Preparation and characterization of Si3N4-based composite ceramic tool materials by microwave sintering

Si₃N₄-based composite ceramic tool materials with (W,Ti)C as particle reinforced phase were fabricated by microwave sintering. The effects of the fraction of (W,Ti)C and sintering temperature on the mechanical properties, phase transformation and microstructure of Si₃N₄-based ceramics were investigated. The frictional characteristics of the microwave sintered Si₃N₄-based ceramics were also studied. The results showed that the (W,Ti)C would hinder the densification and phase transformation of Si₃N₄ ceramics, while it enhanced the aspect-ratio of β-Si₃N₄ which promoted the mechanical properties. The Si₃N₄-based composite ceramics reinforced by 15 wt% (W,Ti)C sintered at 1600 °C for 10 min by microwave sintering exhibited the optimum mechanical properties. Its relative density, Vickers hardness and fracture toughness were 95.73 ± 0.21%, 15.92 ± 0.09 GPa and 7.01 ± 0.14 MPa m^1/2, respectively. Compared to the monolithic Si₃N₄ ceramics by microwave sintering, the sintering temperature decreased 100 °C,the Vickers hardness and fracture toughness were enhanced by 6.7% and 8.9%, respectively. The friction coefficient and wear rate of the Si₃N₄/(W,Ti)C sliding against the bearing steel increased initially and then decreased with the increase of the mass fraction of (W,Ti)C., and the friction coefficient and wear rate reached the minimum value while the fraction of (W,Ti)C was 15 wt%.     

The cutting performance of Al2O3 and Si3N4 ceramic cutting tools in the milling plywood

ABSTRACT

This research focuses on the cutting performance of Al₂O₃ and Si₃N₄ ceramic cutting tools in up-milling plywood, the results of which are as follows. First, whether the tool material is Al₂O₃ or Si₃N₄ ceramic, the cutting forces at low-speed cutting were less than those at high-speed cutting, and the machining quality at low-speed cutting was greater than that at high-speed cutting. Then, whether at low- or high-speed cutting, the cutting forces of Al₂O₃ cutting tools were higher than those of Si₃N₄ cutting tools, and the machining quality of plywood milled by Al₂O₃ ceramic cutting tools was poorer than that milled by Si₃N₄ ceramic cutting tools. Finally, Si₃N₄ ceramic cutting tools were more suitable to machine the wooden productions with much glue content than Al₂O₃ ceramic cutting tools for the better machined quality.     

Effects of fine grains and sintering additives on stereolithography additive manufactured Al2O3 ceramic

Al₂O₃ ceramics are fabricated by stereolithography based additive manufacturing in present reports. To improve the densification and performance of Al₂O₃ ceramic, the introduction of fine grains or sintering additives has been studied by traditional fabrication techniques. However, no research has focused on the effects of adding fine grains and sintering additives on the stereolithography additive manufactured Al₂O₃ ceramic. In this study, both fine grains and sintering additives were added firstly, and then the effects of fine grains and sintering additives on the relative density, microstructure, mechanical properties, and physical properties of the stereolithography additive manufactured Al₂O₃ ceramics were investigated. Finally, defect-free Al₂O₃ ceramic lattice structures with high precise and high compressive strength were manufactured.     

Degradation evaluation of Si3N4 ceramic surface layer in contact with molten Al using microcantilever beam specimens

Although Si₃N₄ ceramics are often utilized as structural components in the Al casting industry due to their excellent properties, they occasionally suffer breakage after long-term use. In this study, the bending strength, fracture toughness, and Young’s modulus in the vicinity of the Si₃N₄ ceramic surfaces after contact with molten Al were evaluated using microcantilever beam specimens, which were fabricated using a focused ion beam technique. Fracture testing of the specimens was carried out by nanoindentation. The bending strength of the ceramic surface before and after contact with molten Al was 5.89 ± 1.33 and 3.03 ± 0.28 GPa, respectively. The fracture toughness of the corroded layer in Si₃N₄ ceramics also decreased compared to that of the polished surface. Using fractography by observation with scanning electron microscopy, it was shown that changes in the grain boundary glassy phase resulted in the degradation of strength and fracture toughness.     

