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).     

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%.     

Fabrication of New Porous Metal-Bonded Grinding Wheels by Hip Method and Machining Electronic Ceramics

Grinding wheels with different abrasive grains and different bonding materials were fabricated using hot isostatic press (HIP) sintering. Poly-crystal diamond powder of #1000 mesh size, single-crystal diamond powder of #1000 mesh size, and synthetic single-crystal diamond abrasive grains of #325 mesh size were used as abrasive grains. Cast-iron, and two different particle sizes of iron powders were used for the bonding material. The grinding capacity of these grinding wheels as well as conventional grinding wheels was evaluated by constant-pressure-grinding method to grind Al₂O₃-TiC component ceramics, which are typical electronic ceramics used for magnetic memory devices. The hardness of the bonding materials, the adhesion strength between abrasive diamond grains and the bonding materials, and the porosity of sintered body strongly relate to the grinding capacity. The porous bonded grinding wheels showed higher grinding capacity than the conventional wheels. The HIP method enables to fabricate excellent porous metal-bonded grinding wheels.     

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.     

Influence of holding time on the interfacial solid solution and mechanical properties of agglomerated white fused alumina abrasives

In this paper, the aging relationship between holding time and the interfacial solid solution was utilized to prepare high-performance agglomerated white fused alumina (AWA) abrasives. The influence of holding time on the interfacial solid solution and mechanical properties of AWA abrasives were systematically investigated, and the grinding performance was thoroughly analyzed. The results showed that increasing the holding time caused the Al₂O₃ to violently infiltrate the interface between the white fused alumina (WA) particles and the vitrified bond, which led to the precipitation of a large amount of β-spodumene and monoclinic celsian in the vitrified bond and transformed the simple mechanical bonds between the WA particles and the vitrified bond into stronger chemical bonds. Thus, it was possible to control the mechanical properties of the AWA abrasives by adjusting the holding time. Specifically, after sintering at 760 °C for 4h, the single particle compressive strength and impact toughness reached the maximum values of 26 N and 63%, respectively. In comparison with the WA grinding wheel, the grinding ratio of the AWA grinding wheel was increased by 17.9% and the workpiece surface roughness was reduced by 21.1%.     

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.     

金属铝粉和纳米Al2O3粉对陶瓷结合剂性能的影响

将金属铝粉、纳米Al₂O₃粉引入基础陶瓷结合剂,通过红外光谱分析陶瓷结合剂玻璃结构,X射线衍射表征其物相变化,并测试其耐火度,利用扫描电镜分析陶瓷结合剂立方氮化硼(CBN)复合材料的微观结构,并测试抗折强度,系统分析了金属铝粉、纳米Al₂O₃粉的单掺及复掺对陶瓷结合剂性能的影响。结果表明,金属铝粉使陶瓷结合剂耐火度升高,玻璃结构没有明显改变,部分铝粉转变为Al₂O₃,添加金属铝粉的陶瓷结合剂CBN复合材料抗折强度随烧结温度升高而提高。纳米Al₂O₃粉使陶瓷结合剂耐火度降低,呈玻璃相,但有少量Al₂SiO₅晶体和Li_xAl_xSi_3-xO₆晶体析出,添加纳米Al₂O₃粉的陶瓷结合剂CBN复合材料烧结温度720 ℃时出现较高抗折强度,达93.7 MPa。金属铝粉和纳米Al₂O₃粉的复掺有利于玻璃网络结构的键合,陶瓷结合剂以玻璃相为主,也有少量晶体析出,二者复掺对提高陶瓷结合剂CBN复合材料抗折强度更有优势,但烧结温度也相应升高,烧结温度740 ℃时抗折强度达最高值,为97.4 MPa。     

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.     

