Microstructure,mechanical properties and toughening mechanisms of graphene reinforced Al2O3-WC-TiC composite ceramic tool material

The low fracture toughness of Al₂O₃-based ceramics limited their practical application in cutting tools. In this work, graphene was chosen to reinforce Al₂O₃-WC-TiC composite ceramic tool materials by hot pressing. Microstructure, mechanical properties and toughening mechanisms of the composite ceramic tool materials were investigated. The results indicated that the more refined and denser composite microstructures were obtained with the introduction of graphene. The optimal flexural strength, Vickers hardness, indentation fracture toughness were 646.31?±?20.78?MPa, 24.64?±?0.42?GPa, 9.42?±?0.40?MPa?m^1/2, respectively, at 0.5?vol% of graphene content, which were significantly improved compared to ceramic tool material without graphene. The main toughening mechanisms originated from weak interfaces induced by graphene, and rugged fractured surface, grain refinement, graphene pull-out, crack deflection, crack bridging, micro-crack and surface peeling were responsible for the increase of fracture toughness values.     

Ultrasonic-assisted preparation of complex-shaped ceramic cutting tools by microwave sintering

Complex-shaped ceramic tools were prepared by ultrasonic-assisted molding technology and microwave sintering. A uniaxial ultrasonic vibration compaction system was designed. The effects of ultrasonic vibration and molding pressures on mechanical properties and microstructures of A₂O₃ and Al₂O₃/SiC complex-shaped milling cutters were investigated by simulations and experiments. The results indicated that the density was distributed unevenly within the green ceramic tool samples, especially poor in the tool edges. These drawbacks were well improved by ultrasonic-assisted molding technology and microwave sintering. Applying ultrasonic vibration during the compaction process of green ceramic tool samples could improve the densification, hardness and reduce the randomness of mechanical properties of the sintered ceramic tool materials, especially for the difficult-to-sinter composite ceramics (with poor density). For A₂O₃ ceramic tool, fully dense microstructure was achieved, and for Al₂O₃/SiC ceramic tool, the cutting edges showed better density than that of the interior body, which was beneficial to improve the abrasion resistance of cutting tool.     

Controllable synthesis of SiC@Graphene core-shell nanoparticles via fluidized bed chemical vapor deposition

SiC@Graphene (SiC@G) core-shell nanoparticles were successfully prepared by a facile fluidized bed (FB) chemical vapor deposition (CVD) method. SiC@G core-shell nanoparticles with an average size of 10 nm and graphene from 1 to 5 layers with a controllable thickness were obtained by finely adjusting the experimental temperatures. The formation of SiC nanoparticles and graphene layers was confirmed by the results of X-ray diffraction (XRD) and Raman Spectroscopy. The graphene content in SiC@G core-shell nanoparticles prepared at different temperatures was measured from thermogravimetric analysis (TG), which varied from 5.89% to 11.88 mass%. From X-ray photoelectron spectroscopy (XPS) results, no absorption assigned to Si-O band was detected, indicating the effective protection of the SiC nanoparticles against oxidation by the graphene shell to resist oxidation of SiC nanoparticles. This novel method of preparation of SiC@G core-shell nanoparticles could be applied to large-scale production and find diverse applications in related fields.     

Friction and wear behavior of microwave sintered Al2O3/TiC/GPLs ceramic sliding against bearing steel and their cutting performance in dry turning of hardened steel

An Al₂O₃/TiC/GPLs (ATG) composite ceramic tool material was fabricated by microwave sintering. The tribological properties of ATG during sliding against GCr15 bearing steel were studied, to investigate the effects of sliding speed and normal load on the friction coefficient and wear rate. In addition, the cutting performance of ATG tools for machining of hardened alloy 40Cr steel was experimentally studied and compared with those of commercial tools. The results showed that the added graphene platelets enhanced the wear resistance and reduced the friction coefficient of the tool material. Furthermore, upon adding graphene platelets, the ability of the tools to resist breakage and their cutting depth improved. The cutting length of the microwave- sintered ATG ceramic tools was approximately 125% higher than that of hot-pressed ceramic tools and 174% higher than that of cemented carbide tools.     

