Amorphous Co-rich microwires with excellent soft magnetic and mechanical properties produced by melt-extraction technique are emerging as a multifunctional material for a variety of applications ranging from ultrasensitive magnetic field sensors to structural health self-monitoring composites. There is a pressing need for enhancing these properties to make the microwires practical for integration into new technologies. Conventional heat treatments at temperature below crystallization may improve the magnetic softness of an as-quenched amorphous wire, but usually deteriorate the good mechanical characteristic of the wire due to crystallization. To overcome this, we propose a new approach that utilizes the advantages of a multi-step Joule current annealing method to design novel (nanocrystal, amorphous)/amorphous core/shell structures directly from as-quenched amorphous microwires. These results show that the density and size of nanocrystals in the core can be optimized by controlling the Joule current intensity, resulting in the large enhancement of soft magnetic and giant magneto-impedance properties, while the amorphous shell preserves the excellent mechanical strength of the microwire. This study also provides a new pathway for the design of novel core/shell structures directly from rapidly quenched amorphous magnetic materials that are currently exploited in high frequency transformers, sensing and cooling devices.

作为电气系统组件,IGBT(绝缘栅双极型晶体管)模块在轨道交通领域有着广泛应用.封装材料的性能直接影响IGBT模块的使用寿命和稳定性.A1-50％ Si合金是IGBT模块较为理想的封装材料.采用粉末冶金结合双向分级热压致密化成型工艺,制备了A1-50％ Si合金材料.使用OM、SEM方法(扫描电子显微镜)分析热压态及热处理态合金的显微组织.结果 表明,在烧结温度为720℃且保温50 min后,能够获得Si相尺寸与分布控制较好的合金;在热扩散温度为540℃,扩散处理3.5h后,能够有效熔断纤维状与细针状共晶硅.

In this work, the dislocation etching pit morphology and etching kinetics on the A‐{11 2¯ 0} plane of sapphire crystal (α‐Al2O3) are studied experimentally. The results show that the etch pit exhibits a subrhombic 3D morphology, which is consistent with the atom arrangement symmetry of the A plane. Further analysis shows that the two adjacent sides of the rhombic etch pits correspond to the directions [3 3¯ 0 1¯ ] and [3 3¯ 02], respectively; both of them are in the atomic close‐packing direction of A plane. The etch pits are controlled by a chemical reaction between Al2O3 and potassium hydroxide (KOH) with the reaction activation energy of 51.7 kJ mol−1, which is developed in a manner of kinematic wave by the step moving with a constant speed.

Techniques to fabricate patterned sapphire substrates (PSSs) have attracted much attention in recent decades. Wet etching behaviors and crystalline sapphire processes are critical for PSSs applications to improve the performance of light-emitting diodes. This study investigated the shape evolution behaviors and associated kinetics of cavities on the c-{0001} plane in crystalline sapphire during wet etching. It was revealed that wet etching reduces the cavity aspect ratio, and the cavity shape is a complicated structure constructed by 15 faceted planes of c-{0001}, r-{1102}, p-{1123}, m-{1010}, and s-{1101} families. A constant etching rate was demonstrated, suggesting the step flow mechanism of etching. The etching activation energy of crystalline sapphire is reduced by preformation of cavities as elucidated by the Arrhenius kinetic model followed during the etching process. This study provides new insight into wet etching behaviors of crystalline sapphire and might open up a way for fabricating sapphire substrate with large aspect ratio patterns.

伴随着微电子封装技术高速发展,单一的封装材料已经难以满足当前高密度集成微波组件封装所需的综合性能需求.在简述了微电子封装技术对材料的需求以及金属基材料存在的不足的基础之上,文中引入了 一种新型微电子封装材料—梯度硅铝合金,开展了全方位的工艺验证,包括多芯连接器与盒体热失配、LTCC电路片与盒体热失配、盒体形变、法兰盘强度与激光焊接等单点工艺技术应用验证研究,随后进行了产品应用验证研究.在验证的基础上总结出了梯度硅铝作为封装材料的应用边界.研究结果丰富了微电子封装材料体系,推动了微电子封装技术的发展.

