In recent years, materials have evolved across all fields. The goal is to develop materials that are increasingly resistant while also being lightweight, stainless, and tough. All these mechanical and physical properties require increasingly complex microstructures, which can directly affect the cutting process. Adding additive manufacturing to this equation—with its ability to produce even more complex structures—makes mastering the cutting process difficult and its prediction nearly impossible.The objective of this paper is to investigate, in the case of an additively manufactured stainless steel (316L) produced using different manufacturing routes, the relationships between microstructure and the cutting process. The analyses are based on the observation of the cutting process through post-mortem examinations of chips, chemical analyses of material evolution, as well as microstructural characterizations such as EBSD tests. In addition, a specific setup was developed to ensure that each test applies a mechanically oriented load with respect to the build plane. Finally, the cutting process partly relies on the creation of a crack initiated by the tool. This crack then becomes the beginning of the shear within the primary shear zone. One possible indicator of machinability is toughness. Part of this study therefore explores the impact of toughness modification on the cutting process.

The durability of thermal barrier coating (TBC) systems is strongly influenced by the interaction between oxidation of the metallic bond coat and its mechanical behavior. While the response of bond coats under isothermal monotonic loading has been widely studied, the effect of thermal cycling remains poorly understood, even though cyclic loading naturally arises from the mismatch in coefficients of thermal expansion between the ceramic top coat, thermally grown oxide, metallic bond coat, and the superalloy substrate. In this work, high-energy X-ray diffraction was used to investigate the strain and stress evolution in the β -(Ni, Pt)Al bond coat of a standard TBC deposited on a nickel-based single-crystal superalloy during thermal cycling. Before in situ cycling, some of the studied specimens were aged through long furnace cycles. Strains and stresses in the β phase were quantified in situ using the sin^2ψ method combined with micromechanical modeling. The results reveal that plastic deformation in β is strongly controlled by evolving interfacial effects and by the cyclic β⇌γ ' phase transformation during thermal cycling. These mechanisms govern the accumulation of plastic strain in β and may promote rumpling, spallation, and ultimately TBC degradation. This study provides new mechanistic insight into bond-coat plasticity under thermal cycling.

Microplasticity of a polycrystalline Ni-based superalloy was investigated using phase contrast tomography (PCT) and laser scanning confocal microscopy (LSCM). Incremental tensile testing was performed on three miniaturized specimens to investigate strain localization at low plastic deformation at room temperature and 650 ∘C. Microplasticity events, such as slip activity, deformation twinning, and grain boundary sliding, are free to emerge at the specimen surface and generate sub-micrometer topographic features. High resolution digital image correlation was conducted using LSCM to have a description of the in-plane and out-of-plane kinematics of the specimen surface. Despite slip amplitudes substantially smaller than the voxel size, PCT was capable to evidence the out-of-plane component of slip traces at the onset of plasticity. The technique was also used at 650 ∘C, a temperature at which grain boundary sliding occurs, but surface reactivity is severe enough not to allow for topographic measurements using LSCM. Therefore, PCT was found particularly adapted to evidence “surface” microplasticity events hidden by an extra surface oxidation layer.

High-speed nanoindentation mapping (HSNM), electron backscatter diffraction (EBSD), electron microprobe analyses (EPMA), and high resolution-microscale laser induced breakdown spectroscopy (HR-mu LIBS), were used to characterize the evolution of the elastic anisotropy of a commercially pure titanium (CP-Ti) having a gradient of oxygen concentration. CP-Ti samples were pre-oxidized in air at 655 degrees C for 120 h to create a 35 mu m-deep gradient of oxygen within Ti, the oxygen-rich layer (ORL). Wedge-cut samples were prepared to spread the ORL over hundreds of micrometers instead of tens of micrometers for cross-sections. EPMA and HR-mu LIBS were used to quantify the oxygen distribution within the ORL in a relative and absolute manner, respectively. The Vlassak-Nix theory was used for inverse identification of the stiffness matrix terms as a function of the oxygen content. The stiffness matrix as a function of the oxygen concentration was used to simulate the stress-strain distribution at the sub-grain level in the ORL under tensile macroscopic loading. Configurations with and without external oxide were numerically tested to investigate the role of the oxide layer on the stress distribution within the ORL as well as the crystallographic texture.

