Microstructure and mechanical properties of WC–C nanocomposite films

WC–C nanocomposite film was prepared by using a hybrid deposition system of r.f.-PACVD and DC magnetron sputtering. W concentration in the film was varied from 5.2 to 42 at.% by changing the CH₄ fraction of the mixture sputtering gas of Ar and CH₄. Hardness, residual compressive stress and electrical resistivity were characterized as a function of W concentration. Raman spectroscopy, XRD and high resolution TEM were employed to analyze the structural change in the film for various W concentrations. In the present W concentration range, the film was composed of nano-sized WC particles of diameter less than 5 nm and hydrogenated amorphous carbon matrix. Content of the WC particles increased with increasing W concentration. However, the mechanical properties of the film increased only when the W concentration was higher than 13 at.%. Structural analysis and electrical conductance measurements evidently showed that the increase in hardness and residual stress occurred as the WC particles were in contact with each other in the amorphous carbon matrix.     

Physical,mechanical and microstructural characterization of TiC–ZrN ceramics

This study aims to investigate the impact of zirconium nitride (ZrN) additive on the microstructural features and physical-mechanical characteristics of TiC. For this objective, two different samples, namely monolithic TiC and TiC-5 wt% ZrN, were produced by spark plasma sintering method at 1900 °C for 10 min under 40 MPa. X-ray diffraction, field emission scanning electron microscopy, and thermodynamical evaluations confirmed the formation of a single solid solution of (Ti,Zr)(C,N), along with a carbon-rich secondary phase in the doped ceramic. The monolithic TiC provided a higher relative density (95.5%) than the ZrN-doped sample. The fractographical assessment revealed a change in the fracture mode of TiC from transgranular to intergranular with introducing the ZrN additive. Reinforcing TiC with ZrN resulted in a Vickers hardness of 2640 HV_0.1 kg, a flexural strength of 444 MPa, and a thermal conductivity of 14.9 W/mK. Furthermore, the TiC–ZrN sample presented a higher coefficient of friction (0.37 on average) compared to the monolithic TiC (0.34 on average).     

Microstructure and mechanical properties of B4C–TiB2 ceramic composites prepared via a two-step method

B₄C–TiB₂ ceramic composites were fabricated by a two-step method. First, B₄C–TiB₂ composite powders were synthesized from TiC–B powder mixtures at 1400 ℃, then mixed with commercial B₄C powders by ball milling and the B₄C–TiB₂ ceramic composites were prepared by hot pressing at 1950 ℃. This two-step method not only effectively refined TiB₂ grains, but also allowed the composition of the composites to be freely designed. The microstructure and mechanical properties of the composites were investigated. The results showed that the B₄C–TiB₂ ceramic composite with a 10 wt% TiB₂ content obtained the ideal comprehensive performance, with a volume density, Vickers hardness, bending strength, and fracture toughness of 2.61 g/cm³, 35.3 GPa, 708 MPa, and 5.82 MPa m^1/2, respectively. The advantages of the in-situ reaction process were fully exerted by the two-step method, which made a remarkable contribution to the excellent properties of B₄C–TiB₂ ceramic composites.     

Microstructures and mechanical properties of B4C–SiC intergranular/intragranular nanocomposite ceramics fabricated from B4C,Si, and graphite powders

B₄C–SiC intergranular/intragranular nanocomposites with high hardness and high toughness were fabricated through mechanochemical processing with B₄C, Si, and graphite powders and subsequent hot pressing without any sintering aid. The milled powders are composed of stacking-disordered SiC and nanocrystalline B₄C. Most nano/micron-sized SiC particles are homogeneously dispersed in B₄C matrix, and some nano-sized SiC and B₄C particles are embedded into B₄C grains to form an intergranular/intragranular structure. The disordered characteristic of the milled powders is the essential factor for the formation of the intragranular structure, sudden densification within the narrow temperature range (1700–1900 °C), and the preparation of dense samples under a relatively low temperature (1900 °C). The relative density, Vickers hardness, and fracture toughness of the samples sintered at 1950 °C are 98.6%, 34.3 GPa, and 6.0 MPa m^1/2, respectively. The intergranular/intragranular structure plays an important role in improving fracture toughness and hardness of the composites.     

