Composite Ceramic Tool Material Research Articles

Mechanical properties and thermal shock resistance of TiB2‒B4C composite ceramic tool materials at microscopic scale

AbstractA finite model incorporating microstructure was developed to investigate the thermal shock resistance of TiB2‒B4C composite ceramic cutting tool materials. Numerical simulations were conducted to analyze changes in the transient temperature field and thermal stress field during the thermal shock process. TiB2‒B4C composite ceramic tool materials were fabricated using discharge plasma sintering technology. With different B4C contents, different sintering temperatures and holding times as study variables, optimization of the sintering process parameters and ceramic material components was achieved through testing the mechanical and microscopic morphology of the ceramics. Thermal shock water quenching experiments were performed, and the strength‐decay method was employed to assess the thermal shock resistance of TiB2‒B4C ceramics. The findings indicate that the optimal sintering conditions are temperature of 1700°C and holding time of 5 min. The TiB2‒B4C ceramic material containing 20 vol% B4C exhibits superior comprehensive mechanical properties and thermal shock resistance, and its relative density, fracture toughness, hardness, and flexural strength were 99.3%, 6.8 MPa m1/2, 22.8 GPa, and 598 MPa, respectively. The critical thermal shock temperature difference falls within the range of 400°C‒500°C.

Design and optimization of TiB2‐based ceramic tool materials based on fuzzy theory

AbstractBased on the material properties and fuzzy theory, a new design method of TiB2‐based composite ceramic tool material was proposed, and the TiB2‐based composite ceramic tool material with excellent friction and wear resistance was designed. Initially, the fuzzy evaluation method was used to establish the matrix of the friction and wear resistance of the material, and the TiB2‐based material component with excellent friction and wear resistance was determined. Ultimately, based on the principle of fuzzy cognitive map, the correlation mapping of “sintering process–microstructure–mechanical properties” was established, and the composition ratio and sintering process were optimized. The results show that the TiB2–TaC–TiC ceramic tool material had excellent friction and wear resistance. When the volume content of TaC was 8 vol.%, the volume content of TiC was 20 vol.%, the heating rate was 100°C/min, the holding time was 8 min, the sintering temperature was 1600°C, and the sintering pressure was 50 MPa, the mechanical properties were hardness 23.5 GPa, bending strength 438 MPa, and fracture toughness 10.26 MPa∙m1/2.

The crack-healing and strength recovery mechanisms for the new developed Ti(C,N)-TiSi2-WC composite ceramic tool materials with crack-healing ability

Because the ceramic tool life will be reduced due to the crack growth, it is necessary to develop the new ceramic tools with crack-healing ability for improving the ceramic tool life. Ti(C,N)-TiSi2-WC composite ceramic tools were fabricated by vacuum hot pressing sintering technology. The Vickers hardness tester was used to prefabricate cracks with different lengths. The crack-healing abilities of materials were researched by air and vacuum heat treatments. The effects of different healing conditions on crack-healing behaviors were investigated based on the strength recovery and microstructure of crack morphology. The healing conditions included healing temperature, healing time, crack length and healing atmosphere. It could be found that the surface cracks were entirely healed after air heat treatment, but locally healed after vacuum heat treatment. After air heating at 800 °C for 90 min, the restoration ratio of flexural strength of the crack-healed samples returned to 109.02% compared to that of the smooth specimen. The strength of the crack-healed specimen would be fully recovered when the crack length was less than 400 μm. After vacuum heating at 1000 °C for 60 min, the recovery of the flexural strength of the crack-healed samples returned to 49.73%. X-ray diffraction and scanning electron microscope technology were used to analyze compositions and microstructure of crack-healed specimens. In the air atmosphere, the liquid filling of SiO2 and TiO2 and crack closure caused by WSi2 and MoSi2 were confirmed as the crack-healing mechanisms. SiO2 and TiO2 were produced by high temperature oxidation reaction of TiSi2 and WSi2. WiS2 and MoSi2 were new phases formed during sintering and heat treatment, and their formation could be explained by thermodynamically feasible reactions. In the vacuum atmosphere, local filling of the crack with silicide solid solutions such as WSi2, MoSi2 and NiSi was the main crack-healing mechanism.

Effect of CaF2@SiO2 on Si3N4/TiC Composite Ceramic Materials: Molecular Dynamics Analysis and Material Preparation

Molecular dynamics simulations allow to investigate the microscopic evolution of a structure, and can also point the way to tool material design. In this paper, the effect of adding CaF2 and CaF2@SiO2 on the Si3N4/TiC system is studied using molecular dynamics simulations. The results show that the system with the addition of CaF2@SiO2 to the model has a higher hardness than the system with the addition of CaF2. In order to obtain the optimum parameters for self-lubricating ceramic tools, the effect of adding different amounts of CaF2@SiO2 on the Si3N4/TiC system was investigated. The Si3N4/TiC/CaF2@SiO2 system achieved optimum mechanical properties when four CaF2@SiO2 were included in the model. By analyzing the effect of the sintering temperature on the system, it was deduced that the hardness achieved a maximum value of 15.89 GPa and the modulus of elasticity reached 132.53 GPa when the sintering temperature was at 2073 K. Based on this sintering parameter, the Si3N4/TiC/CaF2@SiO2 composite ceramic tool material was experimentally prepared with the mechanical properties of 15.66 GPa hardness and 128.08 GPa modulus of elasticity. The experimental results were consistent with the simulation results.

