Depth profile analyses of nc-TiC/a-C:H coating prepared by balanced magnetron sputtering

Nanocrystalline titanium carbide embedded in an hydrogenated amorphous carbon matrix (nc-TiC/a-C:H) shows high hardness and Young's modulus together with low wear and low friction coefficient. In this paper, we report on the preparation of well adherent nc-TiC/a-C:H coatings ~ 5 μm thick on stainless steel substrates using a well balanced magnetic field configuration and only very low power RF bias on the substrate. Hardness and Young's modulus of these coatings are 43 GPa and 380 GPa, respectively. The mechanical properties – hardness and Young's modulus – measured from the coating's top reach the values obtained at optimized experiments where the unbalanced magnetic field configuration was used. A simple method of depth profiling suitable for evaluation of mechanical properties of several micrometers thick coatings is developed and employed. The paper reports on the depth profile analyses of the coating hardness, Young's modulus, composition and morphology.     

The effect of vacuum annealing on the microstructure,mechanical and electrical properties of tantalum films

The microstructure, mechanical and electrical properties of vacuum annealed tantalum films were studied. X-ray diffraction spectra confirmed the presence of mixed (α and β) phases in the as-deposited Ta films. After vacuum annealing (at 750 °C for 1 h), the metastable β-phase was completely transformed to stable α-phase. The grain size increased (from 35 ± 3 nm to 92 ± 3 nm) with the increase in annealing temperature. The mixed (α and β) phases resulted in higher hardness and higher Young's modulus. The film annealed at 750 °C for 1 h exhibited lower resistivity (52 ± 4 μΩ-cm), lower hardness (H = 10.4 ± 1.3 GPa) and lower Young's modulus (Y = 185 ± 5 GPa) as compared to the as-deposited and annealed (at temperature < 750 °C) films. This is attributed to the phase transformation from β to α at an annealing temperature of 750 °C.     

Electro-stiffening in polypyrrole films: Dependence of Young's modulus on oxidation state,load and frequency

Electrochemically driven actuation of polypyrrole in aqueous sodium hexafluorophosphate (NaPF₆) solution has been shown to produce repeated large strains (>6%) at low voltages and with high conductivity, making it one of the most promising electroactive conducting polymers. Little is known about the voltage dependent stiffness of this version of the polymer. This information is important in determining the strain as a function of load. In this paper the complex Young's modulus (storage and loss components) of a hexafluorophosphate-doped polypyrrole film in aqueous NaPF₆ electrolyte at different oxidation states, under various loads and as a function of the frequency of the applied load, is investigated. Uniformity of doping was ensured by allowing enough time to reach steady state charge levels, and the creep during measurements was minimized by using preconditioning cycles. The results of this study show that storage modulus decreases (from 1 GPa to 0.80 GPa) as the polypyrrole oxidation potential increases (from ?0.4 V to +0.4 V versus Ag/AgCl reference electrode). The loss modulus, on the other hand, increases from 55 MPa to 80 MPa. An increasing trend in the Young's modulus is also observed with the applied load. The storage modulus increases from 0.65 GPa to 1 GPa by increasing the applied load from 0.2 MPa to 2.5 MPa. The modulus is found to increase with time through the experiment, which may be due to stretch alignment of the polymer. It is also observed that complex Young's modulus increases in proportion to the logarithm of frequency.     

Mechanical and barrier properties of MOCVD processed alumina coatings on Ti6Al4V titanium alloy

This study focuses on the implementation of different aluminum oxide coatings processed by metal-organic chemical vapor deposition from aluminum tri-isopropoxide on commercial Ti6Al4V titanium alloy to improve its high temperature corrosion resistance. Films grown at 350 °C and at 480 °C are amorphous and correspond to formulas AlOOH, and Al₂O₃, respectively. Those deposited at 700 °C are composed of γ-Al₂O₃ nanocrystals dispersed in a matrix of amorphous alumina. Their mechanical properties and adhesion to the substrates were investigated by indentation, scratch and micro tensile tests. Hardness and rigidity of the films increase with increasing deposition temperature. The hardness of the coatings prepared at 350 °C and 480 °C is 5.8 ± 0.7 GPa and 10.8 ± 0.8 GPa respectively. Their Young's modulus is 92 ± 8 GPa (350 °C) and 155 ± 6 GPa (480 °C). Scratch tests cause adhesive failures of the films grown at 350 °C and 480 °C whereas cohesive failure is observed for the nanocrystalline one, grown at 700 °C. Micro tensile tests show a more progressive cracking of the latter films than on the amorphous ones. The films allow maintaining good mechanical properties after corrosion with NaCl deposit during 100 h at 450 °C. After corrosion test only the film deposited at 700 °C yields an elongation at break comparable to that of the as processed samples without corrosion. The as established processing–structure–properties relation paves the way to engineer MOCVD aluminum oxide complex coatings which meet the specifications of the high temperature corrosion protection of titanium alloys with regard to the targeted applications.     

