Electron Backscatter Diffraction Research Articles

Research on microplastic deformation of Inconel718 under the conditions of high temperature and high strain rate

The compression experiments of the nickel-based superalloy Inconel718 were carried out with the help of split Hopkinson pressure bar device, and the microstructure evolution law in the compression deformation of the alloy was studied by means of optical microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the dislocation theory, a three-dimensional discrete dislocation dynamics model is established. By simulating the dynamic evolution of the discrete dislocation, the interaction of the dislocation itself and the formation of the dislocation microstructure were captured, and further explore the microplastic deformation process of Inconel718. The results show that deformation conditions significantly affect the rheological behavior and dynamic recrystallization behaviour. The cross slip of dislocations is closely related to temperature and strain rate, which in turn affect the dislocation configuration. The deformation mechanism of Inconel718 under the conditions of high temperature and high strain rate is jointly dominated by dislocation slip and twin deformation. As the temperature increases, the average Schmidt factor increases, and more dislocation slip systems are activated. As the strain rate increases, the number of deformation twins increases, while the thickness of deformation twins decreases.

The effect of retained austenite on rolling/sliding contact fatigue of high carbon steel

Rolling contact fatigue (RCF) is significantly influenced by retained austenite (RA). To study the impact of the RA on fatigue life and pit formation, a high carbon steel was tested with three different RA levels ranging from 5 % to 23 % (volume fraction). The variations of the RA with respect to the number of cycles and along the depth were inspected by X-ray diffraction (XRD) technique. The microstructures before and after RCF were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The majority of RA was transformed into martensite at an early stage (before 3×104 cycles) in both surface and subsurface. And the remaining small fraction of RA was transformed during the rest of the testing life, with a final content lower than 5 %. As the depth increased, the rate of RA transformation decreased. The specimen with the highest RA level of 23 % showed the shortest life. The longest RCF life was seen in the specimen with a medium RA level of 15 % due to the formation of the well-developed hardened layer, which helps resisting the pit formation. Based on these observations, it was suggested that a medium level of RA is beneficial for the improvement of the RCF life of the present high carbon steel. The combined effect of the hardness and the RA acts together on resistance to pit formation.

Microstructural Evolution and Phase Transformation on Sn–Ag Solder Alloys under High‐Temperature Conditions Focusing on Ag3Sn Phase

This study investigates the microstructural and phase transformations in Sn–Ag solder alloys under high‐temperature conditions, utilizing X‐ray diffraction, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) analyses. Analytical techniques are employed pre‐ and postcontrolled thermal cycling from 30 to 180 °C, aimed at emulating solder reflow processes. The analysis at room temperature demonstrates pronounced crystalline peaks, suggesting a preferred orientation within the crystal structure. Upon heating, peak broadening suggests grain growth and the onset of recrystallization. SEM and energy‐dispersive spectroscopy analyses corroborate these findings, displaying a fine‐grained, well‐distributed microstructure with a homogenous composition of Sn and Ag elements. EBSD provides insights into the orientation and texture of grains, revealing a weak‐to‐moderate texture across the phases. Postexperiment data indicate a dominant presence of larger grains and significant variation in grain size, with an area‐weighted mean grain size of 68.47 μm and a standard deviation of 8.68 μm; this suggests significant grain growth and coarsening of the Ag3Sn intermetallic compounds. These structural evolutions have crucial implications for the mechanical properties and reliability of the solder alloy in electronic assemblies, underscoring the need for further exploration of lead‐free solder materials in the electronics industry.

Quasi-in-situ observation of fatigue crack growth behavior of friction stir welded 2024-T4 joint

Abstract This study presents a quasi-in-situ observation of the fatigue crack growth behavior in a friction stir welded 2024-T4 joint. The microstructure and fatigue properties of the joint were investigated using electron backscatter diffraction (EBSD) technique, scanning electron microscopy (SEM), and fatigue crack growth tests. The fatigue crack growth behavior of the joint was examined by conducting fatigue crack growth tests with different notch locations. The results show that the sample with the notch in the stir zone (SZ) exhibited the highest resistance to fatigue crack growth, followed by the notched samples of the Advancing side (AS) and Retreating side (RS) weldments. Microstructural observations showed a homogeneous microstructure with a fine grain size in SZ and it was observed that this fine-grained structure significantly enhanced the material's resistance to fatigue crack growth. The experimental results were further analyzed using the Paris model to provide a quantitative understanding of the crack growth behavior. The study underlines the impact of microstructural characteristics and notch location on the fatigue performance of the weldment. Overall, the quasi-in-situ observations and experimental findings contribute to a comprehensive understanding of the fatigue crack growth behavior in friction stir welded 2024-T4 joints.

