Search

Based on finite element simulation analysis, laminated ceramic tool materials with different structures were designed and the effect of laminated structure on tool state was investigated. Residual stresses in ceramic tool materials increase with the number of layers and layer–thickness ratio. Based on the simulation results, SiAlON-SiC-SiCw/SiAlON-Al2O3 ceramic tool materials (SCWAs) were prepared using the spark plasma sintering process, and the influence of residual stress on the mechanical properties and microstructure of laminated ceramic tool materials was studied. The mechanical properties of ceramic materials were significantly improved under the effect of residual stresses. The fracture toughness of SCWA4 with 7 layers and a layer–thickness ratio of 6 was 6.02 ± 0.19 MPa·m1/2, and the front and side flexural strengths were 602 ± 19 MPa and 595 ± 17 MPa, 36.3% and 39.0% higher than homogeneous SiAlON ceramics, respectively. [ABSTRACT FROM AUTHOR]

For addressing the issue of low relative density, poor fracture toughness of boron carbide ceramics, carbon nanotubes (CNTs)‐reinforced B4C‐SiC ceramic composite material was prepared via spark plasma sintering (SPS), and the impact of CNTs on the strengthening and toughening of the composite was studied. The evidence revealed that an appropriate amount of CNTs can enhance the discharge effect and improve the compactness. As the CNTs content increased, the flexural strength and fracture toughness took on a tendency to first rise and then drop. After mixing.5 wt.% CNTs, the flexural strength and fracture toughness were 499 MPa and 5.38 MPa·m1/2, which increased by 59.4% and 28.4%, respectively. The transformation of fracture mode, grain refinement, bridging and pulling‐out of CNTs efficiently enhance the mechanical properties. [ABSTRACT FROM AUTHOR]

The addition of CaF2@SiO2 and SiC whiskers to ceramic tools can improve their flexural strength and fracture toughness, reduce surface damage, and improve their cutting performance. The cutting experiments showed that under the same cutting conditions, the surface roughness of the workpiece processed with the Al2O3/TiC/SiC/CaF2@SiO2 (ATSC10) tool was significantly lower than that of the workpiece processed with the Al2O3/TiC/ SiC (ATS) tool. Additionally, the main cutting force and cutting temperature when cutting with the ATSC10 tool were lower by 30 and 31.7%, respectively. These results were attributed to the precipitation of CaF2 from the nanocoated particles during cutting and the formation of a uniform and continuous lubricating film on the surface of the tool. The wear on the front surface of the ATS tool was mainly adhesive, and that on the back tool surface was mainly abrasive. For ATSC10, the main forms of wear on the tool front surface were adhesive and abrasive, whereas the main form of wear on the tool back surface was abrasive with slight adhesive wear. The addition of nano-coated particles and whiskers improved the mechanical properties of the cutting tool while maintaining good cutting performance. [ABSTRACT FROM AUTHOR]

The Al2O3/Ti(C,N) ceramic material added micron ZrO2 whisker and nano coated CaF2@Al(OH)3 powder was fabricated. The micron ZrO2 whisker was for the toughening and reinforcing phase and the nano coated CaF2@Al(OH)3 powder was the lubricant. For obtaining a ceramic material with optimal comprehensive mechanical properties and friction properties, the influences of different compositions of the ZrO2 whisker and nano coated CaF2@Al(OH)3 powder on the microstructure and mechanical properties were analyzed, respectively. The result demonstrated that as the addition of the ZrO2 whisker was 6 vol% and the addition of the nano coated CaF2@Al(OH)3 powder was 10 vol%, the optimal self-lubricating ceramic material had optimal mechanical properties. The hardness of the ceramic material was 16.72 GPa, the flexural strength was 520 MPa and the fracture toughness reached 7.16 MPa·m1/2. The formation of the intragranular structure, whisker toughening and the phase transition of ZrO2 were the main mechanisms. [ABSTRACT FROM AUTHOR]