Dimensionality reduction is crucial in materials science for extracting patterns from high-dimensional data. This is vital for optimizing material design spaces by cutting computational complexity and for integrating diverse data sources for advanced anomaly detection, identifying structural or functional material deviations. Traditional convolutional autoencoders focus on local features, failing to capture global contextual information essential for predicting material behavior under stress, where overall material properties, grain orientations, morphologies and sizes are key. To address this, a Quaternion-Based Vision Transformer Masked Autoencoder (ViT-MAE) is proposed for polycrystalline materials. This model processes quaternion-valued EBSD orientation maps with a 65% masking ratio, capturing both local and global microstructural features efficiently. Pre-trained on synthetic data using self-supervision, the model achieves robust generalization on real-world EBSD scans by minimizing a misorientation loss function on the quaternion manifold. This work lays the groundwork for advanced multimodal data analysis in materials science, offering an open dataset and pre-trained vision-transformer weights. The goal is to provide a reliable latent space for EBSD orientation maps, advancing future multimodal characterization through latent space merging.

High-temperature oxidation of titanium leads to the formation of an external oxide scale and oxygen ingress into the metallic titanium material. Oxygen ingress can be significant due to the high solubility of O within Ti. An oxygen-rich layer (ORL) thus forms beneath the external oxide scale, exhibiting a brittle behavior. Microtensile specimens were used in order to exacerbate surface effects, i.e., surface reactivity in the case of the oxidation of titanium. Playing with the specimen thickness and pre-oxidation durations, it was possible to evaluate the evolution of tensile strength as well as the reduction in ductility for deep extensions of ORL relative to the specimen thickness (high fraction of ORL). In addition, ultrathin specimen extraction at different locations within the ORL depth aimed at better identifying the gradient of properties within the ORL. This micromechanical approach was applied to a commercially pure titanium (CP-Ti grade 2) and to a structural titanium alloy (Ti6242s). Both strengthening and loss of mechanical properties (yield strength and ductility) were observed depending on the material and oxygen ingress. While CP-Ti demonstrated an increase in mechanical strength up to ORL representing 80 pct of the gage section, Ti6242s experienced a loss of mechanical resistance even for the shortest exposure times (the ORL representing 10 pct of the gage section).

Surface effects were investigated using ultrathin specimens with thicknesses in the order of the grain size of the material. The candidate material was a polycrystalline Ni-based superalloy (Alloy 718) purposely heat treated to document both the effects of the grain size and the metallurgical state, i.e., solid solution and precipitation hardened state, on the polycrystalline-tomulticrystalline behavior. Ultrathin tensile specimens were prepared with a dedicated technique to obtain specimens with thicknesses ranging between 20 and 550 mu m, then tensile tested at room temperature. The polycrystalline-to-multicrystalline transition (PMT) was found to depend on the material grain size relative to the specimen thickness and to impair severely the tensile strength of the material. The yield strength, ultimate tensile strength (maximal stress on the stress-strain curve) and strain-to-failure severely dropped for specimens thinner than approximately two times the grain size of the material regardless of the metallurgical state. Such a decrease in tensile properties is mainly attributed to free-surface effects acting as an escape sink of dislocations, thus leading to a significant decrease of the primary dislocations density within the surface grains in comparison with the core grains. Interestingly, difference in work-hardening behavior with size reduction was found between both precipitation states, the solid solution state being more sensitive with the size reduction. The decrease in tensile properties was not found as expected from the commonly reported "thickness/grain size (t/D)"ratio. Therefore, a numerical approach using a modified Berveiller-Zaoui self-consistent model based on a continuum crystal plasticity approach was conducted in the present paper to distinguish microstructural features acting as strengthening (dislocation accumulation) and softening (dislocation escape at the free-surface) features. 3D numerical materials were produced using Voronoi tessellation methods to represent the fraction of "core grains" versus "surface grains". These fractions were then used as microstructural parameters for the identification of a crystal plasticity model using mean-field homogenization with different populations of grains, i.e., core versus surface features. The present work aimed at distinguishing the mechanical behavior of surface grains from core grains in Alloy 718 Ni-based superalloys using various thicknesses of specimens and different microstructure and metallurgical state variants.