Friction and wear properties of Si3N4-hBN ceramic composites using different synthetic lubricants

This paper presents a tribological investigation of Si₃N₄-hBN composite ceramics using synthetic lubricants. The friction and wear properties of Si₃N₄-hBN ceramic composites sliding against TC4 titanium alloy (Ti6Al4V) were investigated via pin-on-disc tests. An axial compressive load of 10?N was applied with a sliding speed of 0.73?m/s. Three different lubrication conditions including simulated body fluid (SBF), physiological saline (PS) and bovine serum (BS) were used. For SBF lubrication, the friction coefficients and wear rates of Si₃N₄-hBN/Ti6Al4V pairs were varying with the increase of hBN contents. When using 20?vol% hBN, the average friction coefficient and wear rate of Si₃N₄ (0.28 and 3.5?× 10^?4 mm³ N^?1 m^?1) were as good as that of the pure Si₃N₄ (0.34 and 3.69?× 10^?4 mm³ N^?1 m^?1). Meanwhile, the processability of the Si₃N₄ material would be improved by adding hBN. It was worth to mention that when using 30?vol% hBN, the tribological performance of bearing combination deteriorated with extensive wear from the ceramic pin. This may due to the reduction of mechanical property caused by adding hBN and the occurring of tribochemical reaction. According to the worn surface examination and characterization, the main wear mechanism was abrasive and adhesion wear. Scratch grooves were observed on the metal disc, and metallic transform layers were seen on the ceramic pin. Moreover, surface lubrication film consisting of TiO₂, SiO₂·nH₂O, Mg(OH)₂, and H₃BO₃ were formed on the metal disc when using SBF lubrication and 20?vol% hBN content. Among the three lubrication conditions, SBF generally led to the best tribological performance. No surface lubrication film was found during BS and PS lubrications. This may be resulted from the absence of essential ions to promote the formation of surface lubrication film (PS lubrication) and the formation of a protein barrier on the surface of the metal disc (BS lubrication).     

Effects of AlN inorganic binder on the properties of porous Si3N4 ceramics prepared by selective laser sintering

Porous Si₃N₄ ceramics are widely used in the aerospace field due to its lightweight, high-strength, and high wave transmission. Traditional manufacturing methods are difficult to fabricate complex structural and functional ceramic parts. In this paper, selective laser sintering (SLS) technology was applied to prepare porous Si₃N₄ ceramics using AlN as an inorganic binder. And the effects of AlN content on the properties of the obtained ceramic samples were explored. As the AlN content increased, nano-Al₂O₃ and nano-SiO₂ formed the eutectic liquid phase, enhancing the sintering densification and phase transformation of Si₃N₄ poly-hollow microspheres (PHMs). The island-like partial densification structures in Si₃N₄ green bodies increased. During the high-temperature sintering, the eutectic liquid phase partially transformed into the mullite phase or reacted with AlN and Si₃N₄ to form the Sialon phase. With the increase of AlN content, the fracture mode of Si₃N₄ ceramics changed from fracturing along PHMs to fracturing across PHMs. The bonding depth between PHMs increased and the connection between the grains was tighter, so the Si₃N₄ ceramics became denser. With the increase of AlN addition, the total porosity of the porous Si₃N₄ ceramics tended to decrease and the flexural strength gradually increased. When AlN content was 20 wt%, the total porosity and the flexural strength were 33.6% and 23.9 MPa, respectively. The addition of AlN inorganic binder was carried out to develop a novel way to prepare high-performance porous Si₃N₄ ceramics by SLS.     

Reliability prediction of a microwave sintered Si3N4-based composite ceramic tool

The wear life reliability prediction model of microwave sintered Si₃N₄/(W,Ti)C/Y₂O₃/MgO/Al₂O₃ composite ceramic tools based on the random distribution characteristics of hardness and fracture toughness of ceramic tool material was established. It showed that the Vickers hardness of ceramic tool materials followed a normal distribution and the fracture toughness followed a lognormal distribution. Distribution law of wear life can be determined by the joint distribution of hardness and fracture toughness. Experimental research on tool reliability of continuous dry cutting quenched high quality carbon steel T10A was carried out and the applicability of the tool reliability prediction model was verified. The results showed that the error between the theoretical reliable life and the actual life of the ceramic tool was less than 5% under the same reliability when the reliability was above 0.5.     

