Parent Grains Research Articles

Ascertaining the deformation accommodation of a novel Ti-652 alloy by tracking the evolution of slip traces and lattice strain

The exploration of slip modes in metallic materials during deformation has been long suffered from either insufficient statistical accuracy of slip trace analysis or limited spatial resolution by X-ray diffraction. In this work, a combination of slip trace analysis based on in-situ Electron Backscatter Diffraction (EBSD) and lattice strain analysis supported by in-situ Synchrotron Radiation High-Energy X-ray Diffraction (SR-HEXRD) was employed to determine the deformation accommodation mechanisms of a new developed Ti-6Al-5Mo-2Sn-0.3Si-0.5 V (Ti-652) alloy. Different from conventional cases, it was surprisingly found that pyramidal (101̅1)α slip is easier to be initiated than prismatic (101̅0)α within α grains, resulting in the dominant slip modes evolving from prismatic <a> to pyramidal I <c+a>. In addition, in-situ EBSD results show that slip can transfer across grain boundary (GB) in counterintuitive situations with low geometric compatibility factor m′ of 0.5, or with GB misorientations in the range of θ≥24.5°, which are contractive to the slip transfer criterion in hcp structures. Further detailed crystallographic analysis revealed that specific slip transferred across GBs with 24.5°≤θ≤60° because of high Schmid Factor (SF) values, while with θ>60° slip transfer occurred by activating another slip systems. The accumulation of multi-mode slip dislocations induced by deformation accommodation with different phases was suggested to promote the formation of sub-GBs within the deformed parent grain. These findings provide insights of the slip behaviors and property tailoring in Ti alloys.

The dependence of Zener-Hollomon parameter on softening behavior and dynamic recrystallization mechanism of a biodegradable Zn-Cu-Mg alloy

The Zn-Cu-Mg alloy exhibits good strength, ductility, anti-aging and antibacterial properties, which lays the foundation for developing high performance Zn-based biodegradable alloys. However, the constitutive equation and dynamic recrystallization (DRX) behavior of this alloy remain unclear, making the optimization of hot processing parameters almost dependent on trial and error. This work aims to address these issues by investigating the hot compression process. The calculated average activation energy Q of this alloy is 141.338 KJ⋅mol-1, exhibiting excellent heat resistance. The deformed microstructure strongly depends on the Zener-Hollomon parameter (Z=ε˙exp(QRT)). Discontinuous DRX (DDRX) dominates at low lnZ, which has a significantly different orientation from the parent grain. Continuous DRX (CDRX) occurs within the grain and at grain boundaries, and is dominant at middle lnZ, mainly through activation 〈a〉 or/and 〈c+a〉 slip systems. Additionally, the activation of prismatic slip further promote CDRX, and most CDRX grains inherit the 30°[0001] orientation from the parent grains. The volume fraction of DRX demonstrates a decreasing trend followed by an increasing trend with increasing lnZ. At high lnZ, the increase of DRX grains is conducive to weakening the texture, and twin-induced DRX (TDRX) is significantly promoted, leading to an increase in both peak stress and strain hardening rate. Furthermore, the grains with c-axis aligned parallel to the compression direction (CD) are more prone to twinning, while the c-axis perpendicular to CD are the hard orientation of basal slip and compression twins. TEM results reveal that a decrease of c/a value promotes the activation of non-basal slip near the twin boundary, and the highly active 〈c〉 and 〈c+a〉 slips contribute to the increase of strain hardening rate. The results of this study are significant for understanding the workability of Zn-Cu-Mg alloys at high lnZ due to its high efficiency and low cost.

