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The structural evolution and variation in multiferroic properties induced by sintering conditions were investigated in the 0.67(Sm0.12Bi0.88FeO3)–0.33BaTiO3 ceramics. Sintering at various temperatures induces the transition between tetragonal and cubic phases as well as the variation in distortion degree of oxygen octahedra, contributing to the optimization of multiferroic properties. The magnetoelectric coupling effect is induced by the destabilized cycloidal spin structure resulting from the distortion in FeO6 octahedra, and the magnetoelectric coefficient of the ceramics depends on the destabilized degree in the spin structure, which relates to the sintering temperature. The ceramic sintered at 1000 °C with a relatively high dielectric constant shows a remnant magnetization, remnant polarization and magnetoelectric coupling coefficient of ~ 0.55 emu/g, ~ 8.9 μC/cm2 and ~ 5 mV/(cm · Oe), respectively.

To develop a new generation of super–hard abrasive tools, diamond/tungsten carbide (WC) mixed abrasives were brazed onto AISI 1045 (0.45% C) steel substrate by using Ni Cr B Si active filler alloy in a high vacuum furnace. The brazing operation was executed at three different temperatures (1010 °C, 1030 °C, and 1050 °C), with different dwelling times (10 min, 15 min, 20 min, 25 min and 30 min). Scanning electron microscopy, energy dispersive spectroscopy and X–ray diffraction analysis were used to investigate the interfacial characteristics of the brazed diamond/WC mixed abrasives. The results of microstructural analysis showed that several chemical and metallurgical reactions occurred between Ni Cr B Si active alloy and diamond/WC mixed abrasives have occurred during the brazing process. Cr3C2 and Cr7C3 compounds were generated at the brazing interface of diamond and the active alloy. At the same time, the Ni2W4C and NiW and Cr7C3 phases were formed between WC and the active alloy. The bonding force test of the brazed joints was carried out and the results demonstrated that the newly developed brazing tools can be applied in the field of iron material processing with high efficiency and longer working life.

In this study, cubic boron nitride (CBN) abrasive segment specimens were produced via high vacuum brazing using Cu–Sn–Ti composite alloys containing tungsten carbide reinforcing particles. The specimen microstructures and interfacial analysis of the brazed CBN grain were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The mechanical properties of hardness, wear resistance, and three-point bending strength of the fabricated specimens were tested. The specimen shape brazed using the composite Cu–Sn–Ti alloy was better than that of the specimen brazed using the pure Cu–Sn–Ti alloy. TiN and TiB2 phases were maintained between the brazed CBN and composite alloys. Meanwhile, TiC compounds were generated between the alloys and WC particles. The hardness of the specimens increased with increasing WC particle content. However, the S25 specimen containing 25 wt% WC particles, exhibited the highest wear resistance and bending strength, increasing by 26.5% and 25.6%, respectively, compared with those of the CBN segment specimen brazed using pure Cu–Sn–Ti alloy. This study provides strategies for developing multilayer brazing CBN abrasive tools.

The structural evolution of the BiFeO3-BaTiO3 system is one of the debatable topics in multiferroic solid solutions. We investigate the evolution of the crystal structure and its effect on the multiferroicity of the 0.67(SmxBi1−x)FeO3-0.33BaTiO3 (0.05 ≤ x ≤ 0.2) ceramics. All the 0.67(SmxBi1−x)FeO3-0.33BaTiO3 ceramics consist of cubic and tetragonal phases within the whole composition range. The structure changes from the cubic Pm3m to the tetragonal P4mm forming a biphasic region and exhibits an interconvertible behavior with the increment of Sm content. The grain size and its uniformity are mainly dominated by the symmetry of the unit cell, and the relative densities change little for all ceramics. The Sm substitution can effectively optimize the ferroelectricity and regulate the macroscopic magnetization. The optimized remnant polarization reaches ∼6 μC/cm2 at x = 0.12 and a maximum remnant magnetization of ∼0.85 emu/g is observed at x = 0.20. Besides, the varying fractions of the two phases correlate strongly to the enthalpy change which also verifies the appearance of the destroyed ferroelectric state.

