Electron Backscatter Diffraction Research Articles

Effects of heat input on microstructure evolution and corrosion resistance of underwater laser cladding high-strength low-alloy steel coating

The effects of heat input on the microstructure evolution and corrosion resistance of the high-strength low-alloy (HSLA) steel coating obtained by wire-feed underwater laser cladding were studied. Optical digital microscope, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), electrochemical tests, laser microscope and other characterization methods were used. As the heat input increased, the smoothness of the underwater cladding coating improved, with little changes in elemental distribution and phase composition. However, the content of acicular ferrite increased, while the amounts of lath bainite, lath martensite, and granular bainite decreased. As the heat input increased from 0.4 to 0.55 kJ/mm, the grain size increased from 25.3 to 55.9 μm, the proportion of low-angle grain boundaries rose from 61.3 % to 69.1 %, and the texture intensity of the (110) crystal plane increased from 16.22 to 23.83. Meanwhile, the dislocation density decreased from 4.9 × 1014 to 4.1 × 1014 m−2. These changes enhanced the corrosion resistance of underwater coating. As the heat input increased from 0.4 to 0.55 kJ/mm, the corrosion current density decreased from 2.13 × 10−5 to 3.35 × 10−6 A/cm2, and the corrosion potential increased from −0.823 to −0.529 V. Additionally, the depth-to-width ratio of the corrosion pits decreased from 0.255 to 0.053. This study laid the foundation for high-quality in-situ underwater repairs of ships and submarines made of high-strength steel.

Insights into the North Patagonian Massif Lower Crust: Petrology and Microstructure of Granulite Xenoliths

Abstract The continental lower crust constitutes a key zone for understanding the mantle–crust magmatic and mechanical transfers, but its study is hampered by the paucity of lower crust samples. Here, we characterise the petrological, geochemical and petrophysical processes structuring the lower crust of the North Patagonian Massif (NPM; Argentina) using a suite of representative mafic granulite and websterite xenoliths. These xenoliths were entrained by alkaline lavas from five volcanic centres that erupted between the Oligocene and Pleistocene. Electron microprobe and Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS) were used to obtain in situ geochemical data on the minerals, while microstructural data were obtained by Electron BackScatter Diffraction (EBSD). Both granulites and websterites display a granoblastic texture and sometimes a weak inherited magmatic layering. Mafic granulite xenoliths show a plagioclase + clinopyroxene ± orthopyroxene assemblage commonly associated with spinel or titanomagnetite. Websterite xenoliths show an association of clinopyroxene + orthopyroxene + spinel, along with accessory plagioclase. Mafic granulites and websterites have SiO2 contents ranging from 44 to 53 wt %, while their Mg# varies from 53 to 79. Clinopyroxenes are characterised by weak convex upward chondrite-normalised Rare Earth Elements - REE patterns (Light-REE </<< Mid-REE > Heavy-REE) which are similar to clinopyroxene phenocrysts and megacrysts from intra-plate basalts. Calculated liquid in equilibrium with clinopyroxene have similar REE patterns to those found in Cenozoic basalts from the NPM, suggesting that the xenolith suite represents evidence for underplating processes, possibly related to one of the magmatic events that have occurred in the NPM since the Permo-Trias. Mafic granulites and websterites show a weak mineral shape preferred orientation and an associated weak Crystal Preferred Orientation (CPO) related to the magmatic layering. Recorded plastic deformation is associated with the activation of both (100)[001] and (001)[100] slip systems in clinopyroxene, (100)[001] in orthopyroxene and (010)[001] in plagioclase. However, the activation of slip systems is generally not correlated with CPO in granulites, suggesting that the lower crust underwent subsolidus equilibration and weak plastic deformation in an inactive tectonic context, thereby preserving an inherited magmatic layering. Two-pyroxene (Fe–Mg) thermometer and pseudosection calculations define P–T conditions of the main paragenesis at 760°C to 1120°C and 7.2 to 10.3 kbar, which allows to define the Cenozoic geotherm of the NPM crust at 30°C/km and to reconsider the petrologic Moho depth at ca. 40 km.

