Types Of Dislocations Research Articles

Iris Fixation for Intraocular Lens Dislocation: Relocation with Iris Suture Versus Exchange to Sutureless Iris Claw IOL

Background/Objectives: To compare the clinical outcome of suture and sutureless iris fixation techniques for dislocated intraocular lenses (IOLs). Methods: Retrospective cohort study including patients who underwent surgery for late IOL dislocation over a 10-year period. IOL repositioning was achieved either by suturing the original IOL to the iris using the Siepser slipknot technique or by replacing it with a retropupillary sutureless iris claw IOL. Data collected during surgery included the type of dislocation, the need for anterior or posterior vitrectomy, duration of surgery, and intraoperative complications. Six months after surgery we assessed the eye and iris anatomy; refraction, astigmatism, and visual acuity; endothelial cell damage; and rate of postoperative complications. Results: Included in the study were 60 patients: 32 underwent IOL relocation and 28 underwent IOL exchange. Pseudoexfoliation (43.7% and 39.3%) and retinal surgery (34.4% and 28.6%) were identified as the main possible causes for IOL dislocation. The mean duration of the surgery was 62.9 ± 14.9 min for the Relocation group, and was 42.7 ± 11.4 min for the Exchange group (p < 0.001), with similar low intraoperative complication rates (6.25% and 7.14%, respectively). The studied parameters showed no differences between the two groups postoperatively, except for corneal astigmatism which was 1.31 ± 0.45 D in the Relocation group and was 1.89 ± 0.86 D in the Exchange group (p < 0.001). Conclusions: Both suture and sutureless iris fixation techniques for dislocated IOLs yielded similarly favorable outcomes in this study. IOL relocation resulted in less postoperative astigmatism, while IOL exchange offered the advantage of shorter surgical time.

Bridging length and time scales in predictive simulations of thermo-mechanical processes

Abstract This work introduces a theoretical formulation and develops numerical methods for finite element implementation of the formulation so as to extend the Concurrent Atomistic-Continuum (CAC) method for modeling and simulation of finite-temperature materials processes. With significantly reduced degrees of freedom, the CAC simulations are shown to reproduce the results of atomically resolved molecular dynamics simulations for phonon density of states, velocity distributions, equilibrium temperature field of the underlying atomistic model, and also the density, type, and structure of dislocations formed during the kinetic processes of heteroepitaxy. This work also demonstrates the need of a mesoscale tool for simulations of heteroepitaxy, as well as the unique advantage of the CAC method in simulation of the defect formation processes during heteroepitaxy.

Study on micro-deformation in micro-grinding of selective laser melting FeCoCrNi high-entropy alloy based on molecular dynamics

Microscopic deformation behavior is an important part of the study of micro-grinding processing. This paper investigates the removal mechanism in the micro-grinding of selective laser melting FeCoCrNiAl0.5 high-entropy alloy. The micro-grinding process is analyzed through simulation using the molecular dynamics simulation method. The study examines how the thickness of the undeformed chip and the grain size affect the microdeformation behaviors of shear strain, micro-grinding force, the evolution of dislocations, and microstructural transformation. The experimental results confirm that the molecular dynamics simulation model accurately predicts the micro-deformation behavior of FeCoCrNiAl0.5 high-entropy alloy during micro-grinding. The micro-deformation mechanism involves dislocation slip and twinning deformation, while the removal mechanism mainly includes the elimination of axial and dendritic crystals. During micro-grinding, the grinding force experiences small to large fluctuations, and the total length of dislocations gradually increases. As the undeformed cutting thickness increases, the micro-grinding force also gradually increases. Simultaneously, the type of dislocations and laminar dislocation nuclei increase, leading to growth in the total length of dislocations. The number of high shear strain atoms, the micro-grinding force, and the degree of fluctuation in the single crystal high-entropy alloy are higher than those in the polycrystalline material, but the total dislocation length is significantly smaller.

