钼粉末温压成形过程的数值模拟研究

运用MSC.MARC有限元分析软件,采用热-机耦合方法,对钼粉末温压成形过程进行了有限元数值模拟,获得了粉末体形变、应力场和相对密度分布等相关数据,为改善钼粉温压成形工艺及优化工艺参数提供了理论依据.     

Electrochemical behavior and corrosion of iron in aqueous sulfidic solution

This paper discusses the electrochemical behavior and corrosivity of aqueous sulfidic solutions with reference to iron and carbon steel. The chemistry of aqueous sulfidic solutions is reviewed with particular emphasis on stability of various sulfur species in aqueous solutions as a function of pH and solution potential. The thermodynamic predictions of corrosion processes for iron in sulfidic solution are discussed in terms of the potential pH equilibrium diagrams. Considerable discussion of the corrosion and electrochemical behavior of iron in sulfidic solutions includes the role of solution composition on corrosion and polarization behavior. The influence of surface films on corrosion in these systems is also discussed. The paper concludes with a discussion of the role solution composition on hydrogen absorption and embrittlement of iron and carbon steel.     

Investigating corrosion processes in the micrometric range: A SVET study of the galvanic corrosion of zinc coupled with iron

The galvanic corrosion of an iron/zinc pair immersed in aqueous 0.1 M Na₂SO₄ solution has been investigated by using the scanning vibrating electrode technique (SVET). In this way, investigations in the micrometer range of the progress of the electrochemical reactions involved in galvanic process were performed. The anodic oxidation process is observed to be initiated on the zinc sample in a localized manner, whereas the cathodic reaction involving the electroreduction of dissolved oxygen is homogeneously distributed over the iron sample. This later process is the rate determining step in the overall corrosion process, as demonstrated by the changes in the ionic and galvanic currents measured in the system when the area of the iron specimen is varied relative to that of zinc. The occurrence of coupled chemical reactions in the solution phase involving the products of the corrosion reactions could also be deduced from the integration of the ionic currents measured for each half-reaction during a SVET scan. Thus, the corrosion processes involved in the galvanic coupling of iron and zinc have been further understood by using this microelectrochemical technique appropriately, helping to better interpret large scale measurements.     

Warm compaction powder metallurgy of Cu

A series of experiments were carried out using different admixed lubricant contents, different compaction pressures and temperatures in order to study the warm compaction of copper powder. Results show that too much admixed lubricant will lead to the squeeze out of the lubricant from the compact during the warm compaction processing of Cu powder. Results also show that blisters can be found in sintered samples that contain lubricant less than 0.15%(mass fraction). Optimal warm compaction parameters for producing high density powder metallurgy copper material are obtained. Compacts with green density of 8.6 g/cm^3 and a sintered density of 8.83 g/cm3 can be produced by warm compacting the Cu powder, which contains 0.2% admixed lubricant, and is compacted at 145℃ with a pressure of 700 MPa.     

焊后钎剂残渣腐蚀行为分析

采用扫描电子显微镜、电化学工作站等手段对同一型号不同药芯钎料钎剂残渣的腐蚀行为进行了系统研究分析。研究结果表明：钎料和基体在钎剂溶液中均发生了腐蚀,基体的腐蚀速率整体明显高于钎料的腐蚀速率;腐蚀速率随着时间的延长不断降低,但腐蚀并未停止。钎料组织越细,晶界越多,晶界处非规则排列的原子将发生较多腐蚀反应,耐腐蚀性下降。高温加速试验后Fe基体和镀锌层间出现微观裂纹,钎剂中强腐蚀性物质已渗透到界面层;在镀锌层区域,锌元素大量被氧化,形成了ZnO;在残留钎剂层区域,Fe,Zn元素含量较高,耐蚀性较差的Fe元素部分已扩散到残留钎剂层区域,形成铁的氧化物,同时又与NaCl等发生反应,形成FeCl3等物质。 创新点： 探明了钎剂残渣的腐蚀行为,明确其对钎焊接头可靠性的影响程度。     

铜粉螺线管线圈磁脉冲致密试验研究

将电磁成形技术用于粉末材料致密，利用螺线管线圈对铜粉进行了致密试验。分析了放电电压、致密次数、加热温度等因素对压坯致密度的影响。试验结果表明增加放电电压、多次放电、对粉末进行预热，均能提高压坯的平均致密度。在压坯轴向上距离中心越远的位置致密度越低，在径向上距离中心越远的位置致密度越高。     

A study of the inhibition of iron corrosion by imidazole and its derivatives self-assembled films

The self-assembled (SA) films of imidazole and its derivatives were prepared on the iron surface. The protection abilities of these films against iron corrosion in 0.5 M H₂SO₄ solution were investigated using electrochemical impedance spectroscopy (EIS) and polarization techniques. The results of EIS and polarization curves demonstrated that films of the imidazole and its derivatives were able to protect iron from corrosion effectively. XPS was also used for the surface analysis, the results from XPS confirmed the adsorption of imidazole derivatives on the iron surface by monitoring the functional group peaks of the compounds.     

