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We present a machine learning based surrogate modeling method for predicting spatially resolved 3D crystal orientation evolution of polycrystalline materials under uniaxial tensile loading. Our approach is orders of magnitude faster than the existing crystal plasticity methods enabling the simulation of large volumes that would be otherwise computationally prohibitive. This work is a major step beyond existing ML-based modeling results, which have been limited to either 2D structures or only providing average, rather than local 3D full-field predictions. We demonstrate the speed and accuracy of our surrogate model approach on experimentally collected data from a face-centered cubic copper sample undergoing tensile deformation.

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Hydrogen uptake causes hydride formation, lattice strains and other crystallographic changes in Ti6Al4V. To monitor these changes and understand them better, we developed an in situ hydrogen-charging setup for transmission X-ray diffraction, and employed it at a high-energy synchrotron X-ray source. We observed anisotropic lattice expansion by H ingress, as well as hydride formation induced microstrain evolution in both phases. The hydride phase was also crystallographically characterized, including its orientation relationship with the neighboring phases, employing electron backscattered diffraction analysis. Further applications of the presented methodology to investigate H-microstructure interactions are also discussed.

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μ topologically close-packed phase commonly forms in superalloys and its intrinsic deformation is critical for their performance. Atomic configurations of planar defects in μ phase have been investigated by aberration-corrected scanning transmission electron microscopy and geometrical structure analysis. It is found that the basal slip in μ phase is accomplished by synchroshear inside Laves triple-layers, whereas shear deformations on non-basal planes are associated with long-range diffusions or local atomic rearrangements. Distinct from that on (11¯02) pyramidal planes, displacement vectors of planar faults on (1¯101) pyramidal planes deviate from the slip plane, leading to the contraction or dilation faulted regions.

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The promising results of deep learning in image recognition suggest a huge potential for microscopic analyses in materials science. One major challenge for its adoption in the study of materials is the limited number of images that are available to train models on. Herein, we present a methodology to create accurate image recognition models with small datasets. By explicitly taking into account the magnification and by introducing appropriate transformations, we incorporate as many insights from material science in the model as possible. This allows for a highly data-efficient training of complex deep learning models. Our results indicate that a model trained with the presented methodology is able to outperform human experts.

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The role of elemental partitioning between β and ω phase in embrittling an originally ductile ω-containing Ti–12Mo (wt.%) model alloy was studied using transmission electron microscopy and atom probe tomography. It is revealed that the embrittlement of this alloy already occurs after aging at 400 °C for as short as 10 min, when the size, inter-particle spacing and volume fraction of the ω particles remain almost unchanged. The origin of the aging-induced embrittlement is attributed to the significant rejection of Mo (>5 at.%) from the ω particles during aging, which leads to remarkable increase in the shear modulus (>30 GPa) of the ω particles, promoting intense plastic flow localization and facilitating crack nucleation prior to macroscopic yielding.

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We report on a methodology of powder sintering and in-situ press forging, which can be used to manipulate a new bimorphic microstructure in Ti-6Al-4V alloy. The microstructure contains typical triangle colonies with ultrafine lamellar α and β, and their border areas with ultrafine equiaxed α, dispersed nano/ultrafine β, as well as α/β interface L layers. Surprisingly, the bimorphic alloy exhibits excellent mechanical properties under both tensile and compressive conditions, far superior to other Ti-6Al-4V alloys and their composites reported so far. Therefore, this innovative methodology provides a simple and economical method for preparing high-performance metallic alloys in structural applications.

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New insight into the microstructural evolution and the correlative damage mechanisms near fatigue crack tip in a TiB₂/Al composite was conducted by transmission kikuchi diffraction and transmission electron microscopy. It was found that the micro deformation band formed from the crack tip and ran along slip planes. Ultrafine grains were induced in deformation band, where the fatigue crack preferring to grow along these deformation-induced boundaries was first demonstrated as the essential process of crack across parent grains and grain boundaries. Ahead of crack tip, the TiB₂ particles can affect crack growth by impeding the successive propagation of deformation band.

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Synchrotron X-ray microtomography and ptychography were used to characterize the 3D network structure, morphology and distribution of metal carbides in an as-cast IN713LC Ni superalloy. MC typed carbides were found to distribute mainly on the grain boundary between the matrix γ and γ' phase. The differences in solidification cooling rate had a minor influence on the volume fraction of the MC type carbides, but significantly affected the carbide size, distribution and network morphology. Depending on the local composition of the remaining liquid phase and geometric constraints, the carbides can form either spherical or strip or network morphologies. The research demonstrated clearly the advantage and technical potential of using the two complementary tomography techniques synergistically to characterize non-destructively complex multiple-phase structures in three dimensional space with a spatial resolution of ~30 nm.