Despite excellent oxidative properties of the Alloy 718 Ni-based superalloy, long-term exposure to oxidative environments in service creates a chemical gradient in the sub-surface affected by oxidation. Its characterization is key to assessing the evolving mechanical behavior of such affected materials. The present study focuses on the γ'-γ” precipitation depletion induced by the chemical gradient and benchmarks micro-mechanical testing techniques to assess local mechanical properties. Local techniques such as nanoindentation and micro-pillar compression were used to measure both elastic and plastic properties of a pre-oxidized Alloy 718 Ni-based superalloy, having a chemical gradient. These results were compared to a global approach by tensile testing and high resolution-digital image correlation (HR-DIC) on model materials corresponding to regions of the chemical gradient: the solid-solution and the precipitation-hardened Alloy 718. The plastic behavior was investigated in terms of macroscopic yield strength and slip activity. Results obtained by the local and global techniques were found to be different but complementary. The relevance of the association of multiple micro-mechanical tests and sample preparation techniques to probe chemical gradients is discussed and technique advantages and drawbacks are exposed based on the single crystalline or polycrystalline nature of the micro-mechanical testing.

Tensile tests on Alloy 718 Ni-based superalloyNi-based superalloy at 650 ^∘ C at different strain ratesStrain rate revealed a strain-rate dependency on the fracture mode. A change from intergranular to transgranular fracture was observed in air as the strain rateStrain rate increased, mainly when Portevin-Le-ChatelierPortevin-Le-Chatelier (PLC) mesoscopic deformation bands were present. To better understand the link between strain rateStrain rate and fracture mode, a description of the strain localization in the early deformation stage is needed. In this study, high-resolution digital image correlationDigital image correlations (HR-DIC) was carried out at the onset of strain localization, a low strain rateStrain rate (LSR, ϵ̇ = 10 ^-4 s ^-1 ) and at high strain rateStrain rate (HSR, ϵ̇ = 10 ^-2 s ^-1 ). This latter condition aimed at investigating the microplasticityMicroplasticity development within PLC bands. The in-plane and out-of-plane displacement components of each single plastic event were measured to accurately assess and distinguish morphological sliding at grain boundariesGrain boundary (i.e., grain boundary sliding) andGrain boundary sliding dislocation slip. The deformation within the PLC bands was examined at macro, meso, and microscales. Statistical analyses highlighted the distribution and partitioning of these strain localization events related to different microstructural features, including grains, and grain and twin boundaries. Grain boundary slidingGrain boundary sliding was found to be more prominent at LSR. Interestingly, events near and parallel to twin boundaries are particularly intense regardless of the strain rateStrain rate. At HSR, grain boundary slidingGrain boundary sliding is less pronounced, and a high density of intragranular slip bands developed within the PLC bands; based on observations before and after the occurrence of the PLC band.

Irreversible deformation in relation to the microstructure was investigated for a polycrystalline Ni-based superalloy (Alloy 718) from room temperature to 650 °C using high-resolution digital image correlation (HR-DIC) techniques. Interrupted tensile tests were performed under a protective atmosphere to ensure the stability of the speckle pattern to track kinematics fields from surface analyses. In-plane strain localization was captured using HR-DIC on scanning electron microscopy (SEM) images. A statistical analysis of different strain localization events in relation to the microstructural features was conducted, i.e., intragranular slip localization, slip localization parallel to and near Σ3-twin boundaries (Σ3-TB), and grain boundary sliding (GBS). Alloy 718 exhibited slip localization at room temperature and 350 °C. Intense strain localization develops parallel and in the vicinity of Σ3-TB from the onset of the microplasticity. Few intense slip stimulated-grain boundary sliding events were found due to slip localization on both grains adjacent to the grain boundary. At 650 °C, Alloy 718 experienced grain boundary sliding at the onset of the yield without particular slip localization in adjacent grains. At lower temperatures, strain localization parallel to and near Σ3-TB was intense, and intragranular slip localization intensified with increasing macroscopic deformation. Particular microstructural configurations were found at 650 °C leading to premature damage: (i) sub-surface cavitation at grain boundaries, and (ii) grain boundary cracking due to intense shearing near a Σ3-TB.

