Progress and Application of Microstructure Simulation of Alloy SolidificationEI北大核心CSCD

Solidification structures are the interaction links between the alloy components and their mechanical properties. Scientifically comprehending about the formation mechanisms, dominant factors and control methods in alloy solidification has a significant effect on the structure control and optimization. Dendritic structure is the most frequently observed solidification microstructure of alloys and controlled by heat, solute, melt flow, capillary and many other factors. Modelling and simulating can accurately quantify various phenomena and evolution rules in the process of solidification, thus play an increasingly important role in the design, preparation, processing and performance optimization of alloy materials. Over the past two decades, remarkable progress has been made and various models have been proposed in microstructure simulation during alloy solidification process, such as deterministic method, phase field (PF), Monte Carlo (MC) and cellular automaton (CA). With the advantages of clear physical meaning, easily programming and high calculation efficiency, CA method has been widely applied in the study of solidification structure simulation and exhibits great advantages. Considering the current development level of computer hardware, numerical model and calculation method, microstructure simulation of large components mainly adopts macro-microscopic coupling calculation method, such as CA-FD/FE model. The heat transfer and other multi-physical fields are calculated at the level of coarse mesh, where-as nucleation and dendritic growth are simulated at a much finer grid level. This paper reviews the main models and development of CA method used for nucleation simulation. The key aspects in the simulation of dendritic growth including mean solid-interface interface curvature, growth kinetics and the algorithm for eliminating "pseudo anisotropy" are discussed. Based on this, the development and application status of macro-micro coupling model during casting, directional solidification and other manufacturing fields are summarized. Finally, the existing problems and future tendency for simulation of solidification structures are analyzed.     

Research Progress of Numerical Simulation in Steelmaking and Continuous Casting ProcessesEI北大核心CSCD

Because of the complexity of steelmaking and continuous casting processes and their limitation condition for direct measuring and testing, numerical simulation has become an indispensable means to analyze the phenomena and mechanisms occurring in the processes, and since the 1980s, it has made a rapid development. For the converter smelting, some new oxygen lances were designed by using the simulation study of the characteristics of the oxygen lance supersonic jet. Some mathematical models have been established to describe the slag-metal-gas multiphase flow behavior in steelmaking converter, and the flow field, mixing efficiency, metal droplet splashing, lining scouring and other physical phenomena. For the ladle refining, the Euler-Euler model gradually replaces the quasi-unidirectional and Euler-Lagrangian models, and successfully describes the phenomena of bubble turbulent dispersion caused by liquid turbulent fluctuation, and bubble-induced turbulence occurring during bubble floating process. So, some new and important inclusion transport mechanisms and phenomena have been presented. The CFD-PBM model was used to predict successfully the inclusion transport, collision growth and removal behavior in the molten steel, which enriches the inclusions removal theory of ladle refining. The CFD-SRM coupled model was used to accurately describe the slag-metal reaction and desulfurization behavior in a gas-stirred ladle, and the effect of the different content of compositions in synthetic slag and liquid steel, arrangement of bottom blowing tuyeres on the slag-metal reactions and desulfurization efficiency were discussed and clarified. For steel continuous casting, as the heat flow model from the solidified shell to the copper plate of mold was coupled with the thermo/mechanical model of the solidified shell, distributions of mold flux and air gap both along circumference and height directions of the mold were successfully predicted, while founded theoretical backgrounds for designing new mold with inner convex surface and controlling the surface corner crack of micro-alloyed steel. The coupled simulation between flow and electromagnetic fields in mold revealed the flow behavior of molten steel with electromagnetic stirring or braking, the fluctuation characteristic of the slag-steel interface and the distribution characteristic of inclusions in the strand. Based on the volume averaged method, multi-field and multi-phase solidification model successfully clarified the formation mechanism of macro-segregation in continuously cast strand and quantitatively predicted central/centerline segregation indexes in the strand under different casting conditions. In addition, the numerical simulation of the evolution of solidification structure of the continuously cast strand mainly focused on the as-cast grain, and its extension to the dendrite structure needed further more endeavors. Generally speaking, the numerical simulation in steelmaking-continuous casting process is moving towards coupling multi-physical/chemistry phenomena and multi-fields and gradually transits to the microscopic scale.     

