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This study investigated the effect of Pt doping on the microstructure, mechanical and tribological property of the CrN coating. Results showed that this CrN coating exhibited a loose columnar texture and a rough surface with a high Ra value of 3.07 ± 0.035 nm. A prominent coherent growth within the grain appeared in this coating, which provides strong bond strength of coating texture resulting in a high H/E ratio of 0.083. This CrN coating showed an unidirection scratch fracture, but also possessed good wear resistance with a smooth wear track. Pt doping induced a nearly single preferential growth of (200) plane, and resulted in a dense columnar texture and a smooth surface. The Ra value was 2.71 ± 0.285 nm for the CrN–Pt 9.55 coating, and decreased to 1.04 ± 0.14 nm for the CrN–Pt 17.73 coating. However, Pt atoms greatly blocked the coherent growth within the grain, and further degraded the bond strength of coating texture. The CrN–Pt 9.55 coating showed serious multidirection scratch fracture, but also experienced severe wear accompanied with numerous cracks and adhesive debris. In contrast, the hindrance effect and mechanical degradation were further strengthened with the increase of Pt doping content. This CrN–Pt 17.73 coating suffered from most severe fracture damage and debris adhesion during the scratch and sliding wear tests. [ABSTRACT FROM AUTHOR]

In this study, TiB 2 –TiC–Al 2 O 3 gradient composite ceramic tool materials reinforced by VC/Cr 3 C 2 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/Cr 3 C 2 on the grain size were analysed, and it was found that VC/Cr 3 C 2 inhibited TiC dissolution and accelerated Al 2 O 3 re-precipitation, which in turn refined the TiC grains and coarsened the Al 2 O 3 grains. Consequently, crack deflection and intergranular fracture occurred around the TiC grains, whereas trans -granular fracture occurred inside the TiB 2 and Al 2 O 3 grains because rapid Al 2 O 3 precipitation facilitated TiB 2 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. [ABSTRACT FROM AUTHOR]

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 15 min, 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 Al 2 O 3 grains, while the intergranular fracture and crack deflection were observed around the TiC grains. [ABSTRACT FROM AUTHOR]

A water-swellable rubber (WSR) compatibilized by a functional graft copolymer, CPE- g-GMA, has been prepared by blending chlorinated polyethylene (CPE) with a superabsorbent resin (SAR) poly(acrylic acid- co-acrylamide) [P(AA-AM)]. The dependence of the WSR's water-absorbent properties on the SAR and the CPE- g-GMA contents was investigated, such as two cycles of swelling and drying by weight, and the weight percentage loss. The mechanical behavior of WSR was also studied. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 32: E83-E89, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20272 [ABSTRACT FROM AUTHOR]

Homogeneous and functional gradient nanocomposites were prepared using a two-step sintering process at a pressure of 30 MPa. The effects of macro –micro fracture morphologies and element distributions on the mechanical properties of the composites were studied. The results showed that the fracture toughness of the inner layers of the gradient material was almost the same as that of the corresponding homogeneous material. The composition content difference between the gradient layers had a significant influence on the bending strength and hardness. There was little Ni and Mo diffusion in the gradient nanocomposites because of the relatively low contents and suitable processing parameters. A gradient distribution of the metals was ensured. The surface layer thickness had little influence on the flexural strength of the gradient nanocomposite, but it had an obvious influence on the hardness and fracture toughness of the surface. The five-layered gradient composite with a surface layer thickness of 85 μm exhibited the best mechanical properties, including a flexural strength of 1021 ± 35 MPa, fracture toughness of 7.60 ± 0.21 MPa m1/2 and surface hardness of 19.26 ± 0.62 GPa. [ABSTRACT FROM AUTHOR]

Effect of predesigned multi-layer graphene (MLG) gradient on the microstructure as well as mechanical properties of MLG/WC-Co hardmetal has been investigated. Varied organic solvents and surfactants were used to identify the best combination of dispersing medium and dispersant for the dispersion of MLG. Six kinds of designed functionally graded MLG/WC-Co alloys were prepared employing two-step sintering (TSS) method. Results demonstrated that MLG can enhance the densification process and inhibit the grain growth. Meanwhile, MLG with a predesigned gradient opposite the predesigned cobalt gradient can maximally enhance the stability of predesigned cobalt gradient during liquid phase sintering, the generation of residual surface compressive stress and the mechanical properties of MLG/WC-Co composite. The enhancing mechanisms of cobalt gradient stability were systematically discussed by combining theoretical consideration with experimentation. [ABSTRACT FROM AUTHOR]