In this article, the functionally gradient materials and their preparation technology are rough expounded. Then, the technical requirements of gradient AlSi alloy in the field of aeronautical active phased array radar are indicated. After a brief analysis, it is pointed out that the methods above are not suitable for manufacturing gradient AlSi alloy. And the 3D printing additive manufacturing technology can be applied to prepare the gradient AlSi alloy. Through the optimization of laser melting deposition technology and the experimental process design, the AlSi alloy materials are prepared with the distribution of 73Al27Si, 62Al38Si, 50Al50Si, 62Al38Si, 73Al27Si, a total of gradient five layers. The microstructure and physical properties of the material are observed and tested respectively. It is shown that the material is compact without pores or cracks, and there are no pores or cracks at the interlaminar junction. The transition region between AlSi layers has obvious weld pool characteristic. From the test result, it can be seen that the fracture location is 50Al50Si body position. The tensile strength is above 140 MPa. After the temperature impact test and stress simulation, it is proved that the maximum stress value in the different gradient layers is far below the stress limit of the material itself, and the materials meet the requirements of the airborne environment. The physical properties change continuously with the continuous or quasi continuous changes of chemical composition. The T/R module boxes and electronic packaging structures are designed based on the gradient AlSi alloy. The integrated T/R module has also undergone environmental tests and screening validation at various product levels according to GJB 150A-2015 to prove the gradient AlSi alloy qualified. After the attempt of 3D printing laser melting deposition to prepare the gradient AlSi alloy, it is testified that the method and the material are reliable, following with further research in the preparation and basic problems.

We report upon the excellent magnetocaloric effect in melt-extracted DyHoCo medium entropy microwires. The magnetic entropy change (-Delta S-M) reaches a large value of similar to 11.2 J kg(-1) K-1 for a field change (mu(0)Delta H) of 5 T. The large value of -Delta S-M i is resulted from the large magnetic moments of Dy and Ho. In addition, the DyHoCo microwires show a good cooling efficiency; RC1, RC2 and RC3 are evaluated to be similar to 530 J kg(-1), similar to 417 J kg(-1)1 and similar to 279 J kg(-1), respectively, at mu(0)Delta H = 5 T. The DyHoCo microwires undergo a second-order paramagnetic-ferromagnetic transition at the Curie temperature of similar to 35 K. The excellent magnetocaloric property makes the melt-extracted DyHoCo microwires a promising refrigerant for cryogenic cooling application. (C) 2020 Elsevier B.V. All rights reserved.

Chemical wet etching technology is widely applied in semiconductor device fabrication such as the patterned sapphire substrates. However, the etching of pre-formed structure is still lack of investigations, which has po-tential applications in the preparation of particular devices. By using molten KOH etchant, the present work studied the wet etching behaviors of cavity on the A-plane of sapphire crystal in three-dimensional space and revealed the etching kinetics. It was demonstrated that the cavity will evolve into a complicate symmetric shape with multiple facet planes during etching. The width of the cavity is gradually expanded however the depth of the cavity is stable during etching, where the Arrhenius model was held, indicating that the etching process is realized by step flow removal of atoms. The present results improve the understanding of the morphology evolution and relevant kinetics of a pre-formed structure on sapphire crystal during wet etching, which shed further light on the single crystal wet etching technology for device fabrication.

In this paper, the magnetocaloric effect (MCE) of a high-entropy Gd19Tb19Er18Fe19Al25 amorphous microwires fabricated by melt-extracted method are investigated systematically. These microwires exhibit a second-order phase transition from ferromagnetic to paramagnetic states at the Curie temperature of 97 K. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves are irreversible when the temperature lower than the Curie temperature due to the spin glassy freezing behavior. The peak magnetic entropy change (Delta S-M(pk)) for a field change from 0 to 5 T reaches similar to 5.94 J/kg.K. In accordance to two criteria refrigerant capacity, the values of refrigerant capacity (RC) and relative cooling power (RCP) reach similar to 569 J/kg and similar to 733 J/kg at a field change of 5 T, respectively. These results suggest that the melt-extracted Gd19Tb19Er18Fe19Al25 microwires exhibit good MCE and have great potential to use as one kind of high temperature magnetic refrigeration material.

Ni45.6Fe3.6Mn38.4Sn12.4 microwires, with nanoscale γ-phase precipitates that enhance the magnetocaloric effects (MCEs) and mechanical properties, were prepared by a melt-extraction technique and subsequent high temperature annealing. The atomic ordering degree significantly increased after annealing, leading to a considerable increment in the structural entropy change (ΔStr) from 4.5 J/kg·K in the as-extracted microwire to 26.6 J/kg·K in the annealed one, and the magnetization difference (ΔM) from 35 A·m2/kg to 51 A·m2/kg under a magnetic field of 5.0 T. Consequently, a positive magnetic entropy change (ΔSM) peak of 15.2 J/kg·K with working temperature span (ΔTFWHM) of 12 K for the first-order martensite transformation followed by a negative ΔSM peak of −4.3 J/kg·K with ΔTFWHM = 50 K for the second-order magnetic transition under μ0ΔH = 5.0 T was achieved. By employing both magnetizing and demagnetizing processes for magnetic cooling, the two successive inverse and conventional MCEs in Ni–Fe–Mn–Sn microwires may show potential applications for micro-devices and systems.

