Grain refinement of Mg-Ca alloys by native MgO particles

In Mg-Ca alloys the grain refining mechanism,in particular regarding the role of nucleant substrates,remains the object of debates.Although native MgO is being recognised as a nucleating substrate accounting for grain refinement of Mg alloys,the possible interactions of MgO with alloying elements that may alter the nucleation potency have not been elucidated yet.Herein,we design casting experiments of Mg-xCa alloys varied qualitatively in number density of native MgO,which are then comprehensively studied by advanced electron microscopy.The results show that grain refinement is enhanced as the particle number density of MgO increases.The native MgO particles are modified by interfacial layers due to the co-segregation of Ca and N solute atoms at the MgO/Mg interface.Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy,we reveal the nature of these Ca/N interfacial layers at the atomic scale.Irrespective of the crystallographic termination of MgO,Ca and N co-segregate at the MgO/Mg interface and occupy Mg and O sites,respectively,forming an interfacial structure of a few atomic layers.The interfacial structure is slightly expanded,less ordered and defective compared to the MgO matrix due to compositional deviations,whereby the MgO substrate is altered as a poorer template to nucleate Mg solid.Upon solidification in a TP-1 mould,the impotent MgO particles account for the grain refining mechanism,where they are suggested to participate into nucleation and grain initiation processes in an explosive manner.This work not only reveals the atomic engineering of a substrate through interfacial segregation but also demonstrates the effectiveness of a strategy whereby native MgO particles can be harnessed for grain refinement in Mg-Ca alloys.

Integrated multi-scale approach combining global homogenization and local refinement for multi-field analysis of high-temperature superconducting composite magnets

Second-generation high-temperature superconducting(HTS)conductors,specifically rare earth-barium-copper-oxide(REBCO)coated conductor(CC)tapes,are promising candidates for high-energy and high-field superconducting applications.With respect to epoxy-impregnated REBCO composite magnets that comprise multilayer components,the thermomechanical characteristics of each component differ considerably under extremely low temperatures and strong electromagnetic fields.Traditional numerical models include homogenized orthotropic models,which simplify overall field calculation but miss detailed multi-physics aspects,and full refinement(FR)ones that are thorough but computationally demanding.Herein,we propose an extended multi-scale approach for analyzing the multi-field characteristics of an epoxy-impregnated composite magnet assembled by HTS pancake coils.This approach combines a global homogenization(GH)scheme based on the homogenized electromagnetic T-A model,a method for solving Maxwell's equations for superconducting materials based on the current vector potential T and the magnetic field vector potential A,and a homogenized orthotropic thermoelastic model to assess the electromagnetic and thermoelastic properties at the macroscopic scale.We then identify“dangerous regions”at the macroscopic scale and obtain finer details using a local refinement(LR)scheme to capture the responses of each component material in the HTS composite tapes at the mesoscopic scale.The results of the present GH-LR multi-scale approach agree well with those of the FR scheme and the experimental data in the literature,indicating that the present approach is accurate and efficient.The proposed GH-LR multi-scale approach can serve as a valuable tool for evaluating the risk of failure in large-scale HTS composite magnets.

Effect of grain refinement induced by wire and arc additive manufacture (WAAM) on the corrosion behaviors of AZ31 magnesium alloy in NaCl solution

Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufacturing(WAAM)was employed to produce single AZ31 layer.The results revealed that the WAAM AZ31 was characterized by significant grain refinement with non-textured crystallographic orientation,similar phase composition and stabilized corrosion performance comparing to the cast AZ31.These varied corrosion behaviors were principally ascribed to the size of grain,where cast AZ31 and WAAM AZ31 were featured by micro galvanic corrosion and intergranular corrosion,respectively.

Erratum to: Influence of grain refinement on the corrosion behavior of metallic materials: A review

Erratum to:International Journal of Minerals, Metallurgy and MaterialsVolume 28, Number 7, July 2021, Page 1112 The original version of this article unfortunately contained mistakes. Symbols in Table 2 are used incorrectly.