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

Microstructural evolution and dynamic recrystallization mechanisms of additively manufactured TiAl alloy with heterogeneous microstructure during hot compression

Microstructural evolution and dynamic recrystallization (DRX) mechanisms of a Ti−48Al−2Cr−2Nb (at.%) alloy prepared by selective electron beam melting (SEBM) during hot deformation at 1150 °C and 0.1 s−1 were investigated by hot compression tests, optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM). The results show that the initial microstructure of the as-SEBMed alloy exhibits layers of coarse γ grains and fine γ+α2+(α2/γ) lamellar mixture grains alternately along the building direction. During the early stage of hot deformation, deformation twins tend to form within the coarse grains, facilitating subsequent deformation, and a small number of DRX grains appear in the fine-grained regions. With the increase of strain, extensive DRX grains are formed through different DRX mechanisms in both coarse and fine-grained regions, involving discontinuous dynamic recrystallization mechanism (DDRX) in the fine-grained regions and a coexistence of DDRX and continuous dynamic recrystallization (CDRX) in the coarse- grained regions.

Predicting mechanical properties of low-alloy steels using features extracted from Electron Backscatter Diffraction characterization

Machine learning (ML) approaches have recently been increasingly employed to establish quantitative relationships between material composition, processing, microstructure, and properties. However, the complexities of microstructure pose challenges for straightforward modeling, thereby complicating research efforts. This study introduces a series of multi-parametric quantification methods based on Electron Backscatter Diffraction (EBSD) data tailored to the microstructural characteristics of low-alloy steels. These methods include quantification of boundary densities across various misorientation angles, distinct types of boundaries, and geometrically necessary dislocation densities. Through thermomechanical simulation and micro-tensile testing of low-alloy steels, data on yield and ultimate tensile strengths were obtained, alongside EBSD-based extraction of microstructure characteristics. Several ML methods, including Random Forest (RF), Gradient Boosting Decision Trees (GBDT), and Extreme Gradient Boosting (XGBoost), were utilized to predict yield strength (YS) and ultimate tensile strength (UTS) using the aforementioned microstructural features. The GBDT model outperformed other algorithms, demonstrating high accuracy in predicting YS, UTS, and elongation. The model achieved an Mean Squared Error (MSE) of 972.18, an Mean Absolute Error (MAE) of 24.75 and an Coefficient of Determination (R2) of 0.864 for YS, and an MSE of 812.28, an MAE of 22.87 and an R2 of 0.823 for UTS. These results confirm GBDT's effectiveness in predicting mechanical properties from microstructural data.This successful integration of ML with multi-parametric description microstructural features underscores its potential in facilitating material design and development processes.

Effect of processing parameters and carbon to metal ratio on microstructure and mechanical properties of (MoTaTiVW)Cx high entropy carbide produced by reactive spark plasma sintering

(MoTaTiVW)Cx high entropy ceramics with varying carbon to metal ratio in the range of 0.75-0.97 were synthesized by by reactive spark plasma sintering. The effect of ball milling time on particle size, phase evolution and carbon pick-up due to toluene decomposition were studied. Formation of single-phase high entropy carbide having face-centered cubic (FCC) crystal structure was confirmed by X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and Selected area diffraction pattern (SAED) analysis of the sintered compacts. Transmission Kikuchi Diffraction images revealed presence of equiaxed nature of the grains. Transmission electron microscopy images revealed the presence of an intergranular phase at grain boundaries and triple junctions. 3D-Atom Probe Tomography studies showed uniform distribution of elements within the grains with some segregation of impurity elements Fe and Co to the grain boundaries indicating minor contribution of liquid phase sintering to densification. The grain size of single-phase sintered compacts ranged between 1.69 ± 0.60 μm to 4.6 ± 1.0 μm. A low sintering temperature and higher milling time resulted in finer grain size The microhardness was found to increase with milling time and C/M ratio. The microhardness, Young’s modulus and indentation fracture toughness lied between 2221 HV0.1 to 2732 HV0.1, 370 GPa to 473 GPa, 3.6 MPa.m1/2 to 4.4 MPa.m1/2, respectively. The highest microhardness and indentation fracture toughness was found to be 2732 ± 80 HV0.1 and 4.4 MPa.m1/2 on par with reported literature for other high entropy carbides.