A new type of reduced graphene oxide‐encapsulated silicon nitride (Si3N4@rGO) particle was synthesized via an electrostatic interaction between amino‐functionalized Si3N4 particles and graphene oxide (GO). Subsequently, the Si3N4@rGO particles were incorporated into a Si3N4 matrix as a reinforcing phase to prepare nanocomposites, and their influence on the microstructure and mechanical properties of the Si3N4 ceramics was investigated in detail. The microstructure analysis showed that the rGO sheets were uniformly distributed throughout the matrix and firmly bonded to the Si3N4 grains to form a three‐dimensional carbon network structure. This unique structure effectively increased the contact area and load transfer efficiency between the rGO sheets and the matrix, which in turn had a significant impact on the mechanical properties of the nanocomposites. The results showed that the nanocomposites with 2.25 wt.% rGO sheets exhibited mechanical properties that were superior to monolithic Si3N4; the flexural strength increased by 83.5% and reached a maximum value of 1116.4 MPa, and the fracture toughness increased by 67.7% to 10.35 MPa·m1/2. [ABSTRACT FROM AUTHOR]

In order to develop a new ceramic tool material with self-repairing capability, Al2O3/TiC/TiB2 ceramic tool material was prepared by vacuum hot-pressure sintering method. The toughening and strengthening mechanism of TiB2 on Al2O3/TiC substrate was analyzed. The results show that the ceramic tool material has good comprehensive mechanical properties when the TiB2 content is 10 vol.%. Its flexural strength was 701.32 MPa, hardness was 18.3 GPa, and fracture toughness was 6.2 MPa·m1/2, which were improved by 11.6%, 2.2% and 16.1% respectively, compared with the Al2O3/TiC tool material. Fracture surfaces of the Al2O3/TiC/TiB2 ceramic tool material were characterized by SEM, EDS and XRD. The results showed that the fracture mode was a mixture of transgranular fracture and intergranular fracture. The growth of Al2O3 and TiC grains can be effectively inhibited by adding appropriate amount of TiB2, and the internal grains of the material can be refined. The TiB2 has a uniform distribution in the matrix and acts as a diffusion toughening agent. The cutting performance of Al2O3/TiC/10 vol.%TiB2 tool material was further investigated. Experiments conducted on tools made of Al2O3/TiC and Al2O3/TiC/TiB2 materials showed that the main forms of wear for both tools were abrasive wear and bonded wear. The friction coefficient of Al2O3/TiC/TiB2 tools was reduced by 10.77% compared to Al2O3/TiC tools. [ABSTRACT FROM AUTHOR]

Based on the classical Monte Carlo (MC) model and grain growth theory, the model of h-BN@Al 2 O 3 coated solid lubricant was designed and introduced into the simulation system. The Al 2 O 3 /TiB 2 /h-BN@Al 2 O 3 self-lubricating composite ceramic tool model was designed, and the microstructure evolution of tool materials during hot pressing sintering was simulated. The effects of TiB 2 and h-BN@Al 2 O 3 content on the microstructure of ceramic materials were studied, and finally the optimized composition parameters were obtained. The effects of sintering temperature and sintering pressure on the microstructure of tool materials were studied, and reasonable sintering parameters were obtained. The experimental results show that under the sintering temperature of 1650℃ and sintering pressure of 32Mpa, the ceramic material with 10%volTiB 2 and 5%volh-BN@Al 2 O 3 has the best mechanical properties, that is, the bending strength is 610MPa, the hardness is 17.9GPa, and the fracture toughness is 5.17 MPa·m1/2. SEM analysis shows that the grain growth of the material is uniform, the solid lubricant is well combined with the matrix, and the material has a good microstructure. Comparing the simulation results with the previous experimental results, it is found that the results are in good agreement, which indicates that the designed MC model reliably reflects the physical process of material grain growth, and has certain guiding significance for further research on the mechanism of grain growth. [ABSTRACT FROM AUTHOR]

