Corrosion protection of sintered NdFeB magnets by CAPVD Ti2N coating

Sintered NdFeB magnets have poor corrosion resistance and are readily susceptible to corrosion under different environmental conditions. Cathodic arc physical vapour deposited (CAPVD) titanium nitride coating for sintered NdFeB permanent magnets has been investigated in this paper. Tafel extrapolation was employed to study the corrosion behaviour in 3.5% NaCl solution at ambient temperature. The adhesive strength of the coating was estimated with the help of the scratch test. The surface chemistry and coating morphologies were studied with scanning electron microscope (SEM). X-Ray diffraction (XRD) was used for qualitative phase analyses of coatings and substrate. The properties of CAPVD titanium nitride coating were compared with electrodeposited multilayer nickel–copper–nickel coating. It was figured out that the CAPVD titanium nitride coating had better adhesion strength and shifted the free corrosion potential (FCP) of the system towards positive potential, providing protection to the NdFeB substrate. However, the corrosion rate of CAPVD titanium nitride coating was more than the electrodeposited multilayer nickel–copper–nickel coating. The magnetic properties remained comparable.     

Grain growth effects on the corrosion behavior of nanocrystalline NdFeB magnets

Isotropic nanocrystalline Nd₁₄Fe₈₀B₆ magnets with different grain sizes in the range of 100-600 nm have been produced from melt-spun materials by hot pressing at 700 °C and subsequent annealing at 800 °C for 0.5-6 h. The microstructures have been characterized using XRD, SEM, EDX and Kerr microscopy. The effect of grain size on the corrosion behavior of nanocrystalline magnets has been examined in N₂-purged 0.1 M H₂SO₄ electrolyte by in situ inductively coupled plasma solution analysis, gravimetric and electrochemical techniques and hot extraction [H]-analysis. The corrosion resistance increases with increasing grain size of the hard magnetic phase. Nanocrystalline magnets showed an increase in absorbed hydrogen by anodic polarization and abnormal dissolution by cathodic polarization. The corrosion behavior of the magnets in relation to their microstructure is discussed in terms of dissolution, hydrogenation and mechanical degradation.     

The influence of Co and Ga additions on the corrosion behavior of nanocrystalline NdFeB magnets

Isotropic nanocrystalline Nd₁₄Fe₈₀B₆ and Nd₁₂Dy₂Fe_73.2Co_6.6Ga_0.6B_5.6 magnets with different grain sizes in the range of 60-600 nm have been produced from melt-spun materials by hot pressing at 700 °C and subsequent annealing at 800 °C for 0.5-6 h. The microstructure has been characterized using XRD, SEM, energy dispersive X-ray analysis, and Kerr microscopy. The corrosion behavior of NdFeB magnets has been examined on 0.1 M H₂SO₄ by in situ inductively coupled plasma solution analysis, gravimetric and electrochemical techniques. The corrosion hydrogen absorption/desorption behavior has been investigated by thermal desorption analysis and hot extraction methods. Partial substitution of Fe with Co and Ga leads to an improvement in corrosion resistance and reduces the affinity and binding energy for hydrogen in these materials. Coarsening of the microstructure results in a better corrosion performance of these materials. The corrosion behavior of the magnets in relation to phase composition, phase distribution and grain size is discussed in terms of dissolution, hydrogenation and mechanical degradation.     

烧结NdFeB永磁体的腐蚀行为研究

通过静态腐蚀实验,研究了烧结钕铁硼磁体在3.5 wt.% NaCl溶液中浸泡不同时间段的腐蚀特征。采用扫描电镜、拉曼光谱分析各个阶段的腐蚀形貌和腐蚀产物组成,通过动电位极化曲线、电化学阻抗谱研究不同腐蚀阶段磁体表面结构的变化及腐蚀机理,采用等效电路模型模拟各阶段的腐蚀行为。研究结果表明,烧结NdFeB磁体在3.5 wt.% NaCl溶液中依次发生点蚀、选择性晶间腐蚀、全面腐蚀行为,形成的腐蚀产物层结构疏松,只能产生短时减缓腐蚀速率的效果,而富钕相优先溶解会造成主相颗粒脱落,导致磁体粉化、破坏。腐蚀产物类型随腐蚀时间延长而有所变化,主要为铁和钕的氧化物或氢氧化物。     

