Composite Ceramic Tool Research Articles

Cohesive Element Model for Fracture Behavior Analysis of Al2O3/Graphene Composite Ceramic Tool Material

The microstructure model of Al2O3/graphene (AG) composite ceramic tool material is established based on Voronoi tessellation. The cohesive element method was used to simulate the crack growth of AG. The effect of cohesive parameters at the grain boundary of Al2O3 and graphene on the crack propagation was investigated. The results show that the grain strength of graphene is too high, the crack propagation to graphene grains will be hindered and cannot propagate forward. Cracks tend to spread along the paths where the crack propagation drive force was high and the resistance was low. When the interface strength between Al2O3 and graphene was at the weak interface, the crack propagation path and length were relatively straight and short. The average energy release rate G C is 1.042 × 10−3 J/m2, which is 2.4% higher than that of single-phase Al2O3 ceramic tool materials. However, if the interface strength between Al2O3 and graphene was at the strong interface, the crack propagated along graphene particles for a short distance, consuming a large amount of fracture energy. Furthermore, the crack will deflect around graphene grains, which increases the crack propagation length. The average energy release rate G C is 1.039 × 10−3 J/m2, which is 2% higher than that of single-phase Al2O3 ceramic tool materials.

Orentational effect of graphene on the friction and wear behavior of Si3N4/TiC based composite ceramic tool materials

Tribological performance between 45 hardened steel and Si3N4/TiC based composite ceramic tool materials containing 5 wt% graphene platelets with different orientation angle of graphene have been investigated by pin-on-disc tests in dry sliding conditions. The experimental results show that the composite ceramic tool materials with different orientation angle of graphene have different friction coefficients and wear rates. The friction coefficient and wear rate of the developed ceramic tool materials with the 30°orientation angle is 0.46 and 4.29 × 10-6 mm3/N·m, respectively, which is decreased by 31.3% and 63.0% compared with that of the commonly distributed 0° orientation angle. Experimental analysis shows that the improvement can be attributed to the uniform distribution of the adhered tribofilm and the combined effect of graphene pull-out and the contact area between graphene and the friction surface.

Fabrication of TiC-TiB2 composite ceramic tool and its cutting performance in turning austenitic stainless steel

ABSTRACTNew TiC-TiB2 ceramic cutting tool materials TiC-TiB2-Ni-Mo (TBNM8) and TiC-TiB2-Ni (TBN5) with high comprehensive mechanical properties were fabricated by hot pressed sintering with the optimised sintering processes. The cutting performance of TBNM8 in continuously turning austenitic stainless steel (1Cr18Ni9Ti) was experimentally investigated. With the optimal cutting parameters, the cutting performance of TBN5 and commercial tool LT55 were compared in wet and dry turning 1Cr18Ni9Ti. The failure mechanisms of the cutting tools were analysed combined with their high-temperature mechanical properties. The results showed that the tool life of TBN5 and TBNM8 was much longer in continuous dry turning 1Cr18Ni9Ti than that in wet turning, the possible reason was analysed as that the tool materials keeping high mechanical properties at elevated temperature, which led to the great improvement in machining efficiency and good characteristics of environmental friendliness because no cutting fluid was used during the cutting process.

Effects of sintering parameters on microstructure, graphene structure stability and mechanical properties of graphene reinforced Al2O3-based composite ceramic tool material

Graphene reinforced Al2O3-based composite ceramic tool materials were synthesized using hot pressing (HP) under sintering conditions of 1550–1750 °C sintering temperature, 5–30 min dwell time and 25–40 MPa applied pressure in order to investigate the effects of sintering parameters on microstructure, graphene structure stability and mechanical properties of composite ceramic tool materials. Sintering parameters of 1600 °C sintering temperature, 15 min dwell time and 30 MPa applied pressure were demonstrated to be the optimal sintering parameters to obtain dense and refined microstructure. The wrapping mechanism of graphene on ceramic grains was believed to play a significant role in the formation process of this optimized microstructure. Based on Raman spectrum analysis, graphene structure stability was subjected to sintering temperature and dwell time. Graphene structure could be destructed under the high sintering temperature or extended dwell time. And the shortened dwell time was also detrimental to graphene structure stability due to the lower crystallinity. Mechanical properties of composite ceramic tool materials were also optimized under the optimal sintering parameters. Grain refinement and weak bonding interface induced by graphene were responsible for the improved fracture toughness.