In this study, TiB 2 –TiN-based composite ceramic materials modified with NiTi were prepared by a two-step spark plasma sintering process (900 °C/3 min + 1650 °C/5 min). The effects of adding different volume fractions of NiTi (0–12 vol%) on the mechanical properties and microstructure of the ceramic material were investigated. The results showed that the optimal mechanical properties of the composite ceramic were obtained when the NiTi content was 9 vol%. Its flexural strength, fracture toughness and hardness were 942.5 MPa, 5.96 MPa m1/2 and 19.8 GPa, respectively. The addition of NiTi promoted densification during the sintering process, which improved the sinterability and refined the grain size of the materials. The toughening mechanisms were attributed to branching, deflection and bridging of cracks. Furthermore, a new toughening mechanism, phase change toughening was observed due to the addition of NiTi. Its specific manifestation in TiB2–TiN–NiTi cermet materials was the limitation of crack extension, which caused NiTi to transform from austenite to martensite when the crack extended into the region containing NiTi, and this consumed most of the fracture energy. The fracture toughness of the TiB 2 –TiN–NiTi composite ceramic materials was improved by the ability of NiTi to hinder crack growth. [ABSTRACT FROM AUTHOR]

ZrB 2 /SiC ceramic granules with uniform a size and spherical shape were prepared by spray drying technology. ZrB 2 /SiC ceramic granules were added into ceramic matrix, and ZrB 2 /SiC/Si 3 N 4 ceramic tool materials with double composite architectures were prepared by spark plasma sintering technology. The mechanical properties from room temperature to 1100°C were measured. The hardness, flexural strength and fracture toughness at room temperature are 18.0 GPa, 589.0 MPa and 5.93 MPa m1/2, respectively. While the fracture toughness at 1100°C reach 6.1 MPa m1/2 increase by 74.3% compared with the ceramic tool material without double composite architectures. At high temperature, the improvement of fracture toughness is due to the addition of ZrB 2 /SiC ceramic granules that deflect the cracks and propagates along the boundary between the granules and the matrix, which greatly increase the path during the crack propagation process, thereby improving the fracture toughness of the ceramic tool material. [ABSTRACT FROM AUTHOR]

Core-shell particles are considered to be one of the primary strengthening and toughening methods of cermet. In this study, a (W,Ti,Ta)C based cermet was prepared by vacuum hot pressing sintering technology with the addition of c-BN@Al 2 O 3 (Al 2 O 3 coated c-BN). Localized high residual stress around the core-shell particles causes the strengthening and toughening mechanism at short distances behind the crack tip, such as crack deflection, secondary cracks, crack branching, and grain pull-out, even at a small volume fraction of 10 vol%. Compared with cermet without Al 2 O 3 and c-BN, the flexural strength and fracture toughness of the cermet with 10 vol% c-BN@Al 2 O 3 are increased by 35.62% and 28.45%, reaching 1462 ± 49 MPa and 13.68 ± 0.51 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

Based on the finite element model, laminated graphene ceramic tool materials were designed, and the effects of the number of layers and thickness ratio on the residual stress were investigated. According to the simulation design results, laminated Al 2 O 3 –TiB 2 –graphene/Al 2 O 3 –TiN (ATBGN) ceramic tool materials with various structures were prepared using the spark plasma sintering process, and their mechanical properties and microstructures were studied and analyzed. The fracture toughness and flexural strength of ATBGN were 8.65 ± 0.18 MPa m1/2 and 755 ± 25 MPa, respectively, which increased by 66.7% and 21.6%, respectively, compared to those of monolithic Al 2 O 3 –TiB 2 ceramic. Under the synergistic action of graphene and residual compressive stress, the multiscale deflection of cracks and the change in fracture mode occurred, which made the substantial contribution to the improvement in mechanical properties. [ABSTRACT FROM AUTHOR]

