the HAZ can also contribute to the increment of the hetero-deformation-induced strengthening and hardening during deformation. Due to the gradient-phased structure, the low carbon steels under the process of laser cutting have a superior combination of strength and ductility as yield strength of ~487 MPa, tensile strength of ~655 MPa, and total elongation of ~32.7%.

Study on performance enhancement driven by strain-induced α' martensite transformation in a metastable dual-phase titanium alloy

This study improves ductility while maintaining the ultimate tensile strength (UTS) of a Ti-30Zr-5Al-3V alloy without changing chemical composition via microstructural control of the double-phase (α+β). The deformation mechanism of the alloy is controlled by regulating the volume fraction of the β phase, resulting in an ultra-high strain hardening capacity that enhances the material's mechanical properties. The water-quenched specimen exhibits an ultra-high strain hardening capacity attributed to the increase in both back and effective stresses as the deformation proceeds. Heterostructure deformation and the accumulation of geometrically necessary dislocations (GNDs) near grain boundaries induce back-stress strengthening. Effective stress strengthening primarily arises from dislocation reinforcement, including the dynamic Hall-Petch effect caused by strain-induced α' martensite transformation (SIMT) and the hindering effect of GNDs migration. The reorientation and merging of α grains are inconducive to high strain hardenability. However, a lower β phase volume fraction in the air-cooled specimen results in less SIMT, and even small strains could lead to significant grain coarsening. High strain hardening rates could not be maintained solely through back stress strengthening, leading to premature material failure. In comparison to the air-cooled specimen, the water-quenched specimen demonstrates a significantly increased ultra-high strain hardening capability, resulting in enhanced uniform elongation (from ∼3.4 to ∼9.6%) and overall elongation (from ∼6.2 to ∼13.3%) without reducing the UTS.

Mechanisms for dynamic recrystallization in a β-quenched Zr-1Nb-1Sn-0.1Fe alloy during hot compression

In this paper, uniaxial hot compression tests of β-quenched Zr-1Nb-1Sn-0.1Fe alloy under a strain of 0.91 were conducted at various temperatures ranging from 600 °C to 750 °C. The microstructure, texture evolution, deformation mode and dynamic recrystallization (DRX) mechanism were investigated using electron backscatter diffraction (EBSD). The results of the In-Grain Misorientation Axis (IGMA) method showed that the prismatic <a> was the dominant deformation mode when the temperature was 600 °C. The prismatic <a> and pyramidal <a + c> were the dominant deformation modes during hot compression between 650 and 750 °C. To study the mechanism of DRX, the geometrically necessary dislocation (GND) density, grain orientation spread (GOS) and grain reference orientation deviation (GROD) maps were calculated. The results showed that both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during hot compression. When deformed at 600 °C, the recrystallization mechanism was mainly DDRX, while it was mainly CDRX above 600 °C. The change in the DRX mechanism can be attributed to the activation fraction of different slip systems and the resulting development of misorientation.

Study of the mechanism of the strength-ductility synergy of α-Ti at cryogenic temperature via experiment and atomistic simulation

Alpha titanium (α-Ti) is a promising material for making high-performance components for applications in aerospace, marine, energy and healthcare fields. The excellent strength-ductility synergy has been observed for α-Ti at cryogenic temperature. Twinning is generally considered a key mechanism of outstanding cryogenic ductility. The dislocation-grain boundaries (GBs) interaction and void nucleation usually play crucial roles in the plastic deformation of polycrystalline materials, but their effects on the cryogenic ductility of α-Ti are rarely considered. To eliminate this confusion and gain an in-depth insight into the mechanism of the cryogenic strength-ductility synergy of α-Ti, in this work, a series of characterization experiments and molecular dynamics (MD) simulations were designed and carried out. 1) From uniaxial tension tests of the coarse-grained α-Ti sheets at the temperature from 25 to -180 °C, the uniform elongation and post-necking elongation were increased by 92 % and 20 %, respectively. The material maintained a larger strain hardening rate within a greater range of strain at cryogenic temperature compared with room temperature. 2) Via microstructure and fractography observations and the analysis of slip and geometrically necessary dislocation (GND) activities, the uniform plastic deformation was mainly accomplished by prismatic slip, whether at room temperature or at cryogenic temperature. The significantly increased uniform elongation is mainly attributed to the more uniform distribution of GND pile-ups at cryogenic temperature. 3) The MD simulations revealed that cryogenic temperatures made the GBs present a stronger barrier effect on dislocation transmission compared with that at room temperature, contributing to the more uniform distribution of GNDs and lower densities of GND pile-ups. The GBs at cryogenic temperature show a greater ability to resist void nucleation due to the decreased accumulation rate of excess potential energy and increased energy required to void nucleation. The larger strains were thus required to increase the densities of GND pile-ups to induce large stress concentrations for driving void nucleation. This made the uniform elongation of α-Ti increase significantly at cryogenic temperature. This study revealed that the enhanced barrier effect of GBs on dislocation transmission and the improved ability of GBs to resist void nucleation are key mechanisms besides twinning governing the cryogenic strength-ductility synergy of α-Ti. The understanding developed in this work can be useful for the development of new high-performance materials and the precise forming of complex components with high quality.