Dynamic fatigue behavior of Si3N4-based ceramic tool materials at ambient and high temperatures

Dynamic fatigue behaviors of three microwave-sintered Si3N4-based ceramic tool materials in ambient and high-temperature (800 °C) environments were investigated. The flexural strength at different loading rate (0.05 MPa/s, 0.5 MPa/s, 5 MPa/s and 15 MPa/s) was conducted by three-point bending test. The results showed that the subcritical crack growth parameter N of monolithic Si3N4, Si3N4/(W,Ti)C and Si3N4/(W,Ti)C/Ni at ambient temperature was 57.5, 34.8 and 81, respectively. The fatigue resistance performance at ambient temperature was ranked as Si3N4/(W,Ti)C/Ni > monolithic Si3N4 > Si3N4/(W,Ti)C. As the temperature increased to 800 °C, the flexural strength of all samples only decreased slightly, which indicated Si3N4-based ceramic tool materials had good thermal stability. The subcritical crack growth parameter N of monolithic Si3N4 and Si3N4/(W,Ti)C ceramic tool materials did not change, while the value N of Si3N4/(W,Ti)C/Ni decreased by 76.5%. The addition of metal phase can increase the ambient temperature fatigue resistance, while it is detrimental to the high-temperature fatigue resistance due to its weak strength at high temperature. Additionally, defect source caused by the oxidative corrosion was also not conducive to fatigue resistance performance of Si3N4-based composite ceramic tool materials at high temperature.

Biomimetic micro-textures, mechanical behaviors and intermittent turning performance of textured Al2O3/TiC micro-composite and micro-nano-composite ceramics

Abstract This work was conducted to investigate biomimetic micro-textures, mechanical behaviors and intermittent turning performance of textured Al2O3/TiC micro-composite and micro-nano-composite ceramics. Chip characteristics and the geometry features of the structures on the cuticle of Procambarus clarkia were considered in the preparation of the laser-induced biomimetic micro-textures on the composite ceramic surfaces. Characteristics of the biomimetic micro-textures were revealed in terms of geometry, morphology and chemical composition. The connection between the thermal stress resulting from laser pulse and the fractal dimension of the micro-crack on the micro-textures was analyzed and identified. The correlation between the mechanical behaviors (damage and fracture toughness) of the textured composite ceramics and the fractal dimension of the micro-crack was fitted and revealed quantitatively. The performance of the textured composite ceramic tools was pre-evaluated by means of a proposed indicator. Damage, fracture toughness and tool stress were incorporated in the indicator. The indicator and the experimental tool wear were compared for validating the effectiveness of the proposed indicator. It was found that the micro-composite ceramic exhibited greater sensitivity to laser than the micro-nano-composite ceramic did. The damage of the textured micro-composite ceramic was larger than that of the textured micro-nano-composite ceramic when the same laser parameters were utilized in the micro-texture preparation. On the contrary, the fracture toughness of the textured micro-composite ceramic was found to be smaller. There was a negative correlation between the damage of the textured composite ceramic and the fractal dimension of the micro-crack. Conversely, there was a positive correlation between the fracture toughness and the fractal dimension. The performance of the textured micro-nano-composite ceramic tool was better than that of the textured micro-composite ceramic tool. The proposed indicator can be used to predict the combination of laser parameters that resulted in the optimum performance of the textured composite ceramic tool.

Fine grained Al2O3/SiC composite ceramic tool material prepared by two-step microwave sintering

Abstract Fine-grained Al2O3/SiC composite ceramic tool materials were synthesized by two-step microwave sintering. The effects of first-step sintering temperature (T1), content and particle size of SiC on the microstructure and mechanical properties were studied. It was found that the sample with higher content of SiC was achieved with finer grains, and the incorporation of SiC particles could bridge, branch and deflect the cracks, thus improving the fracture toughness. Higher T1 was required for the densification of the samples with higher content of SiC (>5 wt%). The sample containing 3 wt% SiC particles with the mean particle size of 100 nm, which was sintered at 1600 °C (T1) and 1100 °C (T2) for 5 min had the fine microstructure and optimal properties. Its relative density, grain size, Vickers hardness and fracture toughness obtained were 98.37%, 0.78 ± 0.31 μm, 18.40 ± 0.24 GPa and 4.97 ± 0.30 MPa m1/2, respectively. Compared to the sample prepared by single-step microwave sintering, although near full densification can be achieved in both two methods, the grain size was reduced by 36% and the fracture toughness was improved by 28% in two-step microwave sintering.