Al 2 O 3 /TiB 2 and Al 2 O 3 /TiB 2 /graphene nanoplatelets (GNPs) ceramic tool materials were prepared by spark plasma sintering, and the effect of the sintering parameters and different GNPs addition amounts on the densification, mechanical properties, and microstructure have been investigated. The optimum comprehensive mechanical properties of Al 2 O 3 /TiB 2 were obtained at synthesis conditions of 1525 °C under 30 MPa for 5 min. However, the addition of GNPs could promote the densification and improve the mechanical properties. The results show that the ceramic tool material with 0.3 wt% GNPs exhibits mechanical properties superior to those of pure Al 2 O 3 /TiB 2 ; the fracture toughness increases by 41.6% and reaches the maximum value of 7.35 ± 0.23 MPa m1/2, and the flexural strength increases by 6.4%–661 ± 16 MPa. The toughening mechanisms of Al 2 O 3 /TiB 2 /GNPs are explained by graphene pull-out, crack bridging, branching and deflection. [ABSTRACT FROM AUTHOR]

Syntactic foams (SF) with robust impermeable hollow microspheres as density adjuster have drawn much attention because of their easy-tailored low density, high mechanical strength and excellent performance especially when used in high pressure aqueous environment. In this work, specially fabricated hollow silicate glass microspheres (HSMs) with high strength to weight ratio were employed for the controlled fabrication of high strength lightweight syntactic foams. Special attention has been paid on the effects of surface physicochemical status modification of the HSMs on the mechanical strength and mechanical performance evolution in various external environments. It is found that the surface physicochemical status modification of the HSMs contributes more on the enhancement of the fracture toughness compared with that of the compressive strength. Moreover, compared with those of the pristine SF, the mechanical strength of the SF samples after different environmental exposure display a more remarkable improvement due to the surface physicochemical status modification of the HSMs, indicating an enhanced environmental stability. This work provides an additional insight to the mechanical strength and aging resistance control of SF, which holds the potential to be extended to the property improvement of similar composites with various types of silicate or glass fillers. Image 1 [ABSTRACT FROM AUTHOR]

Alumina-coated cubic boron nitride (c-BN) particles (c-BN@Al 2 O 3) were prepared using a heterogeneous nucleation method. Then, they were added to a (Ti,W)C-based cermet tool material after synthesis via vacuum hot-press sintering. The microstructure and mechanical properties of the (Ti,W)C-based cermet tool material with varying c-BN@Al 2 O 3 contents were recorded and analyzed. The results show that with increasing c-BN@Al2O3 concentration, the relative density, flexural strength, fracture toughness, and Vickers hardness all increase first and then decrease, and the average grain size first decreases and then increases. The introduction of Al 2 O 3 into the c-BN particles used for surface modification can improve the wettability and interfacial bonding strength between the c-BN and matrix particles, restrain the grain growth of the matrix particles, and improve the flexural strength of cermet tool materials. The addition of c-BN@Al 2 O 3 also alters the crack propagation mechanism of the cermet tool material and introduces multiple toughening mechanisms to improve the fracture toughness of the cermet tool material. The high hardness of c-BN and Al 2 O 3 is the main reason for the increase in hardness; however, excessive addition of such material reduces the relative density, resulting in a decrease in hardness. [ABSTRACT FROM AUTHOR]