The texture evolution near the shear band and corresponding impact on the microvoid nucleation and crack propagation of Ti6242s alloys under high strain rates

This study investigates the texture evolution near the adiabatic shear bands (ASBs) and its impact of on the adiabatic shear failure mechanism, focusing on microvoid nucleation and crack propagation in Ti6242s alloy with an equiaxed α microstructure under high strain rates, using a split Hopkinson pressure bar (SHPB) for the experiments. To achieve this, the initial microstructure was used to enable the texture with the c-axis perpendicular to the loading direction. After compression, the initial texture transformed into two main texture components through different mechanisms. One texture component, aligned parallel to the loading direction, is strongly associated with the {10 1‾ 2} tensile twins, which were widely distributed near the ASBs with their c-axis are 85° to the parent grains in the initial microstructure. The other texture component, with its c-axis perpendicular to the ASB, is formed by the basal slip activation during adiabatic shear deformation. Besides, it should be noted that twinning resulted in the formation of hard grains (with the c-axis of α-grains parallel to the loading direction), increasing the number of hard-soft grain boundaries. A key finding of this paper is the presence of numerous microvoids near the ASB mainly initiated at soft-hard grain boundaries (approximately 65 %), attributed to stress concentration at the boundaries of soft-hard grains, making these boundaries potential nucleation sites for microvoids. Additionally, basal slip bands in the equiaxed α grains provide rapid channels, accelerating the crack propagation rate. This study provides new insights into refining the adiabatic shear failure mechanism under dynamic loading.

Novel Fe-Mo intermetallic composite synthesized via diffusional-displacive mixed-mode transformation

Transition metal-based intermetallic materials are candidates for high-temperature structural applications. However, they are limited by their low fracture toughness at ambient temperature. Given Fe is a low-cost metal with a low environmental impact, it is necessary to design tough Fe-based intermetallic alloys. We report a novel ferrite-Fe2Mo intermetallic synthesized through arc melting and quenching of Fe0.78Mo0.22 alloy. Diffusional-displacive mixed-mode transformation of the parent ferrite phase resulted in the formation of nanocomposite microstructure. Two distinct microstructure morphologies of the product μ phase were observed: (i) allotriomorphic phase formation at the parent ferrite grain boundaries and (ii) formation of basket-weave Widmanstätten structures at the parent grain interior. Electron probe microanalysis (EPMA) revealed Mo partitioning across ∼800 nm wide Widmanstätten laths, establishing that it is a diffusional-displacive mixed-mode transformation. We performed atom probe tomography (APT) investigations to ascertain the nanoscale Mo solute partitioning. Based on the chemistry of the retained parent ferrite, the Mo partitioning temperature was estimated to be ∼865 °C. Mo partitioned Widmanstätten lath formation is clarified using a shear-assisted diffusional transformation model. APT studies further revealed that the composition of the product μ phase corresponds to stoichiometric Fe2Mo. It is an anomaly since stoichiometric Fe2Mo typically corresponds to λ C14 Laves phase. We explain the mechanism of μ phase formation with Fe2Mo stoichiometry. The nanocomposite exhibits a high hardness (HV2) of 7.54 GPa and excellent toughness (evidenced by resistance to indentation cracking).

Tuning microstructures and tensile properties of the CoNiV medium entropy alloy by minor alloying

The effects of alloying with only 1 at% Al or Nb on the microstructures and mechanical properties of a CoNiV medium entropy alloy (MEA) (i.e., (CoNiV)99M1) have been systematically investigated. Thermodynamic calculations suggest the σ-phase formation temperature is increased from 1143 K in the CoNiV MEA to 1186 K and 1195 K when alloyed with Al and Nb respectively. Similar to the parent CoNiV MEA, solid-solution and grain boundary strengthening contribute immensely to the yield strength of the alloys. In addition, the σ precipitates in the (CoNiV)99Nb1 MEA provide an extra strengthening effect which demonstrates the potential for secondary-phase strengthening of the CoNiV MEA. Our findings reveal that the microstructure tuning capabilities of CoNiV alloys can be harnessed by minor alloying strategies to affect their mechanical properties.

