Types Of Dislocations Research Articles

GLENOHUMERAL DISLOCATION, ANATOMICAL DESCRIPTION, EPIDEMIOLOGY, MECHANISMS OF ACTION, CLASSIFICATION, CLINICAL PRESENTATION, IMAGING PRESENTATION, TREATMENT AND COMPLICATIONS

Introduction: Acute shoulder injuries that are common here include acromioclavicular joint injuries, clavicle fractures, glenohumeral dislocations, proximal humerus fractures and rotator cuff tears. Glenohumeral dislocations are frequently attributed to contact sports, as well as bicycle accidents, falls and high-impact trauma. Patients present several specific characteristics that will depend on the type of dislocation. Objective: to detail the current information related to glenohumeral dislocation, in addition to its description, epidemiology, classification, clinical evaluation, imaging presentation, treatment and complications of the different types of glenohumeral dislocation. Methodology: a total of 32 articles were analyzed in this review, including review and original articles, as well as clinical cases, of which 20 bibliographies were used because the other articles were not relevant for this study. The sources of information were PubMed, Google Scholar and Cochrane; the terms used to search for information in Spanish, Portuguese and English were: glenohumeral dislocation, shoulder pain, upper limb dislocation, shoulder reduction, shoulder dislocation. Results: Shoulder dislocations are usually anterior. In recurrent anterior dislocation, most recurrences occur in the first 2 years and mostly in males. Age at the time of initial dislocation has the greatest influence; incidence is not related to the duration or type of immobilization. The approximate recurrence rate in all age zones is 50%, however it increases to 89% in 14 to 20 year olds. Conclusions: The shoulder joint is frequently associated with dislocations, accounting for a large percentage of all dislocations, with anterior shoulder dislocations being more common. Anatomical, clinical and imaging knowledge play an important role in the diagnosis, allowing a better classification of the type of dislocation, which has a better impact on the treatment. The immobilization and physiotherapeutic approach will vary depending on the pathology, the age of the patient, the existence of recurrence and other complications. KEY WORDS: glenohumeral dislocation, shoulder reduction, shoulder dislocation.

Influence of cooling rate on microstructure and defect evolution in GaAs during solidification

The fabrication of high-quality GaAs crystals is essential to approach optimal performance in optoelectronic and microelectronic devices. In this study, a molecular dynamics simulation study was conducted for the solidification of liquid GaAs at three cooling rates (1010 K s−1, 1011 K s−1, and 1012 K s−1) at 300 K. The structural evolution in terms of crystal structure and defect formation in GaAs was thoroughly investigated using pair distribution function, average atomic energy, the largest standard cluster analysis, and visualization techniques. The results showed that the cooling rate of 1010 K s−1 led to the development of the best crystal quality with ease of eutectic twin grain boundary coherent twin boundary formation. Increasing the cooling rates to 1011 K s−1 and 1012 K s−1 resulted in the amorphous structure. Both high and low cooling rates profoundly affected the formation of As8 structure, but a maximum amount of 2.2% of As8 crystal structure was formed at a cooling rate of 1011 K s−1. The reduction in cooling rate to 1010 K s−1 induced the formation of numerous Schottky and Frenkel types of partial dislocations in the GaAs system. Results of this study can serve as potential guidelines to the theory of crystal growth and may be implemented in the fabrication of high-quality GaAs crystals for optimal device performance.

Screening examination of the cervical spine in patients with Down syndrome

BACKGROUND: Among all the variety of orthopedic pathologies typical for patients with Down syndrome, pathology of the cervical spine, in our opinion, is the most important. Various types of atlantoaxial dislocations can cause significant neurological deficits and decrease patients quality of life.
 OBJECTIVE: To analyze the results of screening examination of patients with Down syndrome for the presence of cervical spine pathology.
 MATERIALS AND METHODS: As part of the screening examination, functional radiographs of the cervical spine in the lateral projection of 60 patients with Down syndrome were evaluated. Priorov NMIC will operate from May 2021 to January 2023.
 RESULTS: Nine of the 60 patients tested exhibited craniovertebral pathology. Three patients have Os odontoideum of the C2 vertebra. In five patients, different types of rotational atlantoaxial displacements were found, and one patient had hypoplasia of the occipital condyles associated with basilar invagination of the C2 vertebral dentition.
 CONCLUSION: The instability of the upper cervical spine is potentially the most dangerous manifestation of orthopedic pathology in Down syndrome. A screening examination with functional cervical spine lateral projection radiographs is recommended for this group of patients.