Functional Outcome of Acromioclavicular joint dislocation Type III injuries treated with Hook Plate

The acromioclavicular joint (AC) dislocation is a complex injury due to the disruption of ligaments and joints, leading to instability and pain. Rockwood type III injuries remain controversial, so clinical evaluation should be taken into consideration before deciding the treatment modalities. The study aimed to evaluate the functional outcome of AC joint dislocation type III injuries treated with a hook plate. A total of 30 patients with AC Joint Dislocation Type III injuries were treated with open reduction and fixation with hook plate during a period of 18 months. The functional outcome was evaluated using constant murley score, the mean score of which was 82 (58-96). There were 7 (23.33%) cases of plate impingement and the symptoms was improved after plate removal. The hook plate is a good fixation device for the treatment of AC joint dislocation -Rockwood type III injuries with minimal complications, as it is a simple procedure, with good functional outcome, without ligamentous procedure and the only drawback is second surgery for implant removal.

Functional and subjective outcomes after surgical management of complex elbow dislocations: a retrospective study.

Dislocations of the elbow are the second most frequent upper-body injury after shoulder dislocations, comprising 11-28% of all elbow injuries. Complex elbow dislocations pose challenging management due to the involvement of critical stabilizing structures. This study aimed to investigate functional and subjective outcomes (MEPS, DASH, Oxford score) in 44 patients with complex elbow dislocations who underwent surgery between 2018 and 2020, with subgroup analysis focusing on gender and age differences. A retrospective analysis was conducted on patients treated at C.T.O. Hospital, Turin, for complex elbow dislocations between January 2018 and December 2020. Surgical approaches included radial head synthesis, coronoid fixation, ligamentous repair, and ulnar nerve management. Postoperatively, patients followed a standardized or individualized program. Data analysis involved t-tests to assess score differences between subgroups. Among the 44 analyzed patients, the mean age was 48years, and the mean follow-up time was 29months. Various types of complex dislocations were identified, with radial head and coronoid fractures classified accordingly. Surgical approaches included multiple methods of reduction and synthesis. While most patients adhered to postoperative programs, subsequent reoperations were conducted in 11% of cases. Scores did not significantly differ between genders, although a trend toward better DASH scores in males was observed. Younger patients showed better, though not statistically significant, outcomes in mobility and functional measures. This study underscores the importance of pre-operative assessment for positive surgical outcomes in complex elbow dislocations. Additionally, findings suggest that younger age may correlate with slightly better functional outcomes. Despite limitations such as retrospective design and sample size, the study enhances our understanding of complex dislocation outcomes and provides valuable insights for future interventions.

Comparison on Hysteresis Loops and Dislocation Configurations in Fatigued Face-Centered Cubic Single Crystals

The aggregation and evolution of dislocations form different configurations, which are the preferred locations for fatigue crack initiation. To analyze the spatial distribution of the same dislocation configuration and the resulting configuration morphologies on different observation planes, several typical hysteresis loops and dislocation configurations in fatigued face-centered cubic single crystals with various orientations were compared. The crystal orientations of these specimens were determined by the electron back-scattering diffraction technique in a Cambridge S360 Scanning Electron Microscope. It is well known that dislocation ladder and wall structures, as well as patch and vein structures, are distributed on their respective observation planes, (12¯1) and (111). These correspond to the point defect direction and line defect direction of dislocations, respectively. Therefore, the wall structures on the (12¯1) and (111) planes consist of point defects and line defects, which can be defined as point walls and line walls, respectively. Furthermore, the walls on the (12¯1) plane consist of Persistent Slip Band ladders connected with each other, corresponding to the formation of deformation bands. The evolution of dislocation patterns follows a process from patch to ladder and from vein to wall. The formation of labyrinths and dislocation cells originates from the activation of different secondary slip systems. In one word, it can help us better understand the physical nature of metal fatigue and failure by studying the distribution and evolution of different configurations.

Do we have to redefine type B-fractures of the rib cartilage?