Al2O3/WB2 composite ceramic tool material reinforced with graphene oxide self-assembly coated silicon nitride

Graphene oxide coated silicon nitride coated powder was prepared by electrostatic self-assembly technique. Microstructure analysis shows that GO is uniformly coated on the surface of silicon nitride and evenly dispersed in the matrix material. The microstructure analysis and performance tests were carried out on ceramic tools with different volume contents of Si3N4@GO coated powder. The results show that when the content of Si3N4@GO is 7. 94 vol%, the comprehensive mechanical properties of Al2O3/WB2/(Si3N4@GO) ceramic tool materials are the best, with the Vickers hardness, flexural strength and fracture toughness 18.7GPa, 740 MPa and 8 .2MPa·m1/2, respectively. Compared with the Al2O3/WB2 ceramic tool material, the ceramic tool with Si3N4@GO coated powder increased the flexural strength and fracture toughness by 30.3% and 36.7%.

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 m1/2, 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.

Effect of metal phases on microstructure and mechanical properties of Si3N4-based ceramic tool materials by microwave sintering

Si3N4-based composite ceramic tool materials were fabricated by microwave sintering. The effects of Ni and Co on the mechanical properties, phase transformation and microstructure of the Si3N4-based composites were studied, and the toughening mechanism was analyzed. The optimum comprehensive mechanical properties with the relative density of 97.15 ± 0.2%, Vickers hardness of 17.28 ± 0.17 GPa and fracture toughness of 6.59 ± 0.12 MPa m1/2 were obtained at 1650 ℃ when the content of Ni was 2 wt%. Ni can promote the formation of grains with high aspect ratio more effectively than Co, but the hardening effect of Co was higher than Ni. Both of two metals would restrain the phase transformation of Si3N4 from α phase to β phase. The main toughening mechanism was the combined action of pulling-out of β-Si3N4 columnar crystals, crack bridging by columnar crystals and crack deflection.

Microstructure and toughening mechanisms of Al2O3/(W, Ti)C/graphene composite ceramic tool material

To toughen the Al2O3 matrix ceramic materials, Al2O3/(W, Ti)C/graphene multi-phase composite ceramic materials were fabricated via hot pressing. The effects of the graphene nanoplates (GNPs) content on microstructure and mechanical properties were investigated. Results showed that the fracture toughness and flexural strength of the composite added with just 0.2 wt% GNPs were markedly improved by about 35.3% (~ 7.78 MPa m1/2) and 49% (~ 608.54 MPa) respectively compared with the specimens without GNPs while the hardness was kept about 24.22 GPa. However, the mechanical properties degrade with the further increase of GNPs’ content owing to the increased defects caused by agglomeration of GNPs. Synergistic toughening effects of (W, Ti)C and GNPs played an essential role in improving the fracture toughness of composites. By analyzing the microstructures of fractured surface and indentation cracks, besides GNPs pull-out, crack deflection, crack bridging, crack branching and crack arrest, new toughening mechanisms such as break of GNPs and crack guiding were also identified. Furthermore, interface stress can be controlled by means of stagger distributed strong and weak bonding interfaces correlated with the distribution of GNPs.

Graphene nanosheets toughened TiB2-based ceramic tool material by spark plasma sintering

One kind of TiB2/TiC composite ceramic tool material toughened by graphene nanosheets was fabricated by spark plasma sintering. Effects of graphene nanosheets on microstructure, mechanical properties and toughening mechanisms were investigated. The results indicated that TiB2/TiC with 0.1 wt% graphene nanosheets sintered at 1800 °C with the holding time of 5 min obtained full densification and optimal mechanical properties. Its fracture toughness and Vickers hardness were 7.9 ± 1.2 MPa m1/2 and 20.0 ± 0.7 GPa, respectively. Excess graphene nanosheets had no effects to toughness improvement. Fracture toughness was increased by 31.7% in comparison with the TiB2/TiC without graphene nanosheets. Toughness enhancement mainly benefited from crack bridging, also slip-stick effect of graphene made it hard to detach and effectively restrained crack extension.