Deformation microstructures of non-irradiated and proton irradiated zirconium alloy from nanoindentation creep tests characterised by TEM

Indentation creep tests were conducted on non-irradiated and proton irradiated Zircaloy-2 at different temperatures. After indentation creep testing, areas beneath the indentation tip were lift-out by (Focused Ion Beam) FIB, then deformation microstructures of the plastic zone were characterized by TEM. We observed that although it has the highest critical resolved shear stress of available slip modes during room temperature plasticity, under creep deformation 〈c + a〉 dislocations play a significant role in the indentation deformation process. These edge 〈c + a〉 dislocations form dipoles that impede dislocation motion and cause work hardening. For non-irradiated samples, 〈c + a〉 dislocation density in samples tested at 300 °C is significantly lower than those tested at room temperature. This may be due to the formation of {11¯01} <1¯012> twins at 300 °C, which is observed in both irradiated and non-irradiated samples. However, there is no decrease in 〈c + a〉 dislocation density at high temperature in irradiated samples. This is hypothesised to be because irradiation induced loops have more effect in impeding the motion of 〈a〉 type dislocations than 〈c + a〉 dislocations. In addition, annealing of 〈c + a〉 dislocation dipoles at 300 °C during creep of the non-irradiated sample may contribute to the decrease in 〈c + a〉 dislocation density. Irradiation induced 〈a〉 loops were swept away by gliding 〈a〉 dislocations during indentation deformation. Irradiation loops that were close to the indent were significantly eliminated while loop-free channels that were parallel with the basal trace formed at positions further away from the indent.

The effect of nanopores on the mechanism of martensitic transformation in pure iron during the heating-cooling cycle: A molecular dynamics study

Numerous molecular dynamics (MD) simulations have been performed to investigate the effect of the nanopores on the martensitic transformation (MT) of pure iron (Fe) during the heating-cooling cycle. As per the simulation results, nanopores can obviously affect the difficulty on MT during the cooling process in two ways: On the one hand, the volume ratio of nanopores to simulation box model (Rp/b) can influence the distribution configuration of stacking fault (SF) to change the type of austenite microstructure during the heating process owing to the obstruction of the nanopores on the dislocation slip. The effect of nanopores is not obvious when Rp/b is less than 2.22 %. The main type of austenitic changes from defect-free/simple-SF types to the intersecting-SF type and, finally, to the dislocation-cell type with an increase in Rp/b from 2.22 % to 17.9 %. The dislocations in intersecting-SF type and dislocation-cell type austenitic microstructures can provide the nucleation site of MT, thus increasing the MT temperature. On the other hand, the high surface energy of the nanopores caused by the incomplete atomic lattice can provide the necessary energy for the nucleation of martensite, which then promotes the occurrence of MT during the cooling process. When the nanopores intersect with the dislocation wall in dislocation-cell type austenitic microstructure, martensite nucleates at the nanopores surface and then grows along the dislocation wall. In the previous investigation of selective laser melting martensitic steel, the nanopore in the microstructure was generally believed harmful to the mechanical property of specimen; however, in this study, it has been observed to promote the MT during solution-quenching heat treatment, which improves the mechanical property by improving the content of martensitic phase. This provides a new perspective in determining the significance of nanopores in microstructures.

Mechanistic investigation of highly bendable magnesium alloy sheet fabricated by short-process manufacturing

In this study, a commercial magnesium alloy AZ31 (Mg-3Al-1Zn-0.3Mn) sheet through a short manufacturing process was found to be ductile and highly formable in bending. Despite possessing a strong basal texture, the short-processed sheet without any annealing can be bent at a small radius, only 0.2 times its thickness in the 90° bending test. Additionally, it could withstand direct deformation by repeated folding-flattening. The in-situ microstructural characterization reveals that extension twin bands with strain localization appear in the bending area. During subsequent flattening, these twin bands underwent detwinning, reducing local strain concentrations and enabling further bending deformation. Such outstanding bend formability originated from the significant 〈a〉-type dislocation loops slipping on the prismatic crystal planes within dynamic-recrystallized grains. These grains underwent a uniform refinement to several microns in the short manufacturing process and exhibited low residual strain. The active prismatic dislocation slip within refined grains was due to its much lower relative activation stress to basal slip (CRSSprism/ CRSSbasal of only ∼1.6) owing to the effective grain boundary hardening. Furthermore, the prismatic dislocation activity was further enhanced when bypassing Al-Mn nano-particles during motion, leaving debris and loops that facilitated easy multiplication.

