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In this paper, the dynamic recrystallization (DRX) mechanism, texture evolution and the effect of γ ′on the microstructure evolution of a new nickel-based superalloy at 1075 °C and strain rate of 0.01 s−1 were systematically investigated. The results showed that the DRX mechanism undergoes significant alterations with the increase of strain. When the strain is 0.07, the discontinuous dynamic recrystallization (DDRX) constitutes the dominant mechanism. As the strain increases to 0.13, the DDRX mechanism transforms into continuous dynamic recrystallization (CDRX), and the dynamic recrystallization (DRXed) grains grow when the strain is further increased to 0.20. The texture evolution indicated that with the increase of strain, the crystal orientation shifts from and to and , and texture intensity initially weakens and then strengthens, which is closely associated with the DRX mechanism. At a strain of 0.07, the texture is primarily influenced by the DRXed grains. As the strain increases to 0.13, the deformed grains become the dominant factor in determining the texture, and at a strain of 0.20, both the DRXed and deformed grains jointly dominate the texture. The CDRX mechanism facilitates the formation of and textures, while DDRX is mainly related to orientation. Additionally, due to the L12 ordered structure of the γ′ phase, dislocations and stacking faults gradually accumulate in the γ′ phase with the increase of strain, while the dislocation density in the γ matrix initially ascends and then descends.

Directed energy deposition (DED) is an additive manufacturing (AM) process based on welding technology and offers the advantages of large build volume, high deposition rate, and ability to fabricate multi-material parts. Epitaxial continuous columnar grain growth is a characteristic microstructural feature of DED processed alloys. In this study, a bamboo-like microstructure (periodic alternation of equiaxed and columnar structure) was produced by adopting an intermittent deposition strategy in 316L stainless steel and Inconel 625. The formation of a bamboo-like alternating microstructure was confirmed through electron backscattered diffraction (EBSD) analysis. Hardness mapping showed that the columnar to equiaxed transition (CET) occurred at the region right below the fusion line. A finite element (FE) model was used to investigate the relationship between the temperature gradient (G) and the solidification rate (R). The FE model showed a low G/R ratio at the region right below the interface promoting the CET. The grain size and material-dependent deformation behaviors are analyzed using digital image correlation (DIC). The lower deformation on the fine-grain regions observed in DIC analysis is attributed to a higher strain hardening rate, which is confirmed through dislocation density analysis on a tensile-interrupted specimen. The periodically alternating grain size coupled with the microstructural changes caused by intermittent deposition strategy result in a better strength-ductility synergy in both single-material and bimetallic specimens.

In this paper, a finite element model is developed to investigate residual stress and microstructural changes in 18CrNiMo7-6 alloy steel during pre-mixed jet strengthening. The model employs a dislocation density-based constitutive relationship, with parameters optimized via a genetic algorithm. A fully coupled stress integration algorithm ensures the numerical stability. The model is validated by experiments, with a maximum error of 2.6% in predicting residual stress. It is shown that the dislocation cell sizes measured from experiments are consistent with that obtained by simulations. As the peening intensity increases, the maximum residual stress, the depth of a residual stress layer, and the thickness of a compressive residual stress layer gradually increase. The rise in residual stress is accompanied by formation of dislocation proliferation and refined microstructural layers. Additionally, the depth of a refined layer increases with a higher pre-mixed jet intensity. While the coverage increase has a minimal impact on the smallest average dislocation cell size, larger shot diameters lead to smaller dislocation cell sizes.

Cyclic bending under tension (CBT) has been shown to increase room temperature elongation-to-failure in various sheet metals beyond that of simple tension. A greater understanding of deformation mechanisms in CBT would allow for its elongation-enhancing effects to be more fully exploited, creating potential for new forming strategies. CBT-induced cyclic bending/unbending stresses combined with applied macroscopic tensile stresses create complex through-thickness stress profiles, where differing hardening behavior is expected near the surfaces compared with the middle of the sheet. This work uses high resolution electron backscatter diffraction characterization of geometrically necessary dislocation density together with X-ray diffraction-based evaluations of total dislocation density and in-plane digital image correlation to provide an in-depth analysis of through-thickness dislocation development and associated hardening rates throughout the CBT process in CP-Ti Grade 4 sheet metal. It was found that dislocation density is relatively uniform across the sheet at lower cycles, increases in the sheet center at higher cycles, and eventually approaches saturation near failure. Namely, dislocation accumulation occurs more slowly in the ratcheting, bending/unbending portions of the sheet (i.e., near the surfaces) from cyclic load reversals, and develops faster in the central tensile portion, where dislocation density up to 1.43x higher than near the surfaces was observed. High dislocation densities in the sheet center were found to precede significant central void accumulation, concentrating damage away from peak surface stresses, presumably contributing to delayed failure.

Cast tungsten carbide (CTC) is a biphasic, pearlitic-like structure composed of WC lamellae in a matrix of W2C. Besides excellent flowability, spherical CTC powders exhibit superior hardness and wear resistance. Nevertheless, the available literature generally fails to explain the physical mechanisms behind such a phenomenon. In the present work, the microstructure and the mechanical properties of the novel centrifugally-atomized spherical CTC have been extensively investigated. This material exhibited an extremely fine microstructure, with WC lamellae of 27–29 nm in thickness and bulk lattice strains of 1.0–1.4 %, resulting in a microindentation hardness of 31.4 ± 1.6 GPa. The results of this study clearly show that centrifugally-atomized CTC is mechanically superior to both spheroidized CTC and conventional cast-and-crushed CTC. In addition, the effect of a series of heat treatments on the bulk fracture toughness and the fatigue life of entire CTC particles was also investigated. The reduction of residual stresses in the bulk of particles upon annealing dramatically increased the indentation fracture toughness, whereas the bulk microindentation hardness remained essentially unaffected. Regarding the fatigue life of entire particles under uniaxial cyclic compressive loading, local phase transformation phenomena at the surface of the particles upon heat treatment were concluded to play the most critical role. Indeed, the cumulative fatigue damage was minimized in surface-carburized CTC powders, where compressive stresses were induced at the outermost surface.