In-situ synchrotron diffraction analysis of deformation mechanisms in an AA5083 sheet metal processed by modified equal-channel angular pressing

Severe plastic deformation (SPD) is a process to significantly improve the mechanical properties of materials by grain refinement. For forming at room temperature (RT), higher strengths can thus be achieved; for increased temperatures (HT), greater elongations can be achieved. This great potential has been chiefly applied only on laboratory scale due to a lack of industrial process design. Equal-channel angular pressing (ECAP) offers the possibility to integrate these advantages in industrial processes. This paper investigates a modified ECAP process for aluminum AA5083 sheet metal. Two passes of ECAP for sheet metal and an additional heat treatment were used. To study the material deformation on a micro-scale, in-situ synchrotron measurements at DESY (Hamburg) were performed to analyze the evolution of lattice strains and dislocation densities during tensile testing. The mechanical properties of the ECAP-processed sheet material reveal an increase in yield strength and a decrease in elongation at RT. Higher strains can be measured for the processed material at elevated test temperatures. In-situ diffraction results show a changed behavior of the ECAP sheet material compared to the reference material for both temperature regimes. These changes are based on the increased defect density in the material, which leads to increased strength at RT. At HT, dynamic recrystallization occurs during tensile testing, and the prevailing deformation mechanisms reconfigure. Electron backscatter diffraction (EBSD) and micrographs are used to interpret and supplement the observations. The findings provide the basis for the in-depth understanding of the deformation behavior of the material and help to apply the ECAP process on an industrial scale.

Role of Ti element in the microstructure and corrosion behavior of nickel-based alloy 825

The influence of Ti content on the microstructure and corrosion behavior of nickel-based alloy 825 in acid oil and gas environments was studied. The pitting corrosion behavior and stress corrosion cracking (SCC) behavior of Alloy 825 were investigated using high-temperature and high-pressure immersion tests, electrochemical tests, and slow strain rate tensile tests. Scanning electron microscopy, electron backscatter diffraction, and 3D microscopy were applied to analyze the microstructure and corrosion performance of the samples. The results showed that the number of inclusions and residual strain increased with the increase of Ti content, and strain concentration was found around the inclusions. The rise in inclusions led to lower pitting potential and a narrower passivation interval. In addition, the enhanced SCC susceptibility of the alloy with higher Ti content may also be attributed to the increase in inclusions.

Twinning–Detwinning-Dominated Cyclic Deformation Behavior of a High-Strength Mg-Al-Sn-Zn Alloy during Loading Reversals: Experiment and Modeling

The deformation behavior of a high-strength Mg-Al-Sn-Zn alloy under loading reversals has been thoroughly examined through a combination of experimental measurements and crystal plasticity modeling. We focused on an age-treated alloy fortified by distributed Mg2Sn particles and Mg17Al12 precipitates, which underwent two distinct loading cycles: tension-compression-tension (TCT) and compression-tension-compression (CTC), aligned with the extrusion direction (ED). The initial and deformed microstructures of the alloy were analyzed using the electron backscattering diffraction (EBSD) technique. Notably, the alloy displays tensile and compressive yield strengths (YS) of 215 MPa and 160 MPa, respectively, with pronounced anelastic behavior observed during unloading and reverse loading phases. Utilizing the elasto-viscoplastic self-consistent model incorporating a twinning–detwinning scheme (EVPSC-TDT), the cyclic stress–strain responses and resultant textures of the alloy were accurately captured. The predicted alternation between various slip and twinning modes during plastic deformation was used to interpret the observed behaviors. It was found that prismatic <a> slip plays an important role during the plastic deformation of the studied alloy, and its relative activity in tensile loading processes accounts for up to ~66% and ~67% in the TCT and CTC cases, respectively. Moreover, it was discerned that detwinning and twinning behaviors are predominantly governed by stresses within the parent grain, and they can concurrently manifest during the reverse tensile loading phase in the TCT case. After cyclic deformation, the area fractions of residual twins were determined to be 7.51% and 0.93% in the TCT and CTC cases, respectively, which is a result of the varied twinning–detwinning behavior of the alloy in different loading paths.

