Magnetic properties and thermal stability of anisotropic bonded Nd-Fe-B magnets by warm compaction

Anisotropic bonded magnets were prepared by warm compaction using anisotropic Nd-Fe-B powder. The forming process, magnetic properties, and temperature stability were studied. The results indicate that the optimal temperature of the process, which was decided by the vis-cosity of the binders, was 110°C. With increasing pressure, the density of the magnets increased. When the pressure was above 700 MPa, the powder particles were destroyed and the magnetic properties decreased. The magnetic properties of the anisotropic bonded magnets were as follows： remanence Br=0.98 T, intrinsic coercivity iHc=1361 kA/m, and maximum energy product BHmax=166 kJ/m3. The magnets had excellent thermal stability because of the high coercivity and good squareness of demagnetization curves. The flux density of the magnets was 35% higher than that of isotropic bonded Nd-Fe-B magnets at 120°C for 1000 h. The flux density of the bonded magnets showed little change with regard to temperature.

Ti/Al_2O_3 Functionally Gradient Material Prepared by the Explosive Compaction/SHS Process

Ti1Al2O3 Functionally Gradient Material (FGM) was prepared by an explosive compaction/SHS process. Ten sheets of the compounding powder were laminated and pressed to get a green body of FGM. It was then compacted explosively By burying the explosive compaction body into a stoichiometric Al/TiO2 mixture and igniting the combustion of the stoichiometric Al/TiO2 mixture, the SHS reaction of the explosive compaction body was initiated by the heat released from the combustion of the stoichiometric Al/TiO2 mixture. In this way, Ti/Al2O3 FGM was synthesized. The adiabatic temperatures of each gradient layer were calculated when the preheating temperatures were 298 K and 1173 K, respectively The microstructure, composition and properties of Ti/Al2O3 FGM and the reaction mechanism of each gradient layer were studied. It was found that Ti/Al2O3 FGM prepared by the explosive compaction/SHS process had a high density and a high microhardness. Its structure, composition and properties showed apparent gradient distribution. The structure of the standard stoichiometric ratio gradient layer of FGM was a network structure. Its reaction mode could be described as follows: Al powder melted first, then the molten Al penetrated into the TiO2 zone and reacted with TiO2, and big pores were left in the original positions of Al powder. The reaction of gradient layers with the addition of Al3O3 as diluents was similar to that of the standard stoichiometric ratio gradient layer, so were their structure and composition. However, the reaction of gradient layers with the addition of Ti as diluents was more complex and the composition deviated slightly from the designed one

AGGREGATE STRUCTURE OF FINE POWDER AND COMPACTION PROCESS

Compacting process of fine powder is greatly affected by the aggregate structure of particles. According to the experiment in which several kinds of silicon nitrides in different partical shape and size were compacted in uniaxialorientation, it is found that the volume compacting rate offorming body differs with the pressure. The aggregatestructure of each sample A, B or C was estimated by applying Cooper's equation to the analysis of the compacting process of each sample

On Numerical Modelling of Industrial Powder Compaction Processes for Large Deformation of Endochronic Plasticity at Finite Strains

Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the compaction processes are to obtain a compact with the geometrical requirements, without cracks, and with a uniform distribution of density. Design of such proc esses consist, essentially, in determine the sequence and relative displacements of die and punches in order to achieve such goals. A.B. Khoei presented a gener al framework for the finite element simulation of powder forming processes based on the following aspects; a large displacement formulation, centred on a total and updated Lagrangian formulation; an adaptive finite element strategy based on error estimates and automatic remeshing techniques; a cap model based on a hard ening rule in modelling of the highly non-linear behaviour of material; and the use of an efficient contact algorithm in the context of an interface element fo rmulation. In these references, the non-linear behaviour of powder was adequately desc ribed by the cap plasticity model. However, it suffers from a serious deficiency when the stress-point reaches a yield surface. In the flow theory of plasticit y, the transition from an elastic state to an elasto-plastic state appears more or less abruptly. For powder material it is very difficult to define the locati on of yield surface, because there is no distinct transition from elastic to ela stic-plastic behaviour. Results of experimental test on some hard met al powder show that the plastic effects were begun immediately upon loading. In such mater ials the domain of the yield surface would collapse to a point, so making the di rection of plastic increment indeterminate, because all directions are normal to a point. Thus, the classical plasticity theory cannot deal with such materials and an advanced constitutive theory is necessary. In the present paper, the constitutive equations of powder materials will be discussed via an endochronic theory of plasticity. This theory provides a unifi ed point of view to describe the elastic-plastic behaviour of material since it places no requirement for a yield surface and a ’loading function’ to disting uish between loading an unloading. Endochronic theory of plasticity has been app lied to a number of metallic materials, concrete and sand, but to the knowledge of authors, no numerical scheme of the model has been applied to powder material . In the present paper, a new approach is developed based on an endochronic rate independent, density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. Although the concept of yield surface has not been explicitly assumed in endochronic theory, it is shown that the cone-cap plasticity yield surface (Fig.1), which is the m ost commonly used plasticity models for describing the behavior of powder materi al can be easily derived as a special case of the proposed endochronic theory. Fig.1 Trace of cone-cap yield function on the meridian pl ane for different relative density As large deformation is observed in powder compaction process, a hypoelastic-pl astic formulation is developed in the context of finite deformation plasticity. Constitutive equations are stated in unrotated frame of reference that greatly s implifies endochronic constitutive relation in finite plasticity. Constitutive e quations of the endochronic theory and their numerical integration are establish ed and procedures for determining material parameters of the model are demonstra ted. Finally, the numerical schemes are examined for efficiency in the model ling of a tip shaped component, as shown in Fig.2. Fig.2 A shaped tip component. a) Geometry, boundary conditio n and finite element mesh; b) density distribution at final stage of