Effect of powder feed rate on the mechanical properties of WC-5 wt%Ni coatings deposited using low pressure cold spray

WC-5 wt%Ni coatings were fabricated onto 3CR12 stainless steel plates using low pressure cold spray deposition. The powder feed rate of the volumetric feeder was varied at 50% (23.6 rpm, 6.8 ± 1 g min^− 1), 75% (35.7 rpm, 10.1 ± 0.9 g min^− 1), and 100% (58.9 rpm, 15 ± 1.1 g min^− 1), and the resulting influence on the mechanical properties of the coatings was investigated. The results were analyzed using a two-parameter Weibull distribution and linear regression analysis. A new parameter to quantify WC particle refinement is proposed. A powder feed rate of 75% produced the best coating properties, achieving a high hardness (2.56 GPa), low porosity (0.55%), high interfacial toughness (12.61 MPa m^0.5), high Young's modulus (69.23 GPa), and good fracture toughness (2.81 MPa m^0.5). This feed rate appeared to be the optimum deposition parameter to produce dense coatings, achieving a high level of Ni plastic deformation and a high amount of refined WC particles, which are too small to cause significant erosion during impact, and are therefore better able to be retained by the ductile binder.     

Mechanical and tribological properties of electrically conductive SiC based cermets

Three different types of SiC based cermets with various content (30, 40, 50 wt.%) of electrically conductive TiNbC phase have been fabricated by hot-pressing without sintering additives. The effect of TiNbC content on the basic mechanical, electrical and tribological properties of SiC-TiNbC cermets was investigated. Tribological properties have been characterized by the ball-on-disc method at the ambient temperature and dry wear conditions with air humidity 35–40% at the load of 5–30 N, sliding distance of 500 m, with the static partner made from SiC. Corresponding wear rate was calculated and wear mechanisms were identified. Resulting materials were relatively hard, with increasing amount of TiNbC the hardness increased from 19.8 ± 1 GPa for 30 wt.% of TiNbC up to 25.4 ± 0.9 GPa at 50 wt.% of TiNbC. The fracture toughness values were independent on TiNbC phase and varied between 2.7 and 2.9 MPa.m^1/2. Similarly, Young's modulus increased from 354 GPa to 435 GPa. It was found that electrical conductivity of SiC cermets was rapidly improved with increased fraction of metallic phases and was three orders of magnitude higher at 30 wt.% TiNbC addition and around four order of magnitude higher at 50 wt.% of TiNbC metallic phase comparing to conventional semiconductive SiC ceramics with electrical conductivity ~ 10 Sm^− 1. Coefficient of friction (between 0.3 and 0.5) and wear resistance (10^− 6–10^− 7 mm³/Nm) were comparable with the wear resistant SiC materials.     

Effect of SiC/ZrC ratio on the mechanical and ablation properties of C/C–SiC–ZrC composites

The effect of SiC/ZrC weight ratio on the mechanical and ablation properties of carbon/carbon composites modified by SiC nanowires reinforced SiC–ZrC ceramics (C/C–SiC–ZrC) was studied. Results showed that C/C–SiC–ZrC composites with a SiC/ZrC ratio of 1:1.5 exhibited good mechanical and ablation properties. The flexural strength and modulus were 201 ± 20 MPa and 18 ± 1 GPa, respectively. After ablation for 120 s, the linear and the mass ablation rate were 0.012 mm/s and 0.0019 g/s. The good performance is attributed to a higher density, the reinforcing effect of SiC nanowires and the proper SiC/ZrC ratio.     