Tribological behavior of ceramic materials (Si3N4, SiC and Al2O3) in aqueous medium

The friction and wear behavior of self-mated Si₃N₄, SiC and Al₂O₃ in water were investigated by varying the test conditions of applied load and sliding speed. It was found that, for self-mated Si₃N₄ and SiC ceramics, the tribochemical reaction resulted in surface smoothening with low friction coefficient at high load and high speed condition. Al₂O₃ shows high friction coefficient, but better wear rate (10⁻¹¹ mm²/N) than other ceramic materials.     

Feasibility of SiAlON–Si3N4 composite ceramic as a potential bone repairing material

In this study, SiAlON–Si₃N₄ composite ceramic are prepared by direct nitridation and investigated to overcome the limitations associated with ceramic Si₃N₄, which includes the difficulty in fabricating ceramic Si₃N₄ into shaped parts for use in the human body. Phase composition and microstructure of the SiAlON–Si₃N₄ composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, and the porosity, bulk density, compressive strength, and ion release were also measured. The biological properties were evaluated by bone cell cultures on the ceramic surfaces. Results show that Si₄Al₂O₂N₆ is formed by the reaction of Al, Si, and Al₂O₃ with nitrogen at high temperature that forms Si₃N₄, thereby fabricating SiAlON–Si₃N₄ composite ceramics. Some α-Si₃N₄ grains underwent a phase transition from α-to β-Si₃N₄ fiber at high temperature. Porosity of the samples increases with increasing Si₃N₄ content, while the bulk density of the samples decreases. The compressive strength increases and then slightly decreases with increasing Si₃N₄ content. Water leaching experiments of the SiAlON–Si₃N₄ composite ceramics reveal that the composites exhibit outstanding chemical stability. Studies using bone cell culture indicate that the cells present a fusiform and extend two or three thin pseudopodia. The phenomena demonstrate that MC3T3-E1 cells have excellent growth activity and have the potential ability to proliferate to osteocytes on the surfaces of the samples, thus suggesting that SiAlON–Si₃N₄ based ceramics are biocompatible and could be implemented as a potential bone-repairing material.     

Influence of laser surface texturing on the flexural strength of Al2O3 and Si3N4

Laser surface texturing (LST) is well known to be capable of improving the tribological performance and reducing the friction of ceramic surfaces. However, the influence of LST on the flexural strength of ceramics has rarely been researched.In this study, we examine the influence of LST on high purity (> 99.5 wt%) dense-sintered fine Al₂O₃ and hot-pressed fine Si₃N₄ with polished and laser-textured surfaces based on the biaxial ball-on-3-balls (B3B) test. A heat transfer simulation of the LST process is performed to understand the occurrence of residual stress. In addition, the B3B strength of Al₂O₃ and Si₃N₄ texture groups is calculated by adapting the previous formula based on the finite element (FE) simulation. Subsequently, the stress distribution in the FE simulation is used to calculate the effective volume and effective surface to study the size effect on both ceramics. It is found that LST improves the strength of Al₂O₃ and Si₃N₄ due to two reasons: it induces compressive residual stress on the tensile-loaded surface of ceramic specimens; more importantly, it reduces the effective volume and effective surface remarkably, thus improving the component strength significantly.     

Synergistic effect of surface textures and DLC coatings for enhancing friction and wear performances of Si3N4/TiC ceramic

To enhance the tribological properties of Si₃N₄ based ceramics, surface textures of dimples combined with DLC coatings are fabricated on Si₃N₄/TiC ceramic surface by nanosecond laser and plasma enhanced chemical vapor deposition (PECVD). The dry friction and wear performances are evaluated by unidirectional sliding friction tests using a rotary ball-on-disk tribometer. Results reveal that the friction and wear properties of Si₃N₄/TiC ceramics are significantly enhanced by DLC coatings or dimpled textures, and the DLC coatings combined with dimpled textures show the best efficiency in reducing friction, adhesion and wear. This improvement can be explained by the synergistic effect of DLC coatings and surface textures, and the synergistic mechanisms are attributed to the formation of lubrication film and secondary lubrication, debris capture of dimpled textures, increased surface hardness and mechanical interlocking effect, and reduced contact area.     