Preparation of In Situ Growth Multiscale β-Sialon Grain-Reinforced Al2O3-Based Composite Ceramic Tool Materials

A kind of multiscale β-sialon grain-reinforced Al2O3 matrix composite ceramic tool material, named ASN, was prepared and studied. For the ASN, β-sialon (molecular formula: Si4Al2O2N6) was synthesized in situ by a hot-pressing and solid-solution reaction process. A total of six samples were prepared at varying sintering temperatures and holding times under vacuum conditions. The solid solution reaction mechanism of β-sialon, the phase composition, mechanical properties, microstructure, and strengthening and toughening mechanisms of the composite ASN were investigated. As a result, within the experimental parameters, an optimal ASN tool material was obtained under a pressure of 32 MPa and at a temperature of 1550 °C for 20 min. The tested mechanical properties of the optimal sample were as follows: flexural strength 997 ± 59 MPa, fracture toughness 6.4 ± 0.3 MPa·m1/2, Vickers hardness 18.2 ± 0.4 GPa, and relative density 98.1 ± 0.2%. According to crystal defect theory, the solid solution reaction mechanism of in-situ-synthesized β-sialon in an Al2O3 matrix involves a double mechanism of unequivalence (or hetero-valence) and interstitial filling. The multiscale β-sialon grains mainly consisted of four grains, which were elongated β-sialon grains with a diameter of 0.3-0.4 μm and an aspect ratio of 6-9, elongated β-sialon grains with a diameter of 70 nm and an aspect ratio of 10, β-sialon whiskers with a diameter of 0.2 μm and an aspect ratio of 12-15, and intragranular β-sialon whiskers with a diameter of 70 nm. The mechanical properties were improved due to strengthening and toughening mechanisms, such as mixed structure mode (intergranular and transgranular), elongated grain pullout, interface bonding, crack reflection, pinning, and bridging.

Theoretical analysis of Si3N4/TiC interfacial properties and material preparation

Computer simulation plays an instrumental role in modern tool material design. In this study, we have calculated the temperature and pressure conditions for the phase transition of Si3N4 from α to β using first principles. The simulation results show that the phase transition temperature is 1330 K at a phase transition pressure of 32 MPa. The modulus of elasticity, hardness, ductile/brittle properties (B/G), Poisson's ratio, elastic anisotropy, and phonon spectral curves at the phase transition point were also calculated for the material at temperatures ranging from 873 K to 2073 K. According to the phase transition conditions, the surface energies of β-Si3N4 and TiC interfaces were calculated, and 4-layer models of Si3N4/TiC interfaces were constructed. The total energy and adhesion work of the Si3N4(110)/TiC(100) interface were analyzed by molecular dynamics. The results show that the Si3N4(110)/TiC(100) interface exhibits the maximum total energy and adhesion work of 12,806.62 eV and 2.33 J/m2, respectively, indicating that the interface bond was the most stable. Furthermore, the mechanical properties of different interface models were calculated and compared. The effects of Si3N4(110)/TiC(100) interfacial 5-layer and 6-layer crystalline surfaces and Si and Ti vacancy defects on the mechanical properties of the interfacial model were further investigated. The Si3N4/TiC composite ceramic tool material was prepared experimentally based on the results of simulation, and the properties show reasonable agreement.

Effects of SiC on phase transformation and microstructure of spark plasma sintered α/β‐SiAlON composite ceramics

Abstractα/β‐SiAlON/SiC composite ceramic tool materials were prepared via spark plasma sintering. The effects of content and size of SiC particles and sintering temperature on phase composition, mechanical properties, and microstructure were investigated. The results indicated that SiC restrained the transformation of β‐SiAlON to α‐SiAlON, but higher SiC content (≥10 wt.%) resulted in a higher Vickers hardness of the composite. The large size of SiC particles raised the densification temperature of α/β‐SiAlON composites, and small SiC particles benefited to improve microstructure. There were more equiaxed α‐SiAlON grains and β‐SiAlON with a larger aspect ratio ( = 5.1) in the α/β‐SiAlON composite containing 100 nm SiC. The sample containing 10 wt.% 100 nm SiC particles sintered at 1700°C had the optimal properties with a Vickers hardness and fracture toughness of 18.5 ± .2 GPa, 6.4 ± .2 MPa m1/2, respectively.

Prediction of macroscopic effective elastic modulus of micro-nano-composite ceramic tool materials based on microstructure model

In order to investigate the effect of microstructure parameters on the elastic modulus, based on the microstructure model represented by Voronoi tessellation, the reasonable macro-micro connection and boundary conditions were proved through the Hill’s lemma, and the uniaxial tensile process of composite ceramic tool materials was simulated. The influences of grain size, second phase volume fraction and nanoparticle volume fraction on elastic properties were studied through numerical simulation, and the elastic modulus of composite ceramic tool materials was predicted. The results showed the elastic modulus of Al2O3-based ceramic tool materials could be increased effectively with the contents of the second phase TiB2 and nano-particle TiC being 20% and 10%, respectively. The numerical simulation results were in good agreement with the experimental results.