NdFeB磁体表面致密化Ni镀层制备及其耐腐蚀性能

采用高能球磨法实现烧结NdFeB磁体表面Ni镀层的致密化,并对致密化后Ni镀层进行膜/基结合力、维氏硬度测试,通过中性盐雾实验和高温PCT实验研究磁体的耐腐蚀性能,采用静态全浸腐蚀实验进一步分析磁体的腐蚀过程。结果显示,球磨处理工艺可以实现磁体表面Ni镀层的致密化,当转速400 rpm,球磨时间为24 h时,Ni-D24/NdFeB磁体的显微硬度由427.95 HV增加至502.67 HV,结合力由16.30 MPa提升至23.85 MPa,具有更好的耐机械损伤性能。镀层的自腐蚀电流密度较Ni/NdFeB磁体降低了1个数量级,耐中性盐雾时间由312 h提升至480 h,具有更好的耐腐蚀性能。     

烧结NdFeB永磁体表面微弧氧化涂层的制备及性能

为了提高烧结NdFeB永磁体的耐蚀性,本文在铝酸盐溶液中采用二步微弧氧化工艺在烧结NdFeB永磁体表面制备了氧化铝陶瓷涂层。微弧氧化过程中,电压-时间曲线可大致分为四个阶段,与阀金属处理的曲线基本一致。烧结NdFeB表面制备的涂层呈现出典型的微弧氧化多孔形貌,厚度大约为5 μm。涂层中仅含有Al₂O₃结晶相,并含有少量的Fe、Nd和P元素。微弧氧化处理后,烧结NdFeB的表面粗糙度有所增加,耐蚀性较基体提高了1个数量级。然后,微弧氧化处理后,烧结NdFeB磁体的剩磁和最大磁能积较未处理NdFeB有所下降。     

Preparation and characterization of TiO_2/acrylic resin composite coatings on sintered NdFeB permanent magnets by electrochemical deposition

The sintered Nd Fe B permanent magnets are widely used in various industries because of their excellent magnetic and comprehensive properties. However, they are seriously hindered to further developments and applications owing to its poor corrosion resistance. In this paper,TiO2/acrylic resin composite coatings were successfully prepared on the sintered Nd Fe B permanent magnets by electrochemical deposition for the first time, and the corrosion behaviors were investigated by using immersion testing and potentiodynamic polarization tests. It is found that the coating is a composite, being composed of polymerized acrylic resin as the matrix and nano-rutile TiO2particles(-200 nm) as the reinforcements. It is about25 lm in thickness and its surface and cross-section exhibit uniform and smooth with no pores, cracks, and other defects. Compared with those of the uncoated Nd Fe B magnets, the weight loss of the coated samples immersed in H2SO4 solution reduces by two orders of magnitude,corrosion current density decreases by four orders of magnitude, and the corrosion potential of the coated sample is shifted in the noble direction by 400 m V. The mechanisms of corrosive resistance enhancement were discussed.     

Impeding corrosion of sintered NdFeB magnets with titanium nitride coating

Sintered NdFeB magnets have poor corrosion resistance that renders them susceptible to corrosion in industrial and marine environments. This paper evaluates the properties of cathodic arc physical vapour deposited (CAPVD) titanium nitride coating for corrosion protection of sintered NdFeB permanent magnets. The performance of titanium nitride coating has been compared to the electrodeposited nickel–copper–nickel multilayer coating. The rates of coatings degradation in simulated marine environment were estimated with electrochemical impedance spectroscopy (EIS). Cyclic polarization was carried out to assess the pitting potential. The surface chemistry and coating morphologies were studied with scanning electron microscope (SEM). X‐ray diffraction (XRD) was used for qualitative phase analyses of coatings and the substrate. It was figured out that the charge transfer resistance of CAPVD titanium nitride coating increased with exposure time. The negative rate of Rp‐degradation for titanium nitride coating compared to the nickel–copper–nickel multilayer for equivalent exposure time is a unique and valuable result. Polarization results showed that ‘pits re‐passivation’ of titanium nitride coating could be responsible for the extended corrosion protection of the NdFeB substrate. The magnetic properties remained comparable for both types of coatings.     

