Effect of TiO2 addition and high magnetic field sintering on properties of vitrified bond CBN composites

Vitrified bond CBN composites, with different amounts of TiO₂ doping, were prepared by conventional sintering and high magnetic field sintering processes. Mechanical properties, cross-sectional morphology, refractoriness, fluidity and structural characterization have been carried out to understand the role of TiO₂ addition and sintering conditions. Results show that TiO₂ addition significantly affected bending strength, refractoriness and fluidity of vitrified bonds. In addition, high magnetic field sintering improved bending strength and the microstructure of vitrified bond CBN composites. Due to high magnetic field sintering, CBN grains were completely covered by vitrified bond and exhibited fewer pores. In addition, high magnetic field promoted the growth of specific grains, such as SiO₂, whereas suppressed grain growth of other crystal phases, such as NaAlSi₃O₈.     

Effects of sintering in a high magnetic field on properties of vitrified bond and vitrified CBN composites

Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field.     

Effects of Y2O3 addition on structure and properties of LZAS vitrified bond for CBN grinding tools application

The effects of Y₂O₃ addition on the structure and properties of Li₂O–ZnO–Al₂O₃–SiO₂ (LZAS) vitrified bonds were firstly investigated for CBN grinding tools application. Glasses and glass-ceramics were characterized using differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy and infrared spectroscopy. The thermal expansion coefficient (TEC), microhardness, bending strength and chemical durability of the obtained products were also evaluated. Results showed that Y₂O₃ acted as the network former in the track of SiO₄ tetrahedrals. Introducing Y₂O₃ in the glasses increased the glass transition temperature and crystallization temperature. The crystallization of the main β-quartz_ss phase increased with increase of Y₂O₃ content. The morphology of the crystals was dependent on the Y₂O₃ content. The TEC (5.15×10⁻⁶/°C) of vitrified bond containing 1.0 mol% Y₂O₃ (Y1.0) was very close to the TEC (5.0×10⁻⁶/°C) of CBN grains. Moreover, Y1.0 vitrified bond exhibits a high microhardness (5.98 GPa), a high bending strength (202 MPa) and a good chemical durability (20 days, DR=2.8×10⁻⁹ g/cm² min), suggesting that it would be a promising material for CBN grinding tool.     

Effect of polycrystalline mullite fibers on the properties of vitrified bond and vitrified CBN composites

The effect of polycrystalline mullite fibers (PMFs) on the properties of vitreous bonds and vitrified CBN composites was investigated. The results show that the addition of PMFs can increase the porosity of composites and reduce the fluidity of binders. The vitrified composites incorporating 6.4 wt% PMFs display excellent mechanical strength, which is enhanced by 21.2% compared with that of composites without PMFs sintered at the optimal sintering temperature. Meanwhile the thermal expansion coefficient of vitrified bond reduces from 6.256×10⁻⁶ °C⁻¹ to 4.805×10⁻⁶ °C⁻¹ with increasing fraction of PMFs. The improvement of mechanical strength is associated with the change of cracking mechanisms of the composites with fibrous crystals and the existence of several observed mechanisms, including fiber pull-out, fiber bridging and rupture.     

Preparation of a novel vitrified bond CBN grinding wheel and study on the grinding performance

The vitrified bond CBN grinding wheels are characterized by high efficiency, high precision, and low environmental pollution. In recent years, the vitrified bond CBN grinding wheel has been widely used in manufacturing industries such as aerospace, automotive, and machine tools. In this study, a novel vitrified bond formulation containing nano SiO₂ and nano CeO₂ is selected to prepare the grinding wheel. The grinding experiments on 45# steel and YG20 alloy indicate that the grinding performance of the nano vitrified bond grinding wheel is significantly better than that of the conventional vitrified bond grinding wheel. The introduction of nano SiO₂ and nano CeO₂ greatly improves the machining performance of the vitrified bond CBN grinding wheel.     

Influence of TiO2 amount on the interfacial wettability and relevant properties of vitrified bond CBN composites

The influence of TiO₂ amount on the microstructure and relevant properties of SiO₂-Al₂O₃-B₂O₃-Na₂O-Li₂O-BaO vitrified bond and vitrified bond CBN composites were systematically studied via SEM, EDS, FTIR, and XPS. Results indicated that adding TiO₂ could regulate the quantity of β-quartz solid solution and rutile crystals in the vitrified bond and considerably affect the thermal properties and mechanical strength of this bond. Under sintering temperature, the dense B₂O₃ oxide layer on the CBN surface diffused into vitrified bond and reacted with Ti⁴⁺ enriched at the interface to form a strong chemical Ti-B bond. This reaction extensively improved the interfacial wettability between the CBN and the vitrified bond. When the TiO₂ amount was 6wt.%, the interfacial wettability significantly improved, and the wetting angle decreased from 68° to 43°. The flexure strength and hardness of the composites were 116.18 MPa and 128 HRB, which were 48.49% and 34.74% higher than those of the basic-formula composites, respectively.     