Numerical Simulation of Macrosegregation in Steel Ingot CastingEI北大核心CSCD

Many key forging components of heavy equipment are manufactured by large steel ingots. Macrosegregation in steel ingots is a key defect formed during the solidification process. Over the past few decades, numerical modeling has played a more and more important role in the study of macrosegregation. Various models have been developed and applied to different ingot casting processes. This paper focused on the application of macrosegregation models to the steel ingot. Firstly, the formation mechanism and influencing factors of macrosegregation were introduced. Then, the existing macrosegregation models and their recent development were summarized. Macrosegregation models accounting for such mechanisms as solidification shrinkage- induced flow and mushy zone deformation were analyzed, respectfully. To model macrosegregation due to solidification shrinkage, the key was to solve the free surface. A simple derivation showed that the multi-phase (including gas phase) models were equivalent to the VOF-based segregation models in dealing with the shrinkage-induced flow. Finally, our recent research work on numerical modeling of macrosegregation in steel ingots was illustrated, including application of the developed multi-component and multi-phase macrosegregation model to a 36 t steel ingot, and numerical simulation of multiple pouring process. The carbon and sulphur concentrations at about 1800 sampling points, covering the full section of a 36 t ingot, were measured. By detailed temperature recording, accurate heat transfer conditions between the ingot and mould were obtained. Typical macrosegregation patterns, including the bottom-located negative segregation and the pushpin-like positive segregation zone in the top riser, have been reproduced both in the measurements and the predictions, The carbon and sulphur concentrations predicted by the three dimensional multi-component and multi-phase macrosegregation models agreed well with the measurements, thus proving that the model can well predict the macrosegregation formation in steel ingots. As for the multi-pouring process simulation, the results show a high concentration of carbon at the bottom and a low concentration of carbon at the top of the mould after the multi-pouring process with carbon content high in the first ladle and low in the last ladle. Therefore, the multiple pouring process could get the initial solute distribution with the opposite form of segregation. Such carbon concentration distribution would reduce the negative segregation at the bottom and the positive segregation at the top of the solidified ingot, thus proving the ability of the multiple pouring process for the control of macrosegregation.     

Experimental Studies and Numerical Simulation on the Nitriding Process of Grain-Oriented Silicon SteelEI北大核心CSCD

Grain-oriented silicon steel (GOSS) is an important functional material used as lamination cores in various transformers. Its magnetic properties are strongly dependent on the sharpness of Goss texture, which is developed during the secondary recrystallization annealing of product. In order to save energy and reduce cut-down operation costs, Nippon steel first lowered the slab-reheating temperature from 1350-1400 degrees C to 1150 degrees C and adopted the nitriding process to form nitride inhibitors before recrystallization annealing in 1970s. In this new process, nitriding is the critical process because it controls the size, distribution and volume fraction of nitride precipitates, which then determines the subsequent development of Goss texture. Although it is of great importance for good quality control of industrial GOSS product, unfortunately, a quantitative mathematic modeling on nitriding kinetics is still in lack. In this work, nitriding kinetics were both measured experimentally and simulated by modeling. The N contents after various nitriding periods and N concentration gradient across thickness were both measured. It has been found that the N content increases slowly at the beginning of 60 s and then much more rapidly during nitriding. There exists a sharp N concentration gradient within the depth of 0.03 mm to the steel sheet surface, which diminishes after about 0.04 mm depth. With the different assumptions on N-transfer coefficient from gas to the steel matrix, the first mathematic modeling on nitriding kinetics of GOSS has been successfully established and solved numerically. The simulation results suggest that only when the N-transfer coefficient, f, changes with time following the Avrami function, f=A(1-exp(-kt(n))), the calculated nitriding kinetics are consistent with the measurements. Such an Avrami-type dependence results from the reduction kinetics of oxide layer on the surface of silicon steel sheet during nitriding, in which both plate-like and spherical oxides were observed at the beginning but most of them became spherical after nitriding.     