The laminated Al 2 O 3 –ZrB 2 –MgO/Al 2 O 3 –TiN–MgO (AZTM) ceramic composites were fabricated by hot-press sintering technology. The mechanical properties, microstructures and fracture behaviors of the laminated AZTM ceramic composites, were investigated comprehensively from the micro and macro scale perspectives. The residual stresses, R -curve behaviors and displacement in the laminated AZTM ceramic composites were calculated and analyzed. Compared to the monolithic Al 2 O 3 –TiN ceramic composite, the remarkable improvement in the fracture toughness of the laminated AZTM ceramic composite was obtained. Micro and macro crack deflection, crack bifurcation, bridging toughening and serrated propagation were helpful to the enhancement of the fracture toughness. An intracrystalline/intergranular mixed microstructure, as well as the combination of intergranular failure and transgranular failure contributed to the improvement of the flexural strength for the laminated AZTM ceramic composite. [ABSTRACT FROM AUTHOR]

In this study, we comprehensively investigate the critical role played by two-stage sintering (TSS) and two-dimensional (2D) graded structure on the sintering behavior and the mechanical properties of Al 2 O 3 -(W, Ti)C–TiN–Ni–Mo two-dimensional (2D) graded nanocomposites. It was observed that the optimal mechanical properties were achieved for tailored TSS conditions (θ 1 = 1700 °C, θ 2 = 1450 °C) and 2D graded structure (45°) with a hardness of 23.20 GPa, a first-layer fracture toughness of 10.56 MPa m1/2, and a flexural strength of 1005 MPa. TSS was more effective in maintaining the predesigned Ni gradient, facilitating the densification process and suppressing the grain growth, as compared to one-step sintering. The 2D graded structure played a more beneficial role in inducing residual surface compressive stress than a one-dimensional (1D) graded structure. Ceramics and metals formed a solid solution where the ceramic was in contact with the metal, which improved the fracture toughness of the 2D gradient material. [ABSTRACT FROM AUTHOR]

The comprehensive effect of the mechanical properties, laminated structure and healing conditions on the self-healing behaviors of laminated Al 2 O 3 -MgO ceramic composites was researched. The flexural strengths before and after healing at the temperatures of 715, 815 and 915 °C for 30 min, 60 min and 90 min were measured. According to recovering rate the best healing condition was 900 °C for 60 min. The crack-healing ability of the laminated Al 2 O 3 -MgO ceramic composites was improved due to the enhancement of the original flexural residual effect and the oxide content effect by the elimination of pores and the filling of cracks. In addition, the factors influencing the original flexural residual effect and the oxide content effect were analyzed. Meanwhile, the effects of the particle size and the healing temperature on the healing ability were analyzed qualitatively based on the healing of a single particle model. [ABSTRACT FROM AUTHOR]

This work investigates the critical roles of two-step sintering (TSS) and laminated structure on the sintering behavior and mechanical properties of functionally graded WC-TiC-Al 2 O 3 nanostructured composite materials doped with Cr 3 C 2 /VC. Results show that excellent mechanical properties are achieved for tailored TSS conditions with a hardness of 27.91 ± 2.3 GPa and a flexural strength of 1423.3 ± 23.5 MPa. The desirable mechanical properties are attributed to the suppressed grain growth without densification deterioration. TSS is more effective in facilitating the favorable dispersion of secondary phase toughening nano-particulates in a WC matrix than conventional sintering (CS). Cr 3 C 2 /VC dopant plays an important role in maximizing and shifting the temperature range of the kinetic window for WC-Al 2 O 3 composites. Al 2 O 3 crack deflection, transgranular Al 2 O 3 , microcracking, WC crack bridging and plate-like WC crack deflection are the major toughening mechanisms. Residual surface compressive stress induced by the graded structure is also an appreciated contribution to the improvement of mechanical properties. [ABSTRACT FROM AUTHOR]

Mechanical and tribological properties of functionally graded multilayer graphene (MLG) reinforced WC-TiC-Al 2 O 3 ceramics prepared employing two-step sintering (TSS) are determined in this paper. Results showed that MLG can act as not only an exceptional reinforcement phase, but also a superior lubricant phase. A 0.1 wt% MLG/WC-TiC-Al 2 O 3 ceramics exhibits ~ 53.3% enhancement in fracture toughness, ~ 73.8% decrement in friction coefficient, ~ 82.65% improvement in wear resistance in comparison with monolithic ceramics. MLG bending, wrapping, interface debonding, MLG wall and network, MLG induced weak interface, grains bridging by MLG, MLG pullout, crack deflection, crack bridging and crack stopping are the major toughening mechanisms. The dramatic improvement in tribological performance is attributed to the self-lubrication of MLG and easily formed friction layer in the contact interface. Furthermore, the unrivalled thermal conductivity of MLG and its rather significant effect in inhibiting the grain growth are the important contribution to the improved tribological performance. Therefore, the functionally graded MLG/WC-TiC-Al 2 O 3 ceramics are conducive to be engineered as high-speed cutting tools. [ABSTRACT FROM AUTHOR]