Investigation on preparation of composite vitrified bonding ultrafine diamond grinding wheel and machining of PcBN inserts

The grinding of polycrystalline cubic boron nitride (PcBN) is hard owing to its high hardness and superior wear-resistance capacity. Machining of PcBN tools via vitrified diamond grinding wheels with a size above 10 μm may lead to brittle fracture instead of a ductile machining because of the poor toughness of cubic boron nitride. A uniformly dispersed M0.5/1.5 diamond grinding wheel with a composite vitrified bonding was fabricated to improve the surface roughness of PcBN inserts. It is demonstrated that the preparation of composite vitrified bonding with various additions of vitrified bonding produced by the melting-quenching technique (VB-MQ) has little effect on the performance of vitrified bonding, such as bending strength, CTE and phase and achieves the uniform dispersion of M0.5/1.5 diamond as the addition of VB-MQ is no greater than 50%. Both the grinding ratios and the surface roughness of PcBN inserts are enhanced.     

Preparation of O′-Sialon-based ceramics by two-stage liquid phase sintering and study on the toughening mechanism of ultrafine-grained sintered clusters

Ultrafine-grained O′-Sialon-based ceramics were prepared by two-stage sintering at 1250 °C, with large particle GH4169 superalloy powder and nano Al₂O₃–Y₂O₃ as composite sintering aids. The effects of these aids on the densification, microstructure, and mechanical properties of O′-Sialon-based ceramics during two-stage sintering were also studied. Studies have shown that the densification process of O′-Sialon-based ceramics promoted by composite sintering additives, presents with the characteristics of two-stage liquid-phase sintering. In the first stage, GH4169 formed ultrafine-grained sintered clusters in the sintered material through liquid phase diffusion. In the second stage, the uniformly dispersed nano Al₂O₃–Y₂O₃ realized the uniform sintering of the material. In the fracture process, the ultrafine-grained sintered clusters hindered the crack propagation and promoted multiple deflections of the crack around the edge of the clusters, achieving the effect of crack deflection toughening. This effect, dominated by ultrafine-grained sintered clusters, significantly improved the fracture toughness of O′-Sialon-based ceramics up to 8.52 MPa m^1/2.     

Microstructural,electrical, and mechanical properties of conductive SiC ceramics fabricated by spark plasma sintering

Nitrogen (N)-doped conductive silicon carbide (SiC) of various electrical resistivity grades can satisfy diverse requirements in engineering applications. To understand the mechanisms that determine the electrical resistivity of N-doped conductive SiC ceramics during the fast spark plasma sintering (SPS) process, SiC ceramics were synthesized using SPS in an N₂ atmosphere with SiC powder and traditional Al₂O₃–Y₂O₃ additive as raw materials at a sintering temperature of 1850–2000°C for 1–10 min. The electrical resistivity was successfully varied over a wide range of 10⁻³–10¹ Ω cm by modifying the sintering conditions. The SPS-SiC ceramics consisted of mainly Y–Al–Si–O–C–N glass phase and N-doped SiC. The Y–Al–Si–O–C–N glass phase decomposed to an Si-rich phase and N-doped Y_xSi_yC_z at 2000°C. The Vickers hardness, elastic modulus, and fracture toughness of the SPS-SiC ceramics varied within the ranges of 14.35–25.12 GPa, 310.97–400.12 GPa, and 2.46–5.39 MPa m^1/2, respectively. The electrical resistivity of the obtained SPS-SiC ceramics was primarily determined by their carrier mobility.     

The structures and dielectric properties of Ba0.80Sr0.20TiO3/Pb0.82La0.18TiO3 composite thick films with addition of PbO–B2O3 glass