Study and Development on Numerical Simulation for Application of Electromagnetic Field Technology in Metallurgical ProcessesEI北大核心CSCD

The application of electromagnetic fields is an important way to control the physical and chemical changes of heat transfer, mass transfer, fluid flow and solidification in metallurgical and material preparation processes. It is of great significance to improve the production efficiency and product quality. In this paper, the authors summarize the research contents and progress of numerical simulation on several typical applications of electromagnetic technology in metallurgical fields in recent years, including the electromagnetic steel-teeming technology using induction heating and induction heating technology of a tundish, the applications of electromagnetic force such as the electromagnetic swirling technology in submerged entry nozzle, the soft-contact mold electromagnetic continuous casting technology and the electromagnetic metallurgical technology for tundish, the influence and control of electromagnetic force on solidified structure evolution, and also the electromagnetic cold crucible technology with comprehensive utilization of induction heat and electromagnetic force. Numerical simulation, as an important research method, is a very important tool in finding out the mechanism and rules of electromagnetic fields during metallurgical and material preparation processes to predict, analyze, and optimize metallurgical processes.     

Research Progress of Modified Polyaniline in Anticorrosive CoatingsEI北大核心CSCD

聚苯胺因其可逆的氧化还原特性在金属腐蚀与防护领域具有广阔的应用前景,目前有关改性聚苯胺对涂层附着力、阻隔性能以及钝化机理的研究比较零散,缺乏系统总结。通过对单一聚苯胺分散性差、疏水性弱等缺陷的分析,报道近年来改性聚苯胺在防腐涂料领域中的研究思路和研究进展,比较不同条件下改性策略的优劣,归纳聚苯胺结构与涂层耐腐蚀性之间存在的联系。进一步论证柔性、疏水基团取代聚苯胺有利于提升涂层抗渗性,改变掺杂剂以及与纳米氧化物、石墨烯等原位聚合制备复合填料也是提升涂层防腐性能的有效途径。展望该行业未来研究和发展的趋势,可为今后聚苯胺的改性工作提供理论指导。     

Modeling and Simulation of Hydrogen Behavior in TungstenEI北大核心CSCD

Based on national strategic needs for fusion energy, our group have investigated the behavior of H isotopes including dissolution, diffusion, accumulation and bubble formation in W using a first-principles method in combination with molecular dynamic method. It is found that the dissolution and nucleation of H in defects follow an "optimal charge density" rule, and a vacancy trapping mechanism for H bubble formation in W has been revealed. An anisotropic strain enhanced effect of H solubility due to H accumulation in W has been found, and a cascading effect of H bubble growth has been proposed. Noble gases/alloying elements doping in W has been proposed to suppress H bubble formation, because these dopants can change the distribution of charge density in defects and block the formation and nucleation of H-2 molecule. These works are reviewed in this paper. Our calculations will provide a good reference for the design, preparation and application of W-PFM under a fusion environment.     

Numerical Simulation and Experimental Study on Porthole Die Extrusion Process of LZ91 Mg-Li AlloyEI北大核心CSCD

Porthole die extrusion is the dominant process to produce hollow profiles due to its high productivity and capacity in producing complex profiles. In this study, the finite element simulation model of porthole die extrusion of LZ91 Mg-Li alloy was established. The effects of extrusion ratio on strain, temperature and flow velocity were studied, and the welding quality was quantitatively evaluated by means of J criterion. The experiments of porthole die extrusion were carried out by varying extrusion ratios. The microstructures of as-cast, homogenized and extruded LZ91 Mg-Li alloy were examined. The results show that the materials near the bridge surface and at the bottom of the bridge have large deformation, while the materials inside the portholes have small deformation. Moreover, with the increase of extrusion ratio, the effective strain of material is increased. Due to the heat generated by plastic deformation and the heat dissipation caused by profile cooling, the temperature of the material on the top of bridge is increased, while that of the material near the die exit becomes lower. The welding quality in the central area of weld seam is lower than that in the edge area of weld seam. With the increase of extrusion ratio, the welding quality is improved. More nucleation is generated in welding zone due to its large strain, resulting in the formation of fine grains. However, the dynamic recrystallization is not complete in the matrix zone, and some coarse grains still remain. Moreover, the material temperature becomes higher with high extrusion ratio, and the phenomenon of grain growth is observed.     