Sintering mechanisms of Al2O3-based composite ceramic tools having 25% Si3N4 additions

A type of Al2O3-based composite ceramic tool material simultaneously reinforced with about 25 wt% α-Si3N4 and β-Si3N4 grains was sintered using the vacuum hot-pressing technology by optimizing process parameters which included different contents of yttria additive, sintering temperature and time. Effects of these process parameters on densification, microstructure and mechanical properties were investigated. The mechanical properties of the composites increased and then decreased with an increase in the yttria content and sintering time. Low content of yttria led to a poor relative density and excess yttria caused inhomogeneous microstructure, which decreased the mechanical properties of the composites. The shorter sintering time led to the elongated β-Si3N4 grains stunted and porosity, and the longer sintering time led to β-Si3N4 grains coarsened and some agglomerations. The experimental results showed that the composite Al2O3/Si3N4 containing 1.5 wt% yttria, which was sintered under a pressure of 32 MPa at 1500 °C for 20 min, had the highest density and the optimal comprehensive mechanical properties. Its relative density, flexural strength, fracture toughness and hardness were 99.6 ± 0.2%, 1093 ± 32 MPa, 6.8 ± 0.2 MPa m1/2, and 19.5 ± 0.3 GPa respectively. The correlations between densification, mechanical properties and microstructure were discussed. The improvement of the mechanical properties was ascribed to equiaxed α-Si3N4 particles and elongated β-Si3N4 grains which induced the toughening and strengthening effects such as the crack deflection, interface debonding, grain fracture and grain pullout. The mixed fracture mode, high density, fine and homogenous microstructure, the stronger interface bonding and the pinning or bridging connection of the core-shell promoted the mechanical properties of the composite ceramic tool materials.

Effect of WEDM surface texturing on Al2O3/TiCN composite ceramic tools in dry cutting of hardened steel

Micro scale textures were fabricated on the rake surface of Al2O3/TiCN composite ceramic cutting tools using WEDM process. The cutting performance of ceramic cutting tools with plain and textured rake surfaces was investigated in the dry cutting of hardened AISI 52100 steel (62 HRC). The performance of cutting tools was evaluated by chip-tool contact length, tool wear, machining forces, cutting temperature, frictional coefficient and chip morphology. Further, a 3D finite element model has been used to study the temperature and stress distribution in the cutting tools. Application of textures obstructing the chip flow direction resulted in uniform stress distribution, and higher groove sliding area ensured maximum reduction of machining forces, material adhesion, cutting and tool temperature. However, the textures parallel to the chip flow direction resulted in bending and curling of chips on the rake face causing an increase of chip-tool contact length and material adhesion as compared to the tools with textures obstructing the chip flow resulting in an increase of friction. The textured tool with textures inclined at an angle to the chip flow direction exhibited the best machining performance as compared to other textured cutting tools. Moreover, this tool exhibited superior anti-adhesion behavior as compared to the conventional cutting tool owing to the reduced chip-tool contact length and area, friction and chip flow angle.

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 15wt% (W,Ti)C sintered at 1600°C for 10min by microwave sintering exhibited the optimum mechanical properties. Its relative density, Vickers hardness and fracture toughness were 95.73 ± 0.21%, 15.92 ± 0.09GPa and 7.01 ± 0.14MPam1/2, 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 15wt%.

Theoretical hardness analysis and experimental verification for composite ceramic tool materials

Abstract High hardness is the most important requirement for the property of cutting tool materials. Based on the assumption that the solid hardness is proportional to the resistance of the chemical bonds within indentation area, the theoretical hardness prediction model of the multiphase composite ceramic tool material was established combining with the hardness theory of multicomponent systems. In order to verify the applicability and accuracy of the theoretical model, validation experiment has been designed from the point of different dimensions and scales of raw materials, including TiC micron particles, SiC whiskers, TiC nanoparticles and SiC nanoparticles. The results showed that the experimental hardness of the materials with whiskers and micron particles addition were in good agreement with theoretical value with the error margin of −0.15 to +0.97%. By comparison, the experimental hardness of the material with nanoparticles addition was about +1.97–3.21% higher than theoretical counterpart. By analyzing experimental results and SEM micrographs, it was concluded that the experimental hardness of composite ceramic materials was scarcely influenced by the grain size of the matrix. And it was inferred that the intragranular and intergranular microstructure in nanocomposite ceramic materials might be the main factor that caused additional increment in experimental hardness.

