充氢球磨及脱氢处理对纳米Nd2Fe14B/α-Fe组织和性能的影响

研究了在氢气氛下机械球磨铸态Nd8Fe86B6合金, 使Nd-Fe-B合金发生歧化反应, 随后在一定温度下进行真空脱氢处理, 并通过粉末压制成形制备纳米双相稀土永磁体. 利用X射线衍射 (XRD)、透射电镜(TEM)、以及原子力显微镜(AFM)等测试手段, 对球磨过程中合金粉末吸氢岐化反应以及脱氢过程中相变及粉末形貌进行分析观察. 实验结果表明, Nd8Fe86B6合金中Nd2Fe14B相发生了吸氢并歧化反应, 球磨20h后获得了晶粒大小为10nm左右的Nd2H5、 FeB和α-Fe歧化组织, 氢化及岐化反应对粉末颗粒细化效果明显, 球磨20h后大部分颗粒尺寸约为70nm, 经过真空脱氢处理后颗粒尺寸约为135nm. 研究得出, 对球磨20h并在700℃下进行脱氢再结合处理获得的粉末进行室温下压制成形, 获得了晶粒组织约为25nm左右的复相组织, 通过振动样品磁强计(VSM)测得压制磁体的磁性能最高为 Br＝0.72T, Hci＝553kA/m, (BH)m=92.5kJ/m3.     

B 含量对高能积磁体磁性能和耐蚀性的影响

通过调整钕铁硼主元B元素含量研究其对高能积磁体磁性能和耐蚀性的影响,结果表明:磁体中B含量小于5.7%时,合金中出现了易基面的Nd2Fe17相,使Br、iHc都比较低;当添加B超过5.9%时,过量的B形成非磁性的富B相,导致磁体Br下降;当B含量在5.7%～5.9%之间时,磁体有较好的磁性能.显微组织研究表明,B元素影响晶粒的尺寸和形状;磁体耐蚀性能研究表明,当B含量过少或过多时均不利于耐蚀性的提高,B含量在5.76%时为最佳添加量.     

烧结过程对Nd-Fe-B永磁材料磁性能与力学性能的影响

分析了烧结过程对Nd-Fe-B永磁材料磁性能和力学性能的影响.当烧结温度为1 373 K时,随烧结保持时间延长,材料剩磁Br先增加后趋于稳定,矫顽力Hci直线下降.成分为Nd25.5Pr7.5FebalNb0.45Cu0.2Al0.55B1.10的磁体样品的抗弯强度在烧结时间为5 h时达到一个最大值后便持续下降,而成分为Nd25.5Pr7.57.5FebalNb0.15Cu0.25Al0.75B1.10的磁体样品抗弯强度是持续下降的.试验结果表明:通过优化合金成分和烧结工艺参数,可以改善烧结Nd-Fe-B永磁材料的磁性能和力学性能,获得综合性能较高的磁体.     

高Ce含量RE-Fe-B烧结磁体元素分布与磁性能研究

为了开发具有商业价值的高Ce含量RE-Fe-B磁体,提高高丰度稀土Ce的利用率,对不同Ce替代量RE-Fe-B磁体的磁性能和微观结构进行了研究。实验结果表明,Ce/(Ce+Nd)质量分数达到40%的双主相磁体仍保持着优良的磁性能,剩磁B_r达到1.31 T,最大磁能积(BH)_max达到310.56 kJ/m³。在Ce替代量为40%的单、双主相磁体中,Nd和Ce元素的置换行为存在差异,单、双主相磁体中Nd元素均偏向于进入主相晶粒,Ce元素则趋于聚集在晶界相或主相晶粒表层,且在双主相磁体中形成贫Ce主相和接近名义成分的(Nd_0.6Ce_0.4)_30.5(Fe, M)_balB_0.97主相。通过观察磁畴翻转分析了单、双主相磁体的磁化行为,研究了双主相磁体矫顽力增强机制：贫Ce主相的高各向异性场对富Ce主相的磁矩起到了钉扎作用。Nd和Ce元素扩散行为的研究为制备高Ce含量、高磁性能的商业化RE-Fe-B磁体提供了依据。     