Cutting performance and wear mechanisms of the graphene-reinforced Al2O3-WC-TiC composite ceramic tool in turning hardened 40Cr steel

The Al₂O₃-WC-TiC-graphene composite ceramic tool (AWTG0.5) fabricated by two-step hot pressing was used to continuously turn the hardened 40Cr steel at different cutting speeds, and its cutting performance and wear mechanisms were compared with the homemade graphene-free AWTG0 ceramic tool and the commercial ceramic tools SG4 and LT55. The cutting performance of the AWTG0.5 tool was significantly better than that of the AWTG0, SG4 and LT55 tools. The contributions of graphene to the mechanical properties, lubricating properties and thermal conductivity of the AWTG0.5 tool were responsible for its higher cutting performance. The main wear mechanisms of the AWTG0.5 tool were adhesive wear and abrasive wear. In addition, it was also found that the anti-friction and wear resistance performances of the AWTG0.5 tool were superior to those of the other three tools. Its good anti-friction and wear resistance performances could be attributed to the formation of a self-lubricating layer induced by graphene pull-out.     

Preparation and performance of an advanced multiphase composite ceramic material

According to the optimum composition achieved from the material design, an advanced 15 vol.% SiC and 15 vol.% Ti(C,N) containing alumina-based multiphase ceramic material with good comprehensive mechanical properties has been fabricated with hot pressing technique. Only under suitable hot pressing conditions and material compositions can better microstructures and mechanical properties be achieved. The optimum hot pressing parameters for the SiC/Ti(C,N)/Al₂O₃ material are as follows: the hot pressing temperature is 1780 °C, the time duration equals to 60 min and the pressure remains 35 MPa. The content of each dispersed SiC and Ti(C,N) phase has significant effects not only on the mechanical properties but on the engineering performances of the ceramic materials. Good wear resistance is found for the kind of ceramic material when used as cutting tools in the machining of the hardened carbon steel. Failure mechanisms are mainly the abrasive wear and the adhesive wear. The developed SiC/Ti(C,N)/Al₂O₃ multiphase ceramic material will be well used as the structural parts with the requirement of high wear resistance such as cutting tools.     

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.     

An advanced self-lubricating ceramic composite with the addition of core-shell structured CaF2@Al2O3 powders

Aiming to improve the performance of self-lubricating ceramic tools, an advanced self-lubricating ceramic composite was developed. Core-shell structure CaF₂@Al₂O₃ powders were synthesized by liquid-phase non-uniform nucleation method. Al₂O₃/Ti(C,N)/CaF₂@Al₂O₃ composite made by adding CaF₂@Al₂O₃ powders exhibited notable improvements in microstructure and mechanical properties as compared with Al₂O₃/Ti(C,N)/CaF₂ composite made by adding uncoated CaF₂ powders. The core-shell coated self-lubricating ceramic tool with different content of CaF₂@Al₂O₃ was designed and prepared by hot pressing sintering process. The results show that when the content of CaF₂@Al₂O₃ is 10 vol%, The composite has the best mechanical properties, the flexural strength, and the fracture toughness and the hardness is 680 MPa, 6.50 MPa·m^1/2, and 17.29 GPa. Compared with the tool material with only CaF₂ solid lubricant added, the above performances were increased by 8.91%, 29.48%, and 14.50% respectively. The influence of different CaF₂@Al₂O₃ content on the physical and mechanical properties and microstructure of the tool material was analyzed.     