Activation of contraction twins during compression and related texture characteristics in α-titanium

This work demonstrates that axial compression along 0002and101¯0 in individual grains of α-Titanium can effectively activate up to six variants of 112¯2112¯3¯ contraction twins (CT). Compression parallel to 101¯0 primarily introduces 101¯2101¯1¯ type extension twins (ET), orienting the c-axis almost along the compression axis. Further compression activates up to six 112¯2112¯3¯ CT variants, each with a specific orientation having Euler angles of (0°−60°+n60°, 63.5°, 30°), where n is the sequence number of the CT variant. All six CT variants may not be activated during uniaxial compression due to the deviation of the parent grains' c-axis from the compression direction (CD) and deformation heterogeneities. The nucleation and interaction of CT variants lead to the formation of coincident site lattice boundaries with characteristics (θ−uvtw) angle axis pair of 63.5°101¯0−∑7b, 51.2°11¯00−∑23a, 60°112¯1−∑19b, and 77.3°18¯70−∑17b. The activation of multi CT variants and their interaction can contribute to grain fragmentation and texture weakening. From statistical analyses, the nucleation and growth of CT variants appeared to follow the Schmid law. However, deviations from the Schmid behavior occurred by the activation of low Schmid factor CT variants and could be attributed to slip and twin activities in neighbor grains.

Parameter optimization and anisotropy mechanism in different build directions of the microstructures and mechanical properties for laser directed energy deposited Ti6Al4V alloy

The effects of laser power, scanning speed, and build directions (BDs) on the microstructural evolution and mechanical properties of laser directed energy deposited (LDEDed) Ti6Al4V alloy were systematically investigated in this study. All the finished LDED specimens were not heat treated and the tensile properties were not influenced by surface roughness. Particularly, the differences in grain size, grain boundary distribution, geometrically necessary dislocation (GND) density, grain orientation spread (GOS), and Schmid factor (SF) of the specimens in different BDs were investigated by scanning electron microscopy, electron backscattering diffraction, transmission electron microscopy, and tensile test. The results showed that the aspect ratio, dilution rate, and deposition angle all tended to increase with increasing laser power and scanning speed. The yield strength and the ultimate tensile strength decreased with the increase of laser power, while the elongation was the opposite. The parent grain reconstruction results indicated that the high-temperature transition phase (β phase) of the 0° LDEDed specimen was equiaxial, whereas that of the 90° LDEDed specimen was columnar. The differences in the β phase of the specimens in different BDs were directly inherited to the corresponding low-temperature sub-phase (α phase), resulting in finer grain sizes, greater GND density, larger GOS, and smaller SF in the 0° LDEDed specimen, thereby contributing to higher strength and hardness. In contrast, these values were reversed for the 90° LDEDed specimen, resulting in better plasticity and toughness. Finally, the anisotropy mechanism of the microstructures and mechanical properties of the LDEDed Ti6Al4V alloy in different BDs were revealed. This work could provide more systematic and comprehensive guidance in parameter optimization and offer valuable insights into the anisotropy mechanism of the microstructures and mechanical properties of LDEDed Ti6Al4V alloy.