A study of the inhibition of iron corrosion in HCl solutions by some amino acids

The performance of three selected amino acids, namely alanine (Ala), cysteine (Cys) and S-methyl cysteine (S-MCys) as safe corrosion inhibitors for iron in aerated stagnant 1.0 M HCl solutions was evaluated by Tafel polarization and impedance measurements. Results indicate that Ala acts mainly as a cathodic inhibitor, while Cys and S-MCys function as mixed-type inhibitors. Cys, which contains a mercapto group in its molecular structure, was the most effective among the inhibitors tested, while Ala was less effective than S-MCys. The low inhibition efficiency recorded for S-MCys compared with that of Cys was attributed to steric effects caused by the substituent methyl on the mercapto group. Electrochemical frequency modulation (EFM) technique and inductively coupled plasma atomic emission spectrometry (ICP-AES), were also applied to make accurate determination of corrosion rates. Validation of the Tafel extrapolation method for measuring corrosion rates was tested. Rates of corrosion rates (in μm y⁻¹) obtained from Tafel extrapolation method are in good agreement with those measured using EFM and ICP methods. Some theoretical studies, including molecular dynamics (MD) and density functional theory (DFT), were also employed to establish the correlation between the structure (molecular and electronic) of the three tested inhibitors and the inhibition efficiency. Adsorption via hydrogen bonding was discussed here based on some theoretical studies. Experimental and theoretical results were in good agreement.     

电解铜粉高速压制成形

研究电解铜粉高速压制成形工艺,探讨冲击能量、压制次数对生坯密度、最大冲击力和脱模力的影响.结果表明:当冲击能量为6 076 J时,试样的生坯密度达到最大,为8.42 g/cm3,相对密度约为95%;当冲击能量相同时,采用两次压制制备的试样的生坯密度较单次压制的高且前者的脱模力较低.高速压制过程中,最大冲击力随冲击能量的增加而逐渐增大,而脱模力较低,仅在45～90 kN之间变化.     

A comparative study on the corrosion behavior of NdFeB magnets in different electrolyte solutions

Sintered NdFeB magnets possess excellent magnetic properties. However, the corrosion resistance property of NdFeB is very poor due to its multiphase microstructure consisting of matrix phase Nd₂Fe₁₄B, Nd‐rich phase, and B‐rich phase. The corrosion behavior of NdFeB magnets in sodium hydroxide (NaOH), sodium chloride (NaCl), nitric acid (HNO₃), and oxalic acid (H₂C₂O₄) solutions was investigated by immersion and electrochemical tests. HNO₃is the strongest corrosive electrolyte compared with the other three solutions. The increase in HNO₃concentration can accelerate the corrosion of NdFeB magnets. NaCl belongs to medium corrosion electrolyte. A NaCl concentration of 0.5 M shows the severest corrosive feature in comparison with other concentrations of NaCl solution. NdFeB hardly suffers corrosion in NaOH and H₂C₂O₄solutions owing to the formation of passivation films on the surface of magnets. Based on the corrosion behavior of NdFeB in different electrolytes, the possible corrosion mechanisms are discussed.     

Microstructure and corrosion behavior of Mg-Sn-Ca alloys after extrusion

Mg-Sn-Ca alloys promise a reasonable corrosion resistance in combination with good creep resistance, likely due to the presence of Ca2-xMgxSn and other phases. The selected alloys with 3% Sn and Ca in the range of 1%-2% have been extruded in order to achieve more homogeneous microstructure compared with the as-cast alloys. Optical microscopy(OM) and X-ray diffraction(XRD) techniques were used to study the microstructure and phases of these alloys. The corrosion behavior of these alloys was investigated by means of salt spray test and potentio-dynamic measurements. The results obtained on the alloys Mg-3Sn (T3), Mg-3Sn-1Ca (TX31), and Mg-3Sn-2Ca (TX32) indicate the presence of the same phases in as-cast and after extrusion, namely Mg2Sn, Ca2-xMgxSn, and Ca2-xMgxSn/Mg2Ca, respectively. However, due to the occurrence of extensive recrystallization in the extrusion process, the grain size has significantly reduced after extrusion. The reduction leads to the improvement of the corrosion resistance after extrusion which is then comparable with the commercial alloy AZ91D.     