After undergoing 75% hot deformation and 40% cold deformation, a variant of TWIP (Twin Induced Plasticity) steel with a composition of Fe–22Mn−2.7Al−0.95C−0.75Si (wt.%) was subjected to annealing at various temperatures (850 °C, 650 °C, 550 °C) for 20min. The recovery annealed C550 sample exhibited a yield strength of 1289.20 MPa, a tensile strength of 1442.29 MPa and an elongation of 30.78%. Characterization and comparison of the samples were conducted using XRD, SEM, EBSD, TEM and uniaxial tensile tests. The yield strength of the sample was assessed through different strengthening mechanisms to analysis the exceptional properties of the recovery annealed sample. Experimental findings indicate that the high-density dislocation and the refinement of slip bands in the recovery annealed C550 samples contribute to their superior performance compared to the partially and fully recrystallized samples.

We investigate the microstructural degradation during rolling contact fatigue (RCF) in a martensitic dual-hardening bearing steel. The dual-hardening steel makes use of both carbide precipitation and intermetallic precipitation hardening. The microstructural degradation leading to fatigue failure is studied using electron microscopy, atom probe tomography, and synchrotron X-ray diffraction (SXRD). The initial microstructure of the steel consists of tempered martensite with a fine dispersion of secondary M7C3, and NiAl precipitates. During RCF testing at 2.2 GPa contact pressure, ferrite microbands develop and the partial dissolution of NiAl and M7C3 precipitates occur within the ferrite microbands. For the RCF testing at higher contact pressure of 2.8 GPa, nanosized ferrite grains develop in the ferrite microbands. The SXRD analysis reveals a decrease in dislocation density in the sub-surface region experiencing microstructural degradation. This is believed to be associated with the rearrangement of dislocations into low energy configuration cells. We conclude this manuscript by proposing a microstructure decay mechanism for martensitic dual-hardening bearing steel that provides insights in the fatigue initiation process.

In the net-zero era, the burgeoning demands within engineering applications require materials that are not only lighter and stronger but also ductile. A robust strain hardening, crucial for achieving high strength and ductility, is challenging due to limited dislocation density evolution. This study discovers a cooperative strain-hardening strategy in a newly designed high-entropy steel (HES) with a density of 6.82 g/cm3. In this lightweight HES, the duplex microstructure of compositionally complex austenite and D03 intermetallic compounds facilitates the interplay between geometrically necessary dislocations (GNDs) and deformation twins (DTs) during plastic deformation. It generates a strain-hardening resilience during deformation and yields a very high dislocation density of 6.62 × 1015 m-2, contributing to strain hardening of over 900 MPa and a large elongation of 47 %. The resilient strain hardening achieved by the GND-DT cooperative strategy can be applied to various heterostructured alloys, offering a pathway for strong and ductile lightweight materials.

The effects of cold rolling reduction ratio, initial grain size, and aging condition (temperature and time) on static strain aging (SSA) behavior were systematically investigated in stable austenitic stainless steel. The aging treatment increased the yield strength (YS) and ultimate tensile strength (UTS), and the SSA effect was more pronounced at higher reduction ratio or smaller initial grain size. The SSA effect occurred in the temperature range of 400∼600 °C, where the accumulated dislocations remained in the form of wavy boundaries. Quantifying the dislocation density clearly showed that the SSA effect was directly related to the dislocation density. The volume shrinkage and increase in thermal expansion coefficient by aging treatment suggested the correlation between SSA behavior and atomic distribution changes. 3D atom probe tomography analysis clearly exhibited the clustering and segregation of solute C atoms during aging treatment. These results suggest that the SSA effect may be attributed to the interaction between solute C atoms and dislocations. Through grain refinement and optimal aging treatment at 500 °C for 1 h, the YS and UTS were significantly increased by 319 MPa and 230 MPa, respectively, to obtain a non-magnetic stainless steel with ultrahigh YS of up to 1600 MPa.

The microstructure and impact toughness of subcritically reheated coarse-grained heat-affected zone (SCGHAZ) of X80 pipeline steels with different Mo content (0Mo and 0.11 wt%Mo) were investigated. Gleeble 3500 thermal simulation experiment was used to simulate the heat-affected zone (HAZ) of X80 pipeline circumferential weld, and the two samples were characterized by a series of material testing techniques such as SEM, TEM, EBSD and XRD. The research showed that: Appropriate addition of Mo element can improve the hardenability of the matrix, increase the content of bainitic ferrite (BF) in the microstructure, refine the BF lath, cause plastic deformation, and reduce local stress concentration. The increase of BF content greatly increases the proportion of high angle grain boundary (HAGB) in order to effectively inhibit crack propagation. On the other hand, Mo element influences precipitation with solid solution, reduces the early energy barrier for nucleation, delays the disappearance of dislocation lines at high temperature, forms high-density dislocation grid, so that it can increase the nucleation site for NbC precipitation, prevent the coarsing of NbC, increases the threshold of external stress required for the generation of micropores induced by precipitation, and hinder crack initiation. The impact toughness of SCGHAZ was significantly improved by adjusting the microstructure and second phase morphology of HAZ by using Mo element microalloying.