Mechanical properties and deformation mechanisms of B4C–TiB2 eutectic composites

Samples of B₄C–TiB₂ eutectic are laser processed to produce composites with varying microstructural scales. The eutectic materials exhibit both load dependent and load independent hardness regimes with a transition occurring between 4 and 5 N indentation load. The load-independent hardness of eutectics with a microstructural scale smaller than 1 μm is about 31 GPa, and the indentation fracture toughness (5–10 N indenter load) of the eutectics is 2.47–4.76 MPa m^1/2. Indentation-induced cracks are deflected by TiB₂ lamellae, and indentation-induced spallation is reduced in the B₄C–TiB₂ eutectic compared to monolithic B₄C. Indentation-induced amorphization in monolithic B₄C and the B₄C phase of the eutectic is detected using Raman spectroscopy. Sub-surface damage is observed using TEM, including microcracking and amorphization damage in B₄C and B₄C–TiB₂ eutectics. Dislocations are observed in the TiB₂ phase of eutectics with an interlamellar spacing of 1.9 μm.     

Multidimensional nano-graphite constructed TiB2–SiC–B4C composite ceramics with the integration of mechanical and electromagnetic properties

The goal of this study is to create structure-functional integrated ceramic matrix composites with high structural strength and electromagnetic absorbing properties. The multidimensional nano-graphite (1-Dimensional rod-like nano-graphite, 0-Dimensional dispersive nano-graphite, and 2-Dimensional lamellar nano-graphite) were employed to construct TiB₂–SiC–B₄C composites via high-energy ball milling, vacuum filtration, and reactive SPS sintering. The microstructure of multidimensional nano-graphite was investigated using XRD and HRTEM and determined to be a crystal-amorphous coexisting. Furthermore, solid solution reaction and interfacial evolution are confirmed as the primary influence on the microstructure of TiB₂–SiC–B₄C composite. A significant improvement occurs on the flexural strength (647.6 MPa) and bending toughness (5.1 MPa m^1/2). Meanwhile, the multi-dimensional nano-graphite gives the TiB₂–SiC–B₄C composite the loss ability of electromagnetic waves, and the matching thickness of the 10 vol% sample is 2.4 mm and the absorption range is 10.4–11.3 GHz.     

Synthesis and performance of TiB2–B4C composites by high pressure of TiC–B mixture

TiB₂–B₄C composites were in situ synthesized and consolidated by high pressure synthesis method from a mixture of TiC and B powders at the pressure and temperature of 5.0 GPa and 1500℃-1900℃. The phase composition, microstructure, density, hardness, thermal conductivity, and electrical resistivity of TiB₂–B₄C composites were analyzed. As the increase in the synthesis temperature, the products were TiB₂ and B₄C phases and that crystallinity improved. TiB₂–B₄C composites were dense without obvious pores. TiB₂–B₄C composites synthesized at 1800℃ obtained the optimized performance, including the relative density of 98.2%, the Vickers hardness of 31.7 ± 1.2 GPa with the load of 9.8 N, the thermal conductivity of 30.3 ± 0.7 W/(m K), and the electrical resistivity of 3.3 × 10⁻³ Ω cm, respectively. The grain size of the TiB₂–B₄C composites changed with the increase in synthesis temperature, leading to the changes in hardness, thermal conductivity, and electrical resistivity.     