Aim of this work was the evaluation and validation of the AO/OTA classification of the anterior chest wall, here especially for the rib cartilage. Study design was a retrospective analysis of patients who were hospitalized with fractures of the thoracic wall in the years 2010-2016. This resulted in a collective of n = 124 patients. All fractures of the anterior chest wall were classified according to their location, dislocation and fracture type according to the AO classification. An analysis of possible subtypes was carried out. 29.0% (36) of the patients had fractures of the rib cartilage. 23 of the 36 (64%) patients had multiple fractures, the total number of single fractures amounted to 94. 53.2% (50) of these fractures were in the right hemithorax, 46.8% (44) in the left hemithorax. 95.7% (90) of the fractures were A-fractures, 4.3% (4) were C-fractures. There were no B fractures. The C fractures also consisted exclusively of A fractures (AA fractures). 59.6% (56) of the fractures showed a dislocation. 30.9% (29) were avulsion fractures of either the osteochondral (22.3% (21)) or the sternocostal junction (8.5% (8)). The costal cartilage obviously does not show typical B fractures as we know them from shaft fractures of long bones. We have compiled a structured analysis in the attached manuscript and validated the classification proposal. In conclusion, we propose an adaptation of the classification proposal based on our data with redefining type B fractures as fractures of the osteochondral joints.

Spatial arrangements and types of dislocations in interfacial networks obtained by Si(001) wafer bonding at low twist angle: A TEM characterization

Two interfacial dislocation networks were obtained in a Si–Si material system by wafer bonding process for low twist angles around 0.2°. For one sample, one of the two initial wafers was rotated with an additional angle of 90° before the bonding. TEM analyses of samples prepared for planar and transverse views show different characteristics in terms of spatial arrangement and dislocation types. Long climbing segments slightly deviated from the [100] axis and short segments a/2<101> are arranged in the dislocation network obtained with an additional rotation and at the lowest twist angle (Ψ = 0.18°) from a <110> axis. Long screw segments a/2<110> and short partial Shockley segments are arranged in the dislocation network obtained without any additional rotation at the highest twist angle (Ψ = 0.27°) from a <110> axis. In both cases, the long and short segments form elongated hexagonal patterns, which are accurately ordered in one set paving the <100> directions or randomly ordered in two perpendicular sets paving the <110> directions, respectively. The results are discussed taking into account the arangement of the surface miscut steps in the initial wafers before the bonding.

Resolving localized geometrically necessary dislocation densities in Al-Mg polycrystal via in situ EBSD

The distribution of geometrically necessary dislocation (GND) densities is critical to understanding the heterogeneous plastic deformation at intragranular scales in polycrystals. In this work, we performed an in situ electron backscatter diffraction (EBSD) measurement during the tensile test on a polycrystalline Al-Mg alloy. The EBSD patterns were processed through the integrated digital image correlation algorithm to enhance angular resolution. Based on the Nye dislocation density tensor, GND densities of 18 dislocation types in fcc crystals were resolved and mapped at macroscopic strains ranging from 5% to 16%. The evolution of GND distribution showed that GNDs were generated near grain boundaries at small strains and later localized at grain interiors along subgrain boundaries and slip bands at large strains. The inhomogeneous increase in GND densities of different dislocation types, representing dislocation substructures, along the subgrain boundaries was disclosed. Meanwhile, high GND densities were observed along the slip bands when a double noncoplanar slip system was activated inside the grains. The obstructed movement of dislocations by Lomer junctions explained the GND storage in different {111} slip planes. The existence of Lomer junctions was proven by Burgers circuit analysis with high-resolution transmission electron microscopy, which explained the increase in [101] screw dislocation density according to the dislocation reaction.