Temperature-driven wear behavior of Si3N4-based ceramic reinforced by in situ formed TiC0.3N0.7 particles

Si₃N₄ as a structural ceramic is desirable for applications in spacecraft, transportation, and energy, but its poor high-temperature properties still do not satisfy the actual requirements. Here, a TiC_0.3N_0.7 reinforced Si₃N₄ ceramic is successfully designed and fabricated via the high-temperature nitridation of TiC_x. It is found that TiC_0.3N_0.7 grains with the size of 1-2 μm are uniformly dispersed in the Si₃N₄ matrix and show a firm bond with substrate. Compared with pure Si₃N₄, the doping of harder TiCN phase can effectively improve ceramic's hardness and fracture toughness at a certain temperature. Importantly, the ceramic material displays extraordinary wear resistance across a wide temperature range (eg, the wear rate of TiC_0.3N_0.7 containing Si₃N₄ over 63 times and 178 times better than pure Si₃N₄ at 600 and 900°C, respectively). More broadly, a correlation between wear mechanism and temperature is established, and the result shows that the mechanical strength and tribochemical oxidation as two key factors determine the wear behavior of the material. These results developed here can provide a springboard for preparation and optimization of multiphase ceramics that serve under high-temperature conditions.     

Effect of MgO/Al2O3 ratio on the crystallization behaviour of Li2O–MgO–Al2O3–SiO2 glass-ceramic and its wettability on Si3N4 ceramic

The composition governs the crystallization ability, the type and content of crystal phases of glass-ceramics. Glass-ceramic joining materials have generated more research interest in recent years. Here, we prepared a novel Li₂O–MgO–Al₂O₃–SiO₂ glass-ceramic for the application of joining Si₃N₄ ceramics. We investigated the influence of the MgO/Al₂O₃ composition ratio on microstructure and crystallization behaviour. The crystallization kinetics demonstrated that the glasses had excellent crystallization ability and high crystallinity. β-LiAlSi₂O₆ and Mg₂SiO₄ were precipitated from the glass-ceramics, and the increase of MgO concentration was conducive to the precipitation of Mg₂SiO₄. Among the glass-ceramic samples, the thermal expansion coefficient of LMAS2 glass-ceramic was 3.1 × 10^?6/°C, which was very close to that of Si₃N₄ ceramics. The wetting test showed that the final contact angle of the glass droplet on the Si₃N₄ ceramic surface was 32° and the interface was well bonded.     

Additive manufacturing of silicon nitride ceramics: A review of advances and perspectives

Silicon nitride (Si₃N₄) ceramic has been widely applied in various engineering fields. The emergence of additive manufacturing (AM) technologies provides an innovative approach for the fabrication of complex-shaped Si₃N₄ ceramic components. This article systematically reviews the advances of the AM of Si₃N₄ ceramic in recent years and forecasts the potential perspectives in this field. This review aims to motivate future research and development for the AM of Si₃N₄ ceramic.     

Dielectric and mechanical properties of porous Si3N4 ceramics prepared via low temperature sintering

Borophosphosilicate bonded porous silicon nitride (Si₃N₄) ceramics were fabricated in air using a conventional ceramic process. The porous Si₃N₄ ceramics sintered at 1000–1200 °C shows a relatively high flexural strength and good dielectric properties. The influence of the sintering temperature and contents of additives on the flexural strength and dielectric properties of porous Si₃N₄ ceramics were investigated. Porous Si₃N₄ ceramics with a porosity of 30–55%, flexural strength of 40–130 MPa, as well as low dielectric constant of 3.5–4.6 were obtained.     

Effect of Si3N4 mesophase on the formation of Al2OC-AlNss in resin-bonded Al–Al2O3 composites

In this study, we developed a novel method for synthesising Al₂OC-AlNss using a solid nitrogen source: a Si₃N₄ mesophase. The two-step sintered Al–Al₂O₃ and Si₃N₄–Al–Al₂O₃ samples were prepared under an atmosphere of nitrogen to investigate the effect of Si₃N₄ on the formation of Al₂OC-AlNss in resin-bonded Al–Al₂O₃ composites. The samples were investigated via XRD and SEM. The results indicated that the synthesis of Al₂OC-AlNss with different morphologies was achieved via the Si₃N₄ mesophase, and its morphology was influenced by the source of AlN. Both Al₂OC-AlNss and Al₄O₄C were formed in the two-step sintered Al–Al₂O₃ sample, whereas only Al₂OC-AlNss was formed in the two-step sintered Si₃N₄–Al–Al₂O₃ sample. Induced by the AlN formed by the nitridation of Al, needle-like Al₂OC-AlNss was generated. Compared to that formed by the nitridation of Al, more AlN nuclei were provided by the reaction between Si₃N₄ and Al. Subsequently, columnar and granular Al₂OC-AlNss were formed. Furthermore, fibre-like Al₂OC-AlNss was also generated via the VS and VLS mechanism. The reaction model was established in this study.     