The influence of low and steady loading on the oxidation behaviour and oxygen diffusion within Ti6242S was investigated at 650 degrees C in air. Electron probe microanalyser (EPMA), secondary-ion mass spectrometry (SIMS) and high energy synchrotron X-ray diffraction (S-XRD) were used to quantify the oxygen distribution within the oxygen-enriched layer beneath the external oxide scale. Rietveld and peak by peak methods were used to evaluate the average response versus the crystal-oriented response of this diffusion process under load. Interestingly, a thermo-mechano-chemical coupling occurs during the creep-oxidation experiment even for moderate applied stresses (25-70 MPa) and demonstrates: (i) a decrease of the oxygen concentration at the metal/oxide interface, and (ii) a curvature change of the oxygen diffusion profile with load application. A qualitative thermomechano-chemical approach is proposed to model the modification of the diffusion law of the oxygen within Ti6242S due to application of a mechanical loading to explain observed experimental results.

The brittleness of an aluminide diffusionDiffusion coating protecting a René 125 Ni-based polycrystalline superalloyPolycrystalline superalloy was investigated over a wide range of temperatures in its as-received and thermally aged form. Isothermal and thermal cycled aging were performed on the coated system at a maximum temperature of 1100 ^∘C . MicrostructureMicrostructure evolutions and damage initiation within the coatingCoating were characterized. Interrupted tensile tests and thermomechanical fatigueFatigue tests were conducted to document critical stress-strain conditions leading to the coatingCoating crackingCoating cracking and lifetime for the case of thermomechanical fatigue loading. Advanced digital image correlationDigital image correlations and acoustic emission techniques were used to detect coating crackingCoating cracking. Isothermal oxidationOxidation orCyclic oxidation cyclic oxidation led to improved strain-to-failure due to metallurgical evolutions and also longer fatigue life under thermomechanical fatigueFatigue conditions.

A nickel-based superalloy is examined during monotonic deformation from ambient to cryogenic temperatures, reaching as low as liquid helium temperature. A detailed multimodal analysis of the microstructure and plasticity is conducted to discern changes in deformation mechanisms and plastic deformation localization under cryogenic conditions. This study employs high-resolution digital image correlation and transmission electron microscopy to identify the deformation mechanisms and understand their influence on plastic deformation localization as the temperature varies. At cryogenic temperatures, unusual plastic deformation localization processes are observed, attributed to the competing activation of a range of deformation processes. Furthermore, a mechanism of slip delocalization, i.e., local plastic deformation homogenization through closely spaced slip, is noted at these extreme temperatures. Ultimately, the impact of the microstructure is identified across the temperature range, from room to cryogenic temperatures.

Titanium and its alloys combine an important mechanical anisotropy and a high capacity to dissolve oxygen. The detailed evolution of the elastic compliance of titanium as a function of its oxygen content is only partially known, despite its importance in structural applications. Here, high speed nanoindentation mapping (HSNM) was conducted on a grade 2 commercially pure titanium (CP-Ti) to probe elastic and hardness anisotropy as well as property evolution as a function of the oxygen content within Ti using pre-oxidized specimens. The oxygen concentration investigated ranged from 600 ppm to 20% atomic. Pre-oxidation of the CP-Ti was performed at 700 degrees C for 100 h under air to create a gradient of oxygen content within the metal, denoted oxygen-rich layer (ORL). Local oxygen content was quantified using microprobe analyses (EPMA) and crystal orientation using electron backscattered diffraction (EBSD). Reduced modulus and hardness maps were obtained on the preoxidized sample within the ORL and far from the ORL using large but highly resolved nanoindentation technique in continuous stiffness measurement (CSM) mode. Data merging techniques were used on this multi-modal dataset to statistically link local mechanical properties to chemical and crystal orientation information. Oxygen insertion in the Ti lattice was found to significantly increase the hardness and elastic moduli of titanium and was correlated to orientation of the c-axis of the alpha-Ti as a function of the nanoindentation loading direction. Using the Vlassak and Nix theory, it was possible to identify the evolution of the Cij terms of the stiffness matrix as a function of the oxygen content up to 20% at. in O.