Hot tensile features of a commercial 7046 aluminum alloy are investigated through employing high-temperature tensile tests. The evolving mechanisms of microstructures over high-temperature tensile parameters are systematically revealed. A unified dislocation-density related constitutive model is proposed to reconstruct hot tensile stress–strain behaviors. Results imply that the microstructural evolving features are acutely influenced by tensile parameters. The principal softening mechanism converts from dynamic recovery (DRV) to dynamic recrystallization (DRX), as the tensile temperature reaches 350 °C or above. The combined DRX nucleation features containing discontinuous DRX (DDRX) as well as continuous DRX (CDRX) together emerge. Furthermore, the CDRX behavior characterized by substructural nucleation and interaction becomes apparent at low tensile temperature or high strain rate, while the DDRX process is weaken. Through validation, the reproduced tensile stress, grain size as well as DRX fraction are good accordance with experimented values, which proves the proposed dislocation-density related equation can enjoy an outstanding reproduced capacity for the thermal tensile features of a 7046 aluminum alloy.

The impact toughness is the key to determine the service life of high strength wear-resistant steel for the lining boards of large-scale semi-autogenous grinding mill (SAG). It is difficult to predict the impact fracture failure of lining boards when SAG is running, which can cause damage to equipment once it occurs. Therefore, novel high strength wear-resistant steel was designed to improve impact toughness in this study. It is interestingly found that the microstructure contained finer bainite/martensite, and rare retained austenite (around 2 vol.%), which achieved trade-off between impact toughness and strength after the optimal heat treatment scheme (900 °C normalizing → 900 °C quenching → 300 °C tempering). The element segregation of Al and Si was improved and the start temperature of martensitic transformation during quenching was reduced, resulting in the refinement of martensite laths. Thus, the higher density of high-angle grain boundary (HAGB) and dislocation were obtained, which contributed to excellent impact toughness. Based on the instrumented impact curve, the total impact energy can be divided into four parts: elastic deformation energy (Ee), plastic deformation energy (Ed), crack stable propagation energy (Ep1) and crack unstable propagation energy (Ep2). Traditional toughening mechanisms focus on Ep1, which was based on the tortuous crack propagation path. Our experimental results show that Ed was another effective control unit to ensure the toughness. The difference between Ed and Ep1 in improving absorption energy was discussed in detail by combining HAGB density and dislocation density.

In this study, an ultralow temperature resistant bulb flat steel with ultra-high strength and good toughness is prepared to meet the application requirements of hull structural steel for polar ships and large ships. The bulb flat steel with a yield strength of 1292 MPa, elongation of 18.5 % and an impact energy of 53 J at − 196 °C is obtained by quenching and tempering process. In order to reveal the tempering response and strengthening mechanism during the quenching and tempering process of bulb flat steel, multi-scale characterization is carried out to explore the microstructural evolution and nano-precipitation behavior of the ultralow temperature bulb flat steel under different tempering processes. The results indicate that the preferential precipitation of (V, Nb)(C, N) causes dislocation multiplication, and the higher dislocation density in the matrix provides more nucleation sites for M2C. The slower diffusion rate of Mo effectively suppresses the rapid coarsening of M2C, which keep a good coherent relationship between the M2C and the α-Fe matrix. Strain concentration is avoided by synergizing the (V, Nb)(C, N) precipitation and the M2C precipitation of the coherent lattice, thus enabling the ultralow temperature resistant bulb flat steel to maintain ultra-high strength with good plasticity and toughness.

The evolution of the mechanical characteristics, residual stresses, and microstructure of a Cu–Fe–P alloy during machining was investigated, and the influence mechanism of the microstructure on the residual stress and strength of the Cu–Fe–P alloy was confirmed. The findings suggest that the tensile strength, transverse direction (TD), and rolling direction (RD) residual stresses in the cold-rolled state are 516 MPa, −80 MPa and −36 MPa, respectively, which are 76.1%, 93.8%, and 72.2% higher than those in the hot-rolled state, respectively. In addition, after annealing at high temperatures, the tensile strength, TD, and RD residual stresses of the Cu–Fe–P alloy decreased to 344 MPa, −9 MPa and −24 MPa, respectively, which were 33.3%, 88.8%, and 33.3% smaller than those of the cold-rolled alloy, respectively. The strength and residual stress of the Cu–Fe–P alloy are intriguing. The primary influencing aspects of the strength and residual stress are dislocations, grain boundaries, and textures. The residual stress of the Cu–Fe–P alloy may be controlled while maintaining strength by appropriately increasing the proportion of recrystallized grains and decreasing the dislocation density and volume fraction of the Brass texture, respectively. These outcomes serve as a guide for improving the service performance of Cu–Fe–P alloys.

HSLA steels with different polygonal ferrite and granular bainite contents resulting from two different cooling rates were investigated. Micropillar compression tests, electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) experiments were performed to reveal microscopic strength differences and their origin. The obtained results indicate that a higher cooling rate caused a smaller granular bainite substructure size and a higher dislocation density for both ferrite and bainite. In addition, the critical resolved shear stress (CRSS) values for both phases were found to be higher for the faster cooling process. This is ascribed to the increased dislocation density for faster cooling rather than the grain size as will be discussed in the manuscript. Interestingly, the macroscopic yield strength can be closely estimated by the CRSS obtained from micropillar compression considering the corresponding phase fractions. The achieved results can be used in future as input variables for crystal plasticity models.