Deformation of ductile cuttings from sandstone in compaction process and experimental study of influence on porosity

Deformation of ductile cuttings from sandstone in the mechanical compaction process was designed through the "experimental system of triaxial rock deformation",and the influence on porosity was studied by looking into the deformation characteristics of ductile cuttings. The design indexes are as follows: simulated depth 0- 4 000 m,interval depth 500 m,and pressure range 0- 120 MPa at interval of 1. 5 MPa. The experimental results show that the porosity decreases as buried depth increases,indicating a negative relationship between them. The amount of compression was mainly obtained by porosity reduction and cutting deformation. Deformation of ductile cuttings is mainly ductile deformation; and deformation of crystal fragments is mainly expressed as brittle fracture,resulting in decrease of particle size. The research is of certain value for the exploration and development of oil and gas.

THE STRUCTURE CONTROL OF ALUMINUM FOAMS PRODUCED BY POWDER COMPACTED FOAMING PROCESS

A new technique, powder compact foaming process for the production of aluminumfoams has been studied in this article. According to this method, the aluminum pow-der is mixed with a powder foaming agent (TiH_2). Subsequent to mixing, the powderblend is hot compacted to obtain a dense semi--finished product. Upon heating to tem-peratures within the range of the melting point, the foaming agent decomposes to evolvegas and the semi--finished product expands into a porous cellular aluminum. Foamingprocess is the key in this method. Based on experiments, the foaming characteris-tics were mainly analyzed and discussed. Experiments show that the aluminum--foamwith closed pores and a uniform cell structure of high porosity can be obtained usingthis method by adjusting the foaming parameters: the content of foaming agent andfoaming temperature.

Finite element modeling of consolidation of composite laminates

Advanced fiber reinforced polymer composites have been increasingly applied to various structural components. One of the important processes to fabricate high performance laminated composites is an autoclave assisted prepreg lay-up. Since the quality of laminated composites is largely affected by the cure cycle, selection of an appropriate cure cycle for each application is important and must be optimized. Thus, some fundamental model of the consolidation and cure processes is necessary for selecting suitable parameters for a specific application. This article is concerned with the ＂flow-compaction＂ model during the autoclave processing of composite materials. By using a weighted residual method, two-dimensional finite element formulation for the consolidation process of thick thermosetting composites is presented and the corresponding finite element code is developed. Numerical examples, including comparison of the present numerical results with one-dimensional and twodimensional analytical solutions, are given to illustrate the accuracy and effectiveness of the proposed finite element formulation. In addition, a consolidation simulation of AS4/3501-6 graphite/epoxy laminate is carded out and compared with the experimental results available in the literature.

HEAT TRANSFER ANALYSIS DURING ROLLING OF THIN SLAB IN CSP

A mathematical model has been built to numerically predict the thermal history of thin slab during CSP （compact strip process） rolling. To estimate the temperature distribution in the slab mare accurately, the mathematical model combines heat transfer in the slab, in the roll, and at the roll-slab interface during bite. The numerical results agree with on-site running data, which proves the reliabili~, of the mathematical model. The results show that roll chilling has a significant effect on the temperature distribution in the slab.

Comparison between the Requirements of Flowability and Moldability and the Shape Retention of PIM Compacts during Debinding Process

To successfully employ powder injection molding (PIM) as a manufacturing technique, the function of the component, design of the part, material and process should be optimized for overall processing ability of the PIM process. A comparison between the requirements of flowability and moldability and the compacts shape retention has been made in this work. There is often a contradiction between the requirements of flowability and the compacts shape retention. Many works have been done to attain good molding conditions. However, they fail to take into account the effect of some factors that satisfies good molding conditions on the compacts shape retention during debinding. This paper studies the effect of the powder-binder mixture characteristics and the molding conditions on the flowability and moldability and the shape retention of PIM compacts during debinding process so as to attain the benefits of each.