Influence of cBN content,Al2O3 and Si3N4 additives and their morphology on microstructure,properties, and wear of PCBN with NbN binder

Polycrystalline cubic boron nitride (PCBN) tool materials with NbN binder without additives and PCBN with Al₂O₃ or Si₃N₄ micropowder and whisker additives were manufactured and compared. PCBN materials with Si₃N₄ whisker reinforcement have the best mechanical properties of all the evaluated materials. Composites reinforced with Al₂O₃ whiskers have the lowest fracture toughness. However, Al₂O₃ whisker-reinforced tools outperform both commercial and Si₃N₄ reinforced tools when machining hardened steel. Thus Al₂O₃ whisker-reinforced PCBN materials are promising for industrial applications, likely due to their higher resistance to oxidation and diffusional wear mechanisms during cutting operations.     

Fabrication strategy of complicated Al2O3-Si3N4 functionally graded materials by stereolithography 3D printing

For multi-ceramic materials based on the stereolithography (SL) principle, a 3D printing strategy was developed, and then an Al₂O₃-Si₃N₄ functionally graded material (FGM) ceramic part was fabricated using this strategy. Six groups of mixtures, with a Si₃N₄ content gradient of 20 vol% and a certain bimodal particle size distribution, were prepared using UV-curable pastes. A modified formula was proposed to evaluate the relationship between the actual minimum voidage of mixtures and the viscosities of their corresponding pastes. The viscosity of each paste was controlled using the prediction formula and optimization of dispersants. To design theprinting layer thickness, a mathematical relationship was established between Si₃N₄ content and curing depth of paste. The Al₂O₃-Si₃N₄ green body without deformation was printed using optimized parameters such as a layer thickness of 40 μm and a paste viscosity of ∼13,000 mPa·s. Finally, using debinding and sintering, denseparts having a complicated shape were obtained.     

Low-temperature densification by plasma activated sintering of Mg2Si-added Si3N4

In this study, highly dense Si₃N₄ ceramics with excellent mechanical properties were fabricated using Mg₂Si as a sintering additive by plasma-activated sintering at 1400–1500 °C. The effects of the sintering temperature and content of Mg₂Si on the densification, microstructures, and mechanical properties of the Si₃N₄ ceramics were investigated. The mechanism responsible for the effect of Mg₂Si in the promotion of the sinterability of Si₃N₄ is discussed. The results showed that the addition of Mg₂Si could effectively remove the oxide layers on the Si₃N₄ particles and form a liquid phase during the sintering, promoting the densification and phase transition of the Si₃N₄ ceramics. The Si₃N₄ ceramic sintered at 1450 °C with 6.0 wt% of Mg₂Si exhibited the maximum strength of 1050 MPa.     

Fabrication and joining mechanism of Nano-Cu/Si3N4 ceramic substrates

A novel method for fabricating a nano-Cu/Si₃N₄ ceramic substrate is proposed. The nano-Cu/Si₃N₄ ceramic substrate is first fabricated using spark plasma sintering (SPS) with the addition of nanoscale multilayer films (Ti/TiN/Ti/TiN/Ti) as transition layers. The microstructures of the nano-Cu metal layer and the interface between Cu and Si₃N₄ are investigated. The results show that a higher SPS temperature increases the grain size of the nano-Cu metal layer and affects the hardness. The microstructure of the transition layer evolves significantly after SPS. Ti in the transition layer can react with Si₃N₄ and with nano-Cu to form interfacial reaction layers of TiN and Ti–Cu, respectively; these ensure stronger bonding between nano-Cu and Si₃N₄. Higher SPS temperatures improve the diffusion ability of Ti and Cu, inducing the formation of Ti₃Cu₃O compounds in the nano-Cu metal layer and Ti₂Cu in the transition layer. This study provides an important strategy for designing and constructing a new type of ceramic substrate.