The microstructure evolution and strengthening mechanism of materials after shot peening have always been the focus of research. In this paper, a novel coupled constitutive model was proposed to predict the depth of fine-grain of the 2060-T8 aluminum-lithium (Al–Li) alloy after shot peening. Besides, combining the numerical and experimental methods, the influences of shot size on yield stress, dislocation density, and crystal orientation of Al–Li alloy were systematically studied to reveal the strengthening mechanism. The results show that larger shot sizes can significantly improve the depth of the dislocation density layer and the fine-grain layer of 2060 Al–Li alloy. The depth of the refinement layer increases from 50 μm to 80 μm when the shot size grows from 0.3 mm to 0.6 mm. It is found the depth of the grain refinement layer in the experiment is consistent with the depth where is a sudden change of grain size in the simulation. Additionally, electron backscatter diffraction (EBSD) shows that many sub-grains are produced in the material due to high dislocation density, and the proportion of low-angle grain boundaries (LAGB) increases significantly, from 48.3% to more than 98.4%. The crystal orientation in the grain has changed obviously and Goss texture {100} obtained in the deformation band. In contrast, with the increase in shot size, the proportion of the Schmid factor with a high-level trend increases. However, the hardening effect of the material is much greater than the softening effect which results in higher yield stress and microhardness of the top surface.

In the present study, in order to find out a valuable method to decrease the hardness of heat-affected zone (HAZ), elemental partitioning was introduced before welding simulation to realize elemental redistribution. The results demonstrate that about 10% reduction of HAZ hardness can be achieved by introduction of elemental partitioning. During elemental partitioning, the content of retained austenite increases with increasing of elemental partitioned time. Further research reveals that the value of geometrically necessary dislocation density decreases with elemental partitioning. It is found that the alloying elemental contents in the matrix after elemental partitioning are lower than that without elemental partitioning. In addition, the differences of grain size distribution and elemental distribution resulted in elemental partitioning are studied and compared to explain the reason for the reduction in hardness.

Carbon nanotube (CNT)-reinforced aluminum alloys (Al) are considered to be the ideal metal-matrix composites owing to their high strength and elastic moduli. However, they have low ductility. In addition, the inhomogeneity of the structure makes a strong strain gradient during deformation. In this research, a series of simulations under uniaxial tension and shear loading paths were conducted to investigate the mechanical properties of CNT/Al6061 composite. The novel multiple mechanism-based strain gradient models (MMSG) were proposed to study and analyze the correlation between microstructure evolution and macro mechanical responses. The interfacial bonding, grain size, and dislocation density were mainly considered during the simulation. The results of this study can be used to reveal the synergetic strength and ductility of all the structural microstructure, which also affects the strain partition and failure of different phases in CNT/Al6061 composites.

12 μm thick rolled copper foil is the thinnest rolled copper foil that can be stably produced at present, which can be used for the production of high-end Flexible Printed Circuit (FPC) boards. With the miniaturized and multi-functional of various electronic components in the age of 5th Generation (5G) communication, higher requirements have been put forward for the etching performance of rolled copper foil. The microstructure of 12 μm thick rolled copper foil was obtained through thermal treatment at 180 °C for different times, and then the relationship between microstructure and etching performance was systematically studied. The research results show that the etching performance of rolled copper foil improves with the increasing of annealing time. But the etching performance of copper foil annealed for 10 min is better than that annealed for 30 min. Due to the low energy of Low Angle Grain Boundaries (LAGBs), the etching performance of copper foil gradually becomes better with the decreasing of LAGBs proportion. The etching performance of copper foil improves with the decreasing of work-hardening and dislocation density. The lower proportion of {001} crystal planes is the key reason for higher etching rate. The etching performance of copper foil is better with higher Random High Angle Grain Boundaries Network (RHGBN). The amount of grain boundaries decreases with the increasing of grain size, resulting in the decreasing of etching performance. In addition, it is found that the release of residual compressive stress on copper foil surface can also obviously improve the etching performance.

Rapid tempering is a remarkable sustainable and energy-efficient way to modify properties of as-quenched martensite, particularly its toughness and ductility. In this work, tensile and fracture toughness properties, and microstructural evolution of a medium-carbon (0.4 wt%), low-alloy steel under different rapid tempering circumstances are discussed. The hot-rolled and direct-quenched specimens were subjected to rapid tempering treatments (heating rate of about 90 °C/s) to the different tempering temperatures (320–720 °C). As a reference material, one sample was subjected to conventional tempering at 420 °C for one hour. The results indicated that the mechanical properties and microstructural features are influenced considerably by tempering temperature rather than the holding time. Despite the short tempering duration, the strength of tempered martensite dropped (from a max. tensile strength of ∼ 2100 MPa to a min. of ∼ 1100 MPa) while ductility increased with increasing tempering temperature (from a tensile elongation of 4% to ∼ 15%). However, the rapidly tempered sample at 420 °C experienced a loss of fracture toughness as a result of coarse stick-like cementite precipitation. Microstructural observations revealed that, even with a short time frame, tempering temperature plays a significant role in the resulting cementite morphology. At lower tempering temperatures, the cementite precipitates have a stick-like structure, while at higher temperatures, they become more globular/spheroid-like. This change in cementite morphology led to an enhancement in fracture toughness. Overall, the results indicated that, by a proper design of the rapid tempering process, an excellent combination of tensile properties and fracture toughness can be obtained compared to conventional tempering while significantly saving time and energy.