Brittle initiation of dissolution–precipitation creep in plagioclase-rich rocks: insights from the Bergen arcs, Norway

The initiation of ductile shear zones commonly occurs spatially associated with fluid-rock reactions along brittle precursors. In many cases the relative timing of fracturing, fluid infiltration, reaction, and recrystallisation is unclear, making it difficult to disentangle mechanisms of shear zone initiation from subsequent deformation and recrystallisation. Here we present the study of the transition from a dry plagioclase-diopside-garnet-scapolite host granulite-facies lithology to (1) a low strain amphibolite-facies rock, and (2) a transition from low strain to high strain amphibolite-facies lithologies. Hydration of the granulite-facies precursor at amphibolite-facies conditions produces an assemblage comprised dominantly of plagioclase-amphibole-zoisite-clinozoisite-kyanite-scapolite-quartz. Detailed study of plagioclase chemistry and microstructures across these two transitions using Electron Backscatter Diffraction (EBSD) and Wavelength Dispersive Spectrometry (WDS) allows us to assess the degree of coupling between deformation and fluid-rock reaction across the outcrop. Plagioclase behaves dominantly in a brittle manner at the hydration interface and so the initial weakening of the rock is attributed to grain size reduction caused by fracture damage and fluid infiltration at amphibolite-facies conditions. Extensive fracturing-induced grain size reduction locally increases permeability and allows for continuing plagioclase and secondary mineral growth during shear. Based on plagioclase microstructures, such as, an inherited but dispersed crystallographic preferred orientation (CPO), truncation of chemical zoning, and the dominance of fine (5–150 µm), slightly elongate, polygonal grains we conclude that deformation is dominantly facilitated by dissolution–precipitation creep assisted by grain boundary sliding in the shear zone.

Effect of Cold‐Rolling Deformation on Texture Evolution and Tensile Properties of Titanium Foil for Hydrogen Fuel Cell

Preparation of a titanium foil with weak anisotropy is of great significance for the development of bipolar plate materials for hydrogen fuel cell. However, the titanium foil obtained by rolling deformation often suffer from a severe deformation anisotropy due to the formation of a specific texture feature. In this study, the texture feature of pure titanium foil with different cold‐rolling reduction is characterized by electron back‐scattered diffraction (EBSD), and the effect of cold‐rolling deformation on texture evolution and tensile properties of titanium hfoil are systematically investigated. The results show that the cold‐rolling reduction could significantly affect the tensile anisotropy of titanium foil by regulating the texture characteristics. At the low level of cold‐rolling reductions (0%–30%), the texture of titanium foil is mainly pyramid texture, causing the obvious tensile anisotropy. At the medium level of cold‐rolling reductions (50%), strong basal‐plane texture components are appeared, causing that the activated slip system along transverse direction (TD) or normal direction (ND) is almost the same, and thus the tensile anisotropy gradually diminishes. At the high level of cold‐rolling reductions (70%), the intensity of basal‐plane texture becomes weak, and the tensile anisotropy appears in titanium foil again. The findings could provide theoretical guidance and technical support for the preparation of weak anisotropic titanium foil for hydrogen fuel cell.

Microstructural Evolution and Mechanical Behavior of Pure Aluminum Ultra-Thin Strip under Roller Vibration

As the demand for lithium-ion batteries increases, higher quality requirements are being placed on pure aluminum ultra-thin strips, one of the main materials used in lithium-ion battery current collectors. Roller vibration during the rolling process of pure aluminum ultra-thin strips is unavoidable and significantly affects the quality of the strips. This paper uses 1A99 pure aluminum ultra-thin strips as raw materials and employs a controlled vibration method during the rolling process to obtain products under two conditions: stable rolling and vibrational rolling. The surface and cross-section of the aluminum strips were characterized using scanning electron microscopy (SEM), and the microstructure of the surface and cross-section was studied using electron backscatter diffraction (EBSD) technology. The results show that, during stable rolling, the surface quality of the aluminum strip is good without defects. Under vibration, obvious vibration marks appear on the surface of the aluminum strip, showing characteristics of peaks and troughs. With the increase in strain at the trough position, there is a transition from low-angle grain boundaries to high-angle grain boundaries, and the grain size is uneven at the peak and trough positions, with noticeable grain refinement at the troughs. At the same time, under the influence of vibration, the aluminum strip induces a different texture morphology from conventional rolling. Due to the different plastic strains at the peak and trough positions, a texture alternation phenomenon occurs at these positions. The tensile test results indicate that aluminum strips exhibit poor mechanical properties under roller vibration, with the reduction in mechanical performance primarily attributed to the uneven microstructure distribution caused by roller vibration.