添加Ga、Nb对NdDyTb-FeCo-B烧结磁体显微组织和磁性能的影响

研究了复合添加Ga、Nb对NdDyTb-FeCo-B烧结磁体的显微组织和磁性能的影响。结果表明:添加0.1%Ga、0.5%Nb磁体的矫顽力iHc、剩磁Br、最大磁能积(BH)max均较好。用SEM电镜对显微组织进行分析,发现添加Ga后晶粒大小均匀,形状规则化。在烧结过程中Ga原子置换Nd2Fe14B相中Fe原子形成Nd2Fe14-xGaxB二次主相,使反磁化核不易形成和扩展,从而改善磁体的磁性能。     

金属表面派瑞林防腐蚀涂层的制备与防护性研究

文章利用化学气相沉积法在铜样品表面涂覆派瑞林（Parylene C）涂层,研究了工艺参数对Parylene C涂层沉积速率的影响。扫描电镜形貌分析结果显示,制备的Parylene C涂层具有良好的连续性。利用电化学工作站测定了Parylene C涂层的表面电阻并推测其抗腐蚀性,并对比了光辐照对涂层电极电位的影响,结果表明：Parylene C涂层对金属绝缘防护能力很强,可见光波段辐照对涂层电极电位的影响较小,在大湿度盐雾环境中,Parylene C涂层能够保证金属导体间的良好防潮绝缘性能。     

添加混合稀土的廉价Nd-Fe-B的研究

Nd-Fe-B永磁材料不仅具有很高的磁性能 ,而且不含资源紧缺的战略物资钴 ,因而其应用前景非常广阔。但人们希望其价格再降低 ,所以开发廉价磁体非常必要。可以通过降低原材料的成本 ,达到降低磁体成本的目的。实验对以混合稀土取代Nd Fe B合金中的钕的廉价铁基稀土永磁进行了研究 ,结果表明 :随着混合稀土的增加 ,磁性能有所下降 ,但在合金中添加少量的Al,Co,Nb ,可使磁体的磁感矫顽力 BHC上升 ,剩余磁感应强度Br、磁能积 (BH) m稍有下降。     

烧结Nd-Fe-B磁体中氧的存在形态及与性能的关联

主要制备了两种成分的速凝带:Nd=Dy6Tb2Fe69B和(Nd80Pr0)22Dy6Tb2Fe69B.通过粉末冶金工艺,将速凝带制成磁体A,B和C.A的成分为Nd=Dy6Tb2Fe69B,B和C的成分为(Nd80Pr20)=Dy6Tb2Fe69B.制备C时,在氢碎过程中,通人一定量的氧气.在A和B中,氧含量几乎相同,C的氧含量相对较高.A和C的磁性能相似,而在电镜结果中,B中发现晶粒长大.实验发现,氧原子以不同形式存在于晶界相中,揭示了不同氧对磁体组织及磁性能的影响.应用FullProf Suite软件对测得的X射线衍射数据进行了精修,估算了晶界相中最多可以容纳3000 ppm的氧原子.     

液相扩散对钕铁硼磁体性能和组织结构的影响

用双合金工艺在Nd13.05Dy0.23Fe80.12B6.5铸片主合金中分别添加质量分数为3％～20％的富稀土铸锭辅合金Nd38.2Cc11.8Fe44.88Al4.12B,研究在钕铁硼永磁体中用Ce部分地取代Nd时对永磁体的磁性能的变化规律.实验结果表明,在一定的烧结及热处理工艺条件下,辅合金加入量介于8％ ～ 12％(质量分数)时,磁体的内禀矫顽力和磁能积相对较高,对剩磁的影响不大.显微成分分析表明,采用双合金法,使组织中细小的颗粒状富稀土相增多,形成了更多的对矫顽力有贡献的富稀土相,并且富稀土相分布于晶界上.     