Molecular Dynamics Study on the Mechanical Behaviors of Nanotwinned Titanium

Titanium and titanium alloys have been widely applied in the manufacture of aircraft engines and aircraft skins, the mechanical properties of which have a crucial influence on the safety and lifespan of aircrafts. Based on nanotwinned titanium models with different twin boundary spacings, the impacts of different loadings and twin boundary spacings on the plastic deformation of titanium were studied in this paper. It was found that due to the different contained twin boundaries, the different types of nanotwinned titanium possessed different dislocation nucleation abilities on the twin boundaries, different types of dislocation–twin interactions occurred, and significant differences were observed in the mechanical properties and plastic deformation mechanisms. For the {101-2} twin, basal plane dislocations were likely to nucleate on the twin boundary. The plastic deformation mechanism of the material under tensile loading was dominated by partial dislocation slip on the basal plane and face-centered cubic phase transitions, and the yield strength of the titanium increased with decreasing twin boundary spacing. However, under compression loading, the plastic deformation mechanism of the material was dominated by a combination of partial dislocation slip on the basal plane and twin boundary migration. For the {101-1} twin under tensile loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane and crack nucleation and propagation, while under compression loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane and twin boundary migration. For the {1124} twin, the interaction of its twin boundary and dislocation could produce secondary twins. Under tensile loading, the plastic deformation mechanism of the material was dominated by dislocation–twin and twin–twin interactions, while under compression loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane, and the product of the dislocation–twin interactions was basal dislocation. All these results are of guiding value for the optimal design of microstructures in titanium, which should be helpful for achieving strong and tough metallic materials for aircraft manufacturing.

Influence of the type of atlantoaxial dislocation secondary to os odontoideum on sagittal alignment and balance of the subaxial cervical spine after posterior atlantoaxial fusion.

This retrospective study aims to investigate the effect of the type of atlantoaxial dislocation due to os odontoideum on the sagittal alignment and balance of the cervical spine after posterior atlantoaxial fusion. Data of 48 consecutive patients who underwent posterior C1-C2 fusion to treat atlantoaxial dislocation/instability due to os odontoideum were retrospectively reviewed. Radiographic variables, namely the T1 slope (T1S), C1-C2 angle, C2-C7 angle, C1-C2 sagittal vertical axis (SVA), C2-C7 SVA, and modified atlas-dens interval (MADI), were measured preoperatively, immediate postoperatively, and at final follow-up. Patients were divided into three groups based on the preoperative MADI. Differences within and between groups in radiographic variables and relationships between the investigated variables were analyzed. The MADI was correlated with the preoperative to postoperative changes in the C1-C2 angle (r = 0.776, P < 0.05) and C2-C7 angle (r = -0.357, P < 0.05). In the group with anterior atlantoaxial dislocation, the C1-C2 angle and C2-C7 SVA were significantly enlarged at final follow-up (P < 0.05), while the C2-C7 angle was significantly reduced (P < 0.05). The changes in C1-C2 angle and C2-C7 angle were opposite between the posterior group and the anterior dislocation group. The direction/type of atlantoaxial subluxation correlates with the changes in lower cervical curvature after atlantoaxial fusion. Patients with atlantoaxial posterior dislocation and atlantoaxial instability are less likely than those with atlantoaxial anterior dislocation to develop loss of lordosis after posterior atlantoaxial fusion.

Clinical treatment of traumatic hip dislocation in children: a single-centre retrospective study

This study aimed to analyse the treatment and outcomes of traumatic hip dislocation (THD) in children. Clinical data of children with THD were collected at our clinical centre from 1 June 2012 to 1 January 2023. Demographic data, injury mechanism, type of dislocation, combined injuries, reduction time, reduction method, and radiographs were analysed. The Merle d’Aubigné–Postel hip score was used to evaluate hip function and complications at the final follow-up. A total of 19 children with THD were enrolled, including 12 male and seven female patients, with an average age of 8.28 ± 0.99 years. Posterior dislocation was the main type of dislocation (89.47%). Fifteen patients (78.95%) had experienced high-energy injuries and traffic accidents were the main causes of injury (47.37%). Closed reduction was performed as soon as possible, and open reduction was performed if necessary. The hip scores of 18 patients (94.74%) were excellent. One patient had osteonecrosis of the femoral head, with a hip function score of 10 (moderate). High-energy injuries, such as traffic accidents, have gradually become the main cause of injury. The prognosis for THD in children is generally good.