Sn对烧结钕铁硼合金磁性能影响的微磁学分析

通过Ｋｒｏｎｍｕｌｌｒ微磁学顽力模型拟合不同温度下测得的矫顽力,分析了Ｓｎ对三元ＮｄＦｅＢ合金和ＮｄＤｙＦｅＢ合金磁性能的影响及与显微的关系。发现掺杂Ｓｎ并未改变合金的矫顽力机制,在１５０℃以下,合金的反磁化过程由形核控制;在１５０℃以上,则由畴壁钉扎控制。然而,掺杂Ｓｎ却使两者的局部有效产因子Ｎｅｆｔ都减小,同时也增大了晶凿表面缺陷对矫顽力的影响。局部退磁因子上,是ＮｄＤｙＦｅＢＳｎ俣金矫顽力提     

锡对烧结钕铁硼合金热处理行为的影响

研究了Sn，Al，Dy等元素对烧结钕铁硼合金热处理行为的影响。发现Dy和Al的影响很小，含Dy和Al的钕铁硼合金，其热处理行为与三元钕铁硼类似；而Sn对该合金的热处理行为有重大影响。添加少量Sn(约0.1%)就能使合金热处理温度范围变宽，且获得最佳性能的热处理温度移向高温。但是含Sn合金在525～625?℃回火，矫顽力反而比回火前低。X射线衍射发现，这样的合金有明显的α-Fe衍射峰出现。实验表明，仅用晶粒表面光滑化不足以解释合金的热处理行为，还应考虑亚稳相转变对热处理行为的影响。在优化热处理工艺条件下，制得(BH)max=223.7kJ/m3,Hci＞2.11MA/m的Nd27Dy6Fe65.35Al0.4B1.1Sn0.15合金。     

钨酸盐作海水缓蚀剂可行性讨论

主要简述了钨酸盐作为低毒、无公害的无机缓蚀剂在金属防腐蚀方面的应用.首先从化学及电化学、点腐蚀、表面分析等方面介绍单一钨酸盐的缓蚀机理,它属于钝化膜、阳极型的缓蚀剂,当其浓度很低时起加速腐蚀的作用,属于"危险型缓蚀剂",因此,单一钨酸盐作为水处理剂时使用浓度很高;其次讨论了钨酸盐与其它缓蚀剂复配时,钨酸盐的使用量得以降低,而且缓蚀率也大大地提高;最后总结了钨酸盐缓蚀剂在各种水质中的缓蚀机理,提出了钨系缓蚀剂应用于海水中有一定的可行性,但其缓蚀机理需进一步讨论研究.     

过渡层对钕铁硼表面蒸发镀铝涂层耐腐蚀性能的影响

目的提高钕铁硼磁体表面Al防护涂层的结合强度及耐腐蚀性能。方法通过磁控溅射在钕铁硼磁体表面沉积Al过渡层,用高偏压进行轰击后,使用离子辅助蒸发镀技术沉积Al防护涂层。用扫描电子显微镜观察涂层表面及截面形貌,电化学工作站及盐雾试验检测涂层腐蚀性能,拉伸试验评价涂层与基体结合强度。结果随着磁控溅射靶电流从10 A提高到25 A,所制备的Al层自腐蚀电压从-0.7367 V递减到-0.9075 V,耐中性盐雾腐蚀性能下降。在用相同工艺制备表面离子辅助蒸发镀Al防护涂层的前提下,磁控溅射靶电流为25 A时制备的100 nm和500 nm过渡层的防护涂层耐盐雾腐蚀时间分别为48 h和36 h,耐腐蚀性能不如无过渡层的纯蒸发镀铝涂层(72 h);磁控溅射靶电流为15 A制备的100 nm和500 nm过渡层的防护涂层耐盐雾腐蚀时间分别为96 h和103 h,其耐腐蚀性能优于无过渡层的纯蒸发镀铝涂层。采用过渡层技术的Al防护涂层结合强度均大于40 MPa,与钕铁硼基体结合良好。结论过渡层技术均可使Al涂层与Nd Fe B基体结合良好,合适的过渡层工艺可提高离子辅助蒸发镀铝涂层的耐腐蚀性能。     

Corrosion protection of iron by α,ω-diphosphonic acid layers

Protective layer formation of α,ω-diphosphono-alkane compounds on iron surface was studied. Layer formation proved to be a spontaneous process on iron, and can be accomplished by simple immersion into an aqueous solution of phosphono compounds, resulting in a thin dense multimolecular adsorption layer with a high corrosion protection effect. The mechanism of inhibition and time dependence of layer formation is presented.     