Nd2Fe14B/α-Fe纳米晶复合永磁材料的计算机模拟研究

采用计算机模拟的方法计算了 Nd2 Fe1 4B/α- Fe纳米晶复合永磁材料的磁性能 ,并对软磁相比例及不规则晶粒对磁性能的影响进行了研究。结果显示 ,当软磁相比例增加时 ,由于软磁相高的饱和磁极化强度以及软硬磁相间的交换耦合作用的影响 ,剩磁逐渐增加 ,但矫顽力则随着软磁相的增加而逐渐下降。不规则晶粒对磁体的剩磁基本没有影响 ,但降低矫顽力。     

Hydrogen Effect against Hydrogen Embrittlement

The well-known term “hydrogen embrittlement” (HE) expresses undesirable effects due to hydrogen such as loss of ductility, decreased fracture toughness, and degradation of fatigue properties of metals. However, this article shows, surprisingly, that hydrogen can have an effect against HE. A dramatic phenomenon was found in which charging a supersaturated level of hydrogen into specimens of austenitic stainless steels of types 304 and 316L drastically improved the fatigue crack growth resistance, rather than accelerating fatigue crack growth rates. Although this mysterious phenomenon has not previously been observed in the history of HE research, its mechanism can be understood as an interaction between hydrogen and dislocations. Hydrogen can play two roles in terms of dislocation mobility: pinning (or dragging) and enhancement of mobility. Competition between these two roles determines whether the resulting phenomenon is damaging or, unexpectedly, desirable. This finding will, not only be the crucial key factor to elucidate the mechanism of HE, but also be a trigger to review all existing theories on HE in which hydrogen is regarded as a dangerous culprit.     

Hydrogen sulphide

Hydrogen sulphide (H2S) is the primary chemical hazard in natural gas production in 'sour' gas fields. It is also a hazard in sewage treatment and manure-containment operations, construction in wetlands, pelt processing, certain types of pulp and paper production, and any situation in which organic material decays or inorganic sulphides exist under reducing conditions. H2S dissociates into free sulphide in the circulation. Sulphide binds to many macromolecules, among them cytochrome oxidase. Although this is undoubtedly an important mechanism of toxicity due to H2S, there may be others H2S provides little opportunity for escape at high concentrations because of the olfactory paralysis it causes, the steep exposure-response relationships, and the characteristically sudden loss of consciousness it can cause which is colloquially termed 'knockdown.' Other effects may include mucosal irritation, which is associated at lower concentrations with a keratoconjunctivitis called 'gas eye' and at higher concentrations with risk of pulmonary oedema. Chronic central nervous system sequelae may possibly follow repeated knockdowns: this is controversial and the primary effects of H2S may be confounded by anoxia or head trauma. Treatment is currently empirical, with a combination of nitrite and hyperbaric oxygen preferred. The treatment regimen is not ideal and carries some risk.     

Hydrogen in iron

The applicability of advanced permeation techniques to the study of hydrogen and deuterium in iron and iron alloys is described. Time lag measurements lead to detailed information about hydrogen transport processes, including lattice diffusivities and trap binding energies and densities. The experimental technique couples gas phase charging of palladium coated specimens with the sensitive electrochemical detection method. In both annealed and deformed iron the trap binding energy for hydrogen and deuterium is 50 to 58 kJ/mol, while the trap density varies from about 10²⁰ m^-3 for annealed iron to over 10²³ m^-3 for heavily deformed iron. For the metallic glass Fe₄₀Ni₄₀P₁₄B₆ hydrogen transport occurs between energetically equivalent sites, with no evidence of trapping. The site density was estimated as about 6 x 10²⁹ m^-3 . The hydrogen concentrations studied were several orders of magnitude less. Hydrogen and deuterium in iron differs only in their lattice diffusivities. The diffusivity ratio conforms nearly to the classical inverse square root of mass ratio, but shows a slight temperature dependence. The solubilities, trap binding energies, and partial atomic volumes of the two isotopes in iron are identical.     

Hydrogen in iron

The applicability of advanced permeation techniques to the study of hydrogen and deuterium in iron and iron alloys is described. Time lag measurements lead to detailed information about hydrogen transport processes, including lattice diffusivities and trap binding energies and densities. The experimental technique couples gas phase charging of palladium coated specimens with the sensitive electrochemical detection method. In both annealed and deformed iron the trap binding energy for hydrogen and deuterium is 50 to 58 kJ/mol, while the trap density varies from about 10²⁰ m^-3 for annealed iron to over 10²³ m^-3 for heavily deformed iron. For the metallic glass Fe₄₀Ni₄₀P₁₄B₆ hydrogen transport occurs between energetically equivalent sites, with no evidence of trapping. The site density was estimated as about 6 x 10²⁹ m^-3 . The hydrogen concentrations studied were several orders of magnitude less. Hydrogen and deuterium in iron differs only in their lattice diffusivities. The diffusivity ratio conforms nearly to the classical inverse square root of mass ratio, but shows a slight temperature dependence. The solubilities, trap binding energies, and partial atomic volumes of the two isotopes in iron are identical.     