The strength contribution via heterostructure in a Mg-Gd-Zn-Mn alloy

Deformation by extrusion is an effective means to enhance the performance of magnesium alloys. However, the resulting microstructure heterogeneity always lead to poor plasticity. Therefore, it is crucial to explicit the impact of heterogeneous structure on the deformation mechanism of the alloys. In this work, the microstructures evolution, mechanical properties, and fracture mechanism of Mg-xGd-1Zn-0.5Mn (x = 0, 2, 4, and 6) alloys were investigated. The elongation reached its maximum (40%) when the Gd content was 2%, which was attributed to the formation of the RE-texture and grain refinement. As the Gd content was further increased, the alloy developed a heterostructure consisting of both undynamic recrystallization (UDRX) grains and dynamic recrystallization grains (DRX). The exist of the heterostructures resulted in an increased strength which was attributed to the influences of texture strengthening derived from UDRX grains, the lamellar LPSO fiber strengthening and fine grain strengthening of DRX grains. At the initial stage of deformation in the heterostructure, the basal slip of DRX grains play a dominant role, while the UDRX grains strengthens the alloy effectively. The lamellar LPSO precipitated in the UDRX grains suppressed twinning effectively. As the concentrated stresses were enough to break through the barrier for twining of LPSO, numerous twins nucleated in the deformed grain thus resulting in the nucleation of cracks. During the process of tensile deformation, twins experienced greater basal slip resolved shear stress than that of the parent grains, resulting in significant basal slip activated due to twin. Consequently, there was a high stress concentration at the twin boundaries, leading to the nucleation of cracks. The varied deformation amount also resulted in the crack initiating at the interface of DRX grain and UDRX grain. This investigation provides valuable insights into the influence of a heterostructure on the deformation mechanism of Mg-Gd-Zn-Mn alloys.

Static recrystallization behavior of biomedical Co-29Cr-6Mo-0.16 N alloy with negative stacking fault energy

Static recrystallization (SRX) behavior of Co-29Cr-6Mo-0.16 N (CCMN) alloy subjected to a prior compression to 30% at room temperature and a subsequent annealing at 1000 °C was ex-situ observed by using an electron backscatter diffraction (EBSD). Ascribed to the large negative stacking fault energy of the alloy at room temperature, it was found that the microstructure of alloy compressed at room temperature is characterized by plenty of intersected strain-induced martensitic transformation (SIMT) ε phase bands with a mean interval of 2–3 μm, which divided the parent grains into fine pieces surrounded by high angle boundaries (HABs). The static recrystallization of CCMN alloy in the subsequent annealing at 1000 °C takes place in terms of transient transition of the HABs into Σ3n boundaries and reorientation of new grains.

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 &lt;a&gt; 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.

Microstructure and texture evolution in AZX311 Mg alloy during in-plane shear deformation

The current study examined the deformation mechanisms, microstructure, and texture evolution in AZX311 Mg alloy sheets subjected to in-plane shear (IPS) deformation. Different levels of shear strains, with values 0.05, 0.10, and 0.15, were applied along the rolling direction (RD) using a specialized in-plane shear testing jig. The strain measurement for the applied shear deformation was conducted utilizing the digital image correlation (DIC) technique. The strain distribution was found to be nearly homogeneous over sufficiently large areas, thereby allowing the microstructural measurements to yield relevant statistical data. A thorough microstructural examination across the thickness using electron back-scattered diffraction (EBSD) revealed that the application of IPS strain led to the formation of a significant number of tensile twins (TTWs) in the sheet. This was evidenced by the emergence of two satellite peaks at the periphery of the pole figures. As the shear strain increased, the proportion of TTWs in the material also increased, encompassing the entire parent grain and leading to the formation of what has been termed as “all-twinned microstructure”. The microstructural and texture investigation after IPS deformation revealed that TTWs were the dominant deformation mechanism that defined the microstructure and texture under IPS deformation, while dislocation slip activity was dominated by prismatic slip, as evidenced by the resolved shear stress analysis in this study. Consequently, this research highlights the effect of IPS deformation on the microstructure and texture evolution throughout the thickness of an Mg alloy sheet and elucidates the underlying mechanisms.