A model of strain hardening for stage IV based on lattice curvature induced dislocations and grain fragmentation

A new model is presented for the interpretation of the nearly linear Stage IV large strain hardening behavior observed in polycrystalline metals. The approach is based on the orientation change of the grains that induces a curvature of the crystallographic lattice and produces geometrically necessary dislocations (GNDs). The GND density is dependent on grain size, the latter is decreasing in a reciprocal manner with plastic strain in Stage IV. The GNDs are added to the dislocation density present at the end of Stage III in the Taylor relation to obtain an analytical formula for the strain hardening behavior of the material. The model is applied to polycrystalline nickel, copper, and commercially pure aluminum and produced good agreement with experiments. As grain fragmentation is a common phenomenon of all metals during large strain at low temperature, this model explains the universal nature of Stage IV.

Synergistic effect of fatigue and hydrogen-induced damage under asymmetric loading of TRIP steel

This study investigates the synergistic assessment of cyclic plasticity damage and hydrogen-induced cracking of transformation-induced plasticity (TRIP) steel subjected to asymmetric strain-controlled fatigue loading. The presence of hydrogen in TRIP steel results in cyclic softening throughout its life, suppressing the hardening behavior induced by martensitic transformation. The mild hardening observed in hydrogen-free specimens is attributed to the predominance of hardening induced by martensitic transformation over cyclic softening. The increase in mean strain leads to higher mean stress relaxation, suppressing the compressive stress developed during the deformation-induced martensitic transformation phenomenon. Geometrically necessary dislocation (GND) density map and fractographic images substantiate the hydrogen-enhanced decohesion failure mechanism, decreasing fatigue resistance for hydrogen-induced TRIP steel. The failure mechanisms of the fatigue damage due to the ingress of hydrogen atoms in the material are proposed for further insights.

In-situ EBSD tensile revealing the evolution mechanism of high angle grain boundaries in Al–Zn–Mg alloy profile with heterogeneous structures

The evolution of grain boundary (GB) of an Al–Zn–Mg alloy profile with heterogeneous structures is studied based on in-situ EBSD tensile. This evolution is not only related to its grain boundary misorientation angle (GBMA) and slip transfer parameter (m'/(Δb/b)) but also to the behavior of the geometrically necessary dislocation (GND) tensor in the deformation. The effect of GBMA and m'/(Δb/b) for three types of high angle grain boundary (HAGB) on GND density and back stress has been revealed. The increase of GND density is not obvious near the HAGBs with 45°–55° GBMA of neighboring coarse grains or neighboring fibrous grains. The optimal grain boundary for forming back stress is the HAGBs between coarse grain and fibrous grain, which has 35°–45° GBMA and a low m'/(Δb/b). The back stress is hard to form near these HAGBs with 25°–35° GBMA and a low m'/(Δb/b). Combined with the neighboring grain type, slip transfer and GBMA, the new criterion is proposed to predict GND behavior near HAGBs.