Modeling of the intrinsic softening of γ-carbides in cemented carbides

Cemented carbides are widely used materials in industrial applications due to their remarkable combination of hardness and toughness. However, they are exposed to high temperatures during service leading to a reduction of their hardness. A common practice to damp this softening is to incorporate transition metal carbides in cemented carbide compositions, which keeps the hardness relatively higher when temperature increases. Understanding the underlying mechanisms of this softening is crucial for the development of cemented carbides with optimal properties. In this work, atomic-scale mechanisms taking place during plastic deformation are analyzed and linked to the effect that they have on the intrinsic macro-scale softening of the most common TMC used in cemented carbides grades (TiC, ZrC, HfC, VC, NbC and TaC). The proposed model uses the generalized stacking fault energy obtained from density functional theory calculations as an input to Peierls-Nabarro analytical models to obtain the critically resolved shear stress needed for deformation to occur in different slip systems. Subsequently, this information is used to predict the hardness variation across the temperature service range experienced by cemented carbides in wear applications.In addition to the prediction of hot-hardness for TMC, the obtained results also offer valuable insights into the intrinsic mechanisms governing TMCs deformation. The results facilitate the identification of dominant dislocation types influencing plasticity within distinct temperature regimes, define energetically favorable slip systems, and predict the brittle-ductile transition temperature in these materials. For instance, for group IV carbides at low temperatures, the slip system with a lower GSFE is {110}<11̅0> and around 30% of their melting temperature, the GSFE of partial slip in {111}<12̅1> becomes lower, changing the dominant slip mechanism and characterizing the Brittle-Ductile transition.

Understanding the formation mechanisms and stability of the Anti-Phase boundaries (APBs) in Al-Fe B2

Al-Fe B2 alloys (with ordered Body Centered Cubic lattice, BCC) are an example of high strength, brittle materials containing multiple crystal defects, such as dislocations, vacancies and Anti-Phase Boundaries (APB). Although latter were reported to play a major role in mechanisms influencing mechanical properties, reports on formation mechanisms of APBs are limited and contradictory. To close this gap in understanding, FexAl1−x alloys were studied in Transmission Electron Microscope (TEM). Changing the Long-Range Order, η, parameter (calculated using statistical thermodynamics according to the composition of the samples) from 1 (50 at% Fe, i.e., perfect order) to η = 0.53 (68 at% Fe) caused an increase in density of the <111> type dislocations. At η = 0.53 – APBs have started to form. These experimental results were in-line with Density Functional Theory calculations. Since above 68 at% Fe, D03-type structure has also formed in the B2 grains, its role in formation of the APBs was assessed. It was determined that these two phenomena are not related. Therefore, outcomes of current research are of general applicability to other B2 structures regardless existence of D03 or lack of such additional ordering. Furthermore, driven conclusions have a potential to impact the BCC-based High Entropy Alloys, where B2 is the matrix.

An ambient ductile VNbTa refractory medium-entropy alloy with super rolling formability

Refractory multiple-principal element alloys (RMEAs) systems have drawn particular attentions in recent years due to their great potential for high-temperature application. However, most of RMEAs exhibit tensile brittleness, oxidation, and phase decomposition, which limit their potential applications. Hence, developing new RMEAs with excellent ductility has become one of the urgent tasks for RMEAs’ applications. Here, a ductile VNbTa equiatomic RMEA has been fabricated by vacuum arc melting. The VNbTa alloy exhibits high tension strength (σ0.2 = 1033 MPa), outstanding fracture elongation (εf >19 %), super rolling formability (>80 % thickness reduction), and work hardening at room temperature (RT). The high strength of VNbTa alloy is mainly associated with solid solution strengthening and local lattice distortion induced by the misfits of atomic sizes and mechanical moduli of various elements. The super formability of VNbTa alloy attributes to the mobility of a/2<1 1 1>-type dislocations and the formation of kink bands at RT. This study not only clarifies the phase stability, lattice distortion, strengthening, elastic and plastic mechanisms of the ductile VNbTa alloy by combining experiments and theoretical calculations, but also provides more helpful information to design RMEAs with superior ductility at room temperature.