Improving flangeability of multiphase steel by increasing microstructural homogeneity

Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,the microstructural homogeneity was advanced by adjusting the hard martensite/austenite(M/A)islands.The strength-flangeability was measured via uniaxial tensile tests and hole expansion tests.Their microstructures were characterized using a scanning electron microscope equipped with an electron backscatter diffraction detector and a transmission electron microscope.Nanoindentation tests were supplementally used to quantitatively reveal the microstructural homogeneity of the steels.Results show that the adjusted multiphase steel achieves an excellent ultimate tensile strength(~800 MPa)and flangeability(~135%hole expansion ratio).A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600℃.This microstructure consists of soft polygonal ferrite,blocky bainitic ferrite,and hard M/A islands.The volume fraction of M/A islands is around 5%,and the average size is less than l pm.Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity.Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late,which resulted in a positive flangeability.Moreover,avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance.

Anisotropic NdFeB/SmCoCuFeZr composite bonded magnet prepared by warm compaction process

Anisotropic NdFeB/SmCoCuFeZr composite bonded magnets were prepared by warm compaction process. The effects of adding SmCoCuFeZr magnetic powder on the properties of anisotropic bonded NdFeB magnet were investigated in this work. The results show that, both magnetic properties and temperature stability of the bonded magnet can be improved by adding fine SmCoCuFeZr magnetic powder. In the present study, the optimal content of SmCoCuFeZr magnetic powder was about 20 wt.%, in this case, the Br, Hcj, and（BH）maxof the NdFeB/SmCoCuFeZr composite magnet achieved 0.943 T, 1250 kA/m, and168 kJ/m^3, respectively.

Preparation and Compaction Behaviour of Poly(methyl methacrylate) Coated Iron Microparticles

The poly（methyl methacrylate）（PMMA） coatings onto surface of iron particles were electrochemically prepared and the effect on both surface structure and internal structure of the resulted material after compaction was carried out.The electrochemical polymerization treatment was performed in a fluidized bed electrolyzer using sulphuric acid solution containing potassium persulphate and methyl methacrylate（MMA）.The surface topography and the microstructure of the samples were observed by scanning electron microscopy（SEM） and optical microscopy（OM）.It was found that the PMMA layer coated onto iron particles results in improvement of their compressibility compared with uncoated powders,and classical lubricants are not necessary for compacting particles coated.

In-situ observation and analysis of solidified structure evolution of S50C steel in soaking furnace

The evolution of solidified structure of S50C steel during heat treatment in compact strip production process was studied through an ultra-high-temperature confocal scanning laser microscope.It was found that the solidified structure consisted of dendritic crystals with secondary dendrite arm spacing ranging in 32-120μm,where carbon segregation was evident,and the dendrite arms wereα-Fe.The insignificant change was observed at a soaking temperature of 1180℃,whereas at 1300℃,the finer structure firstly disappeared,and then,the coarsening decreased,indicating that carbon tended to be homogenized.Therefore,the microsegregation was improved at 1300℃for 15 min.The phase transformation ofα-Fe→γ-Fe enhanced the carbon diffusion,and the evolution of the equivalent radius req was controlled by carbon diffusion.The diffusion coefficient of carbon(D=15μm2/s)was determined by using the inverse problem method.

Measurement and correlation of supercritical CO_(2) and ionic liquid systems for design of advanced unit operations

Ionic liquids combined with supercriticalfluid technology hold great promise as working solvents for developing compact processes.Ionic liquids,which are organic molten salts,typically have extremely low volatility and high functionality,but possess high viscos-ities,surface tensions and low diffusion coefficients,which can limit their applicability.CO_(2),on the other hand,especially in its supercritical state,is a green solvent that can be used advantageously when combined with the ionic liquid to provide viscosity and surface tension reduction and to promote mass transfer.The solubility of CO_(2) in the ionic liquid is key to estimating the important physical properties that include partition coefficients,viscosities,densities,interfacial tensions,thermal conductivities and heat capacities needed in contactor design.In this work,we examine a subset of available high pressure pure component ionic liquid PVT data and high pressure CO_(2)-ionic liquid solubility data and report new correlations for CO_(2)-ionic liquid systems with equations of state that have some industrial applications including:(1)general,(2)fuel desulfurization,(3)CO_(2) capture,and(4)chiral separation.New measurements of solubility data for the CO_(2) and 1-butyl-3-methylimidazolium octyl sulfate,[bmim][OcSO4]system are reported and correlated.In the correlation of the CO_(2) ionic liquid phase behavior,the Peng-Robinson and the Sanchez-Lacombe equations of state were considered and are compared.It is shown that excellent correlation of CO_(2) solubility can be obtained with either equation and they share some common characteristics regarding inter-action parameters.In the Sanchez-Lacombe equation,parameters that are derived from the supercritical region were found to be important for obtaining good correlation of the CO_(2)-ionic liquid solubility data.