Grain structure tailoring strategy for heterogeneous lamella SiCp/2024Al composites with exceptional strength-ductility synergy

In this work, a novel grain structure tailoring strategy using one-stepped planetary ball milling, different from conventional powder metallurgy routes that pre-prepared components with different microstructures and then mixed them up, was implemented to fabricate micro- and nano-sized SiC particles (m- & n-SiCp)/2024Al composites with heterogeneous lamella structure. The controllable transformation from homogeneous to heterogeneous grain structures is achieved via nonuniformly distributed n-SiCps induced local grain refinement. Heterogeneous lamella composites exhibit a superior modulus-strength-ductility synergy of 95.3 GPa in Young's modulus, 750.7 MPa in tensile strength and 4.9 % in uniform elongation, particularly with no less than 145 % and 175 % improvements in ductility and toughness, compared with homogeneous composites. Compressive stress relaxation experiments were conducted to reveal the structural dependence of plastic deformation behaviors. Sustainedly rising hetero-deformation induced (HDI) stress produced by extra geometrically necessary dislocation (GND) accumulation at heterogeneous soft/hard domain interfaces and sequential activation of multiple dislocation mediated mechanisms based on load transfer in heterogeneous lamella composites contribute to the enhanced strain hardening capacity, which offers intrinsic toughening. Also, extrinsic toughening originates from enhanced microcrack multiplication and crack-tip blunting.

New insights on dislocation forming mechanism of nickel-based superalloy fabricated by laser powder bed fusion

In this work, the forming mechanism of dislocation in laser powder bed fusion (LPBF) built IN738LC alloy was elucidated by studying the intrinsic relationships between the density and distribution of dislocation and the orientation and size of dendrite. The substructures with different dislocation densities and cell spacings were customized by controlling solidification conditions, and analyzed by multi-scale characterizing methods. The results show that an increase in geometrically necessary dislocation (GND) density from 1.48 × 1014 to 1.82 × 1014m−2 is accompanied by a decrease in cell spacing from 1046 nm to 640 nm as the solidification rate increases. However, the relationship between GND density and cell spacing doesn't follow Ashby's model. This indicates that GNDs are not entirely generated by thermal strain itself. On the other hand, the characterization results of cell structures show that a number of misfit dislocations are formed by the thermal strain induced deflection growth of the dendrites. These prove that the dislocations are comprehensively generated by thermal strain itself and dendritic deflection growth.

Designing strong and ductile heterogeneous lamella-structured Mg alloy via diffusion bonding

Achieving superior strength-ductility synergy in Mg alloys is a critical issue for engineering applications. To address the trade-off between strength and ductility, the introduction of heterogeneous lamellar structures has recently proven be an effective strategy. In this study, we fabricated an AZ31/WE43/AZ31 alloy with heterogeneous lamellar structure using diffusion bonding (DB). Increasing the DB temperature enhanced the diffusion behavior, resulting in the precipitation and growth of Al2(Y, Nd) phases within the interfacial diffusion zone. Additionally, grain growth occurred, leading to a reduction in the heterogeneity of the grain size in individual AZ31 and WE43 layers. The sample fabricated at 460 °C, which exhibited relatively high heterogeneity and strong interfacial bonding, demonstrated a good combination of yield strength (202.4 MPa), ultimate tensile strength (315.8 MPa), and elongation (19.4 %). These mechanical properties significantly surpassed those of the original individual materials and exceeded the rule-of-mixture predictions. The excellent strength-ductility synergy observed in this alloy can be attributed to the presence of heterogeneous deformation-induced stress (HDI stress), which promotes extensive activation of non-basal dislocation slips. Furthermore, in-situ tensile tests demonstrated that the pile-up of geometrically necessary dislocations (GNDs) at the heterogeneous interface contributed to the superior HDI strengthening and HDI strain hardening. Overall, this study provides new insights into the fabrication of heterogeneous lamella-structured Mg alloys with strength-ductility synergy.