Formation,ductile deformation behavior and soft-magnetic properties of (Fe,Co,Ni)–B–Si–Nb bulk glassy alloys

Fe-based [(Fe,Co,Ni)_0.75B_0.2Si_0.05]₉₆Nb₄ bulk ferromagnetic glassy alloy rods with the diameters up to 4 mm were synthesized by copper mold casting. The addition of Ni element caused no decrease in glass-forming ability and fracture strength, but increased the compressive deformation ductility of this Fe-based bulk glassy alloy system. The glassy alloy rods exhibit super-high fracture strength over 4000 MPa, high Young's modulus over 200 GPa, elastic strain of 0.02 and plastic strain up to 0.005. The bulk glassy alloys also exhibit good soft-magnetic properties, i.e., high saturation magnetization of 0.8–1.1 T, low coercive force below 3 A/m, and high permeability of 1.6–2.1 × 10⁴ at 1 kHz. The success of synthesizing a super-high strength Fe-based bulk glassy alloy with some compressive plastic strain and good soft-magnetic properties is encouraging for future development of Fe-based bulk glassy alloys as new engineering and functional materials.     

Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

W-ZrC composites prepared by reactive melt infiltration of Zr2Cu alloy into partially carburized W preforms

W-ZrC composites without residual WC have been prepared for the first time by reactive infiltration at 1300 °C for 1 h in vacuum using a molten Zr₂Cu alloy and a newly designed partially-carburized W powder as raw materials. The as-synthesized composites consist of two major phases of W and ZrC, in which the content of W is 65 vol%. The reaction time needed to produce a fully densified W-ZrC bulk ceramic is distinctly shortened by this means, as contrasted with conventional WC/W or WC preforms. The microstructural evolution during reactive melt infiltration is investigated to obtain a better understanding of reaction mechanisms and mechanical properties of the W-ZrC composites derived by infiltrating Zr₂Cu alloy into partially carburized W preforms. The flexural strength, Young's modulus and fracture toughness for the W-ZrC composite are 554 MPa, 339 GPa and 9.7 MPa·m^1/2, respectively.     

Microstructural development and mechanical properties of reactive hot pressed nickel-aided TiB2-SiC ceramics

TiB₂-SiC composites with different amounts of Ni (0, 2 and 5 wt.%) added as sintering aid were fabricated by reactive hot pressing (RHP). The mechanical properties were assessed under ambient conditions and the flexural strength was further tested in the temperature range of 700–1000 °C. The microstructures of the composites were characterized by a scanning electron microscope (SEM), transmission electron microscope (TEM) and energy-dispersive spectrometer (EDS). The flexural strength degradation mechanism occurring at elevated temperatures was studied. Addition of a moderate amount of Ni led to an improvement of the mechanical properties at room temperature. For the investigated ceramic composites, TiB₂-SiC-5 wt.% Ni sample showed significantly enhanced mechanical properties, i.e., a flexural strength of 1121 ± 31 MPa, a fracture toughness of 7.9 ± 0.58 MPa·m^1/2, a hardness of 21.3 ± 0.62 GPa, and a relative density of 98.6 ± 1.2%. Ni distributed along grain boundaries improved the interface strength. The improved fracture toughness was ascribed to crack deflection, grain rupture and crack shielding effect of Ni. A substantial strength degradation occurred at elevated temperatures, which was attributed to softening of the grain boundaries, surface oxidation and sliding of grain boundaries. The elastic modulus was found to decrease with increasing temperature.     

Effect of vacuum annealing on characteristics of the HCl-doped polyaniline pellets

Powders of HCl-doped polyanilines were prepared by using a solution polymerization process and then were pressed to the polyaniline pellets. The pellets were annealed in vacuum at 140, 200 and 260 °C for times up to 120 min, respectively. Electrical property and micromorphology of the pellets were studied by using a four-point probe technique and a scanning electron microscopy. The conductivity of the pellets decreases sharply when the annealing time reaches 30 min and then decreases gradually with further increasing annealing time. When the pellets are annealed under the conditions of 200 °C/120 min, 260 °C/90 min and 260 °C/120 min, the resistance of the pellets could not be measured by the four-point probe technique and the pellets show an insulating characteristic. The breakdown voltage increases with increasing annealing temperature and time. The maximum breakdown voltage is about 875 V/cm. The degradation of the conductivity is mainly attributed to the loss of chlorine in the polyaniline pellets. The micromorphology of the pellets becomes heterogeneous with thermal aging.     

Effects of carbamide shape and content on processing and properties of steel foams

Spherical and irregular carbamide particles covered with Fe–1.5% Mo steel powder have been employed to produce foams using space holder-water leaching technique in powder metallurgy. Foams having porosities between 49.2% and 71.0% were produced after sintering at 1200 °C for 60 min. The effect of carbamide shape and content on the foams’ processing, microstructure and mechanical properties has been evaluated. Using irregular carbamide particles and increasing its content decreased leaching time. The extents of specimens’ volumetric expansion after carbamide leaching and volumetric shrinkage after sintering also depended on volume fraction and carbamide shape. Final porosity was directly related to the added fraction of carbamide. Pore shape was similar to initial carbamide particle shape. Foams having irregular pore shape were observed to have compressive yield strengths between 20 MPa and 92 MPa and Young's moduli between 0.45 GPa and 2.69 GPa. The corresponding values for foams having spherical pore shape varied between 25 MPa and 112 MPa and between 0.71 GPa and 2.91 GPa, respectively. The foams’ strength increased with increasing relative density. Microstructure having spherical pores resulted in better compressive behavior.     