The mechanism investigation of ultrasonic roller dressing vitrified bonded CBN grinding wheel

To clarify the ultrasonic roller dressing mechanism of the vitrified bonded cubic boron nitride grinding wheel (V-CBN), the collision number model between the diamond dresser and CBN grits was established based on the geometric and kinematics analysis. The influence of each dressing parameter on the collision number was analyzed and discussed. The grinding experiment was performed on the bearing raceway with the dressed V-CBN grinding wheel, results obtained discovered that there was an inverse relationship between the collision number and the surface roughness and runout of the workpiece. Additionally, compared with conventional dressing, ultrasonic dressing has the advantage in improving the surface quality because it can produce more collision numbers and raise grit retention. In words, the collision number can be used to predict the dressing effect, which provides a reference for formulating an appropriate dressing process for V-CBN to improve the workpiece surface quality and production efficiency.     

Effects of Al2O3 addition on sintering behaviour,microstructure, and physical properties of Al2O3/vitrified bond CBN composite

The effects of Al₂O₃ content on the sintering behaviour, microstructure, and physical properties of Al₂O₃/vitrified bonds (SiO₂–Al₂O₃–B₂O₃–BaO–Na₂O–Li₂O–ZnO–MgO) and Al₂O₃/vitrified bond cubic boron nitride (CBN) composites were systematically investigated using X-ray diffraction, differential scanning calorimetry, dilatometry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Various amounts of Al₂O₃ promoted the formation of BaAl₂Si₂O₈ and γ-LiAlSi₂O₆, increasing the relative crystallinity of the Al₂O₃/vitrified composite from 85.0 to 93.2%, resulting in residual compressive stress on BaAl₂Si₂O₈, thereby influencing the thermal behaviour and mechanical properties of the Al₂O₃/vitrified composite. The bulk density, porosity, flexural strength, hardness, and thermal conductivity of 57.5 wt% Al₂O₃ sintered at 950 °C were 3.12 g/cm³, 6.1%, 169 MPa, 90.5 HRC, and 4.17 W/(m·K), respectively. The coefficient of thermal expansion of the bonding material was 3.83 × 10^?6 °C^?1, which was comparable to that of CBN, and the number of N–Al bonds were increased, which boosted the flexural strength of the Al₂O₃/vitrified CBN composite to 81 MPa. The excellent mechanical properties, compact structure, and suitable interfacial bonding state with the CBN grains of the Al₂O₃/vitrified composite make it a promising high-performance bonding material for superhard abrasive tools.     

Fabrication of porous structure vitrified bond diamond grinding wheel via direct ink writing

Porous vitrified bond grinding wheels with complex structure, high porosity, controllable pore size have fundamental application in high efficiency and precision grinding of hard and brittle materials. In this paper, direct ink writing (DIW) is proposed to fabricate three kinds of grinding wheels, including solid structure, triangle structure, and lattice structure. Moreover, the rheological property of ceramic ink with different doses of xanthan gum (XG) solution was investigated to ensure printability, demonstrating 3% XG solution can meet requirements. Additionally, the effect of sintering temperature and pore former (PMMA) contents on size shrinkage rate, morphology, mechanical strength, and porosity et al. were studied. The results indicate that the diamond grinding wheel with 30 vol% PMMA and sintered at 670 °C possess the best comprehensive performance. Besides, grinding performance was evaluated by surface morphology, surface roughness, and material removal rate. Among the DIW-fabricated wheels, triangle structure grinding wheel and lattice structure grinding wheel possess a higher material removal rate than solid structure grinding wheel. Therefore, the porous structure grinding wheels fabricated by DIW present the advantage of controllable porosity, excellent self-sharpening ability, and higher bond strength, which may pave the way for designing a new generation vitrified bond diamond grinding wheel.     