Microstructure Transformation of Undercooled Cu-Ni-Co Alloy and Refinement Mechanism under High Undercooling

The molten Cu60Ni35Co5 ternary alloy was undercooled by fluxing method and solidified by natural cooling method.The microstructure of all undercooled samples were analyzed.It is found that the rapidly solidified Cu60Ni35Co5 alloy has undergone two grain refinement phenomena within the undercooling range,and its microstructure and morphology change with the undercooling through the transformation process of“coarse dendrite-equiaxed dendrite-oriented fine dendrite-equiaxed crystal”.The refined structure with the maximum undercooling?T of 253 K was selected for electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM)tests.EBSD results show that the refined structure contains a high proportion of large angle grain boundaries(LAGBs),a large number of randomly oriented grains,and high proportion of twins,while TEM results show that the dislocation density in most areas is relatively low.The above characteristics confirm that the solidification structure is refined due to recrystallization behavior under high undercooling.

Effect of Co on Microstructure Transformation and Refinement Mechanism of Undercooled Cu-Ni Alloy

Both Cu60Ni38Co2 and Cu60Ni40 alloy were naturally cooled after rapid solidification from the liquid phase.The transformation law of the microstructure characteristics of the rapidly solidified alloy with the change of undercooling(DT)was systematically studied.It was found that the two alloys experienced the same transformation process.The refinement structures under different undercoolings were characterized by electron backscatter diffraction(EBSD).The experimental results show that the characteristics of the refinement structure of the two alloys with low undercooling are the same,whereas,the characteristics of the refinement structure with high undercooling are opposite.The transmission electron microscope(TEM)results of Cu60Ni38Co2 alloy show that the dislocation network density of low undercooled microstructure is lower than that of high undercooled microstructure.By combining EBSD and TEM,it can be confirmed that the dendrite remelting fracture is the reason for the refinement of the low undercooled structure,while the high undercooled structure is refined due to recrystallization.

Plethysmograph training:A refinement for collection of respiration data in mice

Inhaled chemicals can harm the airways.Different effects can result in distinct changes in respiratory patterns;the type of change indicates where and how the respiratory system is affected.Furthermore,changes in respiratory patterns may be detected at much lower substance concentrations than those that cause more serious effects,such as histopathological changes.Changes in respiratory patterns can be studied experimentally by monitoring the breathing of mice placed in plethysmographs and exposing head-out to the test substance.The method is well established;however,it is not known if training mice in being restrained in the plethysmograph could increase the quality of data collection.Here we report the results of training mice to be restrained in plethysmographs for 5 consecutive days,with respect to body weight,respiratory parameters,and time spent in the plethysmograph,before they are removed because of unstable breathing patterns.The mice tolerated the procedure better(measured by time in the plethysmograph)on the second day of training than the first day.Training did not change the breathing parameters between days.Breathing parameters stabilized within 5 min after the mice were placed in the plethysmographs on all days.There was an average of 3%weight loss between the first and last days of the training,indicating that the training procedure placed some strain on the animals.Training reduces the number of mice attempting to escape from the plethysmograph.

Recent advances on grain refinement of magnesium rare-earth alloys during the whole casting processes:A review

High-performance cast magnesium rare-earth(Mg-RE) alloys are one of the most important materials among all developed Mg alloy families, and have shown great potential in military and weapons, aerospace and aviation, orthopedic implants, etc. Controlling grain size and distribution of it is key to the promising mechanical performance of Mg-RE alloy casting components. During the casting of a real component, nearly every procedure in the fabrication process will influence the grain refinement effect. The procedure may include and may not be limited to the chemical inoculations, possibly applied physical fields, the interfere between grain refiner and purifications, and the casting techniques with different processing parameters. This paper reviews the recent advances and proposed future developments in these categories on grain refinement of cast Mg-RE alloys. The review will provide insights for the future design of grain refinement techniques,the choosing of processing parameters, and coping strategies for the failure of coarsening for cast Mg-RE components with high quality and good performance.

Influence of strain rate on grain refinement and texture evolution under complex shear stress conditions

