Metal dusting of Fe3Al and (Fe,Ni)3Al

Metal dusting is a deterioration of metallic materials in strongly carburizing atmospheres under disintegration into a dust of carbon and fine metal particles (coke). The intermetallic compound Fe₃Al is also very susceptible to metal dusting and disintegrates under formation of vast amounts of coke. The mechanism corresponds to the metal dusting of iron and steels, Fe₃C is formed as an intermediate and the Al is oxidized. With increasing Cr-addition and with increasing Ni-content in alloys (Fe,Ni)₃Al-Cr the materials become more resistant, Ni₃Al is not attacked by metal dusting.     

Martensitic and magnetic transformation of Co41Ni32Al24Sb3 and Co41Ni32Al27 alloys

The martensitic transformation and magnetic property of Co41Ni32Al27 and Co41Ni32Al24Sb3 alloys were investigated by optical microscopy（OM）, scanning electric microscopy（SEM）, energy dispersive X-ray spectroscopy（EDS）, X-ray diffractometry （XRD）, differential scanning calorimeter analysis（DSC） and vibration sample magnetometer（VSM） methods. The results show that martensitic crystal structure of Co41Ni32Al24Sb3 alloy is still Llo type. Both martensitic transformation temperature Tm and Curie point Tc are in linear relation to quenching temperature. Tm increases by 9 K and Tc increases by 7.5 K for every 10 K increasing in quenched temperature. Quenched from same temperature, Tm of Co41Ni32Al24Sb3 alloy is higher than that of Co41Ni32Al27 alloy by 76 K, meanwhile Tc is higher by 18 K. The melting point of Co-Ni-Al alloy is decreased by the Sb addition, eutectic structure appears in Co41Ni32Al24Sb3 alloy annealed at l 573 K, which indicates that the alloy is partially melted, whereas Co41Ni32Al27 alloy can be annealed at 1 623 K without melted. The martensitic transformation temperature range of Co41Ni32Al24Sb3 alloy is 22-29 K, only half that of Co41Ni32Al27 alloy. This is a very important result to benefit the achievement of large magnetic field induced strain on Co-Ni-Al based alloy. The results of Tm and Tc were explained by total average s＋d electron concentration and magnetic valence number Zm respectively.     

Effect of severe plastic deformation on the structure and low-temperature internal friction of Fe3Al and (Fe,Cr)3Al

Internal friction (IF) in severely deformed Fe-26Al and Fe-26Al-5Cr (at. %) alloys based on the Fe₃Al intermetallic compound has been studied in a temperature range from ?180 to 650°C. A group of low-temperature IF maxima have been detected in the temperature range from ?130 to 100°C at a frequency of 1.4–2.2 kHz. A comparative analysis of the revealed peaks has been carried out for Fe₃Al both with and without chromium. The thermal stability of some IF maxima which form a group of low-temperature peaks in the severely deformed state has been studied. The activation energies for the maxima detected have been evaluated. An assumption has been made about the dislocation-related mechanism of the peak origin, some of which appear to be of the Hasiguti type. Within the framework of this assumption, the height and stability of some IF maxima in the Fe-26Al-5Cr alloy, as compared to those in the Fe-26Al alloy, can be explained by increasing mobility of dislocations (dislocation segments) due to alloying with chromium.     

热处理工艺对磁控形状记忆合金Co38Ni34Al27Mn1显微组织及磁性能的影响

采用电弧熔炼法制备Co38Ni34Al27Mn1磁控形状记忆合金,并对合金进行热处理.采用金相显微镜、X射线衍射仪及振动样品磁强计等研究热处理工艺对Co38Ni34Al27Mn1合金显微组织、相结构及磁性能的影响.研究结果表明:1573 K加热冰水淬火后得到β相和γ相,而1623、1673 K加热冰水淬火后合金中可观察到板条状马氏体,且β相、γ相和马氏体相共存.随着热处理温度的提高,合金晶粒长大,γ相体积分数减小,马氏体含量增加,饱和磁化强度从42.51 emu·g-1增加到45.43 emu·g-1,矫顽力从48 Oe减小到30 Oe;在1673 K淬火,随加热保温时间的增加合金晶粒变大,饱和磁化强度从44.31 emu·g-1增加到47.29 emu·g-1.     