Investigation of the Dislocation Behavior of 6- and 8-Inch AlGaN/GaN HEMT Structures with a Thin AlGaN Buffer Layer Grown on Si Substrates

Developing cost-effective methods to synthesize large-size GaN films remains a challenge owing to the high dislocation density during heteroepitaxy. Herein, AlGaN/GaN HEMTs were grown on 6- and 8-inch Si(111) substrates using metal–organic chemical vapor deposition, and their basic properties and dislocation evolution characteristics were investigated thoroughly. With the insertion of a 100 nm thin AlGaN buffer layer, bow–warp analysis of the epitaxial wafers revealed excellent stress control for both the 6- and 8-inch wafers. HR-XRD and AFM analyses validated the high crystal quality and step-flow growth mode of GaN. Further, Hall measurements demonstrated the superior transport performance of AlGaN/GaN heterostructures. It is worth noting that dislocations tended to annihilate in the AlN nucleation layer, the thin AlGaN buffer layer, and the GaN buffer layer in the initial thickness range of 200–300 nm, which was indicated by ADF-STEM. To be specific, the heterointerfaces exhibited a significant effect on the annihilation of c-type (b = &lt;0001&gt;) dislocations, which led to the formation of dislocation loops. The thin inserted layers within the AlGaN buffer layer played a key role in promoting the annihilation of c-type dislocations, while they exerted less influence on a-type (b = 1/3&lt;112¯0&gt;) and (a+c)-type (b = 1/3&lt;112¯3&gt;) dislocations. Within an initial thickness of 200–300 nm in the GaN buffer layer, a-type and (a+c)-type dislocations underwent strong interactions, leading to considerable dislocation annihilation. In addition, the EELS results suggested that the V-shaped pits in the AlN nucleation layer were filled with the AlGaN thin layer with a low Al content.

Radiological characteristics and injury mechanism of Logsplitter injury: a descriptive and retrospective study

BackgroundLogsplitter Injury is a type of high-energy ankle fracture dislocation. The mechanism of injury has not been described in detail. A detailed understanding of the radiological features and pathological changes can further guide treatment.MethodsBetween April 2009 and December 2018, a retrospective analysis was conducted on 62 patients with Logsplitter injury. The study analysed the characteristics of fibular injury, tibial injury, syndesmosis injury, medial injury and lateral ligament injury on preoperative X-ray and CT scans. The incidence of the different injury types was summarised. The correlation between Logsplitter injuries and the mechanisms causing them were analysed using the Lauge-Hansen classification of ankle fractures.ResultsThe study provides data on the types of fractures observed. Of the total fractures, 98.4% were open fractures. The fibula injuries were classified as no fracture (1.6%), transverse or short oblique fractures (61.3%), butterfly fragments (25.8%), and comminuted fractures (11.3%). The tibial injuries included compression of lateral articular surfaces (38.7%) and posterior compressions (6.5%). Medial injuries, including medial malleolar fractures, accounted for 87.1%, and deltoid ligament rupture accounted for 12.9%. The study found that injuries to the syndesmosis consisted of simple ligament ruptures (11.3%), Tillaux fractures (8.1%), Volkmann fractures (43.5%), and Tillaux and Volkmann fractures (37.1%). In 12.9% of cases, there was a complete rupture of the lateral collateral ligament. Based on the Lauge-Hansen classification, 87.1% of injuries were pronation-abduction injuries, while 8.1% were pronation and external rotation injuries, and 1.6% were supination external rotation injuries. Furthermore, 3.2% of cases could not be classified.ConclusionThe pathoanatomic characteristics of Logsplitter injury are diverse, with some cases accompanied by collateral ligament injury. It is important to note that these evaluations are objective and based on current results. The most common injury mechanism is vertical violence combined with abduction, although in some cases, it may be a vertical combined external-rotation injury.Level of evidence(4) case series.Trial registrationThis study has been approved by the ethical research committee of the Honghui Hospital of Xi’an Jiaotong University, under the code: 202,003,002.