The static softening behavior and dislocation density evolution of TA15 titanium alloy during double-pass hot deformation were investigated under the deformation temperatures (910 °C–970 °C) and holding time (0s–2200s). The microstructure evolution of primary α phase was observed by optical micrograph (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The evolution of dislocation density was investigated via X-ray diffraction (XRD) and W–H model. The results showed that the globularization behavior of primary α phase is emerged during the inter-pass of double-pass hot deformation. The globularization process is promoted by the extension of the inter-pass holding time and the increase of the deformation temperature. The groove of primary α phase is preferentially generated when the inter-pass holding time within 1000s. Subsequently, that groove of primary α phase is separated and then those α phases are dissolved when the holding time over 1000s, leading to the fraction of α phase reduction. Compared with deformation temperature of 910 °C and 940 °C, all of the primary α phases are completely separated after 1000s of the inter-pass holding time under 970 °C. Additionally, through the analysis of various crystal surface of α phase, the dislocation density in the inter-pass gradually decreases with the holding time and deformation temperature increasing.

The blanket module of nuclear fusion reactor is proposed to be made of reduced activation ferritic martensitic (RAFM) steel. Thus, in order to prevent the unprecedented failure, the creep response of RAFM steel must be studied meticulously. In that direction, physical based creep curve modeling is one of the available choices to obtain the insights about the substructural evolution during the creep deformation, hence enabling to enlighten about material weakening mechanisms. In this paper, experimental creep curves of RAFM steel at varying conditions are simulated employing an improved dislocation density reliant physical model. The microstructure based internal variables are considered for addressing the mechanisms such as hardening, recovery, coarsening of precipitates and creep cavitation. All the simulated creep curves are found to be in reasonable agreement with the experimental creep curves. Furthermore, the evolution of involved eighteen parameters, i.e., dislocation glide velocity, climb velocity, internal stress, climb stress, effective stress, mobile dislocation density, dipole dislocation density, boundary dislocation density, subgrain radius, boundary pressure, boundary dislocation spacing, subgrain mobility and dipole capture spacing is demonstrated and discussed thoroughly.

Fe-XMn-5Si-10Cr-0.9C (X = 10, 15, 20, and 25 wt%) medium entropy alloys (MEAs) with different Mn contents were prepared by magnetic suspension melting in a water-cooled copper crucible, and casted in a negative pressure suction copper mould. The modified Warren–Averbach equation and the thermodynamic model were used to calculate the alloy dislocation density and stacking faults, respectively. The effects of the Mn content on the phase structure, stacking fault energy (SFE), dislocation density, and mechanical properties of the alloy were investigated. The results indicate that the MEAs possess a low stacking fault energy (∼8.50–14.44 mJ/m2) and a unique high as-cast dislocation density (up to 4.8 × 1015 m−2). The microstructure of the as-cast alloys consisted of austenite phase. As loading, the γ → ε martensite transformation occurs and is accompanied by obvious work-hardening behaviour. A low SFE and high ΔSmix improved the storage capacity of the dislocation density, promoted the formation of ε-martensite, and improve the strength and plasticity. Both the SFE and ΔSmix increased with an increase in the Mn content, and the dislocation density initially increased and then decreased. Optimising the Mn content and coordinating the balance between the SFE and ΔSmix can regulate the optimal dislocation density.

The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in grain interiors of strain-hardened specimens from STEM images. The dislocation density in the grain interior monotonically increased as the strain-hardening proceeded, while the dislocation density at the GB increased with strain-hardening up to 20% but slightly decreases upon further deformation to 40%. The decreased dislocation density at the GB was attributed to the formation of deformation twins. After the PWSCC growth test of strain-hardened Alloy 690, the fraction of intergranular (IG) fracture was obtained from fractography. In contrast to the change in the dislocation density with strain-hardening, the fraction of IG fracture increased remarkably when strain-hardened over 20%. From the results, it was suggested that the PWSCC growth behavior of strain-hardened Alloy 690 not only depends on the dislocation density, but also on the microstructural defects at the GB.

High strength and ductility are vital material properties required in alloys used for structural applications at cryogenic temperatures. However, the simultaneous provision of these characteristics is challenging because the two properties are mutually contrasting from the perspective of dislocation motion. Herein, we prepare binary Al-xMg alloys supersaturated with Mg using a combined technique of twin-roll strip casting and subsequent thermo-mechanical treatment; this produces Al alloys with both high strength and ductility at cryogenic temperatures. Experiments show that gradually adding Mg to Al significantly improves cryogenic tensile properties of the alloys. At the cryogenic temperature of the liquid N2 (−196 °C), the Al-5Mg and Al-7Mg alloys exhibit the ultimate tensile strength (UTS) of 370 and 450 MPa with the corresponding ductility of 93% and 87%, respectively. Comparing Al-xMg alloys with differing Mg contents elucidates avenues of simultaneously improving these properties for utilization at cryogenic temperature. This study provides a simple and robust approach for producing low-cost Al-xMg alloys with excellent cryogenic properties for structural applications.