A cBN-Al 2 O 3 -Al cutting tool material was prepared by a dual power spark plasma sintering method, and the effects of sintering temperature, holding time and Al 2 O 3 content on the microstructure and mechanical properties of cBN-Al 2 O 3 -Al cutting tool material were studied. The results showed that the dual power sintering method strengthened the spark plasma generated between the particles, increased the uniform discharge effect of the metal Al in the sintered body, generated a local high temperature and reacted with the activated cBN to produce AlN, and inhibited the phase change of cBN. When the sintering temperature was 1500 °C, the holding time was 5 min, and the pressure was 50 MPa, the overall mechanical properties of cBN-Al 2 O 3 -Al cutting tool material with 50 wt% Al 2 O 3 content were the most optimal, with a hardness of 24.45 GPa, a fracture toughness of 5.92 MPa·m1/2, and a flexural strength of 423 MPa. • cBN-Al 2 O 3 -Al cutting tool material was prepared by pulsed direct current and 200 kHz high-frequency dual power SPS sintering. • The conversion from cBN to hBN was inhibited by dual power supply sintering. • Find the best sintering temperature, holding time, Al 2 O 3 content, respectively 1500 °C, 5 min, 50 wt%. • The maximum hardness and flexural strength are 24.45 GPa and 423 MPa respectively. [ABSTRACT FROM AUTHOR]

ZrB 2 /SiC/WC ceramic tool materials with a WC content of up to 10 vol% were prepared using spark plasma sintering technology. The mechanical properties at room temperature showed that the ZrB 2 /SiC/WC ceramic tool material with a WC content of 5 vol% had the best comprehensive mechanical properties, with a hardness, flexural strength, and fracture toughness of 19.1 GPa, 590 MPa, and 4.9 MPa·m1/2, respectively. With the increase in temperature, the hardness and fracture toughness of the ZrB 2 /SiC/WC ceramic tool materials gradually decreased; however, the flexural strength first increased and then decreased. When the temperature was 600 °C, the flexural strength reached a maximum value of 630 GPa, which was an increase of 6.8% when compared to that at room temperature. The increase in flexural strength was mainly due to the increase in the transgranular fracturing during the fracture process of the ZrB 2 /SiC/WC ceramic tool material. Dry machining tests of 40Cr hardened steel were performed using ZrB 2 /SiC/WC ceramic tools. As the cutting speed increased, the tool life gradually decreased, but the surface quality of the workpiece gradually increased. When the cutting speed was 300 m/min, the tool life of the ZrB 2 /SiC/WC ceramic tool was 15.8 min, and the surface roughness Ra of the workpiece after cutting was between 1.0 and 2.0 μm. According to the wear morphology, adhesive wear was the main form of the ZrB 2 /SiC/WC ceramic tools. • ZrB 2 /SiC/WC ceramic tool materials were prepared by spark plasma sintering technology. • The change trend of the mechanical properties of ceramic tool materials from RT to 1100 °C was studied. • The mechanism of flexural strength change of ZrB 2 /SiC/WC ceramic tool materials at high temperature was studied. • The machining performance of ZrB 2 /SiC/WC ceramic tools at different cutting speeds was analyzed. [ABSTRACT FROM AUTHOR]

In order to improve the mechanical property of self-lubricating ceramic cutting tool, (W,Ti)C based ceramic composites with the additions of nano-sized CaF 2 solid lubricants were produced by vacuum hot pressing. Results showed that nano-sized CaF 2 was mainly located in matrix grains and formed the intragranular self-lubricating nanostructure. The optimal mechanical properties were achieved at 1650 °C and 15 min. The flexural strength, hardness and fracture toughness reaches the maximum of 497 MPa, 16.3GPa and 6.48 MPa·m1/2, respectively. Compared with the ceramic composite without CaF 2 , the fracture toughness was increased by 13.0%. Dry machining tests of hardened 40Cr steel were performed with these ceramic cutting tools. It indicated that with the additions of nano-sized CaF 2 as solid lubricant, the main cutting force and cutting temperature were reduced by 13.2% and 26.9%, the average friction coefficient of rake face was reduced from 0.59 to 0.32. SEM micrograph showed that a self-tribofilm was consistently formed on the rake wear area which has a good self-lubricating effect. • Nano-sized CaF 2 solid lubricant is introduced into ceramic cutting tools. • (W,Ti)C-based ceramic composites with nano-sized CaF 2 solid lubricants were prepared by vacuum hot pressing method. • The flexural strength, hardness and fracture toughness reaches the maximum of 497 MPa, 16.3GPa and 6.48 MPa·m1/2. • CaF 2 effectively reduces the coefficient of friction on the front face of the tool. [ABSTRACT FROM AUTHOR]