Enhanced electromagnetic wave absorption properties of a novel SiC nanowires reinforced SiO2/3Al2O3·2SiO2 porous ceramic

To realize the broad-bandwidth and high-efficiency absorption characteristics, a novel SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ porous ceramic was successfully fabricated by method of precursor infiltration pyrolysis (PIP). Polycarbosilane (PCS) and ferrocene (Fe(C₅H₅)₂) were used as the precursor and catalyst to incorporate SiC nanowires into the SiO₂/3Al₂O₃·2SiO₂ porous ceramic. The curvy SiC nanowires formed three-dimensional (3D) networks with a proper nanometer heterostructure, thereby consuming the microwave energies. The influence of SiC nanowires contents on the microwave absorption properties was investigated. The results indicate that the SiC nanowires contents can be tuned by controlling the PIP cycles, thereby modifying the dielectric properties of as-prepared composite ceramics. The dielectric and electromagnetic wave absorption performances are gradually enhanced with an increasing of SiC nanowires contents. The SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramic exhibits excellent electromagnetic wave absorption abilities when the SiC nanowires content is 23.9% (PIP5). The minimum reflection coefficient (RC_min) of the composite ceramic is −30 dB at 10.0 GHz, corresponding to more than 99.9% of the electromagnetic wave consumption. The effective absorption bandwidth (EAB) can cover the frequency ranges of 8.2–12.4 GHz (the entire X-band) at the thickness of 5.0 mm. In general, the novel SiC nanowires reinforced SiO₂/3Al₂O₃·2SiO₂ composite ceramic can be considered as a promising electromagnetic wave absorbing material.     

Performance of lightweight coated oxide ceramic composites for industrial high speed wood cutting tools: A step closer to market

The introduction of lightweight cutting tips in industrial wood machining could lead to machining at much higher speeds and thus greatly increase efficiency. One possible way to achieve this is through lightweight ceramic composites. An Al₂O₃ ceramic matrix was selected and reinforced with particles resulting in a density of approximately one quarter of the currently used heavy tungsten carbide tools (density of >15 g/cm³). Furthermore, a coating was applied to the ceramic cutting tools in order to increase the stability of the cutting edge. A combination of reduced coefficient of friction, frictional forces and a resulting decrease in temperature can lead to a reduction in chipping at the cutting tip. Chipping has always been the major drawback of ceramic cutting tools for industrial wood cutting. A ceramic composite containing 25 vol% of submicron and nano sized SiC particles shows good mechanical properties with HV₂=21.5 GPa and K_Ic=4.5 MPa m^1/2. This composition performed very well in industrial cutting trials on laminated beech. The cutting performance was increased further by use of an industrially available coating on the tools. The quality of the cut wood surface has always been difficult to characterize when comparing cutting tool materials and is often performed qualitatively by experienced carpenters by touch. The surface quality of the machined laminated beech was for the first time quantitatively characterized using Gelsight 2.5D tactile sensing.     

Composite ceramic materials with SiC fiber

The technology and mechanical characteristics of composite ceramic materials strengthened by discrete and continuous fibers of silicon carbide are described. The introduction of an 8% volume fraction of continuous SiC fibers into cordierite increases its strength by almost a factor of 2. Among composites strengthened by SiC whisker the highest density is exhibited by materials with a matrix of Al₂O₃ - ZrO₂ (580 MPa). Materials with matrices of Al₂O₃ and synthetic mullite have mean ultimate bending strengths of 460 and 420 MPa, respectively. The microstructures of the materials are described.Translated from Ogneupory, No. 8, pp. 3 – 6, August, 1995.     

Pressureless sintering of silicon carbide ceramics containing zirconium diboride

SiC-5 wt.% ZrB₂ composite ceramics with 10 wt.% Al₂O₃ and Y₂O₃ as sintering aids were prepared by presureless liquid-phase sintering at temperature ranging from 1850 to 1950 °C. The effect of sintering temperature on phase composition, sintering behavior, microstructure and mechanical properties of SiC/ZrB₂ ceramic was investigated. Main phases of SiC/ZrB₂ composite ceramics are all 6H-SiC, 4H-SiC, ZrB₂ and YAG. The grain size, densification and mechanical properties of the composite ceramic all increase with the increase of sintering temperatures. The values of flexural strength, hardness and fracture toughness were 565.70 MPa, 19.94 GPa and 6.68 MPa m^1/2 at 1950 °C, respectively. The addition of ZrB₂ proves to enhance the properties of SiC ceramic by crack deflection and bridging.     