Laser shock peening (LSP), a surface modification technique, is promising to enhance the strength and wear resistance for Ni-based superalloys. To understand the strengthening mechanism in a laser shock peened Ni-based superalloy DZ417G, we utilize synchrotron poly- and monochromatic X-ray microdiffraction, as well as electron microscopy and microhardness to quantify the local microstructures and mechanical properties at various depths. In the 1.2-mm-deep hardened layer, the microhardness increases monotonically by ∼50% from the unaffected interior to the surface. Quantitative microdiffraction analysis shows that large amounts of dislocations are introduced by LSP. High densities of 7.1 × 1015 m−2 and 11.8 × 1015 m−2 are seen close to the peened surface for the γ- and γ′-phases, respectively, which are 5 and 20 times of those in the unaffected region. Different gradients of dislocation density are observed for the two phases from interior to surface, and their combined effect accounts well for the hardness increment. Due to the unaltered γ′-precipitates and chemical composition in the LSP affected zone, the large density of dislocations dominates the observed strengthening. Combined poly- and monochromatic X-ray microdiffraction allows quantifying the local microstructures of plastic deformation over a large sampling scale that can hardly be achieved using other materials characterization techniques.

Understanding fatigue phenomena in metals is of great significance for mechanical performance in engineering systems. Microstructural evolution in austenitic stainless steels during cyclic plastic deformation has been studied via diffraction line profile analysis; however, their microstructure-dependent mechanical response upon stress partitioning in the matrix (austenite) and deformation-induced martensite has remained largely unexplored. In this study, the stress response analysis of austenitic stainless steel was performed using neutron diffraction. The phase stress in the austenite correlated well with the dislocation density in the phase. The actual stress in the martensite was nearly half of the assumed stress and the phase stress in the austenite. However, the apparent stress (the residual stress subtracted from the actual stress) was similar to the assumed stress as the martensite contains a fairly large compressive residual stress (approximately 1 GPa). Overall, the loading stresses at peak loads can be explained by sharing stress on the austenite and martensite.

The flow stress reduction during plastic deformation superposed with electric current, commonly referred as ‘electroplasticity’ has been actively researched over the past few decades. While the existence of an electron–dislocation interaction, independent of Joule heating is established, the exact rate controlling mechanism of the observed behaviour lacks consensus. Understanding the governing mechanism is complex due to the combined effect of Joule heating and electron–dislocation interaction. The present work attempts to establish the electroplastic mechanism in AA 6063 alloy and its nanocomposites. The role of microstructure on the electron interaction is investigated by preparing four distinct microstructure from the base alloy. All the samples were subjected to constant amplitude direct current during plastic deformation. The Joule heating effect is decoupled using the experimentally measured temperature history. The potential electroplastic mechanism for the alloy is elucidated by analysing the trend of flow stress reduction with strain and strain rate. It is inferred that micro Joule heating and electron wind effect cannot completely explain the observed electroplastic behaviour in AA 6063. The SiC particles in nano-composites suppressed the electroplastic effect.The observed mechanical behaviour under electric current is in agreement with the trend predicted assuming magnetic depinning mechanism. The reduction of dislocation density quantified using X-ray diffraction is found to concur with the inferred mechanism.

Softening mechanism and microstructure evolution of 2A14 aluminum alloy were studied via isothermal deformation tests under the temperatures range from 573 K to 773 K and strain rates range from 10−3 s−1 to 1 s−1. Microstructures indicated that the grain structure was composed of massive fine sub-grains while only a small quantity of recrystallized grains formed along grain boundaries. The quantity of sub-grains increased with the decrease of deformation temperature or the increase of deformation strain rate, and the correlations between the deformation conditions and the geometrically necessary dislocation (GND) and stored strain energy were illuminated with quantification. The softening mechanism under different conditions was in compliance with the analysis of processing map. The microstructure indicated that the governing dynamic softening mechanism was the dynamic recovery for the temperature below 773 K, and dynamic recrystallization played the dominant role in the softening mechanism at low strain rates for the temperature at 773 K. The Arrhenius constitutive model and physical-based constitutive model considering lattice diffusion have been established, and both two models can well predict the flow stress and GND density of 2A14 aluminum alloy.

In this research, the microstructure evolution in the machined subsurface is numerically simulated through a developed multi-physics model applied to H13 hot work die steel. The multi-physics model based on dislocation density evolution is utilized to predict the change of grain size through finite element analysis by varying cutting parameters. In spite of the cutting conditions, the simulated grain size on the top-most machined surface is around 330 nm, and the machining-affected depth with refined grain varies in the range of 25–45 μm. In addition, the appeared periodical fluctuation of dislocation density and grain size in a wavy configuration induced by the generated serrated chip segments is revealed. The efficacy of the proposed finite element model is verified and the probable mechanism of grain refinement is demonstrated with the assistance of TEM observation, which in turn promotes the in-depth understanding of microstructure evolution during metal cutting.

In this work, a modified synthesis method was deployed to obtain nanocrystalline zinc sulfide from zinc acetate. By utilizing the hydrothermal and sol gel method, the influence of: reaction time, solvent and temperature control were used to tune the properties of zinc sulfide. Our results showed that ZnS(B) (which was obtained by sol gel in water + hydrothermal) typified formation of increased sulfur vacancies while an increase in reaction time resulted in decreased sulfur vacancies. The introduction of chemical defects in ZnS(A) (which was obtained by sol gel in methanol + KOH) resulted in lower crystallite size. We observed that crystallinity improved with increased reaction time and utilization of water as solvent improved the crystallinity of the material as confirmed in ZnS(C) and ZnS(B). Furthermore, our result showed that reaction time influenced dislocation density of the material to a greater extent than type of solvent used. The crystallite size estimated by Scherer formula was in the range 1.35 nm – 18.64 nm while the band gap energy of the ZnS samples were calculated in the range 3.8 eV- 4.6 eV. Utilizing these novel syntheses methods can stimulate new directions in synthesizing ZnS crystals with options of choosing appropriate method for specific applications depending on properties to be traded off.