Herein, composite brazing fillers were fabricated by adding reinforced tungsten carbide (WC) particles into Ni-Cr alloy and the composite segment of diamond grains was prepared by vacuum brazing using the composite fillers at a brazing temperature of 1030 °C for a dwelling time of 20 min. The thermal damage degree of the brazing diamond and mechanical properties, such as hardness, wear resistance and bending strength, of the segment were examined in detail. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were carried out to analyze the interfacial characteristics of the brazing diamond and segments. The results revealed that the static strength and impact toughness of the diamond grains, brazed by the composite fillers, were higher than the diamond grains brazed by pure Ni-Cr fillers. Raman spectra also indicated that the degree of graphitization and thermal damage of the diamond had been reduced. In the brazing process, the chemical and metallurgical reactions occurred between the composite fillers and diamond grains, which resulted in the formation of Cr3C2 and Cr7C3 compounds. At the same time, bonding phases were formed between WC particles and Ni-Cr particles. Furthermore, WC particles reduced the reaction intensity of the diamond and fillers, which resulted in the molding of the segments into a fixed shape. When the additive amount of WC particles was 30%, the hardness, wear resistance and bending strength of the composite diamond grains segment matrix reached the highest values. Moreover, the mechanical properties of the diamond grains, brazed by Ni-Cr filler and added WC particles were higher than the segment brazed by pure Ni-Cr fillers. The present study opens up avenues for further research on the development of multilayer brazing superhard abrasive tools.

The ternary (1−x)(0.8BiFeO3-0.2BaTiO3)-xK0.5Na0.5NbO3 (0 ≤ x ≤ 0.5) solid solutions have been successfully synthesized by a solid-state reaction route. X-ray diffraction and Rietveld refinement studies reveal the phase transition from the rhombohedral and tetragonal phases to the single tetragonal phase with x increasing. The average grain size decreases initially and then increases as x increases, whereas the remnant magnetization shows an opposite trend and reaches the maximum value of ~2.09 emu/g at x = 0.3. An enhanced remnant polarization of ~8.6 μC/cm2 appears at x = 0.3 due to the structure distortion and the decrement of defects. Moreover, the remanent polarization and the relative permittivity reach the maximum value of ~20.14 μC/cm2 (10 Hz) and ~644 (1 kHz) at x = 0.5, respectively, and the corresponding dielectric loss decreases to the lowest value of ~0.022 (1 kHz). These results indicate that the properties of ternary BFO-BTO-KNN solid solutions can be modulated by adjusting the K0.5Na0.5NbO3 content to adapt to different application needs.

To improve the performance of grinding wheels for rail, a composite grinding wheel was developed by combining brazed diamond sheets and original resin grinding wheel. An experimental methodology for grinding process was established to study the grinding wear characteristics of the brazed sheet. The results indicate that with increasing working load, the wear rate of the brazing sheet increases and the grinding ratio decreases. In addition, the temperature rise becomes faster and the proportion of oxidation products in the grinding debris increases. Brazing alloy shows melt-slip phenomenon when grinding was performed continuously for a long time. When the worn brazing material is mixed with iron debris, the mixture hinders agglomeration and shrinkage of the molten debris.

The 0.6BiFeO3–0.4Bi0.5K0.5TiO3 + x mol% MnO2 ceramics (BFKT–xMn, x = 0, 2.5, 5, 7.5 and 10) have been successfully synthesized via a conventional solid-state reaction method. All the ceramics possess a morphotropic phase boundary formed by rhombohedral and tetragonal phases. A room temperature magnetoelectric (ME) coupling coefficient of 30.12 mV cm−1 Oe−1 is observed for the first time in the undoped BFKT ceramic. The appropriate addition of MnO2 can optimize the electrical insulation and ferroelectricity of BFKT ceramic due to the decreased densities of impurity and grain boundary, and thus enhance the magnetoelectric coupling effect significantly. The BFKT–2.5Mn ceramic exhibits a high remanent polarization of 36.2 μC/cm2 at a maximum electric field of 70 kV/cm and a high ME coupling coefficient of 42.56 mV cm−1 Oe−1 as well. Meanwhile, the leakage current density of the BFKT–2.5Mn ceramic maintains at a low value of 1.83 × 10−8 A/cm2 (at a maximum electric field of 45 kV/cm). These characteristics indicate the BFKT–2.5Mn ceramic has potential applications in multifunctional devices as lead-free multiferroic materials.