Hydrogen in iron

The applicability of advanced permeation techniques to the study of hydrogen and deuterium in iron and iron alloys is described. Time lag measurements lead to detailed information about hydrogen transport processes, including lattice diffusivities and trap binding energies and densities. The experimental technique couples gas phase charging of palladium coated specimens with the sensitive electrochemical detection method. In both annealed and deformed iron the trap binding energy for hydrogen and deuterium is 50 to 58 kJ/mol, while the trap density varies from about 10²⁰ m⁻³ for annealed iron to over 10²³ m⁻³ for heavily deformed iron. For the metallic glass Fe₄₀Ni₄₀P₁₄B₆ hydrogen transport occurs between energetically equivalent sites, with no evidence of trapping. The site density was estimated as about 6 × 10²⁹ m⁻³ . The hydrogen concentrations studied were several orders of magnitude less. Hydrogen and deuterium in iron differs only in their lattice diffusivities. The diffusivity ratio conforms nearly to the classical inverse square root of mass ratio, but shows a slight temperature dependence. The solubilities, trap binding energies, and partial atomic volumes of the two isotopes in iron are identical.     

Hydrogen Absorption and Release Behavior in Hydrogen Decrepitation Process of Nd-Fe-B Alloys

The behavior of hydrogen absorption and release in hydrogen decrepitation (HD) process of Nd-Fe-B alloys were investigated. The results reveal that the reactivity and the amount of hydrogen absorption in HD process are related to the surface activity of the alloy so that the fresh and active surface has a higher efficiency. The presence of Nd-rich phase at the grain boundary is an essential factor of the HD activity of the alloy at room temperature. On degassing, hydrogen is released from the HD powder continuously with increasing temperature. And the residual hydrogen is as low as 0.0015% at 1073K, which shows that the hydrogen is almost exhaused. It is feasible to remove the hydrogen from the HD powder by heating treatment at the temperature of 523-723K for 1h prior to the magnetic field forming in order to decrease the harmful effect of hydrogen on the easy axis alignment of HD magnet.     

Study on Diffusion of Hydrogen in AB5 Non－Stoichiometric Hydrogen Absorbing Alloys

The diffusion coefficient of hydrogen atoms in the studied alloys was electrochemically measured by chronoamperometry when the metallic hydride microelectrodes were completely discharged. It is found that the diffusion coefficient of hydrogen atoms decreases when cobalt is substituted for a minority of nickel. On the contrary, the diffusion eoefficient increases with the partial substitution of manganese or aluminum for nickel, which is related to the lattice constant and cell volumes of hydrogen absorbing alloys. The lattice constant c is obviously affected by the substitute elements greatly. The result shows that the expansion of cell volume resulted from the increase of value c causes the increase of diffusion coefficient which is especially obvious when the lattice constant is relatively low. However, this relationship is not clear if the lattice constant increases to some extent. It is suggested that this phenomenon is related to the interaction of hydrogen atoms with metallic atoms.     

Study on Diffusion of Hydrogen in AB_5 Non-Stoichiometric Hydrogen Absorbing Alloys

AB5hydrogenabsorbingalloyshavebeenexten sivelyusedontheproductionofnickelmetallichy dridebatteriesbecauseoftheirexcellentperformancesastheactivematerialsofnegatives .Ithasbeenshownthatnonstoichiometrichydrogenabsorbingalloyshavethegreatratecapability ,andthecyclinglifeisim provedbythepartialsubstitutionofSnforNiinLaNi5[1～ 3] .Inordertoobtainspecialhydrogenab sorbingalloyswithhighratecapabilityandrelativelowprice ,someAB5nonstoichiometrichydrogenabsorbingalloysareexplored ,whichisbasedonthes…     

Hydrogen transport by dislocations

A kinetic model is presented for the transport of hydrogen, as Cottrell atmospheres on dislocation, at a rate appreciably in excess of that for lattice diffusion. The particular destinations for the hydrogen which are modeled here are ductile fracture initiation sites such as inclusions and microvoids. The functional predictions of the mechanism are shown to be consistent with available experimental evidence on ductile fracture behavior in the presence of hydrogen.