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Heterogeneous microstructures have been proposed to optimize the mechanical properties in the respect of strength and ductility synergy in many alloy systems. In this work, the multi-phase hetero-structured microstructure consisting of fine grains and coarse grains where the ferrite is embedded in the vicinity of the nano-grains was obtained by regulating the thermomechanical processing parameters. A yield strength of 1.2 GPa which is more than two times higher than the coarse grained counterpart with less uniform elongation loss is achieved in the multi-phase hetero-structured steel. The microscopic load transfer in this complex microstructure is investigated by the in situ high energy synchrotron X-ray diffraction. The persistent strain hardening is ascribed to the hetero-deformation induced stress associated with the joint activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects. As a comparison, the single-phase hetero-structured steel exhibits little lower strength but higher uniform ductility.

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We propose a new approach for the high-throughput experimental evaluation of the phase stability, mechanical and oxidation properties of a Ni-based superalloy. The Bridgman method is used to introduce the gradation of nine elements in a long distance (∼24 mm) and a wide range of microstructural features with η, μ and γ’ phase volume fractions in one sample. Nanoindentation and microstructural observations are utilized to extract the elastic modulus/hardness of a γ-γ’ two-phase structure and evaluate the oxidation layers in an oxidized sample. Our approach makes it possible to obtain huge number of datasets linked to the composition and microstructure of the superalloys.

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Recent researches in the field of high-entropy materials reveal an intriguing result: the multi-component systems combining the chemical elements with diverse valencies and radii can form single-phase solid solutions with the structure of intermetallic Laves phases. Here we report the fabrication of hexagonal Laves phase (C14, prototype MgZn₂) in duodenary TiZrHfNbVCrMoMnFeCoNiAl alloy. The phase is stable after the thermal treatment at 973 K for 50 h. To characterize the material, we examine its electrical conductivity and magnetic properties. The measurements reveal that the Laves phase is a Curie-Weiss paramagnet, which demonstrates metallic conduction and a pronounced Kondo-like anomaly at 80 K. Analysis of experimental data as well as ab initio calculations suggests that chemical complexity and compositional disorder cause strong s-d band scattering and thus the rather high density of d-states in the conduction band.

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Microstructures of both as-quenched and intercritical-annealed medium-Mn steel were investigated by transmission electron microscopy to acquire a better understanding of γ-ɛ and γ-α′ martensitic transformations. The orientation relationships among each phases were determined as (-110)α′//(0001)ε, [111]α′//[11-20]ε for the case of as-quenched sample, and (-110)α′//(-111)γ//(0001)ε, [111]α′//[110]γ//[11-20]ε for the case of intercritical-annealed sample, respectively. In addition, the presences of core-shell type microstructures with the gradient of Mn concentration were confirmed with ɛ–martensite being surrounded by retained γ. Mn concentration of each phase was found dependent on the growth of reversed γ controlled by Mn diffusion during intercritical annealing. It was strongly suggested that the gradient of Mn concentration occurred during intercritical annealing affected the phase stability, which resulted in the formation of ε/γ core-shell microstructures.

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Ultra-high strength is obtained in the simple binary Mg-Gd alloy with only a small extrusion ratio, and its main strengthening contribution is different from that reported in previous works. The tensile yield strength (TYS) of Mg-13Gd alloy can reach 350 MPa by hot extrusion with an extrusion ratio of 4. The strong texture and internal dislocation pinning of the un-dynamically recrystallized (un-DRXed) region with large proportion contribute greatly to the strength of as-extruded alloy. It is found for the first time that aging precipitation only occurs within the large un-DRXed grains but not in the fine DRXed grains. The TYS of extruded + peak-aged alloy increases to 470 MPa. The ultra-high strength is mainly related to texture strengthening and precipitation strengthening, rather than fine grain strengthening and precipitation strengthening in the conventional Mg alloys with large plastic deformation.

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Although superior high temperature tensile yield strength of high entropy superalloys (HESAs) arises from their hierarchical microstructure, the precipitation processes driving its formation remains unclear. In the present study, we analyze the kinetics of γ’ and γ precipitations by treating the concurrent nucleation, growth and coarsening using common computational thermodynamic and kinetic tools to simulate the microstructure genesis and evolution in HESA during thermal treatments. The ability of the simulations to reproduce the experimentally observed microstructure parameters is evaluated. Temperature-time-transformation (TTT) diagrams are calculated to serve as guidelines for further optimization of the hierarchical microstructure of HESAs.

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Laser surface remelting can be used to manipulate the microstructure of cast materials. Here, we present a detailed analysis of Fe₂VAl following laser surface remelting. Within the melt pool, elongated grains grow nearly epitaxially from the heat-affected zone. These grains are separated by low-angle grain boundaries with 1°-5° misorientations. Segregation of vanadium, carbon, and nitrogen at grain boundaries and dislocations is observed using atom probe tomography. The local electrical resistivity was measured by an in-situ four-point-probe technique. A smaller increase in electrical resistivity is observed at these low-angle grain boundaries compared to high-angle grain boundaries in a cast sample. This indicates that grain boundary engineering could potentially be used to manipulate thermoelectric properties.