The effects of cooling rate on structure and multiferroic properties were investigated in the lead-free 0.67Sm0.12Bi0.88FeO3–0.33BaTiO3 ceramics. Cooling in different medium induces the variations of phase fractions, c/a ratio and the distortion degree of oxygen octahedron, which can effectively regulate the multiferroic properties at room temperature. The high-temperature P4mm phase transforms to the Pm3m phase with the decrement of the cooling rate. The magnetoelectric coupling effect is nonlinearly related to the cooling rate, which is induced by the corresponding distortion in FeO6 octahedron. The ceramic cooled in water shows the largest remnant polarization of ~ 20.9 μC/cm2, while the ceramic cooled in furnace shows large remnant magnetization and magnetoelectric coupling coefficient of ~ 0.50 emu/g and 7.3 mV/(cm Oe), respectively.

The polycrystalline Sm and Mn co-substituted bismuth ferrites Bi1-xSmxFe0.95Mn0.05O3 (x = 0.08 and 0.16) with composition near the morphotropic phase boundary have been prepared using a modified solid-state reaction method. The Bi0.92Sm0.08Fe0.95Mn0.05O3 ceramic possesses single rhombohedral phase, whereas the Bi0.84Sm0.16Fe0.95Mn0.05O3 ceramic consists of both the R3c and Pnma phases. The addition of Sm and Mn not only enhances density and grain uniformity but also suppresses the spiral spin modulation which improves the polarization and magnetization. Excellent ferroelectric properties of microdomains are attained in the Bi0.92Sm0.08Fe0.95Mn0.05O3 ceramic. The transition of the nonpolar/antipolar phase to the polar phase and the polarization switching induced by the electric field occur in the Bi0.84Sm0.16Fe0.95Mn0.05O3 ceramic.

In the original article an incorrect magnetic field range was included in Fig. 9a. The corrected figure is presented below.

Diamond, c-BN, Al2O3 and SiC abrasive crystals were brazed onto 0.45%C steel matrix using Cu–Sn–Ti active powder filler alloys in vacuum to develop a new superhard abrasive wheel. The brazing process was carried out in vacuum at the temperatures of 890 °C, 925 °C, and 960 °C for dwell durations from 10 to 30 min, respectively. The interface characteristics of the brazed joints between the abrasive grains and the filler alloys were investigated using optical microscope, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The results by microanalyses show that the element of Ti from the active powder filler was diffused preferentially to the surface of the grains, resulting in a Ti-rich reaction layer in the brazed joints. The microstructure phases of TiC, TiN, TiB, TiB2, TiO and TiSi2 in the grains/active filler interface and Cu–Ti in the active filler/steel interface were confirmed by XRD analysis. The joining of the grains to the 0.45%C steel was realized by the reaction products of Ti-based on the interface. The adhesive strength experiment of the joint interfaces was performed; the results suggest that the grains were not dislodged from the bond interface.

The crystal structure transition and its effect on the multiferroic characteristics were investigated in Ca2Bi4Ti5-xMnxO18 (0 ≤ x ≤ 2) ceramics synthesized by the molten salt method. Mn substitution induces variations in a/b ratio and the distortion degree of oxygen octahedrons, which can effectively regulate the multiferroic properties at room temperature. The structure changes from orthorhombic B2cb to tetragonal I4/mmm with a morphotropic phase region forming in the ceramic at x = 1.5. The Raman spectra manifest that Mn substitution not only alters the vibration mode of MnO6 octahedron but also changes the structural environment of TiO6 in the perovskite lattice. The average grain size increases gradually and the grain size distribution gets homogeneous with the increase in Mn content. All the ceramics show a lossy dielectric behavior. The addition of Mn results in a significant enhancement in macroscopic magnetization and dielectric properties. In addition to this, the magnetoelectric coupling effect has also been improved and a maximum magnetoelectric coefficient of α ≈ 12.3 mV/(cm·Oe) is attained for the ceramic sample with x = 1.5.