Coupling CPFE-CA simulation for grain refinement in ultrasonic elliptical vibration diamond cutting of polycrystalline Cu

While microstructure evolution is commonly observed in severe plastic deformation of polycrystalline metals, modulating the cutting-induced grain refinement in subsurface of polycrystalline metals is promising for promoting the performance of machined surface. In this study, we demonstrate the effectiveness of applying ultrasonic vibration assistance (UVA) in effectively prompting grain refinement of polycrystalline Cu in ultra-precision diamond cutting by experiments and multiscale coupling simulations. Specifically, ordinary cutting (OC) and ultrasonic elliptical vibration-assisted cutting (UEVC) experiments of polycrystalline Cu are carried out, and subsequent cross-sectional characterizations of microstructure evolution in subsurface by metallurgical microscope and electron backscatter diffraction, as well as instrumented nanoindentation tests, are performed, which demonstrates significantly promoted grain refinement in subsurface and increased machined surface hardness by UVA, due to increased dislocation density that is beneficial for the nucleation and growth of dynamic recrystallization. In particular, the multi-scale coupling of crystal plasticity finite element (CPFE) simulation and Cellular Automata (CA) method is firstly established for exploring the microstructural evolution during UEVC and OC of polycrystalline Cu, which is capable of elucidating the underlying correlation of grain refinement behavior in subsurface with characteristics of stress and strain fields in cutting area. Furthermore, the influence of amplitude on the propensity of grain refinement is experimentally and theoretically evaluated, which suggests a critical amplitude of 4 μm that leads to a maximum reduction in grain size by 80.9% and a maximum increase in machined surface hardness by 55.8% in UEVC from that in OC, because of the most pronounced strain accumulation and dislocation activity. The findings reported in this study demonstrate the effectiveness of applying ultrasonic vibration assistance for modulating the grain refinement accompanying strengthening of machined surface in ultra-precision diamond cutting of polycrystalline metals.

Substrate modification for high performance CrAl/CrAlBN multilayers coated TiCN-based cermet through plasma nitriding

The plasma nitriding process was conducted on a TiCN-based cermet that had been coated with a multilayer CrAl/CrAlBN coating deposited via cathodic arc. The intensity of the plasma nitriding was modified by adjusting the anode current of the ionization source. To investigate the interface conditions, techniques such as electron probe X-ray microanalysis, electron backscatter diffraction, and transmission electron microscopy were employed. The results indicated that increasing the anode current led to the formation of a thicker nitrided layer and an increase in the texture coefficient of the (111) plane. Specifically, at an anode current of 200 A, the lattice mismatch degree at the TiCN/CrAlN interface decreased from 16.4 % to 3.7 %, resulting in the formation of a nearly coherent interface. The hardness, adhesion strength, and H/E ratio of the coating reached their peak values, and the coated cutting tool exhibited optimal cutting performance when machining the GH4149 superalloy.