Co,Cr和Ni对Fe3Al金属间化合物相平衡的影响

利用集团变分法,计算了Fe-Al-Co,Fe-Al-Cr,Fe-Al-Ni三元合金700K等温截面的Fe3Al相区,三个三元合金等温截面的计算结果显示,Fe-Al-Ni相图中的Fe3Al相区最小,Fe-Al-Cr相图中的Fe3Al相区最大;根据等温截面的几何性质,可以将Co和Ni看成是一类原子,而Cr原子属于另一类,利用Monte Carlo方法分析了Co,Cr和Ni对Fe3Al金属间化合物原子组态的影响,从不同原子在不同亚点阵上的占位情况和原子组态图都可以看出,Cr原子倾向于占据β亚点阵;Co和Ni原子倾向于占据α亚点阵,也有一部分Co和Ni原子倾向于与Al原子形成B2结构晶粒,分布于DO3晶粒中,这将加剧晶体中缺陷的形成,从Monte Carlo法得到的这些结果,也可以看出Co和Ni属于一类原子,而Cr属于另一类。     

Effect of Cr,Co, and Ti additions on the high-temperature oxidation behavior of Ni3Al

The oxidation behavior of Ni₃Al+2.90 wt.% Cr, Ni₃Al+3.35 wt% Co, and Ni₃Al+2.99 wt.% Ti alloys was studied in 1 atm of air at 1000, 1100, and 1200°C. Isothermal tests revealed parabolic kinetics for all three alloys at all temperatures. Cyclic oxidation for 28 two-hour cycles produced little spallation at 1000°C, but caused partial spallation at 1100°C. Especially, at 1200°C severe spallation in all three alloys was observed. Although additions of Cr, Co, or Ti to Ni₃Al alloys slightly increased the isothermal-oxidation resistance, the additions tended to decrease the cyclic-oxidation resistance. The major difference in the oxidation of the three alloys compared with the oxidation of pure Ni₃Al alloys was the existence of small -Al₂O₃ particles in the middle of the -Al₂O₃ scale and the formation of irregularly shaped Kirkendall voids at the alloy-scale interface.     

Crystallization kinetics and induced magnetic properties of bulk （Fe,Co）-Zr-Nd-B metallic glass

Crystallization kinetics and phase transformation of bulk Fe64 Co7 Zr6 Nd3B20 metallic glass were studied by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Based on the Kissinger analyses, the activation energies for the nucleation and growth during the first, second and third crystallization-stages of the metallic glass are determined to be 294, 475 and 365 kJ/mol, respectively, and the activation energy for the glass transition is determined to be 1 242 kJ/mol. The Johnson-Mehl-Avrami (JMA) analysis under the isothermal condition reveals that the crystallization process is a three-dimensional controlled growth of nuclei at a constant nucleation rate. The crystalline grains are in the size of less than 50 nm after the selected annealing treatments. In the completely crystallized state, the alloy exhibits the maximum coercivity (Hc) of 34.8 kA/m and corresponding energy product of 11 kJ/m^3.     

制备纳米Fe3O4磁性粉体的研究进展

磁流体由于其独特的物理化学性能在机械、化工、医疗和环保等领域具有广阔的应用前景.磁性液体的磁性能来源于纳米磁性粒子,磁流体的磁化强度取决于磁性粒子磁感应强度.另外,磁性粒子的颗粒大小及粒径分布对磁性液体的稳定性是至关重要的因素.因而,制备磁感应强度高、粒径小且尺寸均匀的纳米磁性粒子是获得高性能磁性液体的先决条件.磁性液体的种类很多,其中Fe3O4磁性液体是目前研究较为成熟、应用较多的磁性液体之一.本文概述了Fe3O4纳米磁性粉体常用的制备方法以及最新的研究进展.     

Microstructure and strength of B2-ordered (Ni,Co)Al

A transmission electron microscopy (TEM) investigation of the morphologies and crystal structures of precipitates in supersaturated B2-ordered (Ni,Co)Al has revealed that rod-like precipitates of the (Ni,Co)₂Al phase with a hexagonal structure form parallel to the <111> direction of the B2 matrix. By aging at temperatures below 973 K, a long period superlattice structure of hexagonal (Ni,Co)₂Al was formed. The (Ni,Co)Al hardens appreciably by the precipitation of these phases. An energy dispersive spectroscopy (EDS) was used to analyze the compositions of each phase formed in the B2-(Ni,Co)Al. The effects of the dispersion of the (Ni,Co)₂Al phase on the temperature dependence of the strength of the B2-(Ni,Co)Al have been investigated over a temperature range from 298 K to 1173 K.     