Grain size effects on the early plastic strain localization and slip transfer at grain boundaries were investigated for the Alloy 718 Ni-based superalloy at 650 degrees C. Three microstructures with different grain sizes underwent monotonic tensile tests at 650 degrees C, both in air and under vacuum, until rupture. All the microstructure variants exhibit fully intragranular fracture under vacuum and partially intergranular fracture in air. In this latter case, predominant intergranular fracture mode was found in the fine-grain microstructures. Interrupted tensile tests were also conducted under vacuum with ex-situ SEM high-resolution digital image correlation (HR-DIC) measurements to assess in-plane kinematics fields at the microstructure scale. Out-of-plane displacement jumps were obtained using laser scanning confocal microscopy. Both crystallographic slip within grains and near Sigma 3 twin boundaries (TBs) and morphological sliding happening at grain boundaries (GBs) were documented. Statistical analysis of all plastic events aimed at quantifying strain localization distribution as a function of the microstructure. The fine-grain microstructure was found to have extensive strain localization at grain boundaries, while the coarse-grain microstructure is more prone to intragranular slip development and slip localization near TBs. Different scenarios of slip band/grain boundary interactions were evidenced.

The morphologies of Type-II hot corrosion attacks were investigated at 650 °C for the DS200 + Hf nickel-based superalloy. The relationship between corrosion rate and microstructural features, i.e., grain boundaries, carbides, eutectics, dendrites, was considered at different scales and for three environments. Corrosion tests and related characterizations were carried out on a total of forty-five samples, including different sampling strategies, test conditions (air, air + 150 ppm SO2 and air+ 400 ppm SO2) and exposure times (24, 50 and 100 h). The amount of SO2 in the inlet gas was found to be the main factor in the degradation, affecting both the duration of the incubation period and directly the corrosion rate. The proportion of grain boundaries as well as their orientation did not have any influence on the degradation kinetics. On the contrary, MC carbides and γ + γ′ eutectic pools, i.e., the interdendritic area resulting from the solidification stage, underwent deeper attacks for all gaseous atmospheres. The global mechanism can be explained by the SO3-induced hot corrosion mechanism.

Micromechanical characterization of the oxygen-rich layer (ORL) of a Ti-6Al-4V alloy due to high-temperature oxidation was investigated at room temperature. The tensile strength of the pre-oxidized specimens linearly decreased as a function of the surface fraction of ORL in relation to the gage section, demonstrating a competition between oxygen strengthening and embrittlement. Electron-probe microanalyses and nanoindentation testing aimed at locally assessing the elastic and hardness response of the material as a function of the oxygen content. These properties were used in finite element simulations to quantify stress profiles within the oxygen-graded material for different ORL thickness/specimen thickness couples.

A numerical approach was implemented to precisely stitch together images from the same projector/camera that form a mosaic by regularly moving either the projector/camera or the scene/sample. Such an imaging approach is used, for example, in automated microscopy. The presence of optical distortions can lead to detrimental blurring artifacts in the overlaps. The present development identifies and corrects non-affine distortion functions using the gray-level conservation equation on reduced overlapping regions of adjacent images with sub-pixel accuracy. The present numerical development was first tested on synthetic images with known distortions to confirm that the algorithm is capable of detecting only non-affine distortions. Then, Digital Image Correlation (DIC) was applied to a pair of large laser scanning confocal microscope mosaics (121 images of 1024 × 1024 pixel2, i.e., more than 100 MPixel) created using the proposed non-rigid stitching. The method aims to improve the quality of blended images after stitching using the sample pattern in the overlapped regions. This new numerical development significantly minimizes kinematic field artifacts due to lens distortion in overlapped regions.