Ceramic Tool Materials Research Articles

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 properties of submicron grained alumina ceramic tool material prepared by two-step microwave sintering

Alumina ceramic with submicron grains was prepared by the two-step microwave sintering. Microstructure evolution and densification kinetics of alumina during microwave sintering were studied. The main densification mechanism of alumina ceramic is grain boundary diffusion at the temperature below 1100 °C, while the main densification mechanism is volume diffusion at the temperature from 1200 to 1300 °C. The mean activation energy of grain growth of alumina is 52.36 kJ/mol, and the minimum activation energy of grain growth (48.32 kJ/mol) appears at the holding time of 10 min. Submicron grained alumina ceramic was prepared by two-step microwave sintering (T1 = 1300 °C, T2 = 1100 °C with the holding time of 5 min). The grain size is 0.64 ± 0.16 µm, and its relative density, Vickers hardness and fracture toughness are 98.23%, 18.70 ± 1.01 GPa and 5.28 ± 0.26 MPa m1/2, respectively.

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.

Effects of HfN content and metallic additives on the microstructure and mechanical properties of TiC0.7N0.3-based ceramic tool materials

Effects of HfN content and metallic additives on microstructure and mechanical properties of TiC0.7N0.3-based ceramics were investigated. HfN had very weak inhibition effect on TiC0.7N0.3 grain growth. When HfN content increased from 10 wt% to 20 wt%, flexural strength and fracture toughness became higher, but Vickers hardness was around 20 GPa without significant changes. The optimal mechanical properties of TiC0.7N0.3-20 wt%HfN-Ni-Co were that Vickers hardness was 18.93 GPa, flexural strength was 876.17 MPa and fracture toughness was 7.58 MPa m1/2 in this investigation. Ni-Mo additive exhibited better wettability with TiC0.7N0.3 than the other metallic additives. Ni-Mo additive could inhibit TiC0.7N0.3 grain growth effectively and improve mechanical properties of TiC0.7N0.3-based ceramic. The optimal mechanical properties of TiC0.7N0.3-20 wt%HfN-Ni-Mo ceramic was that Vickers hardness was 19.43 GPa, flexural strength was 1235.88 MPa and fracture toughness was 8.46 MPa m1/2 in this investigation. Its toughening mechanism mainly included crack deflection and crack bridging. In addition, the mixed intergranular/transgranular fracture also could improve fracture toughness.

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.

High temperature mechanical properties of Si3N4/(W, Ti)C graded nano-composite ceramic tool material

A Si3N4/(W, Ti)C graded nano-composite ceramic tool material was developed and its high temperature flexural strength and fracture toughness were studied. With increased testing temperature, the flexural strength demonstrates a tendency to first decrease gradually and then decrease sharply, and the transition temperature is 1000 °C. The softening effect of glassy phases, the oxidation effect and the surface cracks result in the gradual decrease of flexural strength while the growth and merge of microcracks and cavities results in the sharp decrease. The fracture toughness under elevated temperatures increases gradually and then decreases dramatically, and the transition temperature is 1000 °C as well. The plastic deformation behavior, microcrack toughening effect and the healing effect of SiO2 layer result in the gradual increase of fracture toughness while liquefaction of the grain-boundary phase results in the sharp decrease. Due to reasonable composition distribution and induced compressive residual stress in the surface layers, the graded material shows a significantly better high temperature properties than the homogenous one.

Effects of material microstructure and surface microscopic geometry on the performance of ceramic cutting tools in intermittent turning

The present work was performed to reveal the integrated effects of material microstructure and surface microscopic geometry on the performance of Al2O3-based composite ceramic cutting tools in intermittent turning. Influences of material microstructure on the initial elastic modulus and material damage of ceramic cutting tools were evaluated on the basis of the established microstructure models and damage mechanics. The effects induced by tool surface microscopic geometry on cutting forces and tool temperatures were revealed based on finite element simulation. Taking the cutting condition into account, a new indicator was used to reflect the integrated effects of material microstructure and surface microscopic geometry on tool performance. A theoretical method was proposed to acquire the optimal combination of tool material microstructure and tool surface microscopic geometry in terms of too life. When material porosity increased from 0.5% to 2.5%, elastic modulus and tool damage decreased and increased, respectively. Compared to ceramic tool material (A) reinforced only by micro (W, Ti)C particles, the variation of material porosity had less effects on the damage within the tool material (B) which contained both micro (W, Ti)C and nano Al2O3 particles. Designing micro-texture pattern (pattern d) on the tool rake face with both the solid-like and liquid-like properties of the chip considered was most efficient for the reduction of cutting forces and tool temperatures. The optimum combination of tool material microstructure and tool surface microscopic geometry can be achieved by using ceramic tool material B and micro-texture pattern d. The experimental tool lives demonstrated the correctness of the tool performance indicator and the theoretical method for acquiring the optimum combination of tool material microstructure and tool surface microscopic geometry.