The reinforcing effect of multi-layer graphene (MLG) on the fracture toughness and flexural strength of an Al 2 O 3 /TiC ceramic tool material was studied by theoretical analyses and experimental observations. The crack paths induced by Vickers indentation were analyzed using the fractal method to distinguish the possible reinforcing mechanisms. High-level reinforcement was observed in the Al 2 O 3 /TiC ceramic with well-dispersed MLG. The average indentation fracture toughness was 6.14 MPa m 1/2 , against 4.98 MPa m 1/2 for the Al 2 O 3 /TiC ceramic, and the flexural strength improved from 749.6 MPa to 981.5 MPa for the 0.2 wt%-added MLG. The main reinforcing mechanisms are proposed to be the hindering effect of MLG on the crack path and the synergistic effect of weak and strong bonding interfaces, as well as grain refinement. [ABSTRACT FROM AUTHOR]

The effect of VC, Cr 3 C 2 and combination (Cr 3 C 2 and VC with varied weight ratios of Cr 3 C 2 /(Cr 3 C 2 +VC)) on the microstructure and mechanical properties of functionally graded WC-Al 2 O 3 -TiC composite synthesized employing two-step hot-pressing sintering (heated to 1700 °C and then immediately cooled to 1600 °C with a soaking time of 30min) was comprehensively investigated. Combined addition of VC and Cr 3 C 2 with an appropriate ratio to WC-TiC-Al 2 O 3 composite performed a more pronounced effectiveness on inhibiting grain growth and improving the homogeneous dispersion of Al 2 O 3 nano-particulates in WC matrix than single addition of VC or Cr 3 C 2 did. Furthermore, single Cr 3 C 2 addition outperformed VC in grain refinement and uniform distribution of Al 2 O 3 . The experimental results show that excellent mechanical properties are achieved for Cr 3 C 2 -VC additions with Cr 3 C 2 /(Cr 3 C 2 +VC) weight ratio 0.6 with a hardness of 25.64 GPa, a flexural strength of 1209.6 MPa, a fracture toughness of 11.49 MPa mm 1/2 and a surface residual stress of −591.9 MPa. High surface compressive stress, strong interface bonding, crack branching and bridging, crack deflection, microcracking and Al 2 O 3 pullout are the major mechanisms contributing to the drastically enhanced flexural strength and fracture toughness. The five-symmetric-layer graded ceramics developed in this paper provide an exceptional combination of high toughness and high hardness, which are conducive to the application as metal cutting tools. [ABSTRACT FROM AUTHOR]

To optimize the mechanical properties of Ti(C,N)-based cermets used as tool materials, the cermets with different Ni–Co binder contents and Co/(Ni + Co) weight ratios were prepared. The effects of metal binder content and Co/(Ni + Co) ratio on the microstructure and mechanical properties of Ti(C,N)-based cermets were investigated by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and measuring the transverse rupture strength (TRS), Vickers hardness ( HV ) and fracture toughness ( K IC ). The experimental results reveal that increasing Ni–Co binder content can increase the thickness of rim phases by improving the solid solution reaction and the wetting of hard phases. The cermets with 25 wt.% binder addition present good comprehensive mechanical properties, which is attributed to the moderate rim phases and uniformly distributed Ti(C,N) grains. The Co/(Ni + Co) weight ratios in binder have a great influence on the grain sizes and microstructure features of Ti(C,N)-based cermets, in virtue of the synergic effects between the wettability of Co and the solubilizing capacity of Ni on hard phases. The cermets with pure Co as binder exhibit optimal mechanical properties with a TRS of 1767 ± 81 MPa, a hardness of 12.26 ± 0.10 GPa and a K IC of 8.40 ± 0.47 MPa m 1/2 , which meet the requirements for tool materials. And the cermets with a Co/(Ni + Co) ratio of 0.2 have the second best mechanical properties with a TRS of 1848 ± 201 MPa, a hardness of 11.12 ± 0.40 GPa and a K IC of 9.43 ± 0.54 MPa m 1/2 , in which the lower hardness can be further improved by optimizing the compositions and sintering process. [ABSTRACT FROM AUTHOR]