A high-performance full-field spectral crystal plasticity model referred to as MPI-ACC-EVPCUFFT is adapted to study the deformation behavior of additively manufactured Mar-M-509® cobalt-based superalloy. The model features a dislocation density-based hardening law for the evolution of slip resistance, a barrier effect induced by grain morphology to influence the slip resistance, and a slip system-level back-stress law for adjusting the driving force to slip. The model is used to interpret and predict strength of the alloy in tension, compression, load reversal, and low-cycle fatigue as a function of initial microstructure. The initial microstructure varied from sample-to-sample to represent the effects of build orientation and heat treatment. Results show that the model successfully reproduces phenomena pertaining to monotonic and cyclic deformation including the non-linear unloading, Bauschinger effect, and cyclic hardening/softening using a single set of model parameters. Moreover, the model offers insights into fluctuations of mechanical fields and strain partitioning.

A physically-based, mixed-phase structure-property model is presented for microstructure-sensitivity of tensile stress-strain response, including yield stress, ultimate tensile strength, uniform elongation and flow stress (strain hardening), for additively manufactured Ti-6Al-4V. The interdependent effects of solutes, grain size, phase volume fraction and dislocation density are explicitly included. Solid-state phase transformation and dislocation density evolution are incorporated to simulate the effects of martensite dissolution and α-β transformation at high temperature. Predictions are validated by comparison with measured tensile test data for (i) effects of additive manufacturing process conditions (such as build orientation and sample size) on tensile properties, based on the microstructure attributes inherited from the process, and (ii) the effect of temperature on tensile stress-strain response across a broad range of temperatures. The model is thus applicable for rapid process-structure-property prediction, in conjunction with AM process modelling, to capture the effects of key manufacturing variables and for process optimization.

The plastic deformation of the AlSi10Mg alloy manufactured via laser powder bed fusion (LPBF) is incompatible at the microscale, which causes residual strains/stresses and dislocation pile-ups at the Al/Si interfaces and grain boundaries. Hence, it is of fundamental significance to clarify these microscopic properties during plastic deformation. Here, in-situ neutron diffraction is employed to explore the residual strains, stresses, and dislocation density in the LPBF AlSi10Mg during loading-unloading-reloading deformation. It is found that the maximum residual stresses of the Al and Si phases in the loading direction reach up to about −115 (compressive) and 832 (tensile) MPa, respectively. A notable dislocation annihilation phenomenon is observed in the Al matrix: the dislocation density decreases significantly during unloading stages, and the amplitude of this reduction increases after experiencing a larger plastic deformation. At the macroscale, this dislocation annihilation phenomenon is associated with the reverse strain after unloading. At the microscale, the annihilation phenomenon is driven by the compressive residual stress in the Al matrix. Meanwhile, the annihilation of screw dislocations during unloading stages contributes to the reduction in total dislocation density.

Surface integrity is the permanent pursuit of industries for decades, and microstructure is a key factor controlling physical and mechanical properties of machined surfaces. During machining, a complicated non-uniform distribution of deformation fields will be applied to machined surfaces, as a result, microstructure evolution will be significantly influenced. In this study, a coupled finite element (FE) and cellular automata (CA) approach is used to characterize and predict microstructure evolution during high-speed machining oxygen-free high-conductivity (OFHC) copper, where a unique material model is presented to describe both constitutive behaviors and microstructure evolution, and a mixed mechanism of continuous dynamic recrystallization (cDRX) and discontinuous dynamic recrystallization (dDRX) is adopted to show grain refinement and grain growth procedure under gradient distributed fields of strains, strain rates and temperatures in machined surfaces. A similar gradient distribution of grain sizes is obtained through both simulation and experimental results, which validates the predictive model and presents an in-depth understanding of microstructure evolution process during surface formation, and it shows the primary factors influencing the grain size distribution in sub-surface are cDRX-induced grain refinement and dDRX-induced grain growth. Moreover, the gradient distribution of microstructures in refined sub-surfaces could be used to explain mechanisms of sub-surface damage in the future.

Residual stresses evidently affect the strength, fatigue property and machining deformation of the mechanical components. Therefore, stress relief processes are extensively applied in the manufacturing to enhance the mechanical properties of products. In this study, seven 7075 aluminium alloy specimens are treated by thermal- vibratory stress relief (TVSR), thermal stress relief (TSR), and vibratory stress relief (VSR). Finite element (FE) models considering the stress relaxation effects and transient periodic vibration loads are proposed to simulate the TVSR, TSR and VSR process. The residual stresses before and after the processes are measured and compared, and the effectiveness of the FE models is validated. Scanning electron microscope (SEM) and transmission electron microscope (TEM) are used to observe the microstructure and crystal dislocation, respectively. Results show that TVSR can evidently reduce the residual stress in aluminium alloy, and the stress relief rate of TVSR for the peak stress are 20.43% and 38.56% higher than that of TSR and VSR, respectively. It also found that TVSR has no obvious influence on the grain size, but evidently increase the dislocation density. Eventually, the stress relief mechanism of TVSR is analyzed and summarized.