Synthesis,characterization and controlled release properties of zinc–aluminium-beta-naphthoxyacetate nanocomposite

An organic–inorganic nanohybrid nanocomposite was synthesized by co-precipitation method using beta-naphthoxyacetate (BNOA) as guest anion and zinc–aluminium layered double hydroxide (Zn–Al-LDH) as the inorganic host. A well-ordered nanohybrid nanocomposite was formed when the concentration of BNOA was 0.08 M and the molar ratio of Zn to Al, R = 2. Basal spacing of layered double hydroxide containing nitrate ions expanded from 8.9 to 19.5 Å in resulting of Zn–Al-BNOA nanocomposite was obtained indicates that beta-naphthoxyacetate was successfully intercalated into interlayer spaces of layered double hydroxide. It was also found out the BET surface area increased from 1.13 to 42.79 m² g^?1 for Zn–Al-LDH and Zn–Al-BNOA nanocomposite, respectively. The BJH average pore diameter of the synthesized nanocomposite is 199 Å which shows mesoporous-type of material. CHNS analysis shows the Zn–Al-BNOA nanocomposite material contains 36.2 % (w/w) of BNOA calculated based on the percentage of carbon in the sample. Release of BNOA from the lamella of Zn–Al-BNOA was controlled by the zeroth and first order kinetics at the beginning of the deintercalation process up to 200 min and controlled by pseudo-second order kinetics for the whole process. This study suggests that layered double hydroxide can be used as a carrier for organic acid herbicide controlled release formulation of BNOA.     

Effects of graphite nano-flakes on thermal and microstructural properties of TiB2–SiC composites

In the last decades, the production of ultra-high temperature composites with improved thermo-mechanical properties has attracted much attention. This study focuses on the effect of graphite nano-flakes addition on the microstructure, densification, and thermal characteristics of TiB₂–25 vol% SiC composite. The samples were manufactured through spark plasma sintering process under the sintering conditions of 1800 °C/7 min/40 MPa. Scanning electron microscopy images demonstrated a homogenous dispersion of graphite flakes within the TiB₂–SiC composite causing a betterment in the densification process. The thermal diffusivity of the specimens was gained via the laser flash technique. The addition of graphite nano-flakes as a dopant in TiB₂–SiC did not change the thermal diffusivity. Consequently, the remarkable thermal conductivity of TiB₂–SiC remained intact. It seems that the finer grains and more interfaces obstruct the heat flow in TiB₂–SiC–graphite composites. Adding a small amount of graphite nano-flakes enhances the densification of the mentioned composite by preventing the grain growth.     

High-performance B4C–TiB2–SiC composites with tuneable properties fabricated by reactive hot pressing

In this work, we systematically studied the effects of powder characteristics (B₄C, TiC and Si powders) on the existential form of toughening phases (SiC and TiB₂) as well as the overall microstructure and properties of B₄C–TiB₂–SiC composites fabricated by reactive hot pressing. The particle size of the TiC powder plays a largely determining role in the development of novel toughening phases, the TiB₂–SiC composite structure, that are formed in the B₄C matrix, while the Si particle size affects the agglomerate level of the SiC phase. The TiB₂–SiC composite structure and SiC agglomerates enhance the fracture toughness, but decrease the flexural strength. Both the microstructure and mechanical properties of B₄C–TiB₂–SiC composites can be effectively tuned by regulating the combinations of the particle sizes of the starting powders. The B₄C–TiB₂–SiC composites demonstrate flexural strength, fracture toughness and Vickers hardness in the respective range of 567–632 MPa, 5.11–6.38 MPa m^1/2, and 34.8–35.6 GPa.     