Preparation and characterisation of closed-pore Al2O3-MgAl2O4 refractory aggregate utilising superplasticity

ABSTRACT

A novel high closed porosity Al₂O₃-MgAl₂O₄ refractory aggregate has been successfully fabricated by utilising superplasticity with Al₂O₃ and MgO as raw materials, SiC as high temperature pore-forming agent. The effects of the addition amounts of MgO and SiC on porosity, sintering behaviours, phase composition, pore size distribution and microstructure of the refractory aggregate have been investigated. The formation mechanism of the closed pore in the refractory aggregate has been discussed. The results showed that the MgO can improve the superplastic deformation ability of Al₂O₃-based ceramic at high temperature. With the content of MgO and SiC increased, the closed porosity and the pore size increased. The oxidation of SiC improved the sinterability of materials at the initial stage of sintering, and then the released gases due to the further oxidation of SiC promoted the formation of closed pores by motivating the superplastic deformation ability of Al₂O₃-based materials.     

Effects of additives on combustion synthesis of Al2O3–TiB2 ceramic composite

Al₂O₃, SiC and kaolin were employed as additives in combustion synthesizing Al₂O₃–TiB₂ ceramic composite. Effects of the additives on adiabatic temperature, combustion wave velocity, volume change and composite density were studied, and bending strength of the synthesized ceramics was evaluated. By theoretical calculation, the adiabatic temperature of Al–TiO₂–H₃BO₃ system is 2314.85 °C and decreases with increasing the additive addition. With Al₂O₃ addition, the phases presented in the ceramic composite are unchanged, and the phases of SiC and 3Al₂O₃·2SiO₂ emerges when SiC and kaolin are added. The addition of the additives results in a refined TiB₂ particulate size and reduces combustion wave velocity. The highest density is achieved with the addition of kaolin from 10 to 30 wt.% making the volume change from ?4.6 to ?1.2%. The bending strength of the TiB₂–Al₂O₃ composite is improved eight times with the addition of 30 wt.% kaolin.     

Preparation of Al2O3–SiC composite powder from kyanite tailings via carbothermal reduction process

ABSTRACT

Al₂O₃–SiC composite powders were prepared from kyanite tailings mixed with 20% excess carbon coke via carbothermal reduction (CR) reaction. The optimised synthesis condition for synthesising Al₂O₃–SiC composite powders was at 1600°C for 6?h. The equilibrium relationship curves of the condensed phases were presented and the temperature dependence of the phase composition was also studied. The results show that irregular Al₂O₃ and SiC grains first formed at 1500°C, and the elements C, O, Al, and Si randomly distributed in the each crystal particles. The amount of Al₂O₃–SiC composites increased with the increasing synthesis temperature and reaction time. Finally, Al₂O₃–SiC composite bulk materials were further prepared by pressureless sintering using the synthesised Al₂O₃–SiC composite powders as raw materials, and their mechanical properties were investigated in detail. All these results indicate that the CR method can offer a niche application for the development of kyanite tailings.     

Investigation of novel multiscale textures for the enhancement of the cutting performance of Al2O3/TiC ceramic cutting tools

Currently, the high temperature and severe friction conditions at the tool-chip interface are the main reasons for ceramic tool wear failures. Surface texturing as a geometric extension for cutting tools is a promising way to extend their service life. In this study, a novel type of multiscale texture was developed, and its effect on the cutting performance of an Al₂O₃/TiC ceramic cutting tool while machining AISI H13 steel was explored in a conventional cooling environment. The cutting force, cutting temperature, and tool wear morphology were investigated at cutting velocities ranging from 80 to 249 m/min. Microgroove textured Al₂O₃/TiC ceramic tools were prepared for comparison. The results show that the structure of the multiscale textures maintained good integrity over the range of cutting velocities. Thus, the synergistic effect of the microscale and nanoscale textures promoted the introduction and permeation of the cutting fluid. Therefore, the multiscale textures effectively enhanced the cutting performance of the Al₂O₃/TiC ceramic tools.     