Ni3(Al1-xSix)合金的组织性能

以纯Ni、Al和Si块为原料,采用真空熔炼方法制备了Ni₃(Al_1-xSi_x)（x=0、0.1、0.2、0.3）合金,利用X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)等对合金组织性能进行了研究。结果表明,Ni₃(Al_1-xSi_x)合金的主要物相为Ni₃Al及Ni₃(Al, Si)固溶体;合金元素Si的引入,细化了材料晶粒,晶粒尺寸在27.4~73.6 nm之间,合金具有纳米晶结构;随Si含量增加,Ni₃(Al_1-xSi_x)合金硬度和断裂韧性提高,当x=0.3时,合金具有最佳的综合力学性能,其硬度和断裂韧性分别为726 HV0.5和8.35 MPa·m^1/2。     

Effect of a Yttrium Coating on the Oxidation Behavior of Ni3Al (II)

A Y-coated Ni₃Al with a postheattreatment shows much better oxidation resistance than aY-coated Ni₃Al without a postheat treatment.In order to explain the effect of postheat treatment atlow oxygen pressure, postheat treatment after Y-ion plating wasperformed in flowing hydrogen as a function of time.During these treatments, the Y-coated layer was modifiedinto a (Y, Al)O-type oxide by reaction betweenY₂O₃ and Al₂O₃. The thicknessof the modified Y-layer was related to oxygen pressureand time. The Y-modified layer formed by postheattreatment acts as a barrier to the transport of oxygen.The fine (Y, Al)O-type oxide can easily relieve growth stress bypermitting easy plastic deformation, and the (Y,Al)O-type oxide layer can absorb the thermal stressdeveloped in the Al₂O₃ layer. Thetensile stress generated by the difference in thermal-expansioncoefficients of the (Y, Al)O-type oxide and theAl₂O₃ layer compensates the largecompressive stress generated by the difference inthermal-expansion coefficients of the Al₂O₃ layer andthe Ni₃Al alloy.     

元素Tb对(Fe,Co)-B-Si-Nb块体非晶形成及磁性能的影响

用铜模吸铸工艺制备了[(Fe0.5Co0.5)0.72B0.192Si0.048 Nb0.04]100-xTbx和[(FeyCo1-y)0.72B0.192Si0.048Nb0.04]98Tb2块体非晶合金,并用XRD、DSC、振动样品磁强计(VSM)测试和分析了微量稀土元素Tb和不同Fe与Co比例对(Fe,Co)-B-Si-Nh体系玻璃形成能力、热稳定性及软磁性能的影响.试验表明,添加2 at%的Tb,提高了合金的非晶热稳定性和形成能力,制得的非晶合金棒的直径从φ2mm增加到φ3 mm,但饱和磁化强度下降;[(FeyCo1-y)0.72B0.192Si0.048Nb0.04]98Tb2合金随Fe与co比例从5:5增加至7:3时,合金的非晶形成能力呈下降趋势,但均能形成直径为φ2 mm的非晶棒,而其热稳定性和饱和磁化强度随铁含量的增大而提高.     

再结晶Ni3Al(Zr)合金的环境脆性

研究了不同程度再结晶的Ni3Al(Zr)合金在真空和空气中的室温拉伸性能．结果表明，随着再结晶程度的增加，合金的塑性先增加后降低，不完全再结晶的样品表现出良好的拉伸塑性．合金的环境敏感指数随再结晶程度的增加而增加，完全再结晶的样品表现出强烈的环境敏感性．真空和空气中拉伸断口形貌的变化与力学性能变化趋势一致，再结晶程度低的样品的断口形貌为穿晶解理断裂，气氛对其几乎没有影响，而对再结晶程度高和完全再结晶的样品，空气使其沿晶断裂模式倾向增加．     

Structure and magnetic properties ofhigh-performanced Sm2（Co, Fe, Cu, Zr）17 alloys

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核壳结构Ni（Cu，Co）／Al微纳米复合粒子的制备及其与Fe2O3的热反应性能表征

采用置换法通过对溶液中各种参数的控制,实现了在弱酸性条件下Ni(Cu,Co) 3种纳米金属粒子在微米Al粉表面定量、快速地化学沉积,分别制备出核壳结构的Ni(Cu,Co)/Al 3种微纳米复合粒子,并用SEM和XRD方法进行了相应表征.在此基础上,利用DSC分析研究了不同包覆物和升温速率对热反应性能的影响,用Kissinger法求解了热反应的表观活化能Ea,对比了传统微米级Al-Fe2O3混合物与Ni(Cu, Co)/Al-Fe2O3复合材料的热反应性能,同时分别提出了其相应的热反应机制.结果表明,通过对Al粉进行表面改性,其热反应性能明显增强,不同试样与Fe2O3的热反应活性依次为Ni/Al>Cu/Al>Co/Al>Al.同时,降低升温速率不利于热反应的进行.