Increased formability of aluminium alloys has been demonstrated via cryogenic deformation. In previous studies, the microstructures of samples deformed at low temperatures were analysed after reheating to room temperature (RT) and storage. However, after heating the dislocation structure and density of the deformed material do not reflect the cryogenic situation. In this work, we investigate the evolution of flow stress during recovery in Al-Mg and Al-Mg-Si alloys. We examine the RT recovery behaviour of samples pre-strained at 77 K to different strain levels, and evaluate the structural stability upon subsequent deformation. We also study microstructural evolution via in-situ synchrotron X-ray diffraction, starting from initial conditions at cryogenic temperatures to long-term RT-recovery. Recovery of cryogenically deformed samples at RT results in reduction of the flow stress, in dependence on RT storage. The recovery process can be divided into three distinct sections, each based on a different mechanism characterized by either the arranging or the annihilation of dislocations. Subsequent further straining at room temperature after cryogenic forming also generates plastic instabilities and premature fracture due to unfavourable hardening and recovery assisted softening interplay.

The relationship among tensile strength, Vickers hardness and dislocation density for two types of 11Cr-ferritic/martensitic steel (PNC-FMS) was investigated after aging at temperatures between 400 and 800°C up to 45,000h and after neutron irradiation. A correlation between tensile strength and Vickers hardness was expressed empirically. The linear relationship for PNC-FMS wrapper material was observed between yield stress and the square of dislocation density at RT and aging temperature according to Bailey–Hirsch relation. Therefore, it was clarified that the correlation among dislocation density, tensile strength and Vickers hardness to aging temperature was in good agreement. On the other hand, the relationship between tensile strength ratio when materials were tested at aging temperature and Larson–Miller parameter was also in excellent agreement with aging data between 400 and 700°C. It was suggested that this correlation could use quantitatively for separately evaluating irradiation effects from neutron irradiation data containing both irradiation and aging effects.

In the present study, the damping behavior of hybrid composites has been investigated using dynamic mechanical analyzer (DMA). The composites were fabricated with 2, 4, 6, and 8% by weight of rice husk ash (RHA) and SiC in equal proportions using two stage stir casting process. Damping measurements of all the specimens were obtained by dynamic mechanical analyzer (DMA) at different frequencies in air atmosphere. Scanning electron microscope (model JSM-6610LV) was used to study the microstructural characterization of the hybrid composites. It was observed that the dislocation density, which results from the thermal mismatch between the reinforcement and the matrix and the porosity of composites, has a great influence on the damping capacity of hybrid composites. The dislocation damping mechanisms were discussed with regards to the Granato–Lucke theory.

Hybrid metal matrix composites are of great interest for researchers in recent years, because of their attractive superior properties over traditional materials and single reinforced composites. The machinabilty of hybrid composites becomes vital for manufacturing industries. The need to study the influence of process parameters on the cutting forces in turning such hybrid composite under dry environment is essentially required. In the present study, the influence of machining parameters, e.g. cutting speed, feed and depth of cut on the cutting force components, namely feed force (Ff), cutting force (Fc), and radial force (Fd) has been investigated. Investigations were performed on 0, 2, 4, 6 and 8 wt% Silicon carbide (SiC) and rice husk ash (RHA) reinforced composite specimens. A comparison was made between the reinforced and unreinforced composites. The results proved that all the cutting force components decrease with the increase in the weight percentage of the reinforcement: this was probably due to the dislocation densities generated from the thermal mismatch between the reinforcement and the matrix. Experimental evidence also showed that built-up edge (BUE) is formed during machining of low percentage reinforced composites at high speed and high depth of cut. The formation of BUE was captured by SEM, therefore confirming the result. The decrease of cutting force components with lower cutting speed and higher feed and depth of cut was also highlighted. The related mechanisms are explained and presented.

The present study aims at finding the residual stresses on aluminum hybrid composites during turning operation. The composites with varying percentage by weight reinforcement of 2, 4, 6 and 8 RHA and SiC in equal proportions were fabricated using two stage stir casting process. X-ray diffraction was used to study the residual stresses on the surface layer of the machined surface. It was observed that the residual stresses generated during casting were considerably larger when compared to the stresses generated during machining of composites. It was also noticed that the residual stresses were found to decrease with the increase in the reinforcement and increases with the increase in cutting speed. The related mechanisms are explained and presented in this work.

A double stir casting process was used to fabricate aluminum composites reinforced with various volume fractions of 2, 4, 6, and 8 wt% RHA and SiC particulates in equal proportions. Properties such as hardness, density, porosity and mechanical behavior of the unreinforced and Al/x%RHA/x%SiC (x = 2, 4, 6, and 8 wt%) reinforced hybrid composites were examined. Scanning electron microscope (model JSM-6610LV) was used to study the microstructural characterization of the composites. It was observed that the hardness and porosity of the hybrid composite increased with increasing reinforcement volume fraction and density decreased with increasing particle content. It was also observed that the UTS and yield strength increase with an increase in the percent weight fraction of the reinforcement particles, whereas elongation decreases with the increase in reinforcement. The increase in strength of the hybrid composites is probably due to the increase in dislocation density. A systematic study of the base alloy and composites was done using the Brinell hardness measurement and the corresponding age hardening curves were obtained. It was observed that in comparison to that of the base aluminum alloy, the precipitation kinetics of the composites were accelerated by adding the reinforcement. This effectively reduced the time for obtaining the maximum hardness by the aging heat treatment.