Polyaniline (PANI)–Co0.5Mn0.5Fe2O4 nanocomposite: Synthesis,characterization and magnetic properties evaluation

Polyaniline (PANI)/Cobalt-manganese ferrite, (PANI)/Co_0.5Mn_0.5Fe₂O₄, nanocomposite was synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate (APS). Microwave assisted synthesis method was used for the fabrication of core CoFe₂O₄ nanoparticles. The structural, morphological, thermal and magnetic properties of the nanocomposite were investigated in detail by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The average crystallite size of (PANI)/Co_0.5Mn_0.5Fe₂O₄ nanocomposite by the line profile method was 20±9 nm. The magnetization measurements revealed that (PANI)/Co_0.5Mn_0.5Fe₂O₄ nanocomposite has superparamagnetic behavior with blocking temperature higher than 300 K. The saturation magnetization of the composite is considerably low compared to that of CoFe₂O₄ nanoparticles due to the partial replacement of Co²⁺ ions and surface spin disorder. As temperature decreases, both coercivity and strength of antiferromagnetic interactions increase which results in unsaturated magnetization of the nanocomposite.     

Densification and mechanical properties of cBN–TiN–TiB2 composites prepared by spark plasma sintering of SiO2-coated cBN powder

cBN–TiN–TiB₂ composites were fabricated by spark plasma sintering at 1773–1973 K using cubic boron nitride (cBN) and SiO₂-coated cBN (cBN(SiO₂)) powders. The effect of SiO₂ coating, cBN content and sintering temperature on the phase composition, densification and mechanical properties of the composites was investigated. SiO₂ coating on cBN powder retarded the phase transformation of cBN in the composites up to 1873 K and facilitated viscous sintering that promoted the densification of the composites. Sintering at 1873 K, without the SiO₂ coating, caused the relative density and Vickers hardness of the composite to linearly decrease from 96.2% to 79.8% and from 25.3 to 4.4 GPa, respectively, whereas the cBN(SiO₂)–TiN–TiB₂ composites maintained high relative density (91.0–96.2%) and Vickers hardness (17.9–21.0 GPa) up to 50 vol% cBN. The cBN(SiO₂)–TiN–TiB₂ composites had high thermal conductivity (60 W m⁻¹ K⁻¹ at room temperature) comparable to the TiN–TiB₂ binary composite.     

Microstructure and mechanical properties of in-situ hot pressed (TiB2 + SiC)/Ti3SiC2 composites with tunable TiB2 content

Without impurity phases detected, fully dense (TiB₂?+?SiC)/Ti₃SiC₂ composites have been successfully synthesised by in-situ reaction hot pressing. The effect of TiB₂ content on phase composite, sintering properties, microstructure, and mechanical properties of the composites were thoroughly investigated. With TiB₂ content increasing from 0 to 50?vol.-%, the flexural strength increases first and then decreases, whereas fracture toughness, hardness and modulus show a linear increase. The maximum strength of 826?MPa was obtained at 20?vol.-% TiB₂. On the whole, the (TiB₂?+?SiC)/Ti₃SiC₂ composites exhibit a superior comprehensive mechanical properties superior to other reported Ti₃SiC₂-based composites reinforced by singular reinforcement. The significant strengthening and toughening effect induced by the in-situ incorporated TiB₂ can be ascribed to the unique properties of TiB₂ and the synergistic action of many mechanisms including particle reinforcement, pulling out of grains, crack deflection and grain refinement strengthening.     

Synthesis and characterization of corrosion-resistant and biocompatible Al2O3–TiB2 nanocomposite films on pure titanium