Anisotropic plasticity mechanisms in a newly synthesised high entropy alloy investigated using atomic simulations and nanoindentation experiments

This work used atomic simulations and nanoindentation experiments to investigate hardness, modulus alongside sub-surface crystal defects and dislocation mediated plasticity mechanisms leading to anisotropic pile up and local entropy variation in high entropy alloys. The experimental campaign began from Thermo-Calc phase prediction of Ni25Cu18.75Fe25Co25Al6.25 HEA which followed experimental synthesis of the material using arc melting method and experimental nanoindentation using a Berkovich indenter under load-controlled conditions. Through MD simulations, the value of hf/hmax in monocrystalline HEA was consistently found to be larger than 0.7 which suggested pile-up behaviour to dominate and sink-in behaviour to be unlikely. In the case of (110) and polycrystalline HEA substrates, the elastic work in the indentation hysteresis loop was seen to be larger than the (100) and the (111) orientations which explains that the (110) orientation substrate showed least elastic modulus and hardness while the (111) monocrystalline HEA showed the highest elastic modulus and hardness. From the simulations, a “lasso” type loop on the (110) orientation and cross-over of shear loops on the other orientations accompanied by dislocations of type 1/6 < 112 > (Shockley), 1/2 < 110 > (perfect), 1/3 < 001 > (Hirth), 1/6 < 110 > (Stair rod) and 1/3 < 111 > (Frank partials) were seen to manifest an early avalanche of competing plasticity events. The defects accompanying these dislocations in the sub-surface were identified to be FCC intrinsic stacking faults (ISF), adjacent intrinsic stacking faults (quad faults), coherent ∑3 twin boundary and a coherent twin boundary next to an intrinsic stacking fault (triple fault). The EBSD analysis applied to the MD data showed that the (210) orientation and the< 110 > family of directions were seemed to be preferable to plastically deform the FCC phased Ni25Cu18.75Fe25Co25Al6.25 HEA.

Modelling structural colour from helicoidal multi-layer thin films with natural disorder.

A coupled mode theory based on Takagi-Taupin equations describing electromagnetic scattering from distorted periodic arrays is applied to the problem of light scattering from beetles. We extend the method to include perturbations in the permittivity tensor to helicoidal arrays seen in many species of scarab beetle and optically anisotropic layered materials more generally. This extension permits analysis of typical dislocations arising from the biological assembly process and the presence of other structures in the elytra. We show that by extracting structural information from transmission electron microscopy data, including characteristic disorder parameters, good agreement with spectral specular and non-specular reflectance measurements is obtained.

Optimal design of a new Halbach array magnetic roller with axial eddy current force

Non-ferrous metal recovery is of great significance to the sustainable development of resources. Small-sized nonferrous metal particles account for a large proportion of nonferrous metals in solid waste, but the recovery efficiency is low. Eddy current separation is an important technology for physical recovery of non-ferrous metals. Optimizing its magnetic roller is extremely important for improving the recovery efficiency and economy of small-sized non-ferrous metals. In this study, COMSOL Multiphysics is used to establish a three-dimensional transient simulation model of the vertical rotary-drum ECS. On the basis of the two-dimensional Halbach array magnetic roll, the magnetic system of the magnetic roll is designed in the axial direction, so that the particles are subjected to the axial eddy current force opposite to the direction of gravity for the first time. This force can slow down the falling velocity of particles, increase the difference in falling trajectory and repulsion distance, improve recovery efficiency. In addition, due to the generation of axial eddy current force, the interlayer dislocation type magnetic roller can achieve the same recovery effect by only using 1/3 of the length of the basic type magnetic roller. Based on the electromagnetic theory and particle dynamics, by comparing the axial magnetic density distribution of different magnetic rollers, the axial eddy current force and the trajectory of non-ferrous metal particles, the generation mechanism of the axial eddy current force and the magnetic system structure that can generate the axial eddy current force are clarified.