Si 3 N 4 /(W, Ti)C/Co nano-composite ceramic tool materials with multilayered structure were fabricated by hot pressing technology. The composites without Co were used as the surface layers and the composites containing Co were used as the inner layers. The flexural strength, fracture toughness, and hardness of the composites were tested, and the fracture surfaces and indention cracks were observed. The experimental results showed that the flexural strength and fracture toughness were largely increased by the graded structure and the high hardness was still maintained. The five-layer graded nano-composites, with a thickness ratio of 0.2, which were sintered under a pressure of 30 MPa at 1700 °C in vacuum condition for 45 min, had the optimum comprehensive mechanical properties with a flexural strength of 992 MPa, a hardness of 17.83 GPa, and a fracture toughness of 10.5 MPa·m 1/2 . The formation of elongated β-Si 3 N 4 grains and the residual compressive stress in the surface layer induced by the graded structure contributed to the improved properties. A synergistic effect of intergranular and transgranular fracture, crack bridging, and deflection contributed to the strengthening and toughening mechanisms. [ABSTRACT FROM AUTHOR]

An appropriate heating rate in the sintering process is crucial to obtain the Ti(C,N)-based cermets with superior properties. In this paper, Ti(C,N)-based cermets were sintered to investigate the influence of heating rate on the mechanical properties and microstructure of the cermet materials. The transverse rupture strength (TRS), Vickers hardness ( HV ) and fracture toughness ( K IC ) were tested. The microstructure, indention crack, fracture morphology and phase composition of the cermets were also studied by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results reveal that the heating rate has a great influence on the mechanical properties and microstructure of Ti(C,N)-based cermets. The cermets sintered at the heating rate of 3 °C/min between 1300 °C and 1430 °C have the optimum comprehensive mechanical properties with a transverse rupture strength of 1605±107 MPa, a hardness of 12.02±0.25 GPa and a fracture toughness of 10.73±0.40 MPa m 1/2 . The heating rate can affect the reaction among the constituents of Ti(C,N)-based cermets and then influence the elements distribution in the core–rim microstructures and the lattice parameter of Ti(C,N) phase. When the heating rate is between 2 °C/min and 5 °C/min, the lower the heating rate is, the coarser the Ti(C,N) grains become. A higher heating rate is detrimental to the formation of core–rim microstructures, and a lower heating rate can result in grain coarsening and inhomogeneous microstructure. The observation of indention cracks and fracture surfaces show that the intergranular cracks and intergranular fractures mainly occur in the cermets with larger binder mean free path and medium grains. While the cleavage fractures appear more in the cermets with grain coarsening, and the transgranular fractures exist more in the cermets with non-fully developed fine grains. [ABSTRACT FROM AUTHOR]

A suitable sintering method is important to obtain the Ti(C,N)-based cermets with superior properties. In this paper, Ti(C,N)-based cermets were fabricated by hot-pressing sintering (HP) and conventional pressureless sintering (PLS) technology, respectively, to investigate the influence of different sintering methods on the microstructure and mechanical properties of cermets materials. The microstructure, fracture morphology, indention cracks and phase composition were observed and detected using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The transverse rupture strength (TRS), Vickers hardness ( HV ) and fracture toughness ( K IC ) were also measured. The results reveal that all of the Ti(C,N)-based cermets exhibit core–rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. The grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. The sintering process has no influence on the phase composition of cermets, but affects the phase content and crystallinity. The samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness. [ABSTRACT FROM AUTHOR]

The CrWN glass molding coating was synthesized by plasma enhanced magnetron sputtering (PEMS). The effect of annealing environment (e.g., vacuum, N 2 and Air) on the microstructure and mechanical property of as-deposited coating was investigated by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscope (AFM) and nanoindentation tests. Results showed that the as-deposited coating exhibited dense columnar structure consisting of multilayer CrN and W 2 N phases. The vacuum annealed coating showed similar thickness to that of as-deposited coating, but underwent visible surface coarsening because of slight oxygen erosion. The N 2 and air annealed coatings suffered from varying degree of oxidation damage accompanied by the formation of mixed WO 3 -CrWO 4 phases, which consequently resulted in severe thickness expansion and surface coarsening. The vacuum annealing induced a spinodal decomposition of supersaturated solid solution to form nm-sized CrN and W 2 N domains. Strain fields originating from the lattice mismatch eventually caused a pronounced age-hardening in the vacuum annealed coating. Whereas the N 2 and air annealed coatings showed significant mechanical degradation because these loose WO 3 -CrWO 4 oxides degraded the stable matrix structure. Our results clearly demonstrated that vacuum environment effectively suppressed the oxidation damage and mechanical degradation of glass molding coating. • The microstructure and mechanical property of the annealed coating are studied. • The vacuum annealing induces spinodal decomposition and light oxidation damage. • The N 2 and air annealing induce serious volume expansion and surface coarsening. • The vacuum annealed coating shows a pronounced age-hardening effect. • The N 2 and air annealed coatings suffer from remarkable mechanical degradation. [ABSTRACT FROM AUTHOR]