Alumina is widely used as a coating on a metal implant due to its favorable mechanical and biological properties. In this research, in order to improve mechanical and biological properties of alumina, a composition of nanoparticles of alumina (instead of microparticles) and titanium diboride micro powder is introduced. The atmospheric plasma spray (APS) technique was applied to deposit Al₂O₃–TiB₂ on the pure titanium substrate. The properties of Al₂O₃–TiB₂ nanocomposite coatings with various weight percent of TiB₂ (20, 30 and 40 wt%) were experimentally studied. The characteristics of nanocomposite films of TiB₂ (20, 30 and 40 wt%) were analyzed using Field Emission Scanning Electron Microscopy (FE-SEM), energy dispersive electron spectroscopy (EDX) and X-Ray Diffraction (XRD) tests. The XRD spectra exhibited that in addition to alumina and titanium diboride, the films contained titania. Thickness and morphology of the films were calculated from FE-SEM images and the thickness of the optimized coating (Al₂O₃-30 wt% TiB₂) was about 30–45 μm. Also, the roughness, corrosion resistance, hardness and cytotoxicity (MTT) tests were studied. The highest of hardness and roughness of the samples were obtained from Al₂O₃-30 wt% TiB₂. According to the obtained results from the polarization test, Al₂O₃-30 wt% TiB₂ coating had the highest corrosion resistance (222558.9962 Ω cm²). Therefore, the toxicity of Al₂O₃-30 wt% TiB₂ was investigated as the optimized coating and the results confirmed its non-toxicity and biocompatibility.     

Microstructure and mechanical properties of carbon-precursor-added B4C and B4C−SiC ceramics subjected to pressureless sintering

Organic-carbon-precursor-added B₄C and B₄C–SiC ceramics were subjected to pressureless sintering at various temperatures. The carbon precursor increased the densification of the B₄C and B₄C–SiC ceramics sintered at 2200 °C to 95.6 % and 99.1 % theoretical density (T.D.), respectively. The pyrolytic carbon content of the B₄C–SiC composite decreased with increasing SiC content. The graphitization degree of pyrolytic carbon decreased slightly with the amount of carbon precursor and content of SiC. The 95 wt. % B₄C–5 wt. % SiC composite added with 7.5 wt. % carbon precursor and sintered at 2200 °C outperformed the other B₄C–SiC composites, and its sintered density, flexural strength, Young’s modulus, and microhardness were 98.6 % T.D., 879 MPa, 415 GPa, and 28.5 GPa, respectively. These values were higher than those of composites prepared via pressureless sintering and comparable to those of composites fabricated via hot pressing and/or using metal or oxide additives.     

Assessment of mechanical properties at microstructural length scale of Ti(C,N)–FeNi ceramic-metal composites by means of massive nanoindentation and statistical analysis

It is well known the interest of the scientific community in substituting the traditional cemented carbides (WC–Co) by alternative ceramic-metal systems. In this regard, Ti(C,N)-based cermets arise as excellent candidates due to their exceptional mechanical, tribological and thermal properties. In this work, microstructurally different Ti(C,N)–FeNi cermets were processed using a combination of colloidal and powder metallurgy techniques. Three distinct ceramic/metal phase ratios were used: 85/15, 80/20 and 70/30 (volume fraction) of Ti(C,N) and FeNi respectively. Microstructural parameters and micromechanical properties (hardness and stiffness) of the three composite systems and their constitutive phases were assessed. Small-scale hardness was evaluated by means of massive nanoindentation testing and statistical analysis of the gathered data, under the consideration of three mechanically different phases: Ti(C,N) particles, metallic binder and a composite-like one, corresponding to probing regions containing both constitutive phases. It is found that values of local hardness for both composite-like and metallic phases increase as the ceramic/metal phase ratio rises. In particular, local hardness values are determined to be significantly distinct for the metallic binder in the three cermets investigated. Results are discussed and rationalized on the basis of the constrained deformation imposed for the harder phase to the softer and more ductile one. Estimated effective flow stress values for the metallic binder as well as detailed inspection of crack-microstructure interaction and fractographic features point out the effectiveness of FeNi as reinforcement phase and toughening agent for Ti(C,N)-base cermets.     