HIP DISLOCATION, ANATOMICAL DESCRIPTION, EPIDEMIOLOGY, MECHANISMS OF ACTION, CLASSIFICATION, CLINICAL PRESENTATION, IMAGING PRESENTATION, TREATMENT, COMPLICATIONS AND DISLOCATION AFTER TOTAL HIP REPLACEMENT

Introduction: Traumatic hip dislocation is an uncommon injury, approximately making up 2 to 5% of all dislocations generated by high-energy trauma. This type of dislocation can be pure or related to other injuries or alterations such as fracture of the femoral head, femoral neck or acetabulum. Objective: to detail the current information related to hip dislocation, anatomical description, epidemiology, mechanisms of action, classification, clinical presentation, imaging presentation, treatment, complications and dislocation after total hip replacement. Methodology: a total of 30 articles were analyzed in this review, including review and original articles, as well as clinical cases, of which 21 bibliographies were used because the other articles were not relevant to this study. The sources of information were PubMed, SciELO, Google Scholar and Cochrane; the terms used to search for information in Spanish, Portuguese and English were: hip dislocation, proximal femur, femoroacetabular dislocation, prosthetic dislocation. Results: Anterior dislocations account for 10% to 15% of traumatic hip dislocations, with the remainder being assigned to posterior dislocations. The incidence of osteonecrosis of the femoral head is between 2% to 17% of individuals, while 16% form post-traumatic osteoarthritis. The sciatic nerve is affected in about 10% to 20% of posterior dislocations. There is no correlation between early weight bearing and osteonecrosis. Dislocation of the total hip endoprosthesis is observed in about 2% of individuals within one year after surgery. There are dislocation rates of up to 28% following revision and implant exchange surgeries. Conclusions: The capsular ligaments of the hip joint (iliofemoral, ischiofemoral, and pubofemoral) act very importantly in the functional mobility and stability of the joint. Hip dislocations are caused by high-energy trauma, such as traffic accidents, which are becoming more common due to the increase of these. Posterior dislocations are more common compared to anterior hip dislocations. A complete and thorough trauma evaluation is important in the clinical assessment. Those with a posterior dislocation of the hip show marked pain and the hip in flexion, internal rotation and adduction. Those with an anterior dislocation remain with the hip in marked external rotation, slight flexion and abduction. The importance of an anteroposterior projection of the pelvis and a cross lateral projection of the injured hip is emphasized. Treatment may be closed or open reduction depending on the circumstances, clinical situation and associated injuries. Complications such as osteonecrosis may be associated with the time of evolution. The treatment of instability following total hip replacement should follow a standardized algorithm. KEY WORDS: dislocation, hip, femur, acetabulum, prosthesis.

Mechanisms of mobile bearing dislocation in lateral unicompartmental knee replacement.

Mobile bearing dislocation occurs in 1- 6% of Oxford Domed Lateral replacements. Dislocations are predominantly medial, but can occur anteriorly or posteriorly. They tend to occur when the knee is flexed. It is not clear how dislocations can be prevented. A previously described mechanical rig for assessing mobile bearing dislocation was updated so as to study dislocation with the knee in flexion. Sub-categories for the description of each type of dislocation were introduced. Dislocation was only possible when the knee was distracted. As the amount of distraction possible in the knee is variable, the risk of dislocation is related to the amount of distraction in the rig necessary for a dislocation. The type of dislocation requiring the least distraction was medial `edge' dislocation in which the edge of the bearing dislocates onto the tibial wall, which is the most common type of dislocation. The amount of distraction necessary decreased the further the bearing was from the wall and with 50% posterior overhang. Rotation of the knee did not influence the amount of distraction. In conclusion dislocation can only occur if the lateral compartment is distracted. To reduce the dislocation risk, surgeons should aim to position the femoral and tibial components so that the bearing is as close as possible to the wall without jamming against it and the tibial component should be positioned flush with the posterior tibial cortex. If, during the surgery, the mobile bearing can easily be dislocated onto the wall the surgeon should consider changing to a fixed bearing. The tibial component should also be positioned flush with the posterior tibial cortex, as if it is too far forward this may contribute to dislocation.