Investigation of corrosion resistance offered by the Fe-based clad layer under salt spray and electrochemical workstations

The present work aims to evaluate the electrochemical characteristics of the Fe–based alloy coating formed on the 27SiMn steel substrate under neutral salt spray and 3.5 wt% NaCl environments. By adopting the high-speed laser cladding technique, the Fe-based clad layer was fabricated to perform microstructural and electrochemical characterizations. The microstructure and phase of the coating were analyzed using a scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), and its corrosion performance was also discussed using the salt spray corrosion chamber and the electrochemical workstation. The results show that the microstructure of the coating surface contains equiaxed crystals and long dendritic crystals which arise due to the higher solidification rate after the cladding process. The Fe–based coating was rich in FeCr phase throughout its microstructure without the formation of the intermetallic compounds. Compared to the substrate, the corroded surface of the coating tends to be compact containing a few corrosion pits after different corrosion times, which is attributed to the formation of Cr oxide on it. The electrochemical tests on the potentiodynamic polarization curve (PPC) and electrochemical impedance spectrum (EIS) indicate that the corrosion resistance of the coating is superior to the substrate, presenting a higher corrosion potential (−0.298 V), lower passive current density (1.36 × 10−6 A•cm2), and higher charge transfer resistance (8.23 × 106 Ω·cm2). Additionally, the corrosion mechanism of coating in salt spray and electrochemical tests is the local pitting corrosion due to the autocatalytic effect on the localized region, which facilitates Cl− ions penetrating the coating and leads to the dissolution of Fe and Cr oxides.

Fracture mode of Ti(C, N)-based cermets investigated by experiment and simulation calculation

The high hardness and good wear resistance of Ti(C, N)-based cermets confer excellent applicability as cutting tools. However, the lack of in-depth research on the fracture mechanism limits further improvements in toughness. A typical commercial Ti(C, N)-based cermet with a core–rim structure was prepared through low-pressure sintering. The interface characteristics between the complex core, rim, and binder phases were characterised using transmission electron microscopy (TEM), while the actual hardness and modules of these phases were measured through in situ nanoindenter assessments. The crack propagation behaviour of the cermet was analysed using a 70° angle observation method combined with electron backscatter diffraction in scanning electron microscopy (EBSD/SEM). This study identifies a commonly occurring but long-overlooked fracture mode, termed “trans-rim” fracture. The experimental results were verified through simulation calculations. This novel idea offers insights into enhancing the toughness of Ti(C, N)-based cermets.

Study on the effect of phosphorus on anti-softening performance of oxygen-free copper

This study investigates the preparation of oxygen-free copper with varying phosphorus (P) content through vacuum melting and examines the influence of P on the mechanical properties, softening resistance, and microstructure of the material. The results indicate that as the P content increases (≤1400 wt ppm), the grain size of the oxygen-free copper becomes progressively finer, resulting in significant improvements in microhardness and softening temperature. Notably, when the P content reaches 1400 wt ppm, the microhardness and softening temperature (121.4 HV, 341.35 °C) are markedly superior compared to those with a P content of 0.01 wt ppm (101.89 HV, 210.31 °C). Electron backscatter diffraction (EBSD) was used to analyze the samples before and after softening annealing, and it was found that the P element inhibited the recrystallization behavior of oxygen-free copper by hindering dislocation movement, thereby achieving the effect of increasing the softening temperature. Transmission electron microscopy (TEM) results further demonstrate that annealing softening in P-containing oxygen-free copper (1400 wt ppm) predominantly occurs through discontinuous dynamic recrystallization (DDRX) and twinning dynamic recrystallization (TDRX), thereby altering the recrystallization mechanism of the copper.

Temperature-dependent mechanical properties and crystal plasticity parameters for additively manufactured Haynes-214 alloy: Experiments and numerical modeling

Our experimental mechanical testing data demonstrated that the additively manufactured (AM) laser powder bed fusion (L-PBF) Haynes-214 alloy exhibits non-linear mechanical properties as the temperature rises from ambient to 870 °C. To gain a deeper insight into the microstructure–property linkages under thermomechanical loading, it is essential to use crystal plasticity (CP) simulations. This approach can reduce the need to conduct expensive high-temperature experimental mechanical testing and account for crystallographic texture and grain morphology effects, which are known to be important in many AM processed materials. However, calibrating a CP model is time-consuming because individual simulations are computationally expensive and hundreds (or more) of iterations over parameter sets may be required. To address this issue, we have designed a machine learning - differential evolution (ML-DE) CP framework that can accurately interpolate the tensile properties of AM L-PBF Haynes-214 alloy across a wide temperature range from ambient to 870 °C, with minimal reliance on experimental data. The framework uses electron backscatter diffraction (EBSD) measurements to generate statistically equivalent microstructural volume elements to serve as inputs to the CP modeling framework. Stress–strain curves were generated from 1000 CP simulations, which serve as the training data set for the three ML regression algorithms explored: linear, extra-trees, and multi-layer perceptron. These three regression models were independently evaluated to compare their efficiency and identify the most suitable algorithm for the given problem. Results revealed that the extra-trees ML regressor outperforms the other models in both qualitative and quantitative aspects with an R2 of 0.98. Subsequently, the differential evolution optimization approach is employed to calibrate the ML-based CP material parameters with experimental results obtained at various temperatures. Finally, temperature-dependent CP material parameters are formulated. The effectiveness and efficiency of the designed framework are validated through comparison with experimental results, demonstrating a high degree of agreement. These calibrated parametric constitutive equations enable further use of the CP model to study the deformation behavior of this alloy under a wide range of thermo-mechanical loading and service conditions.

Fabrication of hierarchical layered structure in Zr/Ti composite via multi-step heat treatments and its effect on the mechanical properties

The strength and ductility of metallic structural materials are two pivotal properties generally considered mutually contradictory. In the past few decades, numerous heterogeneous materials have been designed and fabricated to overcome this trade-off. Biomimetic-designed hierarchical layered (HL) materials represent a promising approach. In the present study, HL Zr/Ti materials with three hierarchical levels were fabricated via multi-step heat treatments. Scanning Electron Microscopy (SEM), Transmission electron microscope (TEM), Electron Backscatter Diffraction (EBSD), Transmission Kikuchi Diffraction (TKD), and Energy Dispersive X-ray Spectroscopy (EDS) were employed to observe the evolution of the HL microstructure. The mechanical properties of the HL Zr/Ti materials were assessed through hardness and tensile tests, analyzing the influence of microstructural changes in the diffusion layer on the overall mechanical performance. Our results demonstrated that the HL structure could introduce extra strength beyond the rule of mixtures (ROM) due to multiple-scaled hetero-deformation induced (HDI) strengthening. Additionally, the refinement of the second-level layer thickness effectively inhibited crack propagation. This research provides new insights into developing multi-level HL materials with enhanced mechanical properties through cost-effective and scalable manufacturing processes.

Formation of seaweed morphology and enhancing mechanical properties of an A356 alloy by directional solidification

In the present work, regular dendrite and seaweed pattern are produced by controlling the crystal orientation during directional solidification of an A356 aluminium alloy. These morphologies and growth orientation were investigated by electron backscatter diffraction (EBSD), and the results showed that the seaweed pattern mainly prevailed under the (100)[011] orientation. At the same time, the effects of seaweed pattern in the properties of A356 alloy were analysed by room temperature tensile test. It was found that the elongation and toughness of the samples reached 20% and 36J/m3, respectively, for the seaweed; 13% and 24J/m3, respectively, for the regular dendrites; and 8% and 14J/m3, respectively, for the cast ingot. Compared with the regular dendrite samples, the seaweed pattern obtained relatively excellent elongation and toughness. By using scanning electron microscopy (SEM), it is found that the distribution of eutectic silicon particles in seaweed morphology sample is more refined and uniform, which is the main reason for these enhancements.