The effects of different complex shear stress conditions on grain refinement and texture evolution of Mg-13Gd-4Y-2Zn-0.5Zr alloy were investigated.With increasing strain rate,the average grain size of compression-shear(CS)and compression-torsion(CT)samples are decreased,and the grain size of dynamic recrystallization(DRX)grains is also decreased.This is because that the precipitation number ofβphases is increased,and the hindering effect on grain growth can be significantly enhanced.The DRX fractions of CS and CT samples are decreased with increased strain rate.The low DRX fraction at high strain rate is related to the insufficient time for grains to nucleate.The DRX process can be promoted by the PSN mechanism of second phases,and the grain growth can be restricted by the pinning effect.At the same time,the texture strength is enhanced as the strain rate increased.Besides,the kinking degree of lamellar long-period stacking ordered(LPSO)phases is increased.Under complex shear stress conditions,non-basal slip,especially pyramidal slip,is easily activated and the texture is deflected greatly.Compared with the CS samples,CT samples have smaller average grain size,higher DRX fraction,and lower texture strength for a certain strain rate.This is because that the equivalent stress of the CT sample is larger,the stress triaxiality is smaller,so more serious dislocations are piled up near grain boundaries and second phases.At the same time,since CT sample was sheared with torsion,the dislocation movement path can be called“rotational dislocation accumulation”,and the longer distribution path of the CT sample is generated,so more sub-grains and low-angle grain boundaries(LAGBs)are formed.Compared with the CS sample,more huge-angle grain boundaries(HAGBs)and DRX grains are formed from grain boundary to grain interior,so better grain refinement effect is achieved.

Grain refinement and strength enhancement in Mg wrought alloys: A review

Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth(RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization(DRX) plays a crucial role in refining grain size of Mg wrought alloys.Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized,including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy,are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing.

Effect of wide-spectrum pulsed magnetic field on grain refinement of pure aluminium

A wide-spectrum pulsed magnetic field(WSPMF)was obtained by adjusting the number of current pulses and the pulse interval between adjacent pulses.The effect of WSPMF on the grain refinement of pure aluminium was studied.The distribution of electromagnetic force and flow field in the melt under the WSPMF was simulated to reveal the grain refining mechanism.Results show that the grain refinement is attributed to the combined effect of the melt flow and oscillation under a WSPMF.When the pulse interval is 5 ms,the extreme value of electromagnetic force is the highest,and the size of the crystal nucleus is 0.35 mm.In the case of similar flow rates,the grain size gradually decreases as the pulse interval increases.The range of the harmonic frequency of the magnetic field gradually expands with the increase of the pulse interval,which can provide more energy for nucleation at the solid-liquid interface and promote nucleation.

Microstructure Transformation and Refinement Mechanism of Undercooled Cu-Ni-Co Alloy Based on Simulation of Critical Cutting Speed in Ultrasonic Machining

Both Cu60Ni38Co2 and Cu60Ni40 alloy were naturally cooled after rapid solidification from the liquid phase.The transformation law of the microstructure characteristics of the rapidly solidified alloy with the change of undercooling(ΔT)was systematically studied.It is found that the two alloys experience the same transformation process.The refinement structures under different undercoolings were characterized by electron backscatter diffraction(EBSD).The results show that the characteristics of the refinement structure of the two alloys with low undercooling are the same,but the characteristics of the refinement structure with high undercooling are opposite.The transmission electron microscopy(TEM)results of Cu60Ni38Co2 alloy show that the dislocation network density of low undercooled microstructure is lower than that of high undercooled microstructure.By combining EBSD and TEM,it could be confirmed that the dendrite remelting fracture is the reason for the refinement of the low undercooled structure,while the high undercooled structure is refined due to recrystallization.On this basis,in the processing of copper base alloys,there will be serious work hardening phenomenon and machining hard problem of consciousness problems caused by excessive cutting force.A twodimensional orthogonal turning finite element model was established using ABAQUS software to analyze the changes in cutting speed and tool trajectory in copper based alloy ultrasonic elliptical vibration turning.The results show that in copper based alloy ultrasonic elliptical vibration turning,cutting process parameters have a significant impact on cutting force.Choosing reasonable process parameters can effectively reduce cutting force and improve machining quality.

Phase field simulation of grain refinement in silver-based filler metal

Numerical simulation is one of the important auxiliary methods for studying materials-related problems. In this study, phase field simulation was employed to investigate the refinement behavior of BAg55CuZn-x B brazing alloys. Simulation and experimental studies were conducted for B contents ranging from 0 wt.% to 0.2 wt.%. The results demonstrated that the addition of 0.05 wt.% B in the brazing alloy leads to a significant refinement effect. As the B content increases, the grain size further reduces, and a refinement stagnation phenomenon occurs after exceeding 0.15 wt.%. The solidification process of brazing alloys with different B content was predicted by simulation, and the simulation results showed that with the increase of B content, the initial number of nucleation increased, and the radius of the dendrite tip decreased. The simulation results are in good agreement with the experimental findings, providing further evidence of the refining effect of the B element and the reliable predictive capability of the phase field model.