Sol–gel derived Ba_0.80Sr_0.20TiO₃ (BST) and Pb_0.82La_0.18TiO₃ (PLT) powders and a low-melting PbO–B₂O₃ glass powder were mixed to prepare paste. The composite thick films (∼40 μm) were fabricated by screen-printing the paste onto the Al₂O₃ substrates with screen-printed silver bottom electrode and then sintered at the low temperature 650–800 °C, respectively. X-ray diffraction (XRD), transmission microscope (TEM), scanning electron microscope (SEM) and an impedance analyzer were used to analyze the structures, microstructures and dielectric properties of the powders and the composite thick films. The results show that the composite thick films containing sol–gel derived Ba_0.80Sr_0.20TiO₃ and Pb_0.82La_0.18TiO₃ perovskite phases have been fabricated by using the PbO–B₂O₃ glass as a sintering aid. Compared to conventional sintering at ≥1200 °C, high densification of the composite thick films is achieved at temperature as low as 800 °C by the “wetting” and “infiltration” of the liquid phase on the particles. The homogenization of the BST and PLT perovskite phase in the composite thick films is evitable by controlling the sintering temperature and time. The formation of the small amount of pyrochlore phase in composite thick films sintered at 800 °C is resulted from both the volatilization of PbO and the interaction between the PLT and PbO–B₂O₃ glass. The relative dielectric properties of the composite thick films exhibit good temperature-stable behavior, and the variation of the relative dielectric constant is less than 10% in the temperature range 0–300 °C.     

Preparation of fully dense and magnetically controllable CaO-Al2O3-SiO2-Na2O-Fe3O4 glass ceramics by hot pressing

Fully dense and magnetically controllable glass ceramics was successfully synthesized by method of hot pressing using CaO-Al₂O₃-SiO₂-Na₂O glass powder and Fe₃O₄ powder as raw materials. The influences of sintering temperature and time, content and particle size of Fe₃O₄, as well as particle size of glass powder on the densification and magnetic properties of samples were investigated. It was found that the saturation magnetization gradually increased with increasing magnetite content. In addition, the samples containing smaller size magnetite particles had a higher coercivity. However, for samples using smaller size glass powder, magnetite particles could partially dissolve into the glass matrix, which led to the decrease of saturation magnetization and the increase of coercivity. It was also concluded that the precipitation of crystalline phase from smaller size glass powder caused the decrease of degree of densification, and after decreasing the sintering temperature, the degree of densification of product was enhanced.     

微波烧结陶瓷结合剂金刚石砂轮研究

为了提高陶瓷结合剂金刚石砂轮的性能,采用微波烧结技术,通过一系列试验,分析了陶瓷结合剂金刚石砂轮的微波烧结温度、陶瓷结合剂含量和金刚石磨料粒度对其性能的影响。结果表明:微波烧结温度是影响陶瓷结合剂金刚石砂轮性能的最主要因素,远超其余二者;陶瓷结合剂金刚石砂轮试样的洛氏硬度和抗弯强度在740 ℃时达到极大值且气孔率较小,此时洛氏硬度为66 HRB,抗弯强度为76.5 MPa,气孔率为17.8%;由微观组织观察可知陶瓷结合剂金刚石砂轮在740 ℃时可以实现陶瓷结合剂对金刚石磨料的均匀包裹,并且气孔较少。     

The role of K2O on sintering and crystallization of glass powder compacts in the Li2O–K2O–Al2O3–SiO2 system

The effects of K₂O content on sintering and crystallization of glass powder compacts in the Li₂O–K₂O–Al₂O₃–SiO₂ system were investigated. Glasses featuring SiO₂/Li₂O molar ratios of 2.69–3.13, far beyond the lithium disilicate (LD-Li₂Si₂O₅) stoichiometry, were produced by conventional melt-quenching technique. The sintering and crystallization behaviour of glass powders was explored using hot stage microscopy (HSM), scanning electron microscopy (SEM), differential thermal (DTA) and X-ray diffraction (XRD) analyses. Increasing K₂O content at the expense of SiO₂ was shown to lower the temperature of maximum shrinkage, eventually resulting in early densification of the glass-powder compacts. Lithium metasilicate was the main crystalline phase formed upon heat treating the glass powders with higher amounts of K₂O. In contrast, lithium disilicate predominantly crystallized from the compositions with lower K₂O contents resulting in strong glass–ceramics with high chemical and electrical resistance. The total content of K₂O should be kept below 4.63 mol% for obtaining LD-based glass–ceramics.     