Effect of porosity on the grinding performance of vitrified bond diamond wheels for grinding PCD blades

In this paper, the preparation of nano-AlN modified Na₂O–B₂O₃–SiO₂ vitrified bond diamond tools with various porosities is reported. The effects of porosity on the impact strength and grinding properties of the wheels for grinding PCD blades are also discussed. The results show that the porosity not only affects the impact strength of the wheels but also the grinding properties, such as the grinding efficiency, the self-dressing, the service life and the surface roughness of the work pieces. The optimum porosity for nano-AlN modified Na₂O–B₂O₃–SiO₂ vitrified bond diamond wheels for grinding PCD tools is approximately 40.5 vol%.     

Influence of TiO2 on the physical properties of low-temperature ceramic vitrified bond and mechanical properties of CBN composites

The microstructures and properties of vitrified bond abrasive tools made of CBN grains and advanced vitrified bond systems with different TiO₂ doping amounts were investigated. Based on the experimental observations and analysis, the incorporation of TiO₂ in appropriate amount (4 wt.%) was beneficial to the improvement on flowing ability and thermal expansion property of the vitrified bond systems, and mechanical properties of the CBN composites including bending strength and Rockwell hardness were obviously improved. On the basis of discussion for microstructure, the CBN grains were better covered by vitrified bond and acquired less pores when the content of TiO₂ reached 4 wt.%. These results were related to the role of TiO₂ in the glass network structure which was analyzed by Fourier transform infrared spectroscopy (FTIR).     

Preparation of c-axis textured SiC ceramics by a strong magnetic field of 6 T assisted gel-casting process

C-axis textured SiC ceramics were prepared by a strong magnetic field of 6 T assisted gel-casting and subsequent pressureless sintering. The optimal suspension parameters for gel-casting were determined by analyzing the influences of pH value and dispersant content on the stability and dispersibility of suspensions. The effect of sintering conditions on the texture development and properties of SiC ceramics was discussed. It was found that the increasing sintering temperature or holding time promoted the densification process of SiC ceramics. The c-axis of SiC grain was aligned parallel to the magnetic field by applying a strong magnetic field of 6 T. The degree of texture of SiC ceramics showed a slightly increasing trend with the increase of sintering temperature or holding time. When the samples were sintered at 1950 °C for 4 h or 6 h, the large elongated grains were formed in the samples, leading to the extremely evident anisotropic microstructure on different planes. Textured SiC ceramics exhibited the anisotropic bending strength.     

Variations in structure and properties of vitrified bonds and vitrified diamond composites prepared by sol-gel and melting methods at different sintering temperature

Differences in structure and properties of Na₂O–Al₂O₃–B₂O₃–SiO₂ vitrified bonds and vitrified diamond composites prepared by sol-gel and melting methods were methodically discussed. Results showed that the vitrified bond prepared by sol-gel method contained more [AlO₄] tetrahedron and owned higher bending strength, with the maximum value reaching 137 MPa, 31.73% higher than that prepared by melting method (104 MPa). As the sintered temperature rose, coefficient of thermal expansion of the vitrified bond prepared by sol-gel method increased first and then decreased, acquiring a maximum value of 5.75 × 10⁻⁶ °C ⁻¹ at 720 °C, which was still much lower than the minimum value of vitrified bond prepared by melting method (7.02 × 10⁻⁶ °C ⁻¹). The vitrified diamond composite prepared by sol-gel method possessed lower sintering shrinkage than that prepared by melting method, and could be applicable to the production of grinding tools with high dimensional accuracy. What's more, the maximum bending strength of vitrified diamond composites obtained by sol-gel method was 106 MPa, 24.7% higher than that of vitrified diamond composites prepared by melting method (85 MPa).     

Influence of process conditions on preparation of CBN/Fe-based spherical magnetic abrasive via gas atomization

To meet the demand for high-performance magnetic abrasive particles (MAPs) for finishing of difficult-to-machine materials, CBN/Fe-based spherical composite MAPs were prepared via gas atomization under different process conditions. The effects of nozzle type (single-stage and two-stage), second-stage gas pressure (2, 4, 6, and 8 MPa), and the grain size of the CBN abrasive (W7 and W40) on the MAP quality were studied. The MAPs were analysed through scanning electron microscopy and energy-dispersive spectroscopy. The results indicate that the quality of MAPs prepared using two-stage atomizing nozzles is better than that of MAPs prepared using single-stage nozzles. When the second-stage gas pressure was 6 MPa, the prepared MAPs had the best sphericity, and the CBN abrasive was embedded uniformly and densely on the surface of the iron matrix. For MAPs with the same particle size, the iron matrix wrapped more effectively around CBN abrasives with smaller grain sizes. This research is can serve as a methodological reference for understanding the preparation of ceramic/metal-based spherical composite MAPs via gas atomization.     