A comparative study on the clinical efficacy of microplate trans-carpometacarpal joint fixation and non-trans-carpometacarpal joint fixation in treating fractures with dislocation or subluxation of the base of the fourth and fifth metacarpal bones

BackgroundThis study aimed to compare the clinical efficacy of microplate trans-carpometacarpal joint fixation and non-trans-carpometacarpal joint fixation in treating fractures and dislocation or subluxation of the base of the fourth and fifth metacarpal bones.MethodFrom 2015 to 2021, 100 cases of metacarpal basal fractures with dislocation or subluxation were randomly divided into the trans-carpometacarpal joint fixation group (group A) and non-trans-carpometacarpal joint fixation group (group B). Group A (n = 50) comprised 44 males and 6 females, with an average age of 28.8 ± 6.1 y and an Orthopedic Trauma Association (OTA) fracture classification of type B1 (n = 29) or C1 (n = 21). Group B (n = 50) comprised 45 males and 5 females, with an average age of 28.9 ± 5.7 y and an OTA fracture classification of type B1 (n = 28) or C1 (n = 22). All patients were complicated with dislocation or subluxation. The surgery time, fracture healing time, postoperative handgrip strength, and total active motion (TAM) scores of the ring and little fingers were recorded and compared between the two groups. The clinical efficacy of patients was evaluated using scoring methods such as DASH (disabilities of the arm, shoulder and hand), visual analogue scale (VAS), and Mayo at 3, 6, and 12 months after surgery.ResultsThere was no significant difference in the general indexes, surgery time, or fracture healing time between the two groups (P > 0.05). There were no significant differences in handgrip strength and TAM scores of the ring and little fingers between the two groups at 3 and 12 months postoperatively (P > 0.05), but there were significant differences in these indexes 6 months postoperatively (P < 0.05). There were no significant differences in the DASH, VAS, and Mayo scores at 3 and 12 months postoperatively (P > 0.05), but there were significant differences between the two groups in the DASH and Mayo scores (P < 0.05) but not the VAS score (P > 0.05) 6 months postoperatively.ConclusionIn the treatment of fourth and fifth metacarpal basal fractures with dislocation or subluxation, both microplate transarticular fixation and non-transarticular fixation could achieve fracture fixation and healing, and each method had advantages and disadvantages. The clinically appropriate fixation method should be selected according to the experience of the surgeon and the degree and type of fracture and dislocation.

Development and analysis of thick GaN drift layers on 200 mm CTE-matched substrate for vertical device processing

This work reports the epitaxial growth of 8.5 µm-thick GaN layers on 200 mm engineered substrates with a polycrystalline AlN core (QST by QROMIS) for CMOS compatible processing of vertical GaN power devices. The epitaxial stack contains a 5 upmum thick drift layers with a Si doping density of 2 × 1016 cm−3 and total threading dislocation density of 4 × 108 cm−2. The thick drift layer requires fine-tuning of the epitaxial growth conditions to keep wafer bow under control and to avoid the formation of surface defects. Diode test structures processed with this epitaxial stack achieved hard breakdown voltages > 750 V, which is shown to be limited by impurity or metal diffusion from the contact metal stack into threading dislocations. Conductive Atomic Force Microscopy (cAFM) reveals some leakage contribution from mixed type dislocations, which have their core structure identified as the double 5/6 atom configuration by scanning transmission electron microscopy images. Modelling of the leakage conduction mechanism with one-dimensional hopping conduction shows good agreement with the experimental data, and the resulting fitting parameters are compared to similar findings on silicon substrates. The outcome of this work is important to understand the possibilities and limitations of vertical GaN devices fabricated on large diameter wafers.