The effects of synthesis conditions on the structural evolution and multiferroic properties were investigated in Ca2Bi4Ti3.5Mn1.5O18 ceramics synthesized by molten salt methods. An optimized calcining temperature of 800 °C was found to be sufficient for obtaining the desired Aurivillius structure. The ceramics possess a morphotropic phase with the orthorhombic-tetragonal biphasic structure. The weight fractions and unit cell volumes of orthorhombic and tetragonal phases change with varying mass ratio of chlorides/oxides, which can effectively regulate the multiferroic properties at room temperature. The layered structure of several tens nanometers appears in all the Ca2Bi4Ti3.5Mn1.5O18 samples prepared with various chlorides/oxides mass ratios showing lossy ferroelectric behavior. The occurrence of magnetoelectric coupling effect is attributed to long-range magnetic order structure. The ceramic prepared with chlorides/oxides mass ratio equaling to 4 exhibits optimum properties with the highest remnant magnetization of ∼0.06 emu/g and the highest ME coefficient of ∼5.05 mV/(cm·Oe).

In order to expand the application field of tools containing brazed superabrasives, the wear characteristics of brazed diamond sheets, which used in rail-grinding composite grinding wheels, under different grinding time were studied. The brazing sheet’s grinding ratio decreases with time while wear and thermal damage of the diamond abrasive increase. With continuous long-term grinding, the solder shows melt-slip phenomenon, which increases grinding portion of the brazing sheet. Meanwhile, there was partial oxidation of the solder in the wear debris. When the total grinding time is the same, in short-time multiple grinding, the brazing sheet suffers less, higher grinding ratio; the thermal damage of the diamond abrasive is lower and the wear of abrasive is mainly impact crushing, flattening and mechanical shedding.

The temperature dependence of the in-plane saturation magnetization of the Fe3O4/MgO/SrTiO3 multiferroic heterostructure is investigated under various electric fields. The MgO interlayer is utilized to introduce oxygen vacancies into the heterostructure. Compared with the case of the Fe3O4/SrTiO3, a different variation trend of the magnetization has been attained in the Fe3O4/MgO/SrTiO3 since the oxygen vacancies accumulate on the Fe3O4 layer at the negative electric field. The magnetoelectric coupling coefficient of the Fe3O4/MgO/SrTiO3 at an electric field of −500 kV/cm is 1.21 Oe·cm/kV, 42% larger than that of the Fe3O4/SrTiO3. The distribution of oxygen vacancies controlled by the electric field plays an important role in the modulation of magnetization. The insertion of the MgO layer is responsible for the larger magnetoelectric response.

The multiple modulations of strain- and charge-mediated converse magnetoelectric coupling effects have been achieved in a multiferroic heterostructure of SrTiO3(STO)/Fe3O4/Au/PbZr0.52Ti0.48O3(PZT) multilayers grown on a Nb:SrTiO3 substrate. By altering the position of the applied electric field, the heterostructure is divided into three structure parts, i.e., Fe3O4/Au/PZT, STO/Fe3O4, and STO/Fe3O4/Au/PZT. In such an optimized heterostructure, the strain and charge effects can be directly separated, quantified, and co-regulated and the pure strain, pure charge, and the combined strain and charge effects can thus be obtained, respectively. The in-plane magnetization variation behaviors induced by electric fields are different for the three individual modulations, which are closely related to the interfacial strain propagation and interfacial charge accumulation. It is also found that the strain and charge effects can interact with each other as the two interfacial effects coexist.The multiple modulations of strain- and charge-mediated converse magnetoelectric coupling effects have been achieved in a multiferroic heterostructure of SrTiO3(STO)/Fe3O4/Au/PbZr0.52Ti0.48O3(PZT) multilayers grown on a Nb:SrTiO3 substrate. By altering the position of the applied electric field, the heterostructure is divided into three structure parts, i.e., Fe3O4/Au/PZT, STO/Fe3O4, and STO/Fe3O4/Au/PZT. In such an optimized heterostructure, the strain and charge effects can be directly separated, quantified, and co-regulated and the pure strain, pure charge, and the combined strain and charge effects can thus be obtained, respectively. The in-plane magnetization variation behaviors induced by electric fields are different for the three individual modulations, which are closely related to the interfacial strain propagation and interfacial charge accumulation. It is also found that the strain and charge effects can interact with each other as the two interfacial effects coexist.