Numerical Simulation of Heat Generation,Heat Transfer and Material Flow in Friction Stir WeldingEI北大核心CSCD

The heat generation, heat transfer and plasticized material flow in friction stir welding determine directly the microstructure evolution and mechanical properties of weld joints. Numerical simulation of these thermo-physical phenomena is of great significance for getting a deep insight into the underlying mechanisms and optimizing the process parameters of friction stir welding. This article reviews the progress status in numerical simulation of heat generation, heat transfer and plasticized material flow behaviors in friction stir welding, and outlines the unsolved problems. The research work targeting these issues, which has been conducted by the authors' group, is introduced. According to the stress characteristics at the tool-workpiece interface, the expressions of sticking rate and friction coefficient are developed, and this measurement-calculation method lays foundation for improving the accuracy of numerical analysis. Through synthetically considering the characteristics of complex-shaped tools, a three dimensional model of friction stir welding process is established. Three types of tools are taken into consideration, i.e., normal CT (conical-pin tool), ST (conical-pin with 4 flats tool) and TT (conical-pin with 3 flats tool). For the cases in application of these tools, the heat generation, temperature profile, and material flow velocity are analyzed quantitatively. A mathematical model for the whole friction stir welding process including plunge stage, dwell stage, welding stage, and cooling stage is established for numerical analysis of transient development in heat generation rate, temperature and material flow fields in each stages. Based on the status review, the trend in numerical simulation of frictions stir welding is outlooked, and the research focus for next step is proposed.     

Numerical Simulation of Liquid-Solid Conversion Affecting Flow Behavior During Casting Filling ProcessEI北大核心CSCD

Misrun and cold shut are common defects in casting productions, which could make surface accuracy of castings poorer, even leading to cracking and casting scraps in them. The formation process of misrun and cold shut is hard to be observed directly only by experiment measures, since casting filling process is in a state of high temperature flow inside mold. The key to predict the defects accurately is the way to handle the effect of liquid-solid conversion on flow behavior. On the basis of existing methods for treating liquid-solid conversion, a calculation model of mushy region flow behavior through measurement of solid-fraction is developed, which can effectively investigate the flow behavior of mushy region in different stages. Generally, the critical solid-fraction method is adopted for mushy region with high solid-fraction, in consideration of that only the speed of high solid-fraction region is supposed to be zero during casting filling process. The variable viscosity method is applied for mushy region with low solid-fraction, due to casting filling process being unlikely to form toothpaste-like flow. However, the porous medium drag-based model is used for mushy region with middle solid-fraction, because only the middle solid-fraction region can be equivalent to porous medium. Combining the above three methods, a flow-field calculation program considering the effect of liquid-solid conversion on flow behavior during casting filling process is developed, in which finite volume method (FVM) is included for discretization equations; the pressure implicit with splitting of operator (PISO) algorithm is added for coupling pressure and velocity; the volume of fluid (VOF) algorithm is also combined for interface tracking. An numerical simulation of water-filled S-shaped channel is performed in the case of taking no account of liquid-solid conversion, and the simulated results coincide better with the experimental results, which certifies for its accuracy as an adopted model. Since the bottom filling casting craft is commonly used in single-shape casting, a comparison between the calculated results obtained using other single models and those using this model at different control parameters, is needed. The better agreement between them indicates that this new model is appropriate for calculating the flow behavior in mushy region.     

Numerical Simulation of Anomalous Eutectic Growth of Ni-Sn Alloy Under Laser Remelting of Powder BedEI北大核心CSCD

Eutectic is one of the most commonly observed solidification patterns, the growth mor-phology of which is important to materials properties. Anomalous eutectic is typically coarser and globular than lamellar eutectic, which is commonly observed during solidification of binary eutectic alloy, including deep undercooled melt and laser remelting process. The morphological evolution mechanism of anomalous growth is still unknown due to the lack of simulation evidence. During laser remelting process, the anomalous eutectic is sandwiched between lamellar eutectic at the bottom of melt pool. Comparing to deep undercooled melt, laser remelting has simpler temperature field distribution, which can be simplified into directional solidification. Thus, simulations of anomalous eutectic growth in laser remelting process are feasible. In the present work, the anomalous eutectic growth mechanism under laser remelting conditions was simulated using a low mesh induced anisotropy cellular automaton (CA) model. Firstly, a two-dimensional lamellar eutectic CA model of CBr4-C2Cl6 alloy was established, and the morphological transition from 1 lambda O to 2 lambda O was simulated. The calculated results are in good agreement with experiments and phase field simulations. By setting the interface cells containing three phases (alpha, beta and liquid phases), the model can continuously change the alpha and beta phase volume fractions in the CA model, making it easier for the model to capture the instability of lamellar eutectic. Compared with the results of the phase field model, the intermediate 1 lambda O-2 lambda O state of oscillation instability of 1 lambda O and 2 lambda O which is consistent with the experimental results was calculated. Based on the above-mentioned binary eutectic CA model, the lamellar eutectic to anomalous eutectic transition at the bottom of the molten pool was simulated. Under the condition of initial low cooling rate, the fine lamellar eutectic is decoupled, it leads to the overgrowth of beta-Ni3Sn phase. During the subsequent accelerated cooling process, alpha-Ni nucleated in the liquid phase at the front of the solid/liquid interface, and the beta-Ni3Sn phase wrapped around the alpha-Ni phase forming anomalous eutectic morphology. During the laser remelting process, there is indeed a rapid change of solidification rate from zero to scanning speed rate from the bottom to the top of the melt pool, and therefore coincides with the solidification conditions of the variable pulling velocity used in the CA simulations.     

Modification Mechanism of Cerium on the Inclusions in Drill SteelEI北大核心CSCD

Fatigue fracture is the main failure forms of drill steel, and the hard oxide with large size is one of the main reasons for the fatigue fracture of drill steel. Therefore, the miniaturization and softening of inclusion can effectively improve the anti-fatigue performance of drill steel and prolong its service life. Rare earth elements have very good affinity with oxygen and sulfur in molten steel, and the hardness of resulting rare earth compounds is very low. In this work, the rare earth element cerium was added into drill steel to investigate the effect of Ce on the MgAl2O4 and sulfides. The composition, morphology, number, and size of inclusions in drill steel were analyzed by using SEM and EDS. The evolution process and modification mechanism of Ce on MgAl2O4 and sulfides were clarified by experimental results and calculated by thermodynamic software. The type of inclusions in drill steel without Ce addition is MgAl2O4 and (Ca, Mn) S. As the Ce content in drill steel reaches to 0.0078% (mass fraction), the type of inclusions changes to Ce-O and Ce-S. In addition, a few complex inclusions, mixture of Ce-O and MgO, were also found. The size of inclusions in drill steel decreases significantly as the oxides and sulfides were modified into Ce-O and Ce-S. The calculated results show that MgAl2O4 and (Ca, Mn) S in drill steel can be effectively modified into Ce-O and Ce-S as the Ce added into molten steel, and the modification sequence of Ce on the MgAl2O4 is as follows: MgAl2O4 -> CeAlO3+ MgO -> Ce2O3+ MgO -> Ce2O3. The content of Ce in drill steel has great influence on the type of inclusions. The modification mechanism of Ce on MgAl2O4 calculated by Factsage 6.3 agrees well with the experimental observations.     