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.

Computer-aided Design and Preparation for Micro-nano-composite Ceramic Tool Materials

Computer-aided Design and Preparation for Micro-nano-composite Ceramic Tool Materials

Simulation of microstructure evolution coupled with fabrication parameters for two-phase ceramic tool materials

A computer simulation coupled with fabrication parameters for the sintering process of two-phase ceramic tool materials has been developed using a two-dimensional hexagon lattice model mapped from ...

Microstructure design and preparation of Al2O3/TiC/TiN micro-nano-composite ceramic tool materials based on properties prediction with finite element method

The objective of this paper was to improve the accuracy of semi-empirical method used to design ceramic cutting tool materials. The mechanical properties were predicted by employing finite element model of material microstructure, so as to design microstructure and prepare new ceramic materials. Based on the Voronoi and randomness method, the microstructure model representing the complexity and randomness of micro-nano-composite ceramic material microstructure was established. Combining the representative volume element (RVE) of ceramic material microstructure with mechanical tests, the simulations of mechanical tests were conducted to acquire the flexure strength, fracture toughness and hardness of materials. The microstructure models with various parameters were designed and the material properties were predicted to determine the optimal microstructure parameters. Then, The ceramic cutting tool materials possessing the optimal microstructure parameters were developed for machining ultra-high strength steels. The results showed that the mechanical properties of ceramic materials first improved and then declined as the nano-scale TiC volume fraction increased. To obtain the best comprehensive mechanical properties, the contents of micro-scale TiN, TiC and nano-scale TiC were set as 20%, 10% and 10%, respectively. The prepared ceramic materials possessed the flexure strength of 881.4MPa, the fracture toughness of 7.8MPam1/2, and the Vickers hardness of 20.8GPa. This research is beneficial to the development of cutting tool design theory and the improvement of the tool life.

Design, fabrication and mechanical properties of multidimensional graded ceramic tool materials

A type of multidimensional graded ceramic tool materials (MGTMs) was designed and fabricated by vacuum hot-pressing sintering technology. The microstructure and compositional distribution of tool simultaneously changed in two different directions. The tool-chip and tool-workpiece contact regions were designed to have high hardness, and metal phases Mo and Ni were added to produce a gradual increase in toughness from the outer layer to core layer. The effect of orientation angle, thickness ratio and sintering parameters on the mechanical properties and microstructure were investigated. The experimental results showed that the composites, sintered at 1700°C for 15min, with the orientation angle of 30° and a thickness ratio of 0.4, had the optimal comprehensive mechanical properties. In addition, the crack propagation paths were observed to analyze the toughening mechanisms for the multidimensional graded ceramic tool materials. It was found that there is a crack resistance behavior when the crack extended from the outer layer to transition layer. The effect of the angle between the crack and graded interface on crack propagation paths was also investigated and the results indicated that the small angle was favorable for the crack deflection when the cracks passed through the graded interface. The residual thermal stress contributed to the occurrence of the crack bridging and transgranular fracture inside the Al2O3 grains, while the intergranular fracture and crack deflection were observed around the TiC grains.

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%.

Simulation of microcrack initiation in nanocomposite ceramic tool materials

In this work, the microcrack initiation behavior of nanocomposite ceramic tool materials caused by the residual stress initiated during the cooling stage is simulated by means of a micromechanical model based on the Voronoi tessellation and the cohesive element theory. Influences of microstructure morphologies such as nanoparticle size, nanoparticle volume content and microstructure types on the microcrack distribution and material properties are analyzed respectively. The conclusions are useful for providing theoretical basis for the development of nanocomposite ceramic tool materials.

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.