Nano-coated particles and whiskers were used as reinforcing additives for ceramic tool materials to take advantage of synergistic toughening and enhancement mechanisms. An Al 2 O 3 /TiC/CaF 2 @SiO 2 /SiC w ceramic tool material was fabricated by hot-pressing. Self-lubricating ceramic tool materials toughened by nano CaF 2 @SiO 2 coated particles and SiC whiskers were studied. When the addition content of nano CaF 2 @SiO 2 coated particles was 10 vol% and the content of SiC whiskers was 20 vol%, ceramic tool materials with the best comprehensive properties were obtained. The results showed that the hardness of the ceramic tool material was 16.52 GPa, the flexural strength was 698 MPa, and the fracture toughness was 6.89 MPa m1/2. Compared with the ceramic tool material with 10 vol% nano CaF 2 particles and 20 vol% SiC whiskers, the above properties were improved by 7.06%, 31.74% and 19.06%, respectively. The SiC whiskers played a toughening role, while nano CaF 2 @SiO 2 coated particles reduced the porosity, the compactness and also filled between the grain boundaries of the ceramic tool materials during sintering. This improved the interfacial bonding between ceramic grains, which increased the incidence of transgranular fracture in the ceramic tool materials. • Nano-coated particles and whiskers were used as reinforcing additives for ceramic tool materials. • An Al 2 O 3 /TiC/CaF 2 @SiO 2 /SiC w ceramic tool material was fabricated by hot-pressing. • The synergistic toughening mechanism of Al 2 O 3 /TiC/CaF 2 @SiO 2 /SiC w was also explored. [ABSTRACT FROM AUTHOR]

In order to promote the mechanical characteristics of Ti(C,N)-based self-lubricating cermet, Al 2 O 3 coated CaF 2 (CaF 2 @Al 2 O 3) nanocomposite powders are introduced into Ti(C,N) matrix to produce Ti(C,N) self-lubricating cermet materials with multilayer core-shell microstructures (Ti(C,N)/Mo–Co–Ni/CaF 2 @Al 2 O 3) by means of vacuum hot pressing sintering. Firstly, the external of the nano-CaF 2 particles was covered by a layer of nano-Al 2 O 3 , which was based on the principium of heterogeneous nucleation. Then the coated powders were added into the Ti(C,N)–Mo–Co–Ni materials system to form the microstructure of (CaF 2 @Al 2 O 3)@Mo–Co–Ni multilayer core-shell, which was based on based the high-temperature liquid phase diffusion mechanism of Mo–Co–Ni during sintering. The experimental results showed that formation of the multilayered core-shell microstructure could improve the mechanical properties of Ti(C,N) cermet materials. 10 vol% of the CaF 2 @Al 2 O 3 content in TMC (Ti(C,N)/Mo–Co–Ni/CaF 2 @Al 2 O 3) exhibited the optimal performance in the comprehensive mechanical properties, including the hardness of 23.93 GPa, the fracture toughness of 9.94 MPa m1/2, and the flexural strength of 997 MPa. Compared with Ti(C,N)/Mo–Co–Ni cermet materials, the fracture toughness and the hardness of TMC cermet materials was increased by 31.83% and 24.25%, respectively. • The preparation of CaF 2 @Al 2 O 3 coated powder was optimized. • A CaF 2 @Al 2 O 3 @Mo–Co–Ni multilayer core-shell structure was reported. • A Ti(C,N) based cermet material with good mechanical properties was prepared. • Mechanism of formation and toughening of the multilayer core-shell structure was studied. • The main reason for the improvement of mechanical properties is the multilayer core-shell structure. [ABSTRACT FROM AUTHOR]