Mechanical properties of graphene platelet-reinforced alumina ceramic composites

Alumina (Al₂O₃) ceramic composites reinforced with graphene platelets (GPLs) were prepared using Spark Plasma Sintering. The effects of GPLs on the microstructure and mechanical properties of the Al₂O₃ based ceramic composites were investigated. The results show that GPLs are well dispersed in the ceramic matrix. However, overlapping of GPLs and porosity within ceramics are observed. The flexural strength and fracture toughness of the GPL-reinforced Al₂O₃ ceramic composites are significantly higher than that of monolithic Al₂O₃ samples. A 30.75% increase in flexural strength and a 27.20% increase in fracture toughness for the Al₂O₃ceramic composites have been achieved by adding GPLs. The toughening mechanisms, such as pull-out and crack deflection induced by GPLs are observed and discussed.     

Fabrication and mechanical properties of Al2O3-SiCw-TiCnp ceramic tool material

Whiskers and nanoparticles are usually used as reinforcing additives of ceramic composite materials due to the synergistically toughening and strengthening mechanisms. In this paper, the effects of TiC nanoparticle content, particle size and preparation process on the mechanical properties of hot pressed Al₂O₃-SiC_w ceramic tool materials were investigated. The results showed that the Vickers hardness and fracture toughness of the materials increased with the increasing of TiC content. The optimized flexural strength was obtained with TiC content of 4 vol% and particle size of 40 nm. The particle size has been found to have a great influence on flexural strength and small influence on hardness and fracture toughness. It was concluded that the flexural strength increased remarkably with the decreasing of the TiC particle size, which was resulted from the improved density and refined grain size of the composite material due to the dispersion of the smaller TiC particle size. SEM micrographs of fracture surface showed the whiskers to be mainly distributed along the direction perpendicular to the hot-pressing direction. The fracture toughness was improved by whisker crack bridging, crack deflection and whisker pullout; the TiC nanoparticles in Al₂O₃ grains caused transgranular fracture and crack deflection, which improved the flexural strength and fracture toughness with whiskers synergistically. Uniaxial hot-pressing of SiC whisker reinforced Al₂O₃ ceramic composites resulted in the anisotropy of whiskers’ distribution, which led to crack propagation differences between lateral crack and radical crack.     

Synthesis and Bioactivity of Reduced Graphene Oxide/Alumina‐Noble Metal Nanocomposite Flakes

The aim of this study was to describe the modification of the bioactivity of Al₂O₃‐noble metal (Me = Ag, Au, or Pd) composite nanoparticles by the addition of graphene oxide and the formation of a RGO/Al₂O₃‐Me nanocomposite system. The nanocomposite flakes and Al₂O₃‐Me composite nanoparticles were widely characterized. The antibacterial effect was observed only for Al₂O₃‐Ag composite nanoparticles and RGO/Al₂O₃‐Ag nanocomposite flakes, while, in the case of RGO/Al₂O₃‐Ag, a more evident antibacterial effect against Staphylococcus aureus bacteria was observed compared with Al₂O₃‐Ag. In the case of other noble metals (Au, Pd), a slight growth‐stimulating effect was revealed for particular bacterial strains.     

Nondestructive characterisation of alumina/silicon carbide nanocomposites using impedance spectroscopy

Nondestructive evaluation (NDE) of ceramic matrix composites is essential for developing reliable ceramics for industrial applications. In the research described here, impedance spectroscopy has been used to characterise Al₂O₃/SiC nanocomposites nondestructively. Electrical modulus spectra from impedance measurements were used to determine the content of SiC nanoparticles in Al₂O₃/SiC composites. Meanwhile, electrical impedance measurements have been used to characterise the oxidation of Al₂O₃/SiC nanocomposites. Based on the microstructural features of the nanocomposites, equivalent models were developed to calculate the capacitance of the nanocomposites and oxidised specimens. The calculated results were used (i) to examine the relationship between the composition and electrical properties of the Al₂O₃/SiC nanocomposites; (ii) to predict the thickness of oxide scales formed at the surface of the nanocomposites after oxidation. The comparison showed reasonable agreements between theoretical prediction and experimental results.