Microstructural and mechanical characterization of sol gel-derived Si–O–C glasses

The mechanical properties of three silicon oxycarbide glasses pyrolysed under inert (Ar) atmosphere were studied as a function of the pyrolysis temperature. The silicon oxycarbide glasses were prepared from various alkyl substituted alkoxysilanes such as HSi(OEt)₃ and HMeSi(OEt)₂ in different ratios by using the sol-gel method. The Si–O–C-glasses obtained were respectively: (i) silicon oxycarbide network with excess carbon, (ii) stoichometric SiC_xO_2(1−x) where x=0.30 and (iii) silicon oxycarbide matrix with an excess of Si. Si–C bonds introduced in the starting silica gel network can be partially retained in the final glass after pyrolysis under inert atmosphere. After pyrolysis at temperatures between 600–1500 °C, the presence of tetracoordinated C atoms in the silica network results in an improvement of mechanical properties and thermal stability compared with silica glass. By using elemental analysis, density, SEM, BET and XRD (combined with Rietveld-analysis), the glass characterization was performed. Flexural strength (MOR), elastic modulus (E) and Vickers hardness (H_V) were measured and will be discussed in terms of glass composition and microstructure.     

Mechanisms of TiB2 and graphite nucleation during TiC–B4C high temperature interaction

Reactive hot pressing of TiC–B₄C precursors was undertaken at 1800 °C to produce TiB₂ with carbon inclusions. Atomic mechanisms of titanium diboride nucleation, as well as sponge-like carbon inclusions and submicron platelets of graphite precipitation have been investigated. Precursor grain size, green body composition and synthesis time were varied to analyze phase transformation. The carbon left after B₄C high temperature decomposition is shown remaining as graphite sponge-like inclusions. Ab-initio calculations confirm that the boron atoms accumulation on (111) TiC plains leads to tensile stress. The developed stress cleaves TiC grains and enhances further reaction. Most of carbon expelled from TiC during its transformation into TiB₂ forms graphite submicron platelets.     

Effect of ZrB2 on the microstructure,mechanical and tribological properties of Mo–Si–B matrix composites

Composites with good mechanical and tribological properties are in high demand for engineering applications. Toward this aim, the Mo–12Si–8.5B alloy with 2.5–10 wt% ZrB₂ ceramic was prepared. The effects of the ZrB₂ content on the microstructure, mechanical properties, and tribological behavior were thoroughly investigated. The composites exhibited reduced density and enhanced hardness and strength owing to the dispersion strengthening of ZrB₂ particles, thus resulting in improved wear resistance. The frictional properties are highly dependent on the ZrB₂ content and counterpart materials. When coupled with GCr15 steel, it shows much slighter abrasive and adhesive wear; therefore, it presents a more preferable anti-wear performance. The wear rate of the composite with 7.5 wt% ZrB₂ showed a minimum value of 2.71 × 10⁻⁷ mm³N⁻¹m⁻¹.     

Microstructure and mechanical properties of (Zr,Ti)B2–SiC composites obtained by pressureless sintering of ZrB2–SiC–TiO2 powder mixtures

Multiphase ceramics have been highlighted due to the combination of different properties. This work proposes to obtain the multiphase composite of (Zr,Ti)B₂–SiC based on the mixture of ZrB₂, SiC, and TiO₂ sintered without pressure. The effect of TiO₂ addition on solid solution formation with ZrB₂, densification, microstructure, and mechanical properties was investigated. For this, 2.0 wt% TiO₂ was added to ZrB₂–SiC composites with 10–30 vol% SiC and processed by reactive pressureless sintering at 2050 °C with a 2 h holding time. Sinterability, crystalline phases, microstructure, Vickers hardness, and indentation fracture toughness of these composites were analyzed and compared to the non-doped ZrB₂–SiC samples. The XRD analysis and EDS elemental map images indicated the incorporation of Ti atoms into the ZrB₂ crystalline structure with solid solution generation of (Zr,Ti)B₂. The addition of TiO₂ resulted in matrix grain size refinement and a predominant intergranular fracture mode. The relative densities were not significantly modified with the TiO₂ addition, though a higher weight loss was detected after the sample sintering process. The composites doped with TiO₂ showed an increase in fracture toughness but exhibited a slightly lower Vickers hardness compared to composites without TiO₂ addition.