A new magnetocaloric composite composed of three types of soft ferromagnetic Gd‐based microwires with equal mass ratio and close magnetocaloric performances is designed. The Curie temperatures (TC) of these three wires are ≈97, ≈100, and ≈101 K, respectively. However, the magnetization versus temperature curve of the composite sample shows almost a single ferromagnetic–paramagnetic transition at ≈97 K. For a field change of µ0ΔH = 5 T, the maximum entropy change () and refrigerant capacity (RC) of this composite are calculated to be ≈9.98 J kg−1 K−1 and ≈665 J kg−1, respectively. There is a good agreement between the calculated −ΔSM (T) curve and the experimental data, indicating weak magnetic interactions among different wire compositions. Additionally, the calculated universal master curves of the composite and its Gd‐Al‐Co components are fitted very well, which reveals the second‐order type of the magnetic transition for the composite. The designed composite integrates all magnetocaloric properties of its components, suggesting that the Gd‐based amorphous wires with close magnetocaloric properties can be designed as an excellent refrigerant for use in active magnetic refrigerators.

Gd50Al30Co20 wires show excellent magnetocaloric properties and high heat exchange rate due to the microsize. The Weibull and lognormal methods were used for systematically analyzing its mechanical properties for matching the design requirements in cooling system. The wire exhibits average fracture strength of ~ 969.5 MPa and typical fracture behavior of amorphous character. Moreover, the distributions of stresses for tensile strains at 10 values are estimated by probability plot and Chi-square goodness-of-fit test. The random stresses were best fitted by lognormal probability distribution for most studied cases; however, fracture strength was best fitted by Weibull probability distribution. It is interesting to note that the mean and standard deviation of the stresses (to reach specific tensile strain) increase as the tensile strain grows, accompanied by the coefficients of variation of stresses which decrease smoothly. It is concluded that the inhomogeneity of material does cause the scatter of stresses growth, and the scatter could be considerably large.

A novel type of bi-constituent wire composite was obtained by combining melt-extracted Gd50Al30Co20 and Gd55Al20Co25 microwire components with Curie temperature (T-C) of 86 K and 110 K, respectively. For a field change of 5 T, the wire composite possesses a table-like feature spanning a temperature interval of 30 K with value of similar to 8.61 kg(-1) K-1, and enhanced refrigerant capacity (RC) and relative cooling power (RCP) values of similar to 680 J kg(-1) and similar to 863J kg(-1), respectively. The experimental results agree well with those calculated by a simple bi-composition model, demonstrating the possibility of designing wire-based composites with desirable magnetocaloric effects (MCE) for active magnetic refrigeration. (C) 2018 Elsevier B.V. All rights reserved.

采用高能球磨、粉末压制、烧结以及热挤压的方法制备了Cu-SiC-SnO2电触头复合材料,研究了球磨时间、压制压力、烧结温度、烧结时间和挤压温度等参数对材料致密度的影响.通过电寿命试验结合微观分析研究了材料的电烧损性能.结果表明,提高压制压力、球磨时间和烧结温度、延长烧结时间可以提高材料的致密度,随挤压温度升高,致密度呈先增后降趋势.添加SnO2可提高材料的粘度,降低喷溅物含量,增强材料的抗熔焊性及抗电烧损性能.

Giant magnetocaloric effect in Ni-Mn-X (X=In, Sn, Sb) Heusler alloys has been revealed due to the significant shift of the martensite transformation temperatures under a bias magnetic field. However, the magnetic hysteresis during the magnetization and demagnetization cycles creates a large hysteresis loss and reduces the refrigeration capacity. Here we demonstrated that the magnetic hysteresis loss in Ni-Mn-Sb alloys was effectively reduced by Si-doping. The quaternary Ni49.0Mn38.4Sb11.7Si0.9 alloy exhibited martensite and magnetic transitions around room temperature. Maximum magnetic entropy change ΔSm 9.4J/kgK and working temperature interval 7.0K were achieved attributed to the martensite transformation under a magnetic field of 5T. Meanwhile, the average magnetic hysteresis loss for Ni49.0Mn38.4Sb11.7Si0.9 alloy was 2.1J/kg, much smaller than that for Ni49.0Mn38.5Sb12.5 alloy, 11.4J/kg. As a result, a refrigeration capacity of 50.2J/kg was obtained in the Ni49.0Mn38.4Sb11.7Si0.9 alloy. This result shows that Si-doped Ni-Mn-Sb alloys may act as a potential material system for magnetic refrigeration.