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

Abstract An Al 2 O 3 /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.

Mechanical properties and toughening mechanisms of graphene platelets reinforced Al2O3/TiC composite ceramic tool materials by microwave sintering

A type of Al2O3/TiC composite ceramic tool material reinforced with graphene platelets (GPLs) was fabricated by microwave sintering. The effects of GPLs content on the microstructure, mechanical properties and toughness mechanisms of Al2O3/TiC/GPLs composite ceramic tool materials were studied. The experimental results showed that the microstructure of the composite became finer with the incorporation of GPLs. The optimal mechanical properties were achieved with 0.2wt% GPLs. The relative density, Vickers hardness and fracture toughness were 97.7±0.2, 18.5±0.5GPa and 8.7±0.4MPam1/2, respectively. Compared to Al2O3/TiC composites, the Vickers hardness decreased by 12.7%, but the fracture toughness increased by 67.3%. Also, agglomerated GPLs and pores were observed in the new composite ceramic tool materials. The toughening mechanisms were crack deflection, crack bridging, crack branching and pull-out of GPLs.

Wear behavior of an Al2O3/TiC/TiN micro-nano-composite ceramic cutting tool in high-speed turning of ultra-high-strength steel 300 M

An Al2O3-based micro-nano-composite ceramic tool material reinforced with TiN micro-particles and TiC nanoparticles was fabricated by using the hot-pressing technique. The wear behavior of the Al2O3/TiC/TiN micro-nano-composite ceramic cutting tool (AT10N20) in high-speed turning of ultra-high-strength steel 300 M was investigated by comparison with the commercial Al2O3/TiC composite ceramic tool CC650. Worn and fractured surfaces of ceramic cutting tools were observed and analyzed via the scanning electron microscopy (SEM) combined with the energy-dispersive X-ray spectroscopy (EDS). The results showed that the main wear modes of AT10N20 and CC650 were flank wear and rake wear. The crater on the rake face of AT10N20 initially occurred at cutting speed of 400 m/min, while it occurred at cutting speed of 200 m/min for CC650. In addition, the rake wear and flank wear became more severe when the cutting speed attained 400 m/min. The cutting speeds higher than 400 m/min were unfavorable for turning of ultra-high-strength steel 300 M. Wear mechanisms of AT10N20 and CC650 in high-speed turning of the ultra-high-strength steel were abrasion and adhesion.

Microstructure and mechanical properties at room and elevated temperatures of reactively hot pressed TiB2–TiC–SiC composite ceramic tool materials

TiB2-based composite ceramic tool materials with different amounts of TiC and SiC were fabricated via a reactive hot pressing process. The mechanical properties at room temperature and flexural strength at 800–1300°C were tested in ambient air. The composition and microstructure before and after the high-temperature strength tests were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy-dispersive spectrometer (EDS). The flexural strength increment/degradation mechanisms at elevated temperatures were investigated. In-situ synthesized TiC improved the sinterability and mechanical properties of the materials at both room and elevated temperatures. Comparing with TTS (TiB2–15.9wt%TiC–10.6wt%SiC) and TS (TiB2–22.4wt%SiC), TTS3 (TiB2–8.1wt%TiC–16.4wt%SiC) had the optimum room temperature mechanical properties, i.e., flexural strength of 862MPa, fracture toughness of 6.4MPam1/2, hardness of 22.8GPa, and relative density of 99.3%. The improved mechanical properties were ascribed to the fine grain size. The flexural strength of the TTS composite at 800°C was higher than that at room temperature. The improvement of the flexural strength was attributed to the healing of preexisting flaws and the relief of residual stress. Substantial strength degradation took place when the temperature exceeded 1000°C, due to softening of the grain boundaries, surface oxidation and elastic modulus degradation.