Mechanical properties of nano-grain SiO2 glass prepared by spark plasma sintering

Silicon carbide (SiC) layers were deposited on silica (SiO₂) glass powder by rotary chemical vapor deposition (RCVD) to form SiO₂ glass (core)/SiC (shell) powder; this powder was consolidated by spark plasma sintering (SPS). SiO₂ glass powder with a particle size of 250 nm was coated with 5–10-nm-thick SiC layers. The resultant SiO₂ glass (core)/SiC (shell) powder was consolidated to form a nano-grain SiO₂ glass composite at a relative density above 90% by SPS in the sintering temperature range of 1573–1823 K. The Vickers hardness and fracture toughness of the SiO₂ glass composite at 1723 K were found to be 14.2 GPa and 5.4 MPa m^1/2, respectively.     

Increasing the quality of diamond wheels for manual grinding of commercial and art glass

It was shown that use of AS32–AS50 diamond powders (instead of AS6–AS15 powders) combined with a new metal bond with hardness of HB 75–85 (in comparison to M2-01 binder) allows prolonging the lifetime of wheels by 1.5–2 times in grinding articles made of commercial and art glass, reducing the specific diamond consumption, and increasing the cutability of the instrument.     

Enhancement of photoluminescence intensity of sintered CaAlSiN3:Eu2+ red phosphor-bismuthate glass composites

Wavelength converters in white light-emitting diodes are usually made by sintering of phosphor-glass powder compacts. An issue is that the sintering process usually results in the reduction of phosphor amount. In the present study, composites containing CaAlSiN₃:Eu²⁺ red phosphor and Bi₂O₃-B₂O₃-ZnO-Sb₂O₅ glass were fabricated by sintering method. Influences of CaAlSiN₃:Eu²⁺ phosphor content (10 vol%–30 vol%) and sintering temperature (410–430°C) on the residual amount of the phosphor phase and the resulting luminescence intensity of the composites were investigated. The change of CaAlSiN₃:Eu²⁺ content due to sintering was analyzed by X-ray diffraction. The interdiffusion between the CaAlSiN₃:Eu²⁺ and glass matrix was examine by scanning electron microscope equipped with energy dispersive X-ray spectrometry. This paper focuses on the change of luminescence intensity after sintering. It was found that although the content of phosphor CaAlSiN₃:Eu²⁺ reduces after sintering; the luminescent intensity of the composites anomalously increases. The optimum luminescence intensity is 14% higher than that of the as-mixed, unfired powder. It is proposed that the incorporation of Bi³⁺ ions from the glass matrix into the phosphor CaAlSiN₃:Eu²⁺ during sintering improves the luminescence ability of the phosphor particles.     

Permalloy/alumina soft magnetic composite compacts obtained by reaction of Al-permalloy with Fe2O3 nanoparticles upon spark plasma sintering

Composite sintered soft magnetic materials of permalloy/alumina type have been obtained by reactive spark plasma sintering. The composite compacts have been obtained by sintering of Ni71.25Fe23.75Al5 alloy with 3 and 5% (wt.) Fe₂O₃ nanoparticles. The Ni based alloy with large particles (up to hundreds of μm) have been covered by a thin layer of iron ferric oxide nanoparticles (20–40 nm). The as obtained composite particles have been subjected to sintering process using a homemade installation at 900 °C for 10 min. Upon sintering process several reactions between Ni-based alloy and iron oxide are induced, the main phase resulting from reaction is alumina-Al₂O₃ as it results by X-ray diffraction investigations. According to the scanning electron microscopy and energy dispersive X-ray spectroscopy investigations, alumina forms a matrix embedding the Ni-based particles. The alumina matrix is continuous, but the layer has large variation in width, and offers a high electrical resistivity. A mechanism of formation is proposed for the alumina matrix composite compacts when using Al-permalloy powder and iron oxide. The compacts have been tested in DC and AC for magnetic characteristics.