Deciphering the Polymorphism of CaSi2: The Influence of Heat and Composition.

The Zintl phase CaSi2 is a layered compound with stacking variants known as 1P, 3R, and 6R. We extend the series by the 21R polytype formed by rapid cooling of the melt. The crystal structure of 21R-CaSi2 (space group R3̅m) was derived from HRTEM images, and the atomic positions were optimized by using the FPLO code (a = 3.868 Å, c = 107.276 Å). We explore polytype transformations by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and thermal analysis. While 6R-CaSi2 is thermodynamically stable at ambient conditions, nanosized impurities of silicon stabilize 3R-CaSi2 as a bulk phase.

Effect of heat treatment processes on the Cu-electrodeposited through glass vias (TGV) plate

Based on laser-induced deep etching technology and through-hole filling techniques, TGV interposers were successfully fabricated. The residual stress in the Cu overburden film directly affects the yield improvement after subsequent grinding of the interposer. Therefore, we studied the evolution of residual stress, microstructural changes, and micro-nano mechanical properties within the Cu overburden film after heat treatment at different temperatures. Residual stress analysis using the sin2Ψ method with an X-ray diffractometer (XRD) indicates that during the process of increasing temperature from 100°C to 200°C, the internal residual stress in the Cu overburden film changes from compressive stress to tensile stress. Furthermore, the maximum absolute value of the residual stress, 70.09 MPa, appears at room temperature, and the minimum absolute value of the residual stress, 15.59 MPa, occurs after the heat treatment process at 200°C. Electron backscatter diffraction (EBSD) microstructural analysis shows that the application of heat treatment can effectively accelerate static recrystallization (SRX), promote a higher proportion of high-angle grain boundaries (HAGB), and refine grain size. Additionally, a (001) preferred orientation at high residual stress states and a (111) preferred orientation at low residual stress states are observed. Nanoindentation test results indicate that the Cu overburden film treated at 100°C has the most potential for removal during the grinding process.

High-temperature tensile behavior and constitutive model in Co-free Fe40Mn20Cr20Ni20 high-entropy alloy

High-entropy alloys (HEAs) have attracted widespread attention from scholars as a new type of material employed in extreme environments. However, as a main kind of HEAs, many face-centered cubic single-phase HEAs are restricted in industrial applications due to their lower yield strength and high cost when containing expensive elements such as Co. In this study, dispersion strengthening by heat treatment was introduced in low-cost Co-free Fe40Mn20Cr20Ni20 HEA to improve its strength, and its high-temperature tensile behavior and constitutive model were studied to explore its potential application at high temperatures. It is found that when subjected to quasi-static room-temperature stretching, the heat-treated sample exhibits a yield strength of 534 MPa and a tensile plasticity of 26.8%. In addition, the tensile behavior of samples after heat treatment was investigated at high temperature (573–873 K) and low strain rate (10−3–10−1 s−1). The results suggest that the yield strength decreases with increasing temperature and decreasing strain rate. Moreover, at 873 K and 10−3 s−1, the electron backscatter diffraction system and x-ray diffraction results of the deformed sample indicate that the softening curve is driven from the recovery of materials. Finally, the flow stress was predicted using the Arrhenius equation and Artificial Neural Network model (ANN), and the two models were assessed using the average absolute relative error and coefficient of correlation (R). The results showed that the ANN had higher accuracy.

Weld interface metallurgy of dissimilar alloys welded by TIG technique

Abstract TIG welding is an important joining technique for fabricating quality structural components with industrial capability. Dissimilar alloy plates were combined using double-sided tungsten inert gas (TIG) welding. Microstructure evaluation of joints were anayzed by using scanning electron microscopy, optical microscope, energy dispersion spectrometry, elemental mapping, electron back scatter diffraction. DSAW technique increased joint penetration and reduced distortion of joints. In the weld metal zone, austenite, delta ferrite and lath martensite were dominant. The weld pool had high density of Cr7C3 and Fe3C phases and low density of CrFe7C0.45, FeNi, martensite, and Fe3Ni2 phases.