Design and fabrication of TiB2–TiC–Al2O3 gradient composite ceramic tool materials reinforced by VC/Cr3C2 additives

In this study, TiB2–TiC–Al2O3 gradient composite ceramic tool materials reinforced by VC/Cr3C2 additives were prepared through vacuum hot-press sintering. The effects of gradient combination, thickness ratio and sintering process (sintering temperature and soaking time) on the mechanical properties and microstructures of the composites were investigated. The results showed that the high surface compressive stress produced by the adequate gradient combination and thickness ratios refined the grains and increased the crack growth path. By comparison, the sintering temperature and soaking time influenced the grain size and porosity. In addition, the effects of VC/Cr3C2 on the grain size were analysed, and it was found that VC/Cr3C2 inhibited TiC dissolution and accelerated Al2O3 re-precipitation, which in turn refined the TiC grains and coarsened the Al2O3 grains. Consequently, crack deflection and intergranular fracture occurred around the TiC grains, whereas trans-granular fracture occurred inside the TiB2 and Al2O3 grains because rapid Al2O3 precipitation facilitated TiB2 grain growth. The optimum mechanical properties were hardness of 23.59 GPa, fracture toughness of 7.45 MPa m1/2, and flexural strength of 764.11 MPa.

Effect of the Characteristic Size and Content of Graphene on the Crack Propagation Path of Alumina/Graphene Composite Ceramics.

In this paper, the Voronoimosaic model and the cohesive element method were used to simulate crack propagation in the microstructure of alumina/graphene composite ceramic tool materials. The effects of graphene characteristic size and volume content on the crack propagation behavior of microstructure model of alumina/graphene composite ceramics under different interfacial bonding strength were studied. When the phase interface is weak, the average energy release rate is the highest as the short diameter of graphene is 10–50 nm and the long diameter is 1600–2000 nm. When the phase interface is strong, the average energy release rate is the highest as the short diameter of graphene is 50–100 nm and the long diameter is 800–1200 nm. When the volume content of graphene is 0.50 vol.%, the average energy release rate reaches the maximum. When the velocity load is 0.005 m s−1, the simulation result is convergent. It is proven that the simulation results are in good agreement with the experimental phenomena.

Phase field simulation of grain growth in Al2O3-based composite ceramic cutting tool materials containing second phase nanoparticles and pores

A phase field model was established to simulate the grain growth of Al2O3-based composite ceramic tool materials containing second phase nanoparticles and pores. The free energy parameters of the model are directly related to the surface and grain boundary energies of Al2O3 such that the grain growth process can be quantitatively analysed. The model was used to investigate the effects of the volume fraction and size of second phase particles on grain growth in Al2O3 with a certain initial pore volume fraction. Findings show that pores and second phase particles jointly hinder grain growth. When the radii of second phase nanoparticles are the same, as the number of particles increase, most of the grain boundaries occur as straight lines in the microstructure, and grain size decreases. It is beneficial to obtain fine and uniform microstructure. However, when the particles content reaches a certain level, the second phase particles tend to agglomerate at the grain boundary of matrix grains, which will result in a decrease in the properties of nanocomposite ceramic tool materials. The study also found that, at a constant volume fraction of particles, with the decrease of particle radius, the grain size decreases. When the second phase particle size is reduced to 50 nm, relatively more intragranular microstructure was observed, which is considered to be the main reason for increasing the toughness of nano composite ceramic tool materials. Through analyzing the simulation results, the optimal combination of the content and size of the second phase particles can provide theoretical guidance for Al2O3 nano composite ceramic tool materials design and preparation.

The influence of TiB2 content on high temperature flexural strength and reliability of the developed titanium carbonitride based ceramic tool material

n this study, the influence of TiB2 content on flexural strength and reliability of the developed Titanium carbonitride based ceramic tool materials at high temperature was investigated. It was found that the flexural strength of Titanium carbonitride based ceramic tool materials (TB30TW) with 30 wt% TiB2 content was 1.49 times that of Titanium carbonitride based ceramic tool materials (TB20TW) with 20 wt% TiB2 content at room temperature. However, when the temperature exceeded 800 °C, the flexural strength of the two composites tended to be similar. The flexural strength of the TB30TW with higher TiB2 content dropped greatly at high temperature ascribed the oxidation behavior of TiB2. The distribution of measured high temperature flexural strength for TB30TW at 800 °C could well obey a Weibull distribution function, which was consistent with TB20TW. The Weibull distribution shape parameter of the flexural strength of TB30TW was higher than that of TB20TW at 800 °C, then the distribution of the high temperature flexural strength of TB30TW was less discrete than that of TB20TW. The results can serve as reference in the design composite ceramic tool materials and help to evaluate cutting reliability of ceramic cutting tools.

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.

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.

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.