Understanding the relationship between the surface conditions and giant magneto-impedance (GMI) in Co-rich melt-extracted microwires is key to optimizing their magnetic responses for magnetic sensor applications. The surface magnetic domain structure (SMDS) parameters of ~45 μm diameter Co69.25Fe4.25Si13B13.5-xZrx (x = 0, 1, 2, 3) microwires, including the magnetic domain period (d) and surface roughness (Rq) as extracted from the magnetic force microscopy (MFM) images, have been correlated with GMI in the range 1–1000 MHz. It was found that substitution of B with 1 at. % Zr increased d of the base alloy from 729 to 740 nm while retaining Rq from ~1 nm to ~3 nm. A tremendous impact on the GMI ratio was found, increasing the ratio from ~360% to ~490% at an operating frequency of 40 MHz. Further substitution with Zr decreased the high frequency GMI ratio, which can be understood by the significant increase in surface roughness evident by force microscopy. This study demonstrates the application of the domain period and surface roughness found by force microscopy to the interpretation of the GMI in Co-rich microwires.

We report enhancements of both Curie temperature and magnetic refrigerant capacity in Gd-50(Co69.25Fe4.25Si13B13.5)(50) microwires, which were fabricated by the melt-extraction method. For a field change of 5 T, the maximum magnetic entropy change (Delta S-M(max)), the refrigerant capacity (RC) and relative cooling power (RCP) reached high values of 6.56 J kg(-1) K-1, 625 J kg(-1) and 826 J kg(-1), respectively. While the RC is similar to those of our previously reported GdAlCo microwires, a much broader working temperature range of similar to 126 K and a higher Curie temperature of 170 K make the Gd-50(Co69.25Fe4.25Si13B13.5)(50) microwires more attractive for active magnetic refrigeration. (C) 2017 Elsevier B.V. All rights reserved.

Small-sized materials with large surface to volume ratio favor heat transfer during magnetic refrigeration cycling and thus may help enhancing the refrigeration efficiency. Here, high Fe content Ni44.9Fe4.3Mn38.3Sn12.5 polycrystalline microwires were prepared by a melt-extraction technique. The as-extracted microwires were annealed at 1173K for 60min, leading to significant grain growth and formation of a secondary Fe-rich γ phase. The annealed microwire exhibits larger magnetization difference (ΔM) between the austenite and martensite phases and smaller thermal hysteresis compared to the as-extracted microwire. The annealed microwire possesses a magnetic transition to austenite at 299K, followed by a martensitic transformation (MT) from a ferromagnetic austenite to a weak-magnetic martensite at 208K upon cooling. Under a magnetic field of 50kOe, the annealed microwires show a maximum magnetic entropy change ΔSm of 6.9J/kg·K and an effective refrigeration capacity RCeff of 78.0J/kg over a broad working temperature span ΔTFWHM of 20K around the MT. In addition, magnetic transition of the austenite gives rise to ΔSm −3.7J/kg·K and RCmag 232.5J/kg with ΔTFWHM of 85K under 50kOe.

Very recently, we reported that Fe-doped Ni50-xFexMn38.0Sn12.0 alloys exhibited enhanced magnetization difference Delta M between the martensite and austenite phases. Of note is that the alloy with x = 4.2 exhibits a strong metamagnetic transition behavior, i.e. magnetic-field-induced reverse martensite transformation, which is favorable for the magnetocaloric effects. Here, the enhanced magnetocaloric effect related to metamagnetic transition in the selected Ni35.8Fe4.2Mn38.0Sn12.0 alloy was reported. This alloy exhibits a high magnetization difference Delta M of similar to 58 A.m(2)/kg between martensite and austenite phases owing to the magnetic and structural coupling. The doping of Fe leads to a strong metamagnetic behavior, with austenite peak temperature shift Delta A(p)/Delta H reaching -2.4 K/T. As a result, the magnetic entropy change Delta S-m increases rapidly from a starting critical magnetic field similar to 0.2 T and then saturates at various finishing critical magnetic fields, depending on the working temperature. A sizable peak DSm of 33.8 J/kg.K with a working temperature interval of 7 K is obtained under a magnetic field of 5 T, which is responsible for a high relative cooling power RCP of 237 J/kg. These results suggest that Ni45.8Fe4.2Mn38.0Sn12.0 alloy may act as a potential solid-state magnetic refrigerant. (C) 2017 Elsevier B.V. All rights reserved.