In-situ EBSD analysis of hydride phase transformation and its effect on micromechanical behavior in Zircaloy-4 under uniaxial tensile loading

In this work, hydrogen charged Zircaloy-4 has been investigated under an in-situ electron backscatter diffraction during tensile loading. Aim were, first, to distinguish the hydride phase type and its spatial distribution, second to determine hydride phase transformation (HPT) and orientation relationship (OR) subjected to uniaxial tensile condition, and third to correlate the hydrides evolution and their effect on the micromechanical behavior, such as slip mode activation and lattice rotation, of Zircaloy-4. Apart from the applied stress, the analysis reveals that hydride reorientation is strongly related to temperature and loading mode. We noted that deformation induced δ-ZrH1.5 transformed to γ-ZrH and ε-ZrH2, and the former follows the confirmed OR {0001}α//{111}δ/γ with <11 2‾ 0>α//<110>δ/γ, while the latter's OR changed to {10 1‾ 0}α//{121}ε with <11 2‾ 0>α//<100>ε after HPT. The coexistence of δ-ZrH1.5 and γ-ZrH or ε-ZrH2 is observed, and the main corresponding OR is {111}δ//{111}γ with <121>δ//<121>γ, and {100}δ//{110}ε with <110>δ//<100>ε, respectively. The characterized microstructure and the measured lattice rotation results indicate that HPT delayed cracking in hydride and promoted deformation in parent grains. As the strain increases, the maintenance of hydride-matrix (H-M) coherent interfaces restricts further lattice rotation. HPT accelerates the hydride decomposition ascribed to the intensification of hydrogen diffusion under stress, and the hydride and the H-M interfaces act as priority sites for initiating microcracks. The sequence of HPT depends on the possibility of activated slip mode among grains. These findings contribute to developing the understanding of the HPT and hydrogen embrittlement.

Developing a novel Mg[sbnd]2Zn[sbnd]3Li[sbnd]1Gd alloy sheet with high room-temperature formability by introducing an elliptical texture distribution

In recent years, modification of texture distribution has been considered a valid approach to improve the room-temperature (RT) formability of magnesium (Mg) alloys. In this study, a novel Mg2Zn3Li1Gd alloy sheet with weak elliptical-texture was fabricated by cold rolling and subsequent annealing, and it showed an excellent Erichsen (IE) value near 7.1 mm. Both quasi-in-situ electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis indicate that considerable basal and pyramidal dislocations can be activated in the cold rolling process. During annealing, these dislocations can induce nucleation and then cause preferential misorientation relationships around 〈uvt0〉 concerning the nuclei and parent grains, which can facilitate the formation of elliptical texture. Furthermore, the particle-stimulated nucleation (PSN) mechanism and the co-segregation of Zn and Gd at grain boundaries (GB) further weak texture intensity. Finally, the mechanical properties of the Mg2Zn3Li1Gd alloy sheet are significantly improved.

Multimaxima crystallographic fabrics (CPO) in warm, coarse-grained ice: New insights

Multimaxima crystallographic c-axis fabrics (CPOs) commonly observed in coarse-grained ice have been interpreted in several different ways but remain enigmatic. We review previous interpretations of these fabrics and present new data from Storglaciären, northern Sweden, for comparative purposes using both U-stage methods (c-axes only) and electron backscatter diffraction (EBSD) (both c-axis and a-axis orientations). Consistent with most previous studies, microstructures in our study indicate that all grains have been dynamically recrystallized with grain boundary migration as the dominant process. The CPO is characterized by grains oriented favorably for easy glide on the basal plane, given the local kinematics. When a representative sample is obtained, areas on the glacier margin undergoing non-coaxial deformation have a CPO generally consistent with simple shear. Multimaxima CPOs developed in the center of the glacier, which is associated with more coaxial deformation, likely represent a small circle girdle or partial girdle fabric associated with flow-parallel compression. In both locations, sampling bias, resulting from repeat measurements of single parent grains appearing several times as “island grains” in a 2D thin section, is likely responsible for the observed multiple maxima that, with bias removed, simplify to patterns expected for simple shear or coaxial deformation. An earlier study suggesting that multimaxima CPOs may result from twinning is not borne out from our data combining c-axes and a-axes that do not show the symmetry required of twinning.