Structure and properties of powder white iron after plastic deformation

Conclusions  

Magnetic cosserat continuum theory to simulate behavior of magnetic powder during compaction in applied magnetic field

Numerical method based on the Cosserat continuum theory is proposed for simulating behavior of a magnetic powder in an applied magnetic field. The Maxwell stress is induced in the magnetic powder. During powder forming process in the magnetic field, the magnetic particles are thus rotated and transferred by both mechanical and magnetic interaction. To simulate such powder behavior, we formulate a finite element equation considering Maxwell stress based on the Cosserat continuum theory of compressible plasticity. The powder behavior with magnetic alignment during compaction in magnetic field is simulated by the proposed method and the effect of couple-stress on the powder behaviour is discussed.     

TiB2粉末的氧化行为研究

采用TG-DSC热分析仪,对TiB2粉末氧化进行了热重分析;采用等温氧化增重法,对TiB2粉末的氧化行为进行了研究,并对氧化产物进行了XRD分析和SEM分析.结果表明,TiB2粉末的氧化行为,在氧化温度低于1000℃时,其氧化增重与氧化时间之间符合抛物线规律,氧化机理为氧通过产物层的向内扩散为主要控制步骤;当氧化反应温度高于1000℃时,在氧化界面上的化学反应速度成为控制步骤.XRD和SEM分析表明,当氧化温度低于1200℃时,氧化产物相为TiO2(金红石)和B2O3(液相)当氧化温度高于1200℃时,由于B2O3液相转变为气相B2O3,氧化产物为TiO2(金红石).     

Numerical simulation in powder compaction of metallurgy component

1Introduction Forming multi-level component in die compaction,the density is more or less inhomogeneous depending onthe part geometry,the tool design and the frictionbetween powder and die wall[1?3].The productdistortions are result of inhomogeneous densi…     

金属粉末件钢模压制成形模具设计计算方法

在文献 [1 ]的基础上 ,叙述并归纳了金属粉末钢模压制成形坯及相应的压制模具结构的设计与计算方法、内容和步骤 ;并介绍了一典型粉末件的设计计算结果。     

装粉方式对钛粉压制成形影响的数值模拟

用MSC.Marc软件模拟了3种不同装粉方式下钛粉压制成形过程中粉末的流动情况及压坯的密度分布规律.结果表明:粉末装粉方式对粉末压制过程及压坯密度有较大的影响,与平式装粉方式相比,采用凸式装粉,试样的烧结坯密度提高了6%,孔隙分布的均匀性也得到相应的改善.     

The investigation of corrosion behavior of borided AISI 304 austenitic stainless steel with nanoboron powder

In this study, corrosion behavior and mechanical properties of AISI 304 austenitic stainless steel, which was borided with Nanoboron powder, was investigated. The commercially available steel was subjected to a boriding treatment with a size of 10–50 nm Nanoboron powders, at the temperatures of 1223 K to 1273 K with boriding durations of 2 to 4 h. Microstructure characterization of the steel was carried out with optical microscopy, scanning electron microscopy, microhardness and X-ray diffraction analyses. Corrosion tests were made by static immersion into a 10% H₂SO₄ acid solution and weight loss calculations as well as salt spray tests were carried out in accord with the ASTM B-117 standard. Boriding thermal treatment, increased the corrosion resistance of the steel against the acid solution, up to about 4.3 times while in the salt spray tests, weight loss corrosion resistance increased up to tier 2. However, anti-corrosion resistance decreased by 40%, its untreated value.     

Effect of the milling conditions for nanocrystalline iron powders on their corrosion behavior in neutral electrolytes

The corrosion behavior of nanocrystalline iron powders obtained by milling in oxygen-containing organic media (isopropyl alcohol, acetic acid, oleic acid, and its solutions in heptane) was studied. The high corrosion resistances of iron powders obtained by mechanoactivation in oleic acid were associated with a protective surface layer formed by iron oxide and chemisorbed oleic acid or products of its partial degradation. Nanocrystalline iron-based systems that contain oxide phases without forming protective layers were less resistant to corrosion. Original Russian Text ? S.F. Lomayeva, A.V. Syugaev, S.M. Reshetnikov, A.S. Shuravin, O.M. Nemtsova, V.V. Aksenova, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 207–215.     

Study of compaction and ejection of hydrided-dehydrided titanium powder

Three similar varieties of pure Ti hydride-dehydried (HDH) powders were tested for the understanding of the variables that have an influence on the compaction process of Ti powders. The study shows that small differences in the characteristics of the powders lead to very different behaviours in the compaction stage. Compressibility curves, friction with the die walls and ejection forces are discussed in this study. The results are compared with a commercial iron powder as a reference to complete the discussion, as well as to show the enhancements and modifications that should be performed in Ti powders to design an optimized powder suitable for being pressed in an industrial process.