Unveiling the self-annealing phenomena and its effect on microstructure and texture evolution in the room temperature rolled Cu-0.13Sn-0.04Mg alloy

ABSTRACT In this study, we investigated the microstructural evolution of a Cu-0.13Sn-0.04Mg alloy that underwent heat treatment followed by room temperature rolling (RTR). Initially heat-treated specimens were rolled at room temperature (RT) with reduction ratios (RR) of 40% and 75% to perform microstructural and crystallographic textural analyses. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were utilise to examine both initial and deformed microstructures. Both exhibited heterogeneous microstructural distributions. Shear bands (SBs) existed in the initial specimen and became main sites for the nucleation of new grains during heat treatment. A denser presence of SBs was noted in the RTR specimens. Remarkably, an unusual self-annealing phenomenon was observed in these specimens, culminating in the emergence of recrystallized grains at RT. A plethora of such grains was observed in the severely deformed specimens, with numerous nucleating grains appearing proximal to the SBs or deformed grain boundaries (GBs). Time dependent microstructure evolution was observed via ex-situ EBSD technique in the compressed specimens. Formation of new grains, increase in high angle grain boundaries (HAGBs), and dislocation annihilations were observed with the progress of time. The crystallographic texture evolution in the initial specimen was predominantly influenced by the S component. At lower strains, the fractions of Copper component increased, whereas at higher strains, a greater fraction of Brass and S components were induced. Following a 40% RR, a saturation in hardness value was observed, which could be potentially attributable to an accelerated rate of RT recrystallization in the case of 75% RR.

Properties and Microstructure Regulation of Electrodeposited Ultra-thin Copper Foil in a Simple Additive System

Abstract Hydroxyethyl cellulose (HEC) has been commonly used in a variety of complex formulations for acid copper plating. However, the roles of HEC acting in acid copper plating still lacks of systematic investigation. To explore the efficacy of HEC in the deposition of the ultra-thin electrodeposited copper foil (ED-Cu), we designed a simple formulation system, in which HEC was used as the single organic additive. Using electron backscatter diffraction (EBSD), microstructures of the prepared ED-Cu was comprehensively investigated. The results showed that the ED-Cu was characterized by a mixed distribution of columnar and equiaxed crystals. Grain morphology, dislocation density and crystal orientation of the ED-Cu could be regulated by HEC concentration. According to the cyclic voltammetry (CV) and chronoamperometry (CA) results, the introduction of HEC between 0-200 ppm led to a polarizing effect, which marginally increased with the HEC concentration. Meanwhile, the increase of HEC concentration enhanced the nucleation rates of copper and reduced the grain size during instantaneous nucleation. The introduction of the HEC also altered the preferred orientation of the ED-Cu foil. Mechanical results showed that the optimum concentration of HEC addition was 125 mg/L.

Influence of Heat Treatment on Microstructure Evolution and Yield Surfaces of Ni/PU Hybrid Foams

Metal foams are characterized by low weight, high resource efficiency, high relative stiffness, and exceptional energy absorption capacity under compressive load. Nickel/polyurethane (Ni/PU) hybrid foams consist of an open‐cell polyurethane foam coated with a layer of nickel produced by electrochemical deposition. The coating of the PU foams takes place in a flow reactor, in which the electrolyte is pumped through the foam at a defined flow velocity. The macromechanical properties of foam‐like structures depend on the structure of the skeleton, the inherent material properties and, in the case of Ni/PU hybrid foams, the properties of the electrochemically generated nickel layer. To influence their mechanical properties, the Ni/PU hybrid foams are subjected to heat treatment. In the given experimental setup, the parameters flow velocity, temperature, and duration of the heat treatment are each investigated at two different levels. Thus, interactions between the initial microstructure and the type of heat treatment are evaluated by means of X‐ray diffraction (XRD) and electron backscatter diffraction (EBSD) measurements. Interactions between initial mechanical properties and heat treatment are investigated by uniaxial compression tests and superimposed compression‐torsion tests. The knowledge gained is used to control the macromechanical properties of the hybrid foam.