Research Progress on Failure Analysis and Life Assessment of Key Components in Hydraulic SupportsEI北大核心CSCD

煤矿综采液压支架是控制采煤工作面矿山压力的大型核心装备,是现代采煤作业安全防护、作业空间扩大和采煤效率提高的关键,主要由液压件(立柱、千斤顶)、承载结构件(顶梁、掩护梁和底座等)、推移装置、控制系统和其他辅助装置组成,往往在极其恶劣复杂的矿井环境中服役,局部容易发生变形损伤、疲劳和腐蚀。对其关键部件进行失效分析及剩余寿命评估,是推动整机再制造和促进绿色循环经济发展的基本前提条件。对顶梁、底座、连杆、立柱等关键部件的失效形式及原因进行综述与分析,指出结构件的失效原因分析需要受到更多关注。总结支架寿命评估的研究现状,指出目前的研究集中在设计阶段的强度校核和寿命预估上,而关于服役了一段时间的支架的剩余寿命研究仍是空白。最后提出基于断裂力学利用有限元模拟进行剩余寿命评估的发展趋势。     

Research Progress on Surface Impact Strengthening Mechanisms and Application of Nickel-Based SuperalloysEI北大核心CSCD

为满足不断攀升的两机涡轮动力系统的快速发展,表面冲击强化技术在涡轮转子用高温合金表面强化的应用及相应机制的研究受到了广泛关注。然而,高温合金表面硬化层在高温服役环境下的回复、再结晶行为难以避免,由此引起的表面强韧化、抗疲劳效果的退化,成为制约表面冲击强化技术在先进高温合金关键部件深入应用的瓶颈。本文总结了近年来镍基高温合金表面冲击强化机制及应用研究进展,分析了表面冲击强化对镍基高温合金表面强韧性及抗疲劳的作用规律,探究了高温合金表面冲击硬化层在高温及长期时效过程中的显微组织、微结构演化及其对高温稳定性的作用机理。以期为发展镍基高温合金表面冲击强化、提高两机涡轮转子疲劳抗力提供基础。     

Numerical Simulation of Temperature Field and Thermal Stress in ZTA(p)/HCCI Composites During Solidification ProcessEI北大核心CSCD

As advanced wear-resistant materials, it is important to promote the process and application of high chromium cast iron (HCCI) matrix composite reinforced by zirconia toughened alumina ceramic particles (ZTA(p)/HCCI composite). For the purpose of wider applications of this kind of composite, it is urgent to optimize the process parameters of casting process for it. Based on the finite element software the temperature field and thermal stress in ZTA(p)/HCCI composite during casting process were simulated. The temperature fields of castings are investigated using the uniform initial temperature and the non-uniform initial temperature at the beginning of solidification. It is more appropriate to the actual situation at the end of mold filling process when the initial temperature of solidification is considered as an unstable temperature field. The influence from performs with different honeycomb shapes is considered in the calculations of temperature fields of castings. In this work, the thermo-elastic plastic model was used to accurately describe the thermal stress in the castings with different honeycomb shapes of preforms, and the results indicate that the thermal stress in them decreases with the increase of edge number of holes in preforms. Finally, the hot crack in castings is predicted and the shakeout process is optimized. It is concluded that the simulated results are in good agreement with the experimental results.     

Recent Progresses in Modeling of Nucleation During Solidification on the Atomic ScaleEI北大核心CSCD

Nucleation, the starting point of first-order discontinuous phase transformations, has long been an important issue in condensed matter physics and materials science. It plays a key role in determining the microstructures and mechanical properties of crystalline materials. As nucleation occurs at the atomic length scale and the diffusional time scale and is a typical stochastic event, investigating such kind of multiple scale issues will be taken up an enormous challenge. Because of the limitations of present experimental methods, it is still very hard to observe the nucleation process in situ. With the development of computational materials science, a deeper understanding of nucleation process has been obtained with the numerical modeling of nucleation process on the atomic scale. In this paper, some recent developments in modeling and simulation of nucleation process during solidification on the atomic scale are reviewed. Firstly, the development of classical nucleation theory and the step nucleation theory are reviewed. Then the developments in modeling of nucleation process by using the phase field method, Monte-Carlo method, Molecular dynamics method and the phase field crystal model are discussed. After that, some recent progresses in modeling of nucleation process during solidification in our research group by using the phase field crystal model are demonstrated. Finally, the outlooks of the future study on the nucleation during solidification are also presented.     

Recent Progress of New Nonferrous Metal Materials in China

ＲｅｃｅｎｔＰｒｏｇｒｅｓｓｏｆＮｅｗＮｏｎｆｅｒｒｏｕｓＭｅｔａｌＭａｔｅｒｉａｌｓｉｎＣｈｉｎａＱｉｕＸｉａｎｇｄｏｎｇ；ＪｉａＨｏｕｓｈｅｎｇａｎｄＺｈｏｎｇＪｕｎｈｕｉ（邱向东）（贾厚生）（钟俊辉）（ＧｅｎｅｒａｌＲｅｓｅａｒｃｈＩｎｓｔｉｔ...     

Study,on Influence of Processes on the Dehydrogenation Performance of NaAlH4EI北大核心CSCD

In this paper, the effects of preparation process, ball-milling equipments, storing time and ball-milling time on the dehydrogenation performances were analyzed. All the samples were ball-milled by planetary ball mill except for sample 3 which was ball-milled by high-energy vibration ball mill. The results indicate that the above mentioned influence factors present obvious effect on the dehydrogenation performances of NaAlH4. The dehydrogenation amount of the samples turned up and down during ball milling increases by 50wt%. Compared to the samples prepared by planetary mill, the dehydrogenation amount of samples prepared by the high-energy vibration ball mill increases markedly. The results from studying on storing time and milling time show that the dehydrogenation amounts of the samples milled by planetary mill and laid aside for 24 h get an obvious increase. In addition, the amount of the hydrogen release of the samples milled for different time with planetary mill presents significantly difference. The amount of the hydrogen release of the sample milled for 80 min is higher than those milled for 100, 40 and 60 min. However, compared to other influence factors, the effect of ball-milling time on NaAlH4 is smaller.     

Research Progress of Diamond Tool Machining Technology for Ferrous MetalsEI北大核心CSCD

金刚石刀具是超精密加工最理想的刀具之一,但在黑色金属超精密加工领域“石墨化”导致刀具快速磨损,其应用极大地受到了限制。首先,针对金刚石刀具的磨损机理进行介绍。然后,综述金刚石刀具切削黑色金属的几种常见方法,如刀具表面改性、工件表面改性、低温辅助切削、超声振动辅助切削等,通过研究实例来分析各方法的应用效果和存在问题,并从技术层面分析影响金刚石刀具在黑色金属加工领域发展的关键因素。最后,对金刚石刀具切削黑色金属未来的发展趋势进行探讨。总结金刚石刀具在黑色金属领域的加工方法,分析加工黑色金属时抑制金刚石刀具磨损的核心技术,对黑色金属的精密超精密加工具有重要的引领和推动作用。     

Recent Progress of Oxide/Carbide Dispersion Strengthened W-Based MaterialsEI北大核心CSCD

Tungsten (W) plays an important role in the defense industry, aerospace and nuclear industry due to its excellent properties such as high melting point (3410.), high density (19.35 g/cm(3)), high hardness, high elastic modulus, high thermal conductivity, low expansion coefficient and low vapor pressure. However, its disadvantages, such as low temperature brittleness (ductile brittle transition temperature usually above 400 degrees C), low tensile strength, recrystallization embrittlement, high thermal load induced cracking and irradiation embrittlement, affected seriously its processing and servicing performance. Focusing on these problems, carbides/oxide dispersion strengthened W alloys were studied widely. The mechanical properties and other service properties of W were significantly improved by nano scale carbide/oxide dispersion strengthening and microstructure optimization. This article mainly reviews carbide and oxide dispersion strengthening design and the corresponding W-based materials preparation, microstructure and properties of regulation and service performance evaluation, introduces the latest progress of the research and development of the authors' team, and looks forward to the future development trend and the problems to be solved.