Interaction of [formula omitted] prismatic screw dislocations with the [formula omitted] interface side face in [formula omitted] Ti alloys

Slip transmission across α−β interfaces is of great significance in understanding the strength of α−β Ti alloys for aerospace applications. Molecular statics (MS) and molecular dynamics (MD) simulations were conducted to investigate the mechanisms of slip transmission of 〈a〉 prismatic screw dislocations across the α−β interface side face. In these simulations, the α phase consisted of pure HCP Ti whereas the β phase was modeled as Ti60Nb40 BCC random alloy using a Ti–Nb interatomic potential. Firstly, the misfit dislocations structure on the α−β interface side face has been characterized from MS simulations. This predicted dislocation structure is in good agreement with experimental observations in Ti-alloys. Secondly, MD simulations of the interaction of [a1], [a2], and [a3] prismatic screw dislocations with the interface side face in an α−β bi-crystal were performed at different temperatures. A distinct barrier of the interface side face to different types of dislocation transmission was found. The origin of this anisotropy in the slip transmission is due to the relative misalignment of the slip systems between the α and the β phases from the Burgers orientation relationship. Finally, the mechanisms of slip transmission of each dislocation type were analyzed in a detailed atomistic description and compared to experimental observations.

Deformation mechanisms in the cutting process of SiCp/Al composites using the molecular dynamics (MD) approach

In order to clarify the reasons for the emergence of problems such as high machining difficulty and poor machining surface quality encountered in the machining process of SiCp/Al composites, this paper presents a simulation study of the deformation mechanism occurring during the cutting process of SiCp/Al (SiC particle-reinforced Al matrix composites) by using the molecular dynamics (MD) method. The mechanism of strengthening and hardening occurring during cutting of SiCp/Al composites is discussed in terms of the slip expansion of dislocations and the interaction between different types of dislocations. It is found that the presence of SiC balls hinders the slip and expansion of dislocations in the Al (aluminum) matrix, resulting in the strengthening of the Al matrix between the SiC (silicon carbide) balls, mainly because the dislocations in the workpiece interact with each other during the cutting process to form dislocation tangles, stacking layer dislocations and dislocation locks, which hinder the slip and expansion of dislocations and thus increase the strength of the Al matrix. By analyzing the stress distribution inside the workpiece during the cutting process, it is found that the stress inside the workpiece is mainly concentrated in the area where the tool flank face is in contact with the workpiece, which is the main reason for the occurrence of working hardening in SiCp/Al composites.

Dislocation formation in the heteroepitaxial growth of PbSe/PbTe systems

The paper presents a multiscale study of the kinetic processes of the heteroepitaxial growth of the PbSe/PbTe(111) and PbTe/PbSe(001) systems, using the Concurrent Atomistic-Continuum (CAC) method as the simulation tool. The CAC simulations have reproduced the Stranski–Krastanov growth mode and the layer-by-layer growth mode of the two systems, respectively; the pyramid-shaped island morphology of the PbSe epilayer on PbTe(111), the square-like misfit dislocation networks within the PbTe/PbSe(001) interface, and the critical thickness for the PbTe/PbSe(001) system at which coherent interfaces transit to semi-coherent interfaces with the formation of misfit dislocations, all in good agreement with experimental observations. Four types of misfit dislocations are found to form during the growth of the two PbTe/PbSe heterosystems, and hexagonal-like misfit dislocation networks are observed within the PbSe/PbTe(111) interfaces. The growth processes, including the formation of misfit dislocations, have been visualized. Dislocation half-loops have been observed to nucleate from the epilayer surfaces. These half-loops extend towards the interface by climb or glide motions, interact with other half-loops, and form misfit dislocation networks at the interfaces and threading dislocations extending from interfaces to epilayer surfaces. The dominant types of misfit dislocations in both systems are found to be those with Burgers vectors parallel to the interfaces, whereas the misfit dislocations with Burgers vectors inclined to the interface have a low likelihood of generation and tend to annihilate. The size of the substrate is demonstrated to have a significant effect on the formation, evolution, and distribution of dislocations on the growth of PbSe on PbTe(111).

Microstructural evolution of Mg–14Gd–0.4Zr alloy during compressive creep

The present work reports the creep behavior and microstructural evolution of the sand-cast Mg–14Gd–0.4Zr alloy (wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 °C were performed under various applied stresses (i.e., 60, 80 and 100 MPa). Among them, the sand-cast Mg–14Gd–0.4Zr samples examined under 250 °C/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'F phases with an alternate distribution, effectively impeding the basal <a> dislocations movement. However, with the creep time increasing, the fine β'+β'F precipitate chains coarsened and transformed to semi-coherent β1 phase and even to large incoherent β phase (surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones (PFZs) at grain boundaries (GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic <a> dislocations, <c + a> type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain.