Research status and challenges of corrosion and protection of sintered NdFeB permanent magnet materials

The corrosion sensitivity of sintered NdFeB permanent magnet materials limits its application in complex working conditions. Improving the corrosion resistance of magnets and developing excellent protective coatings are the key directions in the field of development. Although a lot of work has been done on the exploration of long-life NdFeB magnets, there are still few systematic studies on the corrosion of NdFeB magnets from technical process to basic theory. On the one hand, the basic research on material corrosion and protection lags behind the research on magnetic properties. On the other hand, it has a great deal to do with the continuous improvement of market requirements for material quality and diversified demand Big deal. In this paper, the latest research results of corrosion-resistant sintered NdFeB permanent magnet materials are reviewed, including the factors affecting corrosion, the basic theories and methods to improve the corrosion resistance of magnets, the basic framework of surface protection strategy and the key technologies in engineering application. Finally, the future prospects and challenges are prospected, and it is expected to point out the direction for the future development.

Improving the corrosion resistance and surface protection technology of NdFeB rare earth permanent magnetic materials has become the key to break through the engineering application of rare earth permanent magnetic materials [1], which is directly related to the continuous improvement of material quality requirements and diversified demand in the market. For this reason, there have been many articles about the corrosion mechanism and surface protection of NdFeB materials in recent 20 years, including material corrosion [2,3], environmental corrosion [4,5] and surface science [6 ~ 11]. It can be seen from these literatures that, based on the corrosion sensitivity of NdFeB materials, on the one hand, alloying is used to regulate the composition and microstructure of materials and improve the corrosion resistance of magnets. For example, metal element M1 (such as Cu, Al, Zn, GA, Ge, Sn, etc.) is added to magnets to form nd-m1 or nd-fe-m1 intermetallic compounds, or metal element M2 is added (such as CO, Ti, Nb, Zr, V, Mo, W, etc.) to form m2-b or fe-m2-b intermetallic compounds. Compared with Nd rich and B-rich phases, the intergranular compounds formed by these compounds have higher corrosion potential, which reduces the electrochemical difference with the main phase (Nd2Fe14B), thus weakening the driving force of interphase corrosion. On the other hand, they are protected by coating on the surface of magnets, such as by chemical conversion and electrochemical oxidation A protective layer is formed on the surface of the material by plating, electroless plating, electrophoresis, physical vapor deposition, organic coating and other composite coating methods. The protective layer can prevent the penetration of corrosive media (such as O2, H2O or Cl -) from the surface to the substrate, so as to protect the substrate from erosion. Driven by the market, with the continuous expansion of the application field of permanent magnet, various technologies are gradually put into practice, and the advantages and disadvantages of each method have been evaluated.
Although the majority of researchers have done a lot of work to improve the corrosion sensitivity of rare earth permanent magnet materials, the corrosion mechanism of NdFeB materials still needs to be further analyzed, and its surface protection technology lags behind the development of materials. So far, some innovative achievements are rare. This is mainly due to many factors affecting its corrosion and protection mechanism analysis, including material matrix, corrosion medium, test environment and technical scheme. These factors will change the intermediate reaction process, thus affecting the composition, structure and protection characteristics of corrosion products. Because of the complexity of characterizing the corrosion product film, it is very difficult to clearly explain the specific mechanism and then formulate effective protection measures. However, according to the above review literature, a lot of valuable information can be extracted to analyze the corrosion and protection mechanism of NdFeB materials. Based on the above literature, this paper summarizes the influencing factors of corrosion of sintered NdFeB materials, expounds the causes of corrosion, and makes a comprehensive review on the recent research related to alloying process to improve the corrosion resistance of magnets and surface protective coating technology, so as to carry out material design and formulate protection strategies in the future, so as to make rare earth permanent magnet materials better meet the needs of social development It is of great significance to break through the key technology in the production of rare earth permanent magnetic materials, develop corrosion-resistant magnetic materials and establish the corresponding surface protection strategy.

Factors affecting material corrosion

In order to improve the corrosion resistance of permanent magnets and improve the reliability of products, we should master the factors that affect the corrosion of materials and analyze the causes of corrosion.

Material factors

Material factor is the internal cause of corrosion, which mainly refers to the corrosion caused by the difference of electrochemical properties between phases. Figure 1 shows the internal structure of NdFeB material. The main phase (Nd2Fe14B) is polygonal and magnetic; the nd rich phase (nd4fe) is distributed along the grain boundary or grain boundary corner of the main phase in thin layer or granular form, which surrounds the main phase grains; the B-rich phase (ND1 + xfe4b4) is massive or granular, which exists in the grain boundary in metastable form, and the volume fraction of each phase is about 84%, 14% and 2% [5].
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Fig.1 Schematic of the microstructure of NdFeB materials

The results [12] show that the electrochemical potentials of the main nd rich and B-rich phases are obviously different. The electrochemical potentials from low to high are in the order of B-rich phase, nd rich phase and Nd2Fe14B phase. In the environment, the nd rich and B-rich phases at the grain boundary will be preferentially corroded. It is not difficult to know from the above analysis that this kind of corrosion battery has the characteristics of “small anode large cathode”. The nd rich phase and B-rich phase with small volume fraction in the magnet will accelerate the corrosion along the grain boundary of the main phase, causing the surrounded main phase grains to fall off, and the generated bulky corrosion products will lead to the pulverization of the magnet and the performance degradation [5]. Fig. 2 [13] shows the magnetic field distribution of NdFeB magnet before and after corrosion. It can be seen that the corrosion of the magnet leads to the obvious change of the magnetic field distribution, and the uneven distribution of the magnetic field further proves that the corrosion degree of each part of the magnet is different.

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Fig.2 Distributions of the magnetic field of a magnetized NdFeB magnet before (a) and after (b) corrosion[13]

According to the latest research results of Academician Li Wei’s team [14, 15] The main reason is that the content of Nd in the grain boundary is significantly reduced after the Nd in the structure is replaced by CE, which makes the rare earth rich phase transition thinner and more evenly distributed. At the same time, the grain size of the main phase becomes smaller and the structure is more compact. The corrosion products are easy to block the transmission channel of the medium, which can block the corrosion.
Therefore, on the one hand, the content of Nd element is reduced to avoid the accumulation of Nd rich phase at the grain boundary; on the other hand, the intergranular structure is regulated to induce the dispersion of Nd rich phase at the triangular grain boundary of the main phase, which narrows the diffusion channel of the corrosion medium and inhibits the corrosion process, so as to improve the corrosion resistance of the magnet [16,17]. On this basis, adjusting the crystal structure of the main phase, ensuring the uniform distribution of each phase and reducing the driving force of corrosion reaction are also one of the efforts to improve the anti-corrosion ability of magnets [18].

Environmental factors

Environmental factors are the external causes of corrosion, including environmental temperature, humidity and corrosive media [4]. As far as the ambient temperature is concerned, when the temperature exceeds 150 ℃, the oxidation rate of Nd element at the grain boundary increases significantly, and the main reaction is shown in equation (1); and with the extension of time, the main phase will also be oxidized.

  • 4Nd+3O2→2Nd2O34Nd+3O2→2Nd2O3 (1)

Humidity is one of the main factors leading to permanent magnet corrosion failure. Therefore, researchers [13,19] studied the influence of humidity on the corrosion of magnets by means of high temperature and high pressure accelerated corrosion experiments with the help of autoclave. The results show that the corrosion of magnets in humid environment is more sensitive than that in high temperature environment, and the existence of water vapor in the environment is a necessary condition for the corrosion of magnets. In addition, research [14] found that the corrosion weight loss of high abundance rare earth permanent magnet ((ce15nd85) 30febalb1m or (ce20nd80) 31febalb1m) in hot and humid environment is lower than that of conventional rare earth permanent magnet (Nd2Fe14B). This result fully shows that reducing the enrichment of rare earth elements at the edge of the main phase and controlling the content of rare earth rich phase are the key to improve the corrosion resistance of rare earth permanent magnet materials.
In addition, the research results [20 ~ 22] show that the corrosion behavior of rare earth permanent magnet materials is closely related to the corrosion medium. For example, the corrosion rate of NdFeB magnet in HCl and H2SO4 is relatively high [23]; the corrosion of Nd rich phase in HCl solution is relatively serious, so the maximum magnetic energy product of the magnet decreases significantly after being corroded by HCl solution, while the influence of HNO3 solution on the main phase is relatively large, so the intrinsic coercivity of the magnet decreases [24]; the surface of the magnet can be passivated in H3PO4 and H2C2O4, and sometimes it can not be completely removed Oxide layer or dirt on the surface of magnet [23,25,26]. The results provide a theoretical basis for revealing the correlation between NdFeB magnet life and environment.
It is worth noting that the development of NdFeB permanent magnet materials has strongly promoted the progress of magnetic surgery technology in the medical field [27]. With the wide application of rare earth permanent magnet materials in medical devices, in order to improve the reliability of the equipment, the corrosion behavior of magnets in body fluids (such as saliva [28], gastric juice [29], bile [30] and so on) has been gradually concerned. It can be seen that the corrosion problem of permanent magnets used in special fields, like many common problems, is an urgent problem to be solved in the development of NdFeB materials, and the diversified needs bring great challenges to the development of NdFeB materials.

Magnetization state

Research [22] shows that the corrosion behavior of rare earth permanent magnets in different magnetization States is significantly different, and the corrosion tendency of magnets in magnetization state is greater, especially in magnetization direction, as shown in Fig. 3 [22]. Costa et al. [31] think that this is caused by the enhanced migration driving force of paramagnetic oxygen molecules in the magnetic field; sueptitz et al. [32] think that under the action of Lorentz force, the ion convection movement in the electrolyte promotes the material transport and improves the electrochemical reaction rate, which is the main reason for the accelerated corrosion rate; Zheng Jingwu et al. [22] put forward that the residual magnetic field on the surface will affect the structure of the electric double layer, A large magnetic overpotential is produced, which leads to the aggravation of corrosion reaction.
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(a) unmagnetized sample(b) axile magnetized sample(c) radial magnetized sample

Fig.3   Schematic representations for effects of remanence on degradation process of NdFeB materials[22]

Magnet density

The porous and uneven structure of NdFeB creates conditions for the erosion of oxygen, water and other media. Figure 4 [13] shows the typical microstructure of NdFeB. Yan et al. [33] have proved that the corrosion resistance of materials with low magnet density is weak by weight loss experiment, hydrogen absorption and oxygen absorption. Therefore, by improving the powder preparation method, adopting advanced molding and sintering process, the microstructure of the magnet is improved, the density of the magnet is increased, and the material with low weight loss rate and corrosion resistance is obtained. The experiment [34] also proved that by adding appropriate amount of heavy rare earth elements such as PR and Dy, controlling the total amount of rare earth, and adopting the technology of sheet casting (SC) + hydrogen crushing (hd), the uniform and dense structure can be obtained, so as to improve the corrosion resistance of the magnet.
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Fig.4 Typical morphology of NdFeB microstructure[13]

Research progress of improving corrosion resistance of NdFeB magnets by alloying

Basic theory

At present, alloying is the main method to prepare corrosion-resistant rare earth permanent magnetic materials, that is, adding alloying elements to the structure, these elements exist in the form of simple substance or form intermetallic compounds. Because the grain boundary in the magnet structure is more sensitive to corrosion, most of the alloying methods are to improve the corrosion resistance of the magnet by regulating the phase composition, structure and distribution of the intergranular phase in the magnet [35]. The basic idea of improving the corrosion resistance of magnets by alloying can be summarized into two aspects: reducing the proportion of Nd rich phase in the structure, optimizing the structure, promoting the formation of uniform and fine grain structure and continuous grain boundary phase distribution, increasing the density of magnets; increasing the electrochemical potential of intergranular phase, reducing the potential difference between the main phase and the intergranular phase, weakening the driving force of corrosion reaction. Based on the dual alloy technology route, the corrosion resistance of the magnet was improved by preparing multi-element alloy powder, adopting heat treatment process, grain boundary reconstruction or grain boundary diffusion [36].

Research progress on improving corrosion resistance of magnets

The alloying elements added in NdFeB permanent magnet materials can be divided into three categories: first, rare earth metal elements represented by Dy, TB, CE, La and Y; second, transition or main group metal elements represented by Cu, Al and GA; third, transition metal elements represented by CO, Ti, Nb and Zr. The three types of alloying elements and their functions are shown in Table 1.

Table 1  Commonly used elements in alloying process and their roles

Element Speciation Role Typical element
Rare earth Nd-M1-Fe Substitute for Nd Dy, Tb, Ce, La, Y
Transition/group element Nd-M2 or Nd-M2-Fe Substitute for Fe Cu, Al, Ga, Zn, Ge, Sn
Transition/group element M3-B or Fe-M3-B Substitute for Fe Co, Nb, Zr, Ti, V, Mo

Note: M1, M2, and M3 represent different alloying elements, respectively.

(1) Class I alloying elements

The production process of adding heavy rare earth elements such as Dy and TB to NdFeB materials has been more than 20 years, and it has been mature at present. At first, the main purpose is to improve the coercivity of magnets and enhance their thermal stability [37 ~ 41]. Later studies [42 ~ 45] found that after sintering, Dy or TB and other elements in the magnet enter the rare earth rich phase at the grain boundary, which not only reduces the nd rich phase, but also disperses it at the edge of the main phase, and the distribution of each phase is more uniform, thus reducing the corrosion sensitivity of the material. With the gradual maturity of “strip throwing + hydrogen explosion” technology and dual alloy process, the addition of multi-element alloy powder has become the mainstream process. For example, dy69ni31 [46, Then, according to the production needs, appropriate amount of auxiliary alloy powder is directly mixed into the main alloy powder, and then the subsequent processes such as pressing and sintering are carried out. The biggest advantage of this process is that it can not only improve the utilization rate of heavy rare earth elements, reduce its content, but also improve the production efficiency.
Since 2015, mass production of high abundance rare earth elements (CE, LA) permanent magnet materials has started. According to the report [52], in 2018, Ningbo Institute of materials technology and engineering, Chinese Academy of Sciences also made great breakthroughs in the R & D and industrialization of high abundance yttrium (y) mixed rare earth permanent magnet materials. Although high abundance rare earth elements (CE, La, y) replace some nd elements, the cost of developing magnets with the same performance is 30% ~ 40% lower than that of ordinary magnets [53], however, the contribution of adding high abundance rare earth elements to the corrosion resistance of materials still needs to be further evaluated, which is mainly due to the fact that a complete process system has not yet been established, and the basic research work on the corrosion of such materials has been carried out It is less [54]. In the future, the development of rare earth permanent magnets with high corrosion resistance and high abundance will be one of the hot spots in the research of permanent magnet materials [3,21].

(2) The second kind of alloy elements

The technology of adding Cu and Al elements to NdFeB permanent magnet materials has been developed in the early 21st century. Research [55] shows that Cu element exists in the form of Cu rich phase besides intermetallic compound (such as ndcu, etc.) at the grain boundary. This discrete element is very disadvantageous to improve the corrosion resistance of the material. Therefore, researchers [56 ~ 58] tried to add Nano Cu and Al particles to the structure, and found that some elements failed to form stable intermetallic compounds. For this reason, researchers first prepared copper or aluminum alloys, such as cu60zn40 [59], al100 xcux [60] or la70al10cu20 [61], and then added Cu and Al elements into the material structure by double alloy process, thus eliminating the discrete Cu rich phase and Al rich phase in the structure. The formation of stable nd6fe13sn compound in the structure is the main reason for adding Sn element to improve the corrosion resistance of the material [62]; the effect of adding GA element on the corrosion resistance of rare earth permanent magnet is still controversial [50]. In addition, according to the latest research results [63, The results show that the corrosion resistance of the magnet can be enhanced by adding mg / MgO nano powder, which is attributed to the low melting point of metal Mg, which improves the wettability of the liquid phase at the grain boundary. The nd-o-fe-mg intermetallic compound formed during the sintering process of the magnet is easy to form a uniform and continuous rare earth rich phase around the main phase grains to make up for the grain boundary defects By changing the microstructure and increasing the density of the magnet, the corrosion resistance of the material is enhanced.

(3) The third kind of alloy elements

The third kind of alloy elements mainly refer to the metal elements with high standard electrode potential such as CO, Nb, Zr and Ti. At the beginning of the 21st century, researchers [65 ~ 67] found that Co element formed intermetallic compounds with high chemical stability at the grain boundary of the magnet structure, such as nd3co [19] or nd64co36 [68], which had a significant effect on reducing the weight loss of the material and improving the corrosion resistance of the magnet. However, the price of metal co is high, and it is not often used in industrial production except for magnets used in special fields. NB element is also helpful to enhance the corrosion resistance of rare earth permanent magnets. The analysis [69,70] shows that the main reason is that Nb element can improve the thermal stability of permanent magnets, thus improving the corrosion resistance of materials. The research [71] shows that the growth of the main phase grain and the rare earth rich phase at the grain boundary is inhibited by the influence of ZrB2, which makes the structure distribution more uniform, so the corrosion resistance of the magnet is enhanced.
It is worth noting that the successful implementation of alloying process is closely related to the current advanced technical means and supporting equipment, such as rapid solidification sheet smelting, hydrogen explosion crushing, spark plasma sintering, etc. The above measures can not only improve the density of the magnet, but also optimize the microstructure of the magnet and improve the distribution of rare earth rich phase at the grain boundary, so as to enhance the corrosion resistance of the magnet. Although the addition of trace elements and the use of dual alloy process have played an important role in improving the corrosion sensitivity of NdFeB permanent magnets, there is still a long way to go to fundamentally solve the corrosion problem of rare earth permanent magnets. This is because the addition of alloy elements can improve the corrosion resistance of the magnet to a certain extent, but the effect is very limited, sometimes it will reduce the magnetic performance, and often increase the manufacturing cost of the material [72]. These factors must be considered carefully when designing alloying process.

Research progress of surface protection technology

The development of NdFeB permanent magnet materials is closely related to the level of its surface protection technology. Under the situation of limited corrosion resistance of permanent magnet, the development of its surface protection coating technology has become another hot topic in the research of rare earth permanent magnet materials [73 ~ 75]. Therefore, there are many reports on the surface protection coating of NdFeB materials, and the main surface treatment methods are as follows Including: chemical conversion, electroplating, electroless plating, electrophoresis, physical vapor deposition, spraying and micro arc oxidation.

Chemical conversion coating

Chemical conversion is an economical surface treatment method. Chemical conversion coating is mostly used for temporary protection or as the bottom layer of organic coating to enhance the adhesion between surface coating and substrate [76]. There are many literatures on chemical conversion coatings [11,20,77,78]. The characteristics of typical conversion coatings have been characterized in detail, including composition, structure, hardness, wear resistance, adhesion, color adsorption capacity, high and low temperature resistance, corrosion resistance and protection performance. The protective ability of conversion film is closely related to its thickness and density. The biggest challenge in conversion film technology is to obtain uniform and defect free film [79]. In the past 20 years, the chemical conversion coating technology on NdFeB surface has not achieved substantial breakthrough. This is mainly because the formation and protection performance of the conversion coating are affected by many factors, such as matrix material, pretreatment process, solution composition, post-treatment process (baking temperature and time), conversion process (temperature, time, pH value and stirring), etc. these factors directly affect the intermediate reaction The composition, structure and properties of the film are determined by the process and final product [80,81]. In addition, the thickness of the conversion film is usually only a few nanometers [82], and the characterization of its growth process, composition and structure is very complex, so it is very difficult to analyze its formation and protection mechanism.

Electroplating, electroless plating and electrophoretic coating

At present, electroplating, electroless plating and electrophoresis are still the most widely used surface protection methods in the rare earth permanent magnet industry [83,84]. The coatings prepared by these three processes have been widely recognized by customers. In the past 10 years, with the gradual improvement of environmental protection laws and regulations, China has established large electroplating parks in Ningbo, Baotou and Ganzhou, and also equipped with mature automatic processing lines, which has laid a good foundation for ensuring the quality of coating [10]. With the continuous expansion of the application field of rare earth permanent magnet materials, customers put forward many new requirements for the metal coating on the magnet surface, so it is urgent to seek new breakthroughs on the basis of these traditional processes [85]. For example, in order to make up for the negative effect of shielding effect of Ni Cu Ni coating on the performance of magnet, researchers are working hard to develop direct copper plating technology on the surface of magnet [86]; in order to reduce the thickness of coating, Zn Ni alloy coating with high corrosion resistance is developed; in order to reduce the corrosion of solution on magnet, organic solution electroplating [87, In order to meet the needs of welding, Zn Sn alloy coating was developed [89]; in order to improve the appearance of decoration, black nickel coating was developed, and so on. In the process of plating with this kind of traditional processing method, the erosion of the solution to the magnet is inevitable, and the treatment before and after plating has an important influence on the quality of the coating.
Although these traditional processing technologies have been very mature for iron and steel materials, there are still many problems that are difficult to solve when using these technologies for surface treatment of NdFeB materials due to the high chemical activity of NdFeB materials and the porous structure of magnet surface. As far as NdFeB permanent magnet materials are concerned, it is the key of surface treatment to provide clean, uniform, dense and blunt substrate surface for pre plating coating before plating. Therefore, the development of advanced pre-treatment technology even has a brighter development prospect than coating technology.

Physical vapor deposition coating

The physical vapor deposition (PVD) technology avoids the corrosion of the solution on the magnet, and can obtain the coating with uniform structure and firm adhesion without environmental pollution. Therefore, this method has attracted much attention in the field of surface protection of rare earth permanent magnet materials [9]. In recent years, aluminum, titanium and zirconium based coatings have been prepared on the surface of NdFeB magnets by evaporation [90 ~ 92], magnetron sputtering [93 ~ 95] and ion plating [96], and the protective properties of these coatings on magnets have been studied.
Mao et al, 97] found that the magnetron sputtered Al film crystals on the surface of NdFeB magnets grow preferentially along the (111) crystal plane, showing columnar structure, and there are many pores in the film. Therefore, Hu Fang et al. [94] prepared multilayer Al films by cyclic Ar + bombardment method, which broke the columnar structure, and finally obtained stacking fault structure, which extended the transmission channel of corrosion medium, thus improving the protection of vacuum Al coating Performance.
However, the PVD process has not been widely used in the industry due to the limitations of NdFeB product diversity and size specifications, as well as cost considerations. In the future, according to the characteristics of NdFeB magnets, designing special fixtures to improve the uniformity of coating, the utilization rate of target elements and production efficiency is the key point of PVD technology in the field of surface protection of rare earth permanent magnet materials.

Other coatings

In addition to the above several coatings, there are also some protective layers which are of great concern. For example, thin organic coating is far better than chemical conversion film and metal coating in corrosion resistance, water resistance and adhesion [98], and adding some additives can give the coating surface a variety of functions, such as anti ultraviolet radiation, fingerprint resistance, self-cleaning, etc., which can meet the diverse needs. In addition, high molecular polymer has the characteristics of diversity, which can give the coating a variety of colors, because of its unique characteristics Therefore, it is expected that ultra-thin and high corrosion-resistant functional organic coatings can make new breakthroughs in the field of NdFeB in the future.
In addition, with the successful application of 3D technology in the manufacture of magnetic materials [99 ~ 101], iron-based coatings (such as Fe Si [102], Fe Co [103] and Fe Ni [104]) can be prepared on the surface of magnets for large size magnets used in military and other special fields by additive manufacturing method, and the gradient structure of composition and structure can be obtained [105, In order to meet the mechanical and corrosion resistance requirements of the coating, as shown in Figure 5 [106], other coatings can also be applied on the surface of the iron-based coating according to the requirements.
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Fig.5 Schematics of functionally graded coatings[106] (a, b) discontinuous and continuous curves, respectively(c-e) schematics of discontinuous coatings that contain interfaces with gradual change in composition, grain orientation, and volume fractions of two types of second-phase particles, respectively(f-h) schematics of continuous coatings in absence of interfaces and with gradual change in grain size, fiber orientation, and volume fraction of second-phase particles, respectively

Summary and Prospect

After 20 years of rapid development, the rare earth permanent magnet material industry pays more attention to material quality and production cost control, so the research and development of corrosion-resistant rare earth permanent magnet materials and its surface protective coating technology usher in a good development opportunity. Under the guidance of the market, the multi polarization development trend of NdFeB materials is more and more obvious, which can be divided into four categories: low-cost magnets, high-performance / high coercivity magnets, magnets for special fields, and emerging high abundance rare earth permanent magnets. Because the composition and microstructure of each type of magnet are quite different, it is necessary to treat them differently when using alloying methods to improve the corrosion resistance of magnets. In addition to considering the high-quality utilization and balanced utilization of rare earth resources, the manufacturing cost of materials should also be considered to meet the diversified needs of the market. Increase investment in basic research on Corrosion of NdFeB materials, incorporate corrosion and protection engineering into the project of rare earth permanent magnetic materials genetic engineering, carry out research on corrosion mechanism of different structures, structures and intergranular, accumulate material corrosion and environmental corrosion data, analyze the corrosion rule and phase structure evolution, and the correlation between composition, structure, magnetic properties and corrosion resistance In order to improve the accuracy of scientific research and shorten the development cycle, and accelerate the industrialization of corrosion-resistant rare earth permanent magnetic materials, the database of material corrosion is established.
The multi-phase structure and corrosion sensitivity of sintered NdFeB material bring great challenges to its surface protection. In the past 20 years, the coating technology of NdFeB magnet surface has not achieved substantial breakthrough. As far as surface coating technology is concerned, it is the key to develop a reliable protective coating based on the requirement oriented, service environment and coating design requirements and material surface characteristics. Surface protection technology has become a comprehensive technology integrating material manufacturing, coating technology and efficient equipment development. For example, surface technologies such as electroplating, electrophoresis, spraying and sputtering have been successfully used to produce low-cost and high coercivity permanent magnets. With the help of these methods, continuous, uniform and controllable thickness coatings are deposited on the surface of magnets. Through grain boundary diffusion treatment, the coercivity of magnets can be accurately controlled, and the problem of poor consistency of sheet products can be solved. It can be seen that although the research and industrial development of surface protection technology of rare earth permanent magnet materials started late due to the lack of core technology and equipment and low overall manufacturing level, the key technology of protective coating also has important strategic significance and significance for the development of resource-saving high-performance rare earth permanent magnet materials and the maintenance of China’s strategic advantage in the rare earth industry Huge economic and social benefits.

Author: WU Yucheng, GAO Zhiqiang, XU Guangqing, LIU Jiaqin, XUAN Haicheng, LIU Youhao, YI Xiaofei, CHEN Jingwu, HAN Peide (https://www.ams.org.cn/CN/Y2021/V57/I2/171)

Source: China Permanent Magnet Manufacturer – www.ymagnet.com

Reference:

  • [1]Jiang W, Shen L D, Wang K, et al.Study on Ni-Ni(S)-Ni(P) multilayer coating by friction-assisted jet electroplating on sintered NdFeB
  • [J]. J. Alloys Compd., 2019, 787: 1089
  • [2]Zhang J X, Zhang T J, Cui K.Mechanism and prevention of NdFeB magnet corrosion
  • [J]. Dev. Appl. Mater., 2001, 16(4): 38
  • [3]Liao X F, Zhang J S, Yu H Y, et al. Understanding the phase structure, magnetic properties and anti-corrosion behavior of melt-spun (La, Y)2Fe14B alloys[J]. J. Magn. Magn. Mater., 2019, 489: 165444
  • [4]Kong X W, Liu G Z, Zhao M J, et al.Research status of corrosion property of sintered NdFeB permanent magnet[J]. Chin. Rare Earths, 2013, 34(6): 69
  • [5]Li H Y, Hao Z Z, Liu Y H, et al.Research progress on corrosion mechanism and surface protection technology of sintered NdFeB permanent magnets[J]. Min. Metall. Eng., 2016, 36(6): 118
  • [6]Yan F Y, Zhao C Y, Zhang L.Advances in protective technology on NdFeB permanent magnetic material[J]. Plat. Finish., 2012, 34(8): 22
  • [7]Liu W, Hou J.Production status and prospect of NdFeB magnet electroplating[J]. Plat. Finish., 2012, 34(4): 20
  • [8]Wang E S.The anti-corrosion technology of NdFeB chemical conversion coating[J]. Plat. Finish., 2013, 35(12): 13
  • [9]Hu F, Xu W, Dai M J, et al.Research progress on physical vapor deposition and related process of NdFeB magnets[J]. Mater. Rev., 2014, 28(3): 20
  • [10]Chen X P, Zhao D L, Li Y, et al.The development of electroplating process and equipment on NdFeB permanent magnet materials[J]. Met. Funct. Mater., 2015, 22(5): 32
  • [11]Peng N, Wang X D, Chen X P, et al.Study on surface protection for NdFeB permanent magnet alloy[J]. Hot Work. Technol., 2016, 45(4): 6
  • [12]Liu W Q, Yue M, Zhang J X, et al.Intrinsic corrosion characteristic of sintered NdFeB permanent magnets[J]. Powder Metall. Technol., 2006, 24: 195
  • [13]Yan G L, McGuiness P J, Farr J P G, et al.Environmental degradation of NdFeB magnets[J]. J. Alloys Compd., 2009, 478: 188
  • [14]Wu Y P, Zhu M G, Shi X N, et al.Corrosion research of (Ce15Nd85)30FebalB1M sintered magnet in hydrothermal environment[J]. J. Chin. Soc. Rare Earth, 2016, 34: 171
  • [15]Wu Y P, Zhu M G, Shi X N, et al.Study on the diversity of corrosion products of (Ce20Nd80)31FebalB1M magnet[J]. Powder Metall. Ind., 2017, 27(5): 36
  • [16]Liu W Q, Yue M, Zhang D T, et al.Corrosion behavior of conventional and spark plasma-sintered Nd-Fe-B permanent magnets in different solutions[J]. Corrosion, 2009, 65: 501
  • [17]Liu W Q, Yue M, Zhang J X, et al.The effect of Nd-rich phase for sintered NdFeB corrosion resistance[J]. Rare Met. Mater. Eng., 2007, 36: 1066
  • [18]Cui J, Kramer M, Zhou L, et al.Current progress and future challenges in rare-earth-free permanent magnets[J]. Acta Mater., 2018, 158: 118
  • [19]Li J J, An G H, Guo C J, et al.Accelerated corrosion behavior of sintered NdFeB magnets in HAST climate[J]. J. Chin. Soc. Rare Earths, 2016, 34: 555
  • [20]Nan H Y, Zhu L Q, Liu H C, et al.Protection of NdFeB magnets by corrosion resistance phytic acid conversion film[J]. App. Surf. Sci., 2015, 355: 1215
  • [21]Zhou L J, Pei W L, Guo X L, et al.Corrosion behavior of low cost sintered Nd-Fe-B magnet containing element Ce[J]. J. Mater. Metall., 2015, 14: 217
  • [22]Zheng J W, Du Z Y, Jiang M Y, et al.Corrosion behavior of Nd-Fe-B sintered magnets at remanence state[J]. Rare Met. Mater. Eng., 2008, 37: 1369
  • [23]Jiang L Q, Zheng J W.Corrosion behavior of sintered NdFeB magnets in various acid solution[J]. Rare Met. Mater. Eng., 2006, 35: 340
  • [24]Xu J L, Huang Z X, Luo J M, et al.Corrosion behavior of sintered NdFeB magnets in different acidic solutions[J]. Rare Met. Mater. Eng., 2015, 44: 786
  • [25]Ding X, Xue L F, Ding K H, et al.Corrosion behavior of the sintered Nd-Fe-B permanent magnets in different acid solutions[J]. J. Cent. South Univ. (Sci. Technol.), 2016, 47: 1105
  • [26]Sueptitz R, Uhlemann M, Gebert A, et al.Corrosion, passivation and breakdown of passivity of neodymium[J]. Corros. Sci., 2010, 52: 886
  • [27]Liu H, Fu S, Fu Q Q, et al.Research status of medical NdFeB implantation surface modification[J]. Prog. Mod. Biomed., 2019, 19: 175
  • [28]Tang Z, Wu J Y, Chen X.In vitro study of the corrosiveness resistance property of NdFeB magnet with different coatings[J]. J. Pract. Stomatol., 2013, 29: 195
  • [29]Tian B Y, Liu H, Fu S, et al. In vitro study on corrosion resistance of different surface modified[J]. China Med. Dev., 2019, 34(3): 5
  • [30]Tian B Y, Liu H, Fu S, et al. In vitro study on the bile corrosion resistance of NdFeB magnets with different coatings[J]. Prog. Mod. Biomed., 2019, 19: 1006
  • [31]Costa I, Oliveira M C L, de Melo H G, et al. The effect of the magnetic field on the corrosion behavior of Nd-Fe-B permanent magnets[J]. J. Magn. Magn. Mater., 2004, 278: 348
  • [32]Sueptitz R, Tschulik K, Uhlemann M, et al. Effect of magnetization state on the corrosion behaviour of NdFeB permanent magnets[J]. Corros. Sci., 2011, 53: 2843
  • [33]Yan G L, Williams A J, Farr J P G, et al. The effect of density on the corrosion of NdFeB magnets[J]. J. Alloys Compd., 1999, 292: 266
  • [34]Zhou L, Liu T, Zhang X, et al. Facters affecting corrosion weight loss of sintered NdFeB magnets and improvement in corrosion resistance[J]. J. Magn. Mater. Dev., 2018, 49(4): 10
  • [35]Wang Z X, Pei K, Zhang J J, et al. Correlation between the microstructure and magnetic configuration in coarse-grain inhibited hot-deformed Nd-Fe-B magnets[J]. Acta Mater., 2019, 167: 103
  • [36]Zhang P, Hu M J, Ke H B, et al. Tuning grain boundary fine structure in Nd65Ni35-added Nd-Fe-B based magnets[J]. J. Magn. Magn. Mater., 2018, 465: 246
  • [37]Tan C L, Bao D X, Yan M.Sintered Nd-Fe-B magnets for high temperatures[J]. Mater. Rev., 2005, 19(4): 97
  • [38]El-Moneim A A, Gebert A, Uhlemann M, et al. The influence of Co and Ga additions on the corrosion behavior of nanocrystalline NdFeB magnets[J]. Corros. Sci., 2002, 44: 1857
  • [39]Li J J, Huang X Y, Zeng L L, et al. Tuning magnetic properties, thermal stability and microstructure of NdFeB magnets with diffusing Pr-Zn films[J]. J. Mater. Sci. Technol., 2020, 41: 81
  • [40]Chen H, Yang X, Sun L, et al. Effects of Ag on the magnetic and mechanical properties of sintered NdFeB permanent magnets[J]. J. Magn. Magn. Mater., 2019, 485: 49
  • [41]Liu W Q, Zha S S, Yue M, et al. Research progress of sintered Nd-Fe-B permanent magnets with high coercivity[J]. J. Beijing Univ. Technol., 2017, 43: 1569
  • [42]Zhang P, Ma T Y, Liang L P, et al. Influence of Ta intergranular addition on microstructure and corrosion resistance of Nd-Dy-Fe-B sintered magnets[J]. J. Alloys Compd., 2014, 593: 137
  • [43]Yu L Q, Huang C C, Yuan Y F.Effect of Nd, Dy content on magnetic properties and corrosion resistance of NdFeB[J]. Powder Metall. Ind., 2008, 18(6): 19
  • [44]Xie Z F, Zhang S M, Gao H Q.Effects on addition of Dy and Nb on microstructure and properties of sintered NdFeB magnets[J]. Chin. Rare Earths, 2013, 34(3): 36
  • [45]Li J, Zhou L, Liu T, et al. Progress of grain boundary diffusion technique with Dy for sintered Nd-Fe-B magnet[J]. Chin. Rare Earths, 2013, 34(3): 86
  • [46]Liu X L, Wang X J, Liang L P, et al. Rapid coercivity increment of Nd-Fe-B sintered magnets by Dy69Ni31 grain boundary restructuring[J]. J. Magn.Magn. Mater., 2014, 370: 76
  • [47]Liu X L, Zhang Y J, Zhang P, et al. Microstructure evolution of Dy69Ni31-added Nd-Fe-B sintered magnets during annealing[J]. J. Magn. Magn. Mater., 2019, 486: 165260
  • [48]Zhou B B, Li X B, Liang X L, et al. Improvement of the magnetic property, thermal stability and corrosion resistance of the sintered Nd-Fe-B magnetswith Dy80Al20 addition[J]. J. Magn. Magn. Mater., 2017, 429: 257
  • [49]Liang L P, Ma T Y, Zhang P, et al. Effects of Dy71.5Fe28.5 intergranular addition on the microstructure and the corrosion resistance of Nd-Fe-Bsintered magnets[J]. J. Magn. Magn. Mater., 2015, 384: 133
  • [50]Zeng L L, Li J J, Huang X Y, et al. Thermal stability and corrosion resistance of sintered Nd-Fe-B magnets with intergranular addition of Dy80Fe13Ga7[J]. Chin. J. Rare Met., 2019, 43: 779
  • [51]Liang L P, Ma T Y, Zhang P, et al. Coercivity enhancement of NdFeB sintered magnets by low melting point Dy32.5Fe62Cu5.5 alloy modification[J]. J. Magn. Magn. Mater., 2014, 355: 131
  • [52]Fan X D, Ding G F, Chen K, et al. Whole process metallurgical behavior of the high-abundance rare-earth elements LRE (La, Ce and Y) and the magneticperformance of Nd0.75LRE0.25-Fe-B sintered magnets[J]. Acta Mater., 2018, 154: 343
  • [53]Binnemans K, Jones P T, Blanpain B, et al. Recycling of rare earths: A critical review[J]. J Clean. Prod., 2013, 51: 1
  • [54]Lei W K, Zeng Q W, Hu X J, et al. Research status and prospect of high abundant rare earth of permanent magnetic materials[J]. Nonferrous Met. Sci. Eng., 2017, 8(5): 1
  • [55]Kim A S, Camp F E.High performance NdFeB magnets (invited)[J]. J. Appl. Phys., 1996, 79: 5035
  • [56]Liu W Q, Sun C, Yue M, et al. Improvement of coercivity and corrosion resistance of Nd-Fe-B sintered magnets by doping aluminium nano-particles[J]. J. Rare Earths, 2013, 31: 65
  • [57]Sun C, Liu W Q, Sun H, et al. Improvement of coercivity and corrosion resistance of Nd-Fe-B sintered magnets with Cu nano-particles doping[J]. J. Mater. Sci. Technol., 2012, 28: 927
  • [58]Zhang P, Ma T Y, Liang L P, et al. Improvement of corrosion resistance of Cu and Nb co-added Nd-Fe-B sintered magnets[J]. Mater. Chem. Phys., 2014, 147: 982
  • [59]Wu Y R, Ni J J, Ma T Y, et al. Corrosion resistance of Nd-Fe-B sintered magnets with intergranular addition of Cu60Zn40 powders[J]. Physica, 2010, 405B: 3303
  • [60]Yan M, Ni J J, Ma T Y, et al. Corrosion behavior of Al100-xCux (15≤x≤45) doped Nd-Fe-B magnets[J]. Mater. Chem. Phys., 2011, 126: 195
  • [61]Zeng H X, Wang Q X, Zhang J S, et al. Grain boundary diffusion treatment of sintered NdFeB magnets by low cost La-Al-Cu alloys with various Al/Cu ratios[J]. J. Magn. Magn. Mater., 2019, 490: 165498
  • [62]Ni J J, Zhou S T, Jia Z F, et al. Improvement of corrosion resistance in Nd-Fe-B sintered magnets by intergranular additions of Sn[J]. J. Alloys Compd., 2014, 588: 558
  • [63]Yang Y, Li Z J, Lv S H, et al. Effect of MgO/Mg nanopowders added to grain boundary on magnetic properties and corrosion resistance of sintered Nd-Fe-B[J]. Rare Met. Mater. Eng., 2020, 49: 1366
  • [64]Li Z J, Wang X E, Li J Y, et al. Effects of Mg nanopowders intergranular addition on the magnetic properties and corrosion resistance of sintered Nd-Fe-B[J]. J. Magn. Magn. Mater., 2017, 442: 62
  • [65]Fernengel W, Rodewald W, Blank R, et al. The influence of Co on the corrosion resistance of sintered Nd-Fe-B magnets[J]. J. Magn. Magn. Mater., 1999, 196-197: 288
  • [66]Zhang P, Ma T Y, Liang L P, et al. Improved corrosion resistance of low rare-earth Nd-Fe-B sintered magnets by Nd6Co13Cu grain boundary restructuring[J]. J. Magn. Magn. Mater., 2015, 379: 186
  • [67]Isotahdon E, Huttunen-Saarivirta E, Kuokkala V T, et al. Corrosion behaviour of sintered Nd-Fe-B magnets[J]. Mater. Chem. Phys., 2012, 135: 762
  • [68]Zhang P, Liang L P, Jin J Y, et al. Magnetic properties and corrosion resistance of Nd-Fe-B magnets with Nd64Co36 intergranular addition[J]. J. Alloys Compd., 2014, 616: 345
  • [69]Hu Z H, Liu G J, Wang H J.Effect of niobium on thermal stability and impact toughness of Nd-Fe-B magnets with ultra-high intrinsic coercivity[J]. J. Rare Earths, 2011, 29: 243
  • [70]Yu L Q, Wen Y H, Yan M.Effects of Dy and Nb on the magnetic properties and corrosion resistance of sintered NdFeB[J]. J. Magn. Magn. Mater., 2004, 283: 353
  • [71]Yu L Q, Zhong X L, Zhang Y P, et al. Production and corrosion resistance of NdFeBZr magnets with an improved response to thermal variations during sintering[J]. J. Magn. Magn. Mater., 2011, 323: 1152
  • [72]Liang L P, Ma T Y, Wu C, et al. Coercivity enhancement of Dy-free Nd-Fe-B sintered magnets by intergranular adding Ho63.4Fe36.6 alloy[J]. J. Magn. Magn. Mater., 2016, 397: 139
  • [73]Xu J L, Xiao Q F, Mei D D, et al. Microstructure, corrosion resistance and formation mechanism of alumina micro-arc oxidation coatings on sintered NdFeB permanent magnets[J]. Surf. Coat. Technol., 2017, 309: 621
  • [74]Xu J L, Xiao Q F, Mei D D, et al. Fabrication and properties of micro-arc oxidation coatings on sintered NdFeB permanent magnets[J]. Rare Met. Mater. Eng., 2018, 47: 1059
  • [75]Xu J L, Xiao Q F, Mei D D, et al. Preparation and characterization of amorphous SiO2 coatings deposited by mirco-arc oxidation on sintered NdFeB permanent magnets[J]. J. Magn. Magn. Mater., 2017, 426: 361
  • [76]Milošev I, Frankel G S.Review-conversion coatings based on zirconium and/or titanium[J]. J. Electrochem. Soc., 2018, 165: C127
  • [77]Huang T, Wang X D, Shi X N, et al. Progress in protection technologies of NdFeB permanent magnets[J]. J. Chin. Soc. Rare Earths, 2018, 36: 394
  • [78]Zhang P J, Cao Y J, Sun W, et al. Synthesis and corrosion resistance of CeO2/silane composite coatings on surface of sintered NdFeB magnet[J]. Trans. Mater. Heat Treat., 2020, 41(1): 123
  • [79]Zaferani S H, Peikari M, Zaarei D, et al. Using silane films to produce an alternative for chromate conversion coatings[J]. Corrosion, 2013, 69: 372
  • [80]Gao Z Q, Zhang D W, Li X G, et al. Current status, opportunities and challenges in chemical conversion coatings for zinc[J]. Colloids Surf., 2018, 546A: 221
  • [81]Gao Z Q, Zhang D W, Liu Z Y, et al. Formation mechanisms of environmentally acceptable chemical conversion coatings for zinc: A review[J]. J. Coat. Technol. Res., 2019, 16: 1
  • [82]Zhang X, Sloof W G, Hovestad A, et al. Characterization of chromate conversion coatings on zinc using XPS and SKPFM[J]. Surf. Coat. Technol., 2005, 197: 168
  • [83]Ouyang Y B, Qiu R, Xiao Y M, et al. Magnetic fluid based on mussel inspired chemistry as corrosion-resistant coating of NdFeB magnetic material[J]. Chem. Eng. J., 2019, 368: 331
  • [84]He W T, Zhu L Q, Chen H N, et al. Electrophoretic deposition of graphene oxide as a corrosion inhibitor for sintered NdFeB[J]. Appl. Surf. Sci., 2013, 279: 416
  • [85]Zhang P J, Xu G Q, Liu J Q, et al. Effect of pretreating technologies on the adhesive strength and anticorrosion property of Zn coated NdFeB specimens[J]. Appl. Surf. Sci., 2016, 363: 499
  • [86]Li Y, Zhu L Q, Li W P, et al.Electrodeposition and properties of copper layer on NdFeB device[J]. J. Mater. Eng., 2017, 45(6): 55
  • [87]Chen J, Xu B J, Ling G P.Amorphous Al-Mn coating on NdFeB magnets: Electrodeposition from AlCl3-EMIC-MnCl2 ionic liquid and its corrosion behavior[J]. Mater. Chem. Phys., 2012, 134: 1067
  • [88]Ding J J, Xu B J, Ling G P.Al-Mn coating electrodeposited from ionic liquid on NdFeB magnet with high hardness and corrosion resistance[J]. Appl. Surf. Sci., 2014, 305: 309
  • [89]Luo C, Qiu X M, Ruan Y, et al. Effect of Bi addition on the corrosion resistance and mechanical properties of sintered NdFeB permanent magnet/steel soldered joints[J]. Mater. Sci. Eng., 2020, A792: 139832
  • [90]Zhang P J, Wu Y C, Cao Y J, et al. Effects of pretreatment technologies on structure and properties of Al coatings on sintered NdFeB substrates via vacuum evaporation[J]. China Surf. Eng., 2016, 29(4): 49
  • [91]Liu J Q, Cao Y J, Zhang P J, et al. Preparation and properties of Al coating on sintered NdFeB magnet surface via vacuum evaporations[J]. Trans. Mater. Heat Treat., 2017, 38(3): 159
  • [92]Chen J, Yang H Y, Xu G Q, et al. Phosphating passivation of vacuum evaporated Al/NdFeB magnets boosting high anti-corrosion performances[J]. Surf. Coat. Technol., 2020, 339: 126115
  • [93]Tao L, Li H Q, Huang Y Q, et al. Structure and corrosion resistance of SiC thin film coated on NdFeB by magnetron sputtering[J]. J. Hefei Univ. Technol. (Nat. Sci.), 2015, 38: 1040
  • [94]Hu F, Dai M J, Lin S S, et al. Influences of cycles argon ion bombardment on structure and properties of Al films deposited by magnetron sputtering[J]. China Surf. Eng., 2015, 28(1): 49
  • [95]Mao S D, Yang H X, Song Z L, et al. Corrosion behaviour of sintered NdFeB deposited with an aluminium coating[J]. Corros. Sci., 2011, 53: 1887
  • [96]Zhang P J, Liu J Q, Xu G Q, et al. Anticorrosive property of Al coatings on sintered NdFeB substrates via plasma assisted physical vapor deposition method[J]. Surf. Coat. Technol., 2015, 282: 86
  • [97]Mao S D, Yang H X, Li J L, et al. Corrosion properties of aluminium coatings deposited on sintered NdFeB by ion-beam-assisted deposition[J]. Appl. Surf. Sci., 2011, 257: 5581
  • [98]Su Y A, Wan P S, Guo H M.Corrosion mechanism and surface protective technology of sintered Nd-Fe-Boron permanent magnetic material[J]. Mater. Rev., 2004, 18(S3): 257
  • [99]Chaudhary V, Mantri S A, Ramanujan R V, et al. Additive manufacturing of magnetic materials[J]. Prog. Mater. Sci., 2020, 114: 100688
  • [100]Périgo E A, Jacimovic J, Ferré F G, et al. Additive manufacturing of magnetic materials[J]. Addit. Manuf., 2019, 30: 100870 
  • [101]He J Z, Lin T, Shao H P, et al. 3D printing of NdFeB rare earth permanent magnet[J]. Chin. J. Rare Met., 2018, 42: 657 
  • [102]Borkar T, Conteri R, Chen X, et al. Laser additive processing of functionally-graded Fe-Si-B-Cu-Nb soft magnetic materials[J]. Mater. Manuf. Process., 2017, 32: 1581
  • [103]Chaudhary V, Kumar Yadav N M S K, Mantri S A, et al. Additive manufacturing of functionally graded Co-Fe and Ni-Fe magnetic materials[J]. J. Alloys Compd., 2020, 823: 153817
  • [104]Mazeeva A K, Staritsyn M V, Bobyr V V, et al. Magnetic properties of Fe-Ni permalloy produced by selective laser melting[J]. J. Alloys Compd., 2020, 814: 152315
  • [105]Liu Z Q, Meyers M A, Zhang Z F, et al. Functional gradients and heterogeneities in biological materials: Design principles, functions, and bioinspired applications[J]. Prog. Mater. Sci., 2017, 88: 467
  • [106]Zhang C, Chen F, Huang Z F, et al. Additive manufacturing of functionally graded materials: A review[J]. Mater. Sci. Eng., 2019, A764: 138209
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