Flow behavior and dynamic recrystallization mechanism of a new near-alpha titanium alloy Ti-0.3Mo-0.8Ni-2Al-1.5Zr

A new near-α titanium alloy Ti-0.3Mo-0.8Ni-2Al-1.5Zr was designed based on Ti-0.3Mo-0.8Ni (TA10). The hot compression tests were carried out at temperatures of 800–970 °C and strain rates of 0.01–5 s−1. The results show that the flow softening phenomenon in the α + β phase region is more distinct than that in the single β phase region. The Arrhenius constitutive models based on strain compensation in the α+β phase region and β phase region were established respectively, and the correlation coefficient between the predicted flow peak stress values and the experimental values reached 0.99365. The hot processing map of the alloy was established, the processing parameters of the peak efficiency: 800 ≤ T ≤ 818 °C, 0.01 ≤ ε˙ ≤ 0.0235 s−1, and 960 ≤ T ≤ 970 °C, 0.01 ≤ ε˙ ≤ 0.0213 s−1. The microstructure evolution and deformation mechanism of the compressed specimens were researched by electron backscatter diffraction (EBSD) technique. There were two nucleation mechanisms for dynamic recrystallization (DRX): sub-grains growth nucleation and high angle grain boundaries (HAGBs) bulging nucleation, the former was continuous dynamic recrystallization (CDRX), and the latter was discontinuous dynamic recrystallization (DDRX). The flow stress in the α+β phase region was softened by CDRX and dynamic recovery (DRV), while the principal deformation mechanisms in the β phase region are DRV and DDRX. The dislocation strain energy and recrystallization ability at different temperatures were quantitatively analyzed by the kernel average misorientation (KAM) and the geometrically necessary dislocation (GND), and the results showed that more complete recrystallization occurred at lower temperature in the α + β phase region. The HCP slip was principally completed by prismatic ⟨a⟩ and pyramidal ⟨c+a⟩ slip systems during the hot compression, while BCC was a mixed mode of {110}, {112} and {113} multiple slips.

Synergic strength-ductility enhancement in bimodal titanium alloy via a heterogeneous structure induced by the slip

In this work, a heterogeneous structure (HS) with an alternating distribution of coarse and fine α lamella is fabricated in bimodal Ti6242 alloy via insufficient diffusion of alloying elements induced by fast heating treatment. Instead of a distinct interface between the primary α phase (αp) and β transformation microstructure (βt) in the equiaxed microstructure (EM), all αp/βt interfaces are eliminated in the HS, and the large αp phases are replaced by coarse α lamella. Compared to the EM alloy, the heterostructured alloy exhibits a superior strength-ductility combination. The enhanced strength is predominantly attributed to the increased interfaces of α/β plates and hetero-deformation induced (HDI) strengthening caused by back stress. Meanwhile, good ductility is ascribed to its uniform distribution of coarse and fine α lamella, which effectively inhibits strain localization and generates an extra HDI hardening. This can be evidenced by the accumulated geometrically necessary dislocations (GNDs) induced by strain partitioning of the heterostructure. Significantly, the HDI causes extra 〈c+a〉 dislocations piling up in the coarse α lamella, which generates an extra strain hardening to further improve the ductility. Such hetero-interface coordinated deformation mechanism sheds light on a new perspective for tailoring bimodal titanium alloys with excellent mechanical properties.

Revealing the temperature-dependent hardening mechanisms of non-uniformly distributed defects for ion-irradiated metals: Experiments and modeling

In this work, an integrated approach including experimental examinations and theoretical modeling was employed to examine the temperature-dependent hardening of structural materials under ion irradiation. Experimental procedures involved the characterization of grain morphology and size distribution by electron backscatter diffraction (EBSD). Irradiation experiments were conducted utilizing high-energy Au-ions at elevated temperatures, with transmission electron microscopy (TEM) employed for observing irradiation-induced defects. Moreover, mechanical properties were assessed through high-temperature nano-indentation tests (HTNIT), revealing the concurrent occurrence of irradiation hardening and high-temperature softening in the considered materials. For theoretical modeling, a mechanistic model was developed to address the depth-dependent hardness. This model innovatively characterized the hardening mechanisms resulting from non-uniformly distributed defects in the irradiated layer while simultaneously incorporating the temperature effect. Calibration of the model demonstrated its capability to elucidate the hardness-depth relationships at different irradiation doses and testing temperatures. Further theoretical analyses indicated distinct evolution laws in irradiation hardening behavior with varying indentation depths, while the increment in temperature accelerated the expansion of the plastic zone, resulting in a moderate indentation size effect (ISE). With increasing indentation depth, the hardening contributions of geometrically necessary dislocations (GNDs) and irradiation-induced defects gradually diminished. At substantial indentation depths, the dominant hardening mechanism was then controlled by statistically stored dislocations (SSDs).