Interplay between deformation and fracture mechanism in gradient nanostructured austenitic stainless steel

The plastic deformation parameters are crucial for the grain size of gradient nanostructured (GNS) materials, and the multiscale grain structure within the GNS layer has a significant impact on fracture behavior. In this study, the detailed depth-dependent microstructures of GNS310S stainless steel fabricated by surface mechanical rolling treatment (SMRT) were investigated, and the relationship between the geometrically necessary dislocation (GND) density and the strain gradient was established through the local misorientation obtained by electron backscatter diffraction. The critical deformation parameters (strain gradient, shear strain, and strain rate) of SMRT-induced grain refinement at different scales were quantitatively evaluated. The tensile results show the yield strength and tensile strength of GNS310S are improved by 103 % and 23.1 % respectively compared to CG310S. Additionally, we elucidate the underlying tensile fracture mechanism of GNS310S stainless steel through detailed microstructural analysis. Due to the poor ductility of the near-equiaxed nanograins, cracking occurred on the surface of the SMRT specimen at low strain during the tensile testing. These cracks evolved into competitive shear offsets and multi-cracks with increased strain on the specimen surface, eventually leading to a hybrid fracture mode. In contrast, the subsurface nanotwinned lamellae layer displayed good ductility during tension, which can accommodate the deformation through lamellae widening and forming secondary twinning. This nanotwinned lamellae layer can suppress the inward propagation of surface cracks when the strain was not large. This work provides new insights into the fabricating parameters of the GNS stainless steel, as well as the deformation and fracture mechanisms.

Comparative study of the strain and strain rate hardening mechanisms and its workability during hot deformation of TC4 titanium alloys

Localized thinning is one of the main defects in hot forming processes, which is determined by the hardening behaviour during deformation. This study focused on building a hot-workability map to prevent localized thinning in wide ranges (650–950 °C & 0.001–1 s−1) for industrial significance. Insights into the associated strain and strain rate hardening mechanisms were provided by visualizing the microstructure evolutions using both in-situ High-Temperature Laser Scanning Confocal Microscope (HTLSCM) and Electron Backscattered Diffraction (EBSD). Results show that the highest uniform strain, up to 0.250, is achieved in the viscoplastic region due to the cooperative strain and strain rate hardening, where dislocation slip, α/β transformation and grain sliding concurrently occur. Significant grain refinement is also achieved. The optimum forming condition was identified in the viscoplastic region and is further verified by forming an ultra-thin large bend component, reducing thickness unevenness from 18.6 % to 13.1 %. This research finding could aid in understanding the effects of strain and strain rate hardening on forming uniformity and further provide scientific guidance for industrial processing parameters selection, reducing localized thinning and hence scrap rates.

Study on the mechanical properties and microstructures of Al-Cu-Mg alloy thick plates obtained by different hot rolling processes

Abstract In the research, the microstructures of large-scale 2324 aluminum alloy thick plates obtained through two different hot rolling processes are investigated by using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Electron Backscatter Diffraction (EBSD). Additionally, the tensile properties of the plates are evaluated at room temperature. The results indicate that the thick plates produced by Process A exhibit higher tensile and yield strengths along the L (longitudinal) and LT (long transverse) directions. The higher proportion of deformed microstructures is an important factor contributing to their enhanced tensile and yield strengths. Meanwhile, the different rolling processes have minimal impact on the kind and distribution of the second phase in the hot-rolled thick plates, with the second phase primarily consisting of Al2Cu and Al2CuMg phases, which are distributed in a streamlined way along the rolling direction of the thick plates. The microstructures of the hot-rolled thick plates obtained from both hot-rolling processes are dominated by deformed structures. The thick plates produced by Process B have relatively smaller grain sizes and a higher degree of fragmentation, making their microstructure more susceptible to recrystallization transformation during subsequent solution heat treatment.