Ruppert's Delaunay Triangulation Refinement Scheme for Optimal RSUs Placement in Vehicle to Infrastructure Communication Network

Road Side Units(RSUs)are the essential component of vehicular communication for the objective of improving safety and mobility in the road transportation.RSUs are generally deployed at the roadside and more specifically at the intersections in order to collect traffic information from the vehicles and disseminate alarms and messages in emergency situations to the neighborhood vehicles cooperating with the network.However,the development of a predominant RSUs placement algorithm for ensuring competent communication in VANETs is a challenging issue due to the hindrance of obstacles like water bodies,trees and buildings.In this paper,Ruppert’s Delaunay Triangulation Refinement Scheme(RDTRS)for optimal RSUs placement is proposed for accurately estimating the optimal number of RSUs that has the possibility of enhancing the area of coverage during data communication.This RDTRS is proposed by considering the maximum number of factors such as global coverage,intersection popularity,vehicle density and obstacles present in the map for optimal RSUs placement,which is considered as the core improvement over the existing RSUs optimal placement strategies.It is contributed for deploying requisite RSUs with essential transmission range for maximal coverage in the convex map such that each position of the map could be effectively covered by at least one RSU in the presence of obstacles.The simulation experiments of the proposed RDTRS are conducted with complex road traffic environments.The results of this proposed RDTRS confirmed its predominance in reducing the end-to-end delay by 21.32%,packet loss by 9.38%with improved packet delivery rate of 10.68%,compared to the benchmarked schemes.

Simultaneous refinement of α-Mg grains and β-Mg_(17)Al_(12) in Mg-Al based alloys via heterogeneous nucleation on Al_(8)Mn_(4)Sm

Due to the significant differences in the formation temperature and crystal structure between the primaryα-Mg and eutecticβ-Mg_(17)Al_(12),it is a great challenge to achieve simultaneous refinement of the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation.Surprisingly,we found that theα-Mg andβ-Mg_(17)Al_(12) in the AZ80 alloy can be simultaneously refined after 0.2 wt.%Sm addition,with the grain size decreasing from∼217±15μm to∼170±10μm and theβ-Mg_(17)Al_(12) morphology changing from a typical continuous network to a nod-like or spherical structure.The simultaneous refinement mechanism is investigated through solidification simulation,transmission electron microscopy(TEM),and differential thermal analysis(DTA).In the AZ80-0.2Sm alloy,many Al8Mn4Sm particles can be observed near the center of theα-Mg grains or inside theβ-Mg_(17)Al_(12).Crystallographic calculations further reveal that the Al8Mn4Sm has good crystallographic matching with both theα-Mg andβ-Mg_(17)Al_(12),so it possesses the potency to serve as heterogeneous nucleation sites for both phases.The promoted heterogeneous nucleation on the Al8Mn4Sm decreases the undercooling required by the nucleation of the primary and eutectic phases,which enhances the heterogeneous nucleation rate,thus causing the simultaneous refinement of theα-Mg andβ-Mg_(17)Al_(12).The orientation relationships between the Al8Mn4Sm and Mg/Mg_(17)Al_(12) are identified,which are[1210]_(Mg)//[010]_(Al8Mn4Sm),(1010)_(Mg)//(301)_(Al8Mn4Sm) and[112]_(Mg_(17)Al_(12))//[010]_(Al8Mn4Sm),(110)_(Mg_(17)Al_(12))//(301)_(Al8Mn4Sm),respectively.Furthermore,the refinement of theβ-Mg_(17)Al_(12) accelerates its dissolution during the solution treatment,which is beneficial for cost saving in industrial applications.Other Al8Mn4RE compounds such as Al8Mn4Y might have the same positive effect on the simultaneous refinement due to the similar physicochemical properties of rare earth elements.This work not only proves the possibility of simultaneously refining the primary and eutectic phases in Mg-Al based alloys via heterogeneous nucleation,but also provides new insights into the development of refiners for cast Mg alloys.