烧结NdFeB磁体热压变形后富Nd相的显微组织

采用热压变形法对NdFeB磁体晶间富Nd相的显微组织进行了研究,实验结果表明,NdFeB磁体经真空热压变形后,富Nd相不再平均地分布在磁体晶间,而是聚集成团块状或从磁体边缘渗出,显微组织分析表明,富Nd相主要是由α-Dd和Nd2Fe17两相组成,与Nd-Fe合金的共晶组织成分接近,对于晶间添加Al元素的磁体,Al溶入晶间形成Nd2Fe15Al2相弥散地分布在晶界上,这有益于磁体矫顽力的提高;对于晶间添加Cu元素的磁体,晶间没有发现有新相产生。     

Structural and magnetic properties of single-stage hot deformed NdFeB magnets prepared by different initial densities

The effects of initial density on the magnetic properties of NdFeB magnets prepared by single-stage hot deformation were investigated in this work. The results show that the values of maximum energy product(BH)m and coercivity Hcjdecrease with the increase of initial density. Under optimum condition, an anisotropic magnet with a maximum energy product of 264 kJám-3was produced using the initial density of 4.4 gácm-3. The influence of initial density on the magnetic properties was discussed on the basis of microstructure and strain energy. It is concluded that the thicker platelet grains are obtained along the Nd2Fe14 B base plane with the initial density increasing.It is mainly because that grain rotation is restricted by high strain energy, which results from high initial density.     

环保型植酸缓蚀剂用于烧结NdFeB材料工序间防锈的研究

目的研究烧结NdFeB材料在工序间的腐蚀行为以及植酸的防锈作用和机制。方法通过SEM、EDS、XRD和XPS测试了试样的表面形貌、元素成分、相成分和元素结合能状态。结果NdFeB的晶间富钕相在工序间发生严重腐蚀,造成主相晶粒脱落,不利于镀层结合力。结论植酸有效地抑制了工序间的腐蚀,其作用机制主要是植酸分子在NdFeB表面的吸附。钕、磷、氧等元素的结合能变化也表明这种吸附包括化学吸附的作用。     

Corrosion resistance and mechanical properties of pulse electrodeposited Ni–TiO2 composite coating for sintered NdFeB magnet

Ni–TiO₂ composite coating which was prepared under pulse current conditions was successfully performed on sintered NdFeB magnet. As a comparison, pure nickel coating was also prepared. The phase structure, the surface morphology, the chemical composition, the anti-corrosion performance of the coatings for magnets, the microhardness and the wearing resistance performance of the coatings were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), electrochemical technique, Vickers hardness tester and ball-on-disc tribometer, respectively. The results revealed that Ni–TiO₂ composite coating provided excellent anti-corrosion performance for the magnets, and showed higher microhardness and better anti-wear performance.     

NdFeB永磁体表面磁控溅射铝防护镀层性能研究

目的研究一种NdFeB永磁体表面腐蚀防护技术。方法采用磁控溅射技术,在烧结NdFeB永磁体表面沉积一层纯铝防护薄膜,然后对纯铝薄膜进行阿洛丁化学转化复合处理,表征膜层的表面和截面形貌,并研究结构及耐腐蚀性能。结果沉积的Al中间层和Al薄膜均结构致密,膜/基界面平整,膜层的自腐蚀电流密度为3.5×10-6A/cm2,说明纯Al薄膜能够对NdFeB永磁体提供有效的防护。阿洛丁化学转化可使铝薄膜表面更加致密,自腐蚀电流密度低至7.9×10-7A/cm2,进一步提高了纯铝薄膜的防护性能。结论 NdFeB永磁体表面磁控溅射镀铝是一种有效且环保的防护技术,可用于替代不环保的电镀防护。     

烧结钕铁硼在各种酸介质中的腐蚀研究

研究了烧结钕铁硼在硝酸、盐酸、硫酸、磷酸及草酸介质中的腐蚀特征。采用动电位扫描及腐蚀失重测试分析了腐蚀行为和特征，采用AFM和SEM观察了酸腐蚀后的NdFeB表面微观形貌。结果表明，烧结钕铁硼在盐酸及硫酸介质中的腐蚀速率最大，在磷酸及草酸介质中呈钝化态，在硝酸中的边缘腐蚀较严重，对磁体的宏观尺寸破坏较大，在各种酸中腐蚀后的微表面都更粗糙了。