Structural insights into T1 precipitation and age hardening by Zn alloying for T6 treated Al–Cu–Li based alloys with a high Cu/Li ratio

T1 (Al2CuLi) nano-phase precipitation has been a major focus in developing new multi-microalloyed Al–Cu–Li alloys. Nevertheless, more understanding is required. This work investigated the effect of Zn alloying on the microstructure and mechanical properties of multi-element Al–Cu–Li alloys with a high Cu/Li ratio using a combination of advanced electron microscopy and first-principles calculations. Zn alloying (i) induced a higher density of geometrically-necessary dislocations after solid-solution treatment, which increased the T1 nucleation rate during the early aging stage; (ii) promoted T1 growth by substituting Al or Cu atoms in the T1 structure; and (iii) profoundly increased the aging kinetics, the age hardening response, and the strength. In addition, the co-segregation of Zn, Mg and Cu at the T1/Al interface helped to stabilize the fine T1 nano-platelets. These structural insights into T1 precipitation and age hardening by Zn alloying can help to guide the optimal design of high-performance Zn micro-alloyed multi-element Al–Cu–Li alloys.

Microstructure and residual stress evolution during cyclic elastoplastic deformation of AISI316L fabricated via laser powder bed fusion

In metal additive manufacturing (MAM), microstructural properties such as texture, residual stresses, and dislocation density have emerged as key factors ruling the resulting mechanical performances. In this study, cylindrical AISI 316L specimens, fabricated with laser powder bed fusion (LPBF), were tested under cyclic elastoplastic (EP) deformation using a constant strain amplitude to highlight the evolution of residual stresses (RS), dislocation density and texture with increasing number of EP cycles, N, across the hardening-softening (H–S) transition stage, in the attempt to find correlations between relevant microstructural parameters and macroscopic properties. The structural and microstructural analysis is carried out through whole powder pattern modeling (WPPM) of neutron diffraction (ND) data and Electron Back-Scattering Diffraction (EBSD) analysis. The H–S transition is found to occur within 7–9 cycles, with RS fading out already after 5 cycles. Across the H–S transition, the trend of the maximum tensile stress correlates closely with the trend of WPPM-calculated total dislocation density, suggesting a major role of dislocations’ characteristics in the evolution of macroscopic mechanical properties. EBSD analysis reveals the rearrangement of geometrically necessary dislocations (GND) into cellular structures, and moderate grain refinement, which are deemed to be responsible for the quick fading of RS in the very early stage of EP loading. ND-based texture analysis reveals a (220) preferential orientation retained throughout the EP tests but with orientation density functions (ODFs) changing non-monotonically with N, suggesting preliminary partial randomization of grains around the deformation axis followed by the recovery of crystallographic anisotropy and more localized ODFs.

Origins of HDI stress in copper–brass laminates with dual-heterostructured interfaces

In this work, a copper–brass hetero-laminate with dual-heterostructured interfaces was fabricated by diffusion welding in combination with cold deformation and annealing. These dual-heterostructured interfaces possess the characteristics of both gradient interface and sharp interface. The evolutions of geometrically necessary dislocations (GNDs) and local strains near these dual-heterostructured interfaces were investigated by in-situ and quasi in-situ tests. By employing a constitutive model, the evolutions of GND density and the HDI synergistic strengthening mechanism were systematically explored. The results demonstrated that the distribution of GNDs and local strains near the coarse/fine-grained interface exhibited a gradient feature, without any obvious concentrations of GNDs and strains, which can be attributed to the transition effect of the gradient interface. Furthermore, the density of sample-scale GNDs accumulated near the coarse/fine-grained interface was found to be at least one order of magnitude lower than that of grain-scale GNDs accumulated near grain boundaries. Both the constitutive model and experimental results confirmed that grain-scale GNDs serve as the primary origins of significant HDI stress, rather than the sample-scale GNDs.