Micropillar compression of single-crystal single-phase (Co, Cu, Mg, Ni, Zn)O

Bulk, polycrystalline (Co, Cu, Mg, Ni, Zn)O was synthesized using solid-state sintering. Micropillars were prepared and mechanically deformed along three crystallographic orientations: (001), (101), and (111). Pillars (001) and (111) cracked, while Pillar (101) remained intact. Pillars (001) and (101) exhibited activated slip systems, confirmed by a large stress drop, and the presence of slip bands, respectively. Schmid factor (SF) analysis was performed to examine the effect of grain orientations on dislocation activity and slip behavior. SF values range from 0 to 0.5, with non-zero values indicating potential for slip. Six slip systems exist in the (Co, Cu, Mg, Ni, Zn)O rock salt crystal structure: 1/2⟨110⟩11¯0. For the (001) orientation, four slip systems are potentially active (SF = 0.5). For the (101) orientation, there are four potentially active slip systems (SF = 0.25). For the (111) orientation, no potentially active slips systems exist (SF = 0). Dislocation structures, which were observed post-compression via transmission electron microscopy, demonstrated variations in size, number, and distribution across the pillar, depending on micropillar orientation. Entangled dislocations created misorientation in Pillar (001), which led to the possible formation of subgrains, while singular dislocations were observed in Pillar (101), and a lack of dislocations was observed in Pillar (111). Zener–Stroh type dislocation entanglement-mediated cracking is the proposed cause of the transgranular-type cracks in Pillar (001). The possible subgrain formation, or lack of formation, respectively, caused intergranular-type cracks to additionally form in Pillar (001), while Pillar (111) only exhibited transgranular-type brittle fracture. In combination, these findings highlight the importance of dislocation activity, without the need for elevated temperature, and grain orientation in controlling the mechanical deformation response in single-phase (Co, Cu, Mg, Ni, Zn)O.

Molecular dynamics study on tribological properties of AlCrFeCoNi HEA at different temperatures

The microscopically wear mechanism of AlCrFeCoNi HEA effected by high temperatures still remains unclear. In this work, the tribological properties of AlCrFeCoNi HEA and tungsten carbide (WC) at temperatures ranging from 250, 400, 550, 700, 850 °C was investigated using molecular dynamics methods. Additionally, the shear strain, contact stress, and energy change at different temperatures were analyzed to explore the atomic wear mechanism. The simulated results indicated that the coefficient of friction and wear rate decrease with the increasing temperature, since the dislocation types decrease and the kinetic energy and total system energy increase. And high temperature can inhibit the synergistic effect of strain accumulation and atomic wear on the surface of AlCrFeCoNi HEAs.

OUTCOMES OF SHOULDER ARTHROSCOPY FOR ACROMIOCLAVICULAR JOINT DISLOCATION WITH EXTRA-GLENOHUMERAL JOINT CORACOID BASE EXPOSURE TECHNIQUE

Background: Acromioclavicular (AC) joint dislocation accounted for 9% of all shoulder injuries. Classical nonanatomic fixations might cause joint instability or redislocation. We aimed to evaluate the effectiveness of shoulder arthroscopy using the extra-glenohumeral joint coracoid base exposure technique for AC joint dislocation. Methods: Our prospective study recruited 20 patients with AC joint dislocation who underwent shoulder arthroscopy using extra-articular coracoid base exposure technique from October 2020 to June 2021. Demographic information, clinical features, and Rockwood type were collected. Our primary endpoint was the Constant score and the improvement in coracoclavicular (CC) distance. Results: The mean follow-up period was 30.75 (min–max 23–40) months. AC joint dislocation of Rockwood type III ([Formula: see text] = 6), type IV ([Formula: see text] = 8), and type V ([Formula: see text] = 6) was assessed; six cases (30%) had combined injuries: four cases had impingement subacromial, one case had Bankart injury, one case had the coracoclavicular joint screw fixation which was failed at the first time. The mean Constant score before surgery was 50.00 ± 6.74, after surgery was 96.50 ± 3.41 ( [Formula: see text] [Formula: see text] 0.001). The mean CC gap before surgery was 20.82 ± 2.20, after surgery was 9.91 ± 1.38 ([Formula: see text] [Formula: see text] 0.001). One case had a loss of reduction with a Constant score of 96. Conclusions: Arthroscopic treatment for acromioclavicular joint dislocation achieved satisfactory outcomes.