In Situ Pure Shear Tests on Textured Magnesium AZ31B Sheets

Pure shear tests of textured magnesium AZ31B sheet samples were carried out using a 5 kN Kammrath &amp; Weiss in situ tension-compression stage in a scanning electron microscope in combination with real-time electron backscatter diffraction lattice orientation mapping. The sample design was optimized to produce a pure shear stress in the central gauge zone. Distributions of the deformation twins were correlated with finite element simulations using a linear-elastic constitutive law considering large deformations to show that twins form in areas where the principal compressive stress σ3* is a maximum and that they form normal to the trajectories of that minor principal stress. Mappings of the same area at different load values revealed the formation and growth of individual twins and their relationship to the internal elastic strain of individual grains as indicated by the internal grain disorientation. All twins observed were of the extension type, with an 86.3° disorientation with respect to the parent grains. A more detailed study was conducted using transmission electron microscopy to correlate with the EBSD observations and to further elucidate the twin structures within samples.

Analysis of dynamic recrystallization through austenite grain reconstruction of additively manufactured martensitic M789 steel

This work examines the hot compression behavior of additively manufactured M789 steel via laser powder bed fusion (LPBF) at temperatures ranging from 850 °C to 1050 °C and strain rates between 0.01 s-1 and 1 s-1. Combined corrections for friction and deformation heating were applied to the flow curves to acquire accurate stress-strain data, followed by phenomenological and physical-based constitutive modelling. In particular, the application of Sellars and Tegart hyperbolic sine model, the Kocks-Mecking model and the Johnson-Mehl-Avrami-Kolmogorov equation facilitated the development of physical material models that accurately depict the behavior of LPBF-fabricated M789 steel, highlighting the inadequacy of traditional models, such as the modified Johnson-Cook model, in capturing the complexities and metallurgical phenomena associated with high-temperature deformation. The activation energy for deformation of M789 steel was determined to be lower than that of conventional M250 steel, indicating an accelerated recrystallization process at elevated temperatures. The study also introduces a novel quantitative analysis of dynamically recrystallized grains via combined austenite parent grain reconstruction (based on the Kurdjumov-Sachs orientation relationship combined with the Markov clustering technique) and shape factor measurements, confirming the occurrence of dynamic recrystallization (DRX). The findings suggest that DRX more readily occurs at higher strain rates and higher deformation temperatures, whereas at lower temperatures, a lower strain rate is preferred to generate a higher fraction of DRX grains along with finer grains. Additionally, the work indicates that specific variants from the Kurdjumov-Sachs orientation relationship are favored during the solidification process in LPBF, which seem to disappear when the alloy is subjected to its austenitization temperature.

Simultaneous enhancement of mechanical and functional properties by heat-treatment in CuAlNi shape memory alloys fabricated by laser powder bed fusion

Laser powder bed fusion (LPBF) is a promising manufacturing method for fabricating Cu-based shape memory alloys (SMAs), but further performance improvement is needed to ensure service stability and broaden the engineering applications. To achieve simultaneous enhancement of mechanical and functional properties of CuAlNi ternary SMAs fabricated via the LPBF process, this study conducts isochronous and isothermal quenching treatments to tailor the microstructure. The heat-treated specimens with a high quenching temperature and long soaking time exhibited high ultimate tensile strength of 696 ± 10 MPa, large ductility of 8.9 ± 0.2%, and excellent recoverable strain under 2% pre-strain with a shape recovery rate of 100%, which were considerably superior than those of as-built specimens (ultimate tensile strength of 612 ± 10 MPa, elongation of 2.6 ± 0.1%, and 1.26% recoverable strain). This is attributed to the element homogenization during heat treatment, release of residual stress, and coordinated martensite network boundary. However, no significant strain platform of martensite reorientation or detwinning was found in the tensile deformation of the as-built and heat-treated samples, due to localized strain concentration in the parent grain. The microstructural evolution under different quenching treatments and the underlying mechanisms for the improvement of mechanical and functional properties are discussed in detail. This work not only reveals the unique functional response of LPBF fabricated Cu-based SMAs, but also provides a simple and effective method to improve their performance.