High-Grade REE accumulation in regolith: Insights from supergene alteration of an apatite-rich vein at the Kapunda Cu mine, South Australia

AbstractThe stratiform and vein-hosted Kapunda Cu deposit in South Australia contains a saprolitized hydrothermal vein with 12.37 wt.% total rare earth oxide (TREO). The vein was analyzed by X-ray diffraction, scanning electron microscopy, synchrotron-based X-ray fluorescence microscopy and electron backscatter diffraction to understand the controls that govern high-grade REE accumulation during periods of intense weathering. Petrological assessments indicate the transformation of an apatite-calcite-aluminosilicate-bearing protolith to a supergene assemblage of Fe-oxides, kaolinite and REE-phosphate minerals that include rhabdophane-(Ce), monazite-(Ce) and florencite-(Ce). This transformation was facilitated by progressive acidification of the weathering fluid, which is indicated by: 1) the increasing crystallinity of authigenic Fe-oxides and kaolinite, which led to REE desorption; 2) the textural evolution and increase in grain size of authigenic REE-phosphates from nanoscopic crystallites, to acicular needles, to micro-scale hexagonal prisms; 3) the late dissolution of REE-phosphates; and 4) the replacement of goethite by jarosite, whose sulfate component originated from the oxidation and weathering of proximal sulfide minerals. Alongside the depletion of pH-buffering carbonate minerals that are indicated by the preservation of calcite menisci, this sulfide dissolution also facilitated acid generation. Results illustrate how highly acidic weathering fluids might facilitate either REE mobilization or REE accumulation in regolith. High-grade REE accumulation under acidic supergene conditions is prioritized when the host-rock contains a significant source of depositional ligands (i.e., phosphate in the form of apatite) that can be readily leached during intense weathering. Exploration companies should therefore assay routinely for REEs in any heavily weathered phosphatic rock, due to the observed efficiency of phosphate minerals as geochemical traps for REE accumulation.

Igneous intrusion origin for the petrofabric of Erg Chech 002

AbstractAchondrites provide an opportunity to examine the igneous processes of differentiated bodies in our solar system. The recent discovery of several silica‐rich achondrites suggests that andesitic crusts were more common among planetesimals than previously thought, though the processes behind their emplacement are not well understood. Here, electron backscatter diffraction (EBSD) is used to investigate the igneous emplacement conditions of Erg Chech 002 (EC 002), a recently discovered ungrouped achondrite representing andesitic magmatism ~2 Myr after the formation of calcium–aluminum‐rich inclusions (CAIs). EBSD analyses of crystallographic preferred orientations (CPOs) for augite and plagioclase feldspar phenocrysts indicate that EC 002 exhibits a weak foliation CPO. Augite misorientation inverse pole figures (mIPF) indicate preferential slip along the (100)[001] system with a distinct shift toward the {0kl}[u0w] system in plastically deformed grains. Our findings support the hypothesis that EC 002 was likely emplaced in the lower regions of a magmatic intrusion. Augite slip signatures suggest that EC 002 crystallization and emplacement were restricted to high temperatures (>800°C) and experienced at least two strain regimes. The distinct shift from a dominant (100)[001] slip system, which corresponds to high temperatures (800–1050°C), to a [0kl][u0w] slip system indicates an increased strain rate due to shock deformation (1–5 GPa) attributed to ejection by hypervelocity impact.

Fatigue prediction through quantification of critical defects and crack growth behaviour in additively manufactured Ti-6Al-4V alloy

The study presents a methodology for predicting the fatigue life and identifying critical defects in additively manufactured (AM) Ti-6Al-4V alloy processed via laser powder bed fusion (L-PBF). Predictions were made on L-PBF Ti-6Al-4V alloy in two conditions: as-built and heat-treated by using X-ray μ-Computed Tomography (μ-CT) for the quantification of the defects and fatigue crack growth (FCG) data. For validation, fatigue life predictions were made on the same specimens on which μ-CT was conducted prior to fatigue testing. FCG and fatigue tests (S-N) highlighted differences in the performance between the as-built and heat-treated conditions: the as-built condition had a lower threshold stress intensity factor range (ΔKth) of 2.16 MPa m1/2 than that of the heat-treated condition, 4.96 MPa m1/2. Differences in fatigue limit were attributed to differences in ΔKth in as-built and heat-treated specimens. To gain mechanistic understanding of these differences near ΔKth cracks were examined using Electron Backscatter Diffraction - Kernel Average Misorientation (EBSD-KAM). It was found that upon heat treatment, the dislocation density increased around near threshold fatigue cracks. Increases in ΔKth are attributed to the increases in β-phase content and α-lath thickness caused by heat treatment.