Unraveling dislocation-based strengthening in refractory multi-principal element alloys

Refractory multi-principal element alloys (RMPEAs) draw great interest with their superior mechanical properties and extremely high melting points, yet the strengthening mechanism remains unclear. Here, we calculate the critical resolved shear stress (CRSS) for a single dislocation to move in RMPEAs consisting of 4 or 5 elements with or without short-range order (SRO) to represent strength by a machine learning-based interatomic potential. The increased CRSS is then attributed to high lattice distortion, elastic mismatch, and SRO strengthening, all of which originate from the solid solution strengthening theory. After detailed research of the CRSS across many RMPEAs systems with different composition ratios, we construct an XGBoost model to predict the CRSS from a few parameters and rank their importance. We find that lattice distortion strongly influences both dislocation types and reduces the screw-to-edge ratio in CRSS, while the elastic mismatch has a more significant impact on the screw dislocation than the edge one.

The Role of Dislocation Type in the Thermal Stability of Cellular Structures in Additively Manufactured Austenitic Stainless Steel.

The ultrafine cellular structure promotes the extraordinary mechanical performance of metals manufactured by laser powder-bed-fusion (L-PBF). An in-depth understanding of the mechanisms governing the thermal stability of such structures is crucial for designing reliable L-PBF components for high-temperature applications. Here, characterizations and 3D discrete dislocation dynamics simulations are performed to comprehensively understand the evolution of cellular structures in 316L stainless steel during annealing. The dominance of screw-type dislocation dipoles in the dislocation cells is reported. However, the majority of dislocations in sub-grain boundaries (SGBs) are geometrically necessary dislocations (GNDs) with varying types. The disparity in dislocation types can be attributed to the variation in local stacking fault energy (SFE) arising from chemical heterogeneity. The presence of screw-type dislocations facilitates the unpinning of dislocations from dislocation cells/SGBs, resulting in a high dislocation mobility. In contrast, the migration of SGBs with dominating edge-type GNDs requires collaborative motion of dislocations, leading to a sluggish migration rate and an enhanced thermal stability. This work emphasizes the significant role of dislocation type in the thermal stability of cellular structures. Furthermore, it sheds light on how to locally tune dislocation structures with desired dislocation types by adjusting local chemistry-dependent SFE and heat treatment.

Exploring the impact of pre-existing helium bubbles on nanoindentation in tungsten through molecular dynamics simulation

Gaining insight into the underlying mechanisms driving nanoindentation-induced behavior in tungsten is essential for comprehending its mechanical properties. Although the plasticity of conventional pure tungsten under nanocontact conditions is well understood, these theoretical constructs may become inadequate when applied to irradiated tungsten due to the interplay between helium bubbles and dislocations. Here, we employed an integrated approach, combining crystal defect theories, molecular dynamics simulations, and machine learning, to explore the initiation and progression of dislocations in tungsten containing helium bubbles during nanoindentation, focusing on elucidating the impact of helium bubbles. In contrast to the typical dislocation nucleation in pure tungsten, the presence of helium bubbles mitigates local shear strain, thereby hindering dislocation nucleation and propagation, leading to a reduction of indentation force. Additionally, we conducted a comparative analysis between samples with and without helium bubbles, examining factors such as atomic displacement, strain localization parameters, dislocation line length, and stress component distribution. More importantly, a significant outcome of our study is the establishment of a relationship between the consistent alteration in the shape of helium bubbles and their size during micro-scale nanoindentation, achieved through machine learning techniques. Our findings reveal that the area occupied by helium bubbles post-nanoindentation is inversely correlated with indentation depth and directly linked to helium bubble size. These discoveries represent a notable advancement in understanding the effects of irradiation to a certain degree.