Prior austenite grain measurement: A direct comparison of EBSD reconstruction, thermal etching and chemical etching

It is well known that the prior austenite grain (PAG) microstructure of steels has a significant impact on their microstructure evolution and mechanical properties. Many PAG measuring techniques have been developed over many decades, with the effectiveness of each varying alloy-to-alloy. Some of the more common techniques, specifically for bainitic and martensitic grades, are thermal etching and picric acid etching, which both involve the preferential etching of PAG boundaries in order to reveal the austenitic microstructure. More recently, parent grain reconstruction techniques using EBSD (electron backscatter diffraction) mapping have shown good promise in recreating PAG microstructures from BCC-FCC orientation relationships, and can now be deployed at speed with the advent of rapid detectors (1000s of pixels per second). This study aims to compare the accuracy and relative advantages/disadvantages of picric acid etching, thermal etching and EBSD reconstruction methods. A TESCAN and NewTec In-Situ Testing (TANIST) capability was used to directly observe and measure the true high-temperature PAG structure during the austenitisation of SA-540 B24 low alloy steel. These high-temperature PAG measurements were then compared to measurements from the same area obtained using thermal etching, picric acid etching and EBSD parent grain reconstructions after quenching to room temperature. Reconstructing the parent austenite grains from EBSD data resulted in the closest measurement of PAG size. PAG boundaries were delineated well by thermal etching but surface effects (such as surface relief and ghost traces) created complexities when identifying the exact position of boundaries. Picric acid etching, which produced the least accurate measurement, was found to reveal PAG boundaries well, however it was limited by its ability to sufficiently etch annealing twin boundaries and its susceptibility to microsegregational effects. EBSD reconstruction and thermal etching were more consistent at reconstructing/revealing these boundaries, although inaccuracies with the techniques were still observed.

Parent Grain Reconstruction in an Additive Manufactured Titanium Alloy

Electron backscatter diffraction (EBSD) is an excellent tool for characterizing the crystallographic orientation aspects of the microstructure of polycrystalline material. In some additively manufactured materials, the material may undergo a phase transformation during the forming process. Although EBSD can only characterize the final microstructure, neighbor information from orientation mapping allows the microstructure before the phase transformation to be reconstructed, provided that the parent–child orientation relationship is known. An investigation of the effectiveness of the reconstruction algorithms for capturing the grain size as well as orientation gradients is undertaken with a focus on additively manufactured Ti-alloy. The EBSD results, coupled with reconstruction algorithms, reveal information on the prior grain size as well as the plastic flow of the material.

In Situ Uniaxial Compression of Textured Magnesium AZ31B

Strain-controlled uniaxial compression tests on textured magnesium AZ31B sheet samples were carried out using a 5 kN Kammrath &amp; Weiss tension–compression in situ stage using a scanning electron microscope in combination with real-time electron backscatter diffraction lattice orientation mapping. The distribution of deformation twins in the samples was studied and correlated with the results of finite element simulation of the elastic strain to show that bands of twinned grains formed in areas where the principal compressive stress (σ3) was a maximum, and they formed normal to the trajectory of the principal direction of σ3. This was correlated with maps of lattice disorientation within the grains, which showed the inclination for twins to grow in alignment with local and larger-scale distributions of elastic strain. Mappings of the same area at different values of strain were made to examine the formation and growth of individual twins within the macroscopic bands of twinned grains. All the twins observed were consistent with the extension-type twin, with 86.3° disorientation with respect to the parent grain. Mappings of the grain internal disorientation were related to the elastic strain, and it was found that twin formation and growth followed the contours of the highest elastic strain within and across grains. The maximum angular disorientation found within the grains was approximately 10°, suggesting that this might correspond to a threshold of elastic strain required to initiate twinning.