磁场对Ni/Al2O3催化剂结构及加氢性能的影响

采用共沉淀法制备了Ni/Al₂O₃加氢催化剂,在制备过程中引入交流电磁场对催化剂做强化制备,通过BET、SEM、XRD和TPR等方法对催化剂做表征,并将该催化剂应用于脂肪酸加氢反应中,考察了磁场强度对催化剂结构及加氢性能的影响。结果表明,制备过程中引入电磁场能够有效降低催化剂颗粒的团聚,增大催化剂的比表面积和平均孔径,提高催化剂的脂肪酸加氢活性。随着磁场强度的增强催化剂还原温度逐渐升高,结构稳定性增强,有效延长了催化剂的使用寿命。     

电场和磁场对催化剂制备过程的影响

综述了近年来电场和磁场在催化剂制备中的影响。从催化剂的成核和长大过程分析了电场和磁场的加入对催化剂形成过程的影响,系统解释了电场和磁场处理与晶粒细化效果、催化活性之间的关系和规律。     

Effect of nano-AlN addition on thermal diffusivity and mechanical strength of porous AL2O3 ceramic composites

In a properly made porous abrasive composite, the vitrified bond should ideally cover the grains and form a continuous network of bridges, and thus part of the heat energy from the grinding process is also transferred to the vitrified bond. Until recently, most studies on the design of composite properties have focused mainly on improving their mechanical strength and wear resistance, but increasingly the very important aspect of their thermal properties is noticed. The vitrified Al₂O₃ composites were made from Al₂O₃ grains, vitrified bond of Na₂OK₂OAl₂OB₂O₃SiO₂ and AlN nanopowder. The increase in porosity in the tested composites is the effect of the AlN decomposition reaction. Crystalline phases were identified in both composites - α-Al₂O₃ and NaAl₁₁O₁₇, but with a different percentage share in individual composites. In composites doped with AlN nanopowder, the proportion of NaAl₁₁O₁₇ crystalline phase decreases, due to its high susceptibility to reduction by Al, obtained from the AlN decomposition reaction. The product of the redox reaction is also Na⁺ ions, which may participate in the formation of the glass phase and thus increasing the fraction of the residual glass phase. As a result of the partial reduction of NaAl₁₁O₁₇ phase, an increase in α-Al₂O₃ content is observed. A higher proportion of α-Al₂O₃ phase with high thermal conductivity can be a factor that increases the rate of heat removal from the work zone.     

添加剂对CBN高速磨削工具用陶瓷结合剂熔融温度的影响

采用正交实验的方法分析了以SiO_2、Al_2O_3+B_2O_3为玻璃形成剂,MgO、P_2O_5、CaCO_3和ZnO四种添加剂对CBN陶瓷结合剂熔融温度的影响,并研究了添加这四种添加剂的陶瓷结合剂在高温下对CBN颗粒的润湿性.同时将其中的三组试样进行熔融、水淬,研究试样水淬前后熔融温度的变化,测定了熔融水淬后试样的物相组成.结果表明:四种添加剂对陶瓷结合剂熔融温度的影响大小为P_2O_5＞MgO＞＞ZnO ＞＞CaCO_3;熔融水淬后的试样化学成分均一,熔融温度降低,熔融试样呈玻璃态.     

添加剂对CBN高速砂轮用低温烧结陶瓷结合剂强度的影响

采用正交实验方法研究了MgO、P2O5、CaCO3、ZnO四种添加剂对陶瓷结合剂强度的影响,通过扫描电镜,分析了添加这四种添加剂的陶瓷结合剂的微观结构.结果表明:四种添加剂对陶瓷结合剂强度的影响从大到小依次是MgO≥ZnO＞ CaCO3≥P2O5;试样随着烧结温度的升高,气孔数量明显增加,形状规则,呈圆形,且气孔表面光滑,分布均匀.     

Rheokinetic study on homogeneous polymer reactions in melt state under strong flow field

A branch reaction of high density polyethylene initiated by Dicumyl peroxide in an internal batch mixer was used to investigate the rheokinetics on homogeneous polymer reactions in melt state under strong flow environment. The effect of shear strength on the reaction process was focused. A real conversion of reaction was put forward from the rheological measurement, i.e., the torque of mixer. A comparison of the reaction conversion from experiment and the chemical kinetic model gave a flow dependent combination rate parameter. A rheokinetic equation was therefore obtained which is in a good accordance with the theoretical prediction by Fredrickson and Leibler [4]. The rheokinetic equation was further verified by a simplified nonisothermal two-dimensional numerical simulation which incorporates macro-convection effect.