Effect of second-phase precipitates on deformation microstructure in AA2024 (Al–Cu–Mg): dislocation substructures and stored energy

The importance of comprehensive multiscale characterisation in advancing our understanding of engineering materials is undeniable but remains a challenging pursuit. Combining complimentary microstructure characterisation techniques, including transmission electron microscopy, electron backscatter diffraction and dark-field X-ray microscopy (DFXM), the formation of deformation microstructures is investigated in presence of shearable and non-shearable hardening precipitates in an industrial aluminium alloy (AA) 2024 (Al–Cu–Mg family). The alloy was used in naturally aged T3 (with shearable co-clusters and Guinier–Preston–Bagaryatsky (GPB) zones) and peak-hardened T8 (with non-shearable S-phase precipitates) states. After cold rolling with thickness reductions varying from 25 to 60% (or corresponding von Mises strain from 0.33 to 1.06), the T8 state revealed a higher sub-boundary density with slightly smaller mean disorientation angle, as compared to those in the T3 state. At a von Mises strain of 0.33, the T8 state exhibited higher long-range orientation gradients, as compared to the T3 state, for higher strain orientation gradients in T3 surpass those in T8 state. With DFXM, distinct 3D substructures are shown, revealing ellipsoidal sub-grains in the T8 state and pancake-like sub-grains in the T3 state. Moreover, the stored energy induced by cold rolling is higher for the T8 state. These results indicate different deformation microstructures, formed in the same AA2024 but hardened by shearable and non-shearable precipitates.Graphical abstract

Enhancing corrosion fatigue performance of 17-4 PH stainless steel by simultaneous aging and plasma nitriding

This study investigated the effects of simultaneous aging and low-temperature plasma nitriding on the corrosion fatigue performance of 17-4 PH stainless steel. Plasma nitriding was conducted under two temperatures of 400 and 500 °C and, for comparison, some other specimens were subjected to aging treatment at the same temperatures and times. Microstructural characterization by scanning electron microscope (FESEM) and electron backscatter diffraction (EBSD) confirmed similar structures at the core in the nitrided and aged specimens, thereby, the influence of nitrogen at the surface of 17-4 alloy could be carefully investigated. X-ray diffraction and grazing incidence X-ray diffraction (GIXRD) identified expanded martensite as the matrix within the nitrided layer, accompanied by CrN, Fe3N, and Fe4N phases. X-ray photoelectron spectroscopy (XPS) analysis revealed high nitrogen concentration, in regions very close to the surface, after nitriding at 500 °C. The N1s spectra shifted towards lower binding energies, indicating interaction between nitrogen and the matrix atoms, and the formation of nitrides in the nitrided layer. The nitrided thicknesses experienced close values at 400 °C (10 h) and 500 °C (5 h), provided at 400 °C the layer was mostly a supersaturated solid solution but at 500 °C it was composed of iron nitrides and chromium nitride. High hardness values of above 1600 HV0.1 were obtained after optimum plasma nitriding as the result of combined effects of solution strengthening induced by nitrogen atoms and the presence of dispersed nitride phases. EBSD results indicated residual stress within the nitrided layer, which would affect the corrosion fatigue resistance. Experimental findings demonstrated that both aging and plasma nitriding substantially enhanced the corrosion fatigue resistance of 17-4 PH stainless steel in 3.5 wt% NaCl. Moreover, simultaneous aging and plasma nitriding proved superior behavior in corrosion fatigue, primarily due to delayed crack initiation and improved fatigue resistance, without the risk of overaging which is detrimental to mechanical properties.

Predicting crack nucleation in commercially pure titanium using orientation imaging microscopy and machine learning

Due to the prohibitively long experimental and simulation times, dwell fatigue (DF) failure prediction in titanium and its alloys is a challenging task. Since most of these failures have a microstructural level origin, this work focusses on utilizing minimal experiments and machine learning for predicting failure initiation points in a given microstructure. Failure initiation points in commercially pure titanium were identified using interrupted tensile and DF tests. Orientation imaging data was used to train a Random Forest model to calculate the relative importance of various grain orientation-based features to crack nucleation. Subsequently a predictive model for identifying locations that are likely to form a DF crack in a microstructure is developed.