From“Car Priority”to“People Priority”: Exploring New Ideas for Refined Road Space Design

Roads are crucial public spaces in cities and serve as a window to showcase the city’s characteristics.They serve not only as a means of urban transportation but also as a crucial spatial carrier for urban communication activities and a significant location for meeting the increasing demands of people for a better quality of life.The current road infrastructure prioritizes the right of way for cars,neglecting the design of sidewalks and green belts within the road’s boundaries,and extension spaces between buildings and boundary lines of roads.There is a pressing need to improve street space in response to the demand for development transformation and the creation of a warmer city.This paper summarizes common problems in current road spaces,draws on the experience of excellent urban road spaces in foreign countries,discusses new ideas for the refined design of road spaces based on the transformation of road planning concepts,and suggests a reference standard for guiding detailed design.Simultaneously,the review of road construction will incorporate the detailed design of road space to enhance the role of planning in guiding and controlling the construction of road works.

Exploration and Practice of Nitrogen Addition Process for LF Refining Ladle Bottom Blowing Nitrogen Steel Liquid

This article discusses and analyzes the law of nitrogen increase in liquid steel and the main factors affect-ing the nitrogen increasing of molten steel,through the way of adding nitrogen to molten steel by bottom blowing nitrogen gas in LF refining process.It is considered that the main factors affecting the nitrogen increasing instability of molten steel are the initial temperature of LF refining,nitrogen relative element,surface active elements[O]and[S]of steel liquid,and bottom blowing rate of ladle.The large-scale production practice shows that T[O]not more than 50×10-6 and[S]is not more than 0.020 in LF refining at the initial temperature of not less than 1570.The liquid steel nitrogen enrichment test is carried out by ladle bottom blowing nitrogen gas after 20 min of refining,the flow rate is set as(6.0~7.0)NL/min per ton,and it is turned to 2 NL/min at 6 min before the end of refining,the nitrogen increasing rate of liquid steel is basically stable at(5~6)×10-6 per minute.

Evaluation of the Impact of Refined Quality Control Management Model on the Qualified Rate of Disinfection and Sterilization of Surgical Instruments in the Sterilization Supply Center

Objective:To evaluate the application value of a refined quality control management model for a sterilization supply center.Methods:A retrospective analysis was conducted on the work situation of the sterilization supply center from January 2021 to January 2023.The work situation before January 31,2022,was classified as the control group;a routine quality control management model was implemented,and the work situation after January 31,2022,was classified as the observation group.The quality of medical device management and department satisfaction between the two groups were compared.Results:The timely recovery and supply rate,classification and cleaning pass rate,disinfection pass rate,packaging pass rate,sterilization pass rate,and department satisfaction score in the observation group were all higher than those of the control group(P<0.05).Conclusion:Implementing a refined quality control management model in the sterilization supply center can improve the quality management level of medical devices and department satisfaction and is worthy of promotion.

面向四面体网格生成的Delaunay refinement器官表面重建

为满足生物医学仿真系统对器官几何模型在Delaunay表面重构和四面体建模两方面的需求,提出一种面向四面体网格生成的Delaunay refinement表面重构算法.算法将从医学体数据中经过等值面提取和简化的初始表面作为输入和边界限定条件,为每个限定点计算局部特征尺寸并构建保护球,计算保护球与限定线段的交点并与限定点一起作为初始点集,生成Delaunay辅助四面体网格,引入一个迭代细分过程恢复边界,最终获得Delaunay重构表面.针对细分过程中的收敛性问题,文中给出了详细的理论证明和算法实例.此外,通过Delaunay四面体生成的对比实验表明该算法在Delaunay器官表面重构和四面体建模两方面兼具有效性和优越性.

Effect of Microstructure Refinement on the Strength and Toughness of Low Alloy Martensitic Steel

Martensitic microstructure in quenched and tempered 17CrNiMo6 steel with the prior austenite grain size ranging from 6 μm to 199 μm has been characterized by optical metallography （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The yield strength and the toughness of the steel with various prior austenite grain sizes were tested and correlated with microstructure characteristics. Results show that both the prior austenite grain size and the martensitic packet size in the 17CrNiMo6 steel follow a HalI-Petch relation with the yield strength. When the prior austenite grain size was refined from 199 μm to 6 μm , the yield strength increased by 235 MPa, while the Charpy U-notch impact energy at 77 K improved more than 8 times, indicating that microstructure refinement is more effective in improving the resistance to cleavage fracture than in increasing the strength. The fracture surfaces implied that the unit crack path for cleavage fracture is identified as being the packet.