Coupled study on in-situ synchrotron high-energy X-ray diffraction and in-situ EBSD on the interfacial stress gradient in layered metals

As one of the heterostructures, the layered structure has attracted extensive research interest as it achieves superior properties to individual components. The layer interface is considered a critical factor in determining the mechanical properties of layered metals, where heterogeneity across the interface results in the strengthening of the soft layer and forming an interfacial stress gradient in the hard layer. However, there is still limited research associated with the formation of interfacial stress gradients in the hard layer, as stress measurement at high spatial resolution remains technically challenging. In the present study, we experimentally quantified the formation of interfacial stress gradients in the Ti layer of Ti/Al layered metal upon tension using in-situ high-energy X-ray diffraction (XRD). The analysis coupling in-situ high-energy XRD and in-situ electron back-scattered diffraction (EBSD) suggested that the interfacial stress gradient in the Ti layer rapidly rose as the Al layer was insufficient to accommodate the deformation of Ti. During the later deformation stage, collective effects of dislocation motion and geometrically necessary dislocation (GND) accumulation in the Al layer determined the evolution of interfacial stress gradients. The maximum interfacial stress gradient is below 0.4 MPa/μm in Ti layers, with a constant range width of 35 μm independent of the macroscopic strain. The present study therefore opens a new window to local stress modification using incompatible component deformation, which is instructive for the design and fabrication of high-performance layered metals.

Probing the impact of grain size distribution on the deformation behavior in fine-grained austenitic stainless steel: A critical analysis of unimodal structure versus bimodal structure

This study investigated the effect of grain size distribution on the deformation behavior in fine-grained (FG) austenitic stainless steels (γ-SSs). Commercial Cr–Mn–N γ-SS was selected as the coarse-grained (CG) specimen, which was cold rolled and then annealed at 1000 °C for 60 s and 700 °C for 3600 s to obtain FG specimens with similar grain sizes but different grain size distributions. The CG specimens annealed at 1000 °C for 60 s and 700 °C for 3600 s were referred to as unimodal-FG and bimodal-FG specimens, respectively. The tensile properties revealed that the yield strength was enhanced from 383 MPa to 685 MPa when the grain size was refined from CG (10.7 μm) to FG (∼1.8 μm). Moreover, the bimodal-FG specimen exhibited a higher total elongation of 48% than 36.5% for the unimodal-FG specimen. Transmission electron microscopy, electron backscatter diffraction and X-ray diffraction were used to identify the microstructural characteristics during tension. The results indicated that the main deformation mechanisms of γ-SSs specimens during tension were dislocation generation and accumulation at the initial stage, deformation twinning at the intermediate stage, and deformation-induced martensite (DIM) at the final stage. Compared with the unimodal-CG counterpart, grain refinement in the unimodal-FG specimens restricted the formation of DIM due to the increased austenite stability. A newly discovered phenomenon was that the bimodal-FG specimens promoted the formation of geometrically necessary dislocation (GND) and DIM compared to the unimodal-FG, which was due to the uneven deformation in grains located on hetero-boundaries (HBs). Moreover, the bimodal-FG specimen was preferentially formed DIM on HBs, especially in the smaller grains side rather than inside larger grains due to the higher stress concentration in smaller grains.

Quantification of melt pool dynamics and microstructure during simulated additive manufacturing

The dynamics of laser spot melting and metallic alloy solidification are investigated through synchrotron x-ray radiography, 3D electron backscatter diffraction data, and computational fluid dynamics (CFD) simulations on a model NiMoAl alloy. Solidification velocities are measured from in-situ images to validate a CFD model of the spot melt. TriBeam tomography is used to reconstruct the melt pool in 3D, characterize the microstructure, and validate the CFD model melt pool dimensions. 3D geometrically necessary dislocation (GND) density calculations reveal extensive deformation at the sample surface. GND calculations integrated with the CFD model reveal that the halo of small, equiaxed grains adjacent to the fusion line is a result of recrystallization that occurred in the heat affected zone. By combining in-situ and ex-situ data modalities across a variety of temporal and spatial length scales, the microstructure formation mechanisms and their relationship to melt pool solidification are quantified.