Effects of HfC addition on microstructures and mechanical properties of TiC0.7N0.3-based and TiC0.5N0.5-based ceramic tool materials

Abstract Effects of HfC addition on microstructures and mechanical properties of TiC 0.7 N 0.3 -based and TiC 0.5 N 0.5 -based ceramic tool materials were investigated. The results showed that the same by-products such as HfN 0.4 , HfNi, Ti 0.76 Hf 0.24 Ni, TiNi 0.85 Co 0.15 and HfCo 6 were discovered in these ceramics. To some extent, HfC additive can inhibit their denitrification in the sintering process. The HfC particles can produce the crack flection and a suitable HfC content can improve mechanical properties of these ceramics effectively. Besides, the TiC 0.5 N 0.5 -HfC ceramics exhibited a poor sinterability compared to TiC 0.7 N 0.3 -HfC ceramics, showing much more pores in fracture and polished surfaces micrographs; grains in TiC 0.7 N 0.3 -HfC ceramics are finer than that in TiC 0.5 N 0.5 -HfC ceramics; the HfC particles dispersion in TiC 0.7 N 0.3 -HfC ceramics is more uniform than that in TiC 0.5 N 0.5 -HfC ceramics; thus, the mechanical properties of TiC 0.7 N 0.3 -HfC ceramics are superior to that of TiC 0.5 N 0.5 -HfC ceramics. In addition, their fracture mechanism is a combination of transgranular fracture and intergranular fracture. As a consequence, the enhancement of their mechanical properties is conducive to the presence of intermetallic compounds, the fine microstructure and the suitable HfC content.

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 microstructure of Al2O3-TiB2-TiSi2 ceramic tool material

Abstract A new type of Al 2 O 3 -TiB 2 -TiSi 2 ceramic tool material was fabricated by vacuum hot pressing technique. TiSi 2 added into present composite ceramic was for better use of its superior oxidation susceptibility to crack-healing of ceramic. The fracture surface of Al 2 O 3 -TiB 2 -TiSi 2 ceramic tool material was observed by Scanning electron microscopy, energy-dispersive spectrometry and X-ray diffraction. The effects of TiSi 2 content, sintering temperature and sintering duration time on mechanical properties and microstructure of the material were discussed extensively. The average grain size was decreased with an increase in the dosage of TiSi 2 . However, an excess of TiSi 2 would cause abnormal growth of grain. Transgranular fracture and intergranular fracture were found on fracture surfaces. It indicated that the optimized content of TiSi 2 was 15 wt%, the optimized sintering parameters of the ceramic tool material were a sintering temperature of 1600 °C, a pressure of 32 MPa and a sintering duration time of 30 min. TiSi and Ti 5 Si 3 were identified as the transformed products of vacuum hot pressing. The optimum comprehensive mechanical properties of the Al 2 O 3 -TiB 2 -TiSi 2 ceramic tool material were measured with the flexural strength, Vickers hardness and the fracture toughness of 711.98±41.48 MPa, 16.89±0.27 GPa and 4.82±0.10 MPa m 1/2 , respectively.

Mechanical properties of two types of Al2O3/TiC ceramic cutting tool material at room and elevated temperatures

Two types of hot pressed ceramic cutting tool material Al2O3/TiCμ and Al2O3/TiCμ/TiCn were studied in this paper. The mechanical properties of the two were tested at room temperature and elevated temperatures (from 600 °C to 1100 °C). The effect of nano-TiC on mechanical properties of these two types of material at both room and elevated temperatures was also included in this paper. Nano-TiC, as the additive, could increase the probability of occurrence of transgranular fracture mode during the fracture, thus improving the mechanical properties of the ceramic cutting tool at room temperature. At high temperature, however, the addition of nano-TiC led to the decrease of their original mechanical properties due to the softening of grain boundary at elevated temperatures. Adding nano-TiC to the ceramic cutting tool materials could refine the matrix grain, resulting in an increase in grain boundary ratio, which made more grain boundaries soften and slip at elevated temperatures. Another important reason for the decrease of mechanical properties of Al2O3/TiC ceramic tool materials at elevated temperatures was the oxidation of TiC. The TiO2 formed by the oxidation of TiC grains on the surface layer was not dense and cracks were generated at elevated temperatures; the TiC of the inner layer, therefore, continued to be oxidized, leading to even more TiC grains available for oxidation.

Effects of metal binder on the microstructure and mechanical properties of Al2O3-based micro-nanocomposite ceramic tool material

The Al2O3−(W,Ti)C composites with Ni and Mo additions varying from 0vol% to 12vol% were prepared via hot pressing sintering under 30 MPa. The microstructure was investigated via X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Mechanical properties such as flexural strength, fracture toughness, and Vickers hardness were also measured. Results show that the main phases A12O3 and (W,Ti)C were detected by XRD. Compound MoNi also existed in sintered nanocomposites. The fracture modes of the nanocomposites were both intergranular and transgranular fractures. The plastic deformation of metal particles and crack bridging were the main toughening mechanisms. The maximum flexural strength and fracture toughness were obtained for 9vol% and 12vol% additions of Ni and Mo, respectively. The hardness of the composites reduced gradually with increasing content of metals Ni and Mo.