The effect of substrate position on the microstructure and mechanical properties of SiC coatings on carbon/carbon composites

In this work, silicon carbide (SiC) coatings were produced on carbon/carbon composites using a chemical vapour deposition (CVD) method. During deposition, the temperature was fixed at 1200 °C and the coatings were produced by placing substrates at three different positions (340, 380 and 420 mm from the inlet) in the CVD reactor. The effect of substrate position on the microstructure and mechanical properties of the SiC coatings were experimentally investigated. The phase composition, surface morphology, defects and microstructure were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman Spectroscopy. The hardness and Young's modulus were measured using a nano-indentation method while fracture toughness was evaluated by micro-indentation. It was found that the deposition rate decreased linearly as substrate position moved far from the reactor inlet. In all coatings, only β-SiC phase was observed with a high density of stacking faults. It was found that the substrate position in the CVD reactor has a significant effect on the microstructure, grain size and crystallinity of the coating. At 340 and 420 mm substrate positions, a well-developed faceted microstructure with high crystallinity was observed while at 380 mm substrate position, the coating having lenticular-like fine grains with low crystallinity was obtained. The hardness values obtained from the top surface of the coatings are found to be higher than those from the cross-section, although the Young's modulus data (measured from the top surface and cross-section) were observed to be similar. At 380 mm substrate position, hardness, Young's modulus and fracture toughness were found to be the lowest compared to that of the coatings produced at 340 and 420 mm substrate positions. It is concluded that the SiC coatings with better mechanical properties can be produced by adjusting the substrate position in the CVD reactor.     

Chromium carbide–CNT nanocomposites with enhanced mechanical properties

Chromium carbide is widely used as a tribological coating material in high-temperature applications requiring high wear resistance and hardness. Herein, an attempt has been made to further enhance the mechanical and wear properties of chromium carbide coatings by reinforcing carbon nanotubes (CNTs) as a potential replacement of soft binder matrix using plasma spraying. The microstructures of the sprayed CNT-reinforced Cr₃C₂ coatings were characterized using transmission electron microscopy and scanning electron microscopy. The mechanical properties were assessed using micro-Vickers hardness, nanoindentation and wear measurements. CNT reinforcement improved the hardness of the coating by 40% and decreased the wear rate of the coating by almost 45–50%. Cr₃C₂ reinforced with 2 wt.% CNT had an elastic modulus 304.5 ± 29.2 GPa, hardness of 1175 ± 60 VH_0.300 and a coefficient of friction of 0.654. It was concluded that the CNT reinforcement increased the wear resistance by forming intersplat bridges while the improvement in the hardness was attributed to the deformation resistance of CNTs under indentation.     

High temperature micropillar compression of Al/SiC nanolaminates

The effect of the temperature on the compressive stress–strain behavior of Al/SiC nanoscale multilayers was studied by means of micropillar compression tests at 23 °C and 100 °C. The multilayers (composed of alternating layers of 60 nm in thickness of nanocrystalline Al and amorphous SiC) showed a very large hardening rate at 23 °C, which led to a flow stress of 3.1 ± 0.2 GPa at 8% strain. However, the flow stress (and the hardening rate) was reduced by 50% at 100 °C. Plastic deformation of the Al layers was the dominant deformation mechanism at both temperatures, but the Al layers were extruded out of the micropillar at 100 °C, while Al plastic flow was constrained by the SiC elastic layers at 23 °C. Finite element simulations of the micropillar compression test indicated the role played by different factors (flow stress of Al, interface strength and friction coefficient) on the mechanical behavior and were able to rationalize the differences in the stress–strain curves between 23 °C and 100 °C.     

Elastic properties of hard cobalt boride composite nanoparticles

This paper reports on the determination of elastic and hardness properties of Co–B composite nanoparticles (CNP). Co boride materials is usually known for their functional properties (hydrogen catalysis, magnetism, corrosion, biomedics), but nanoscale dimensions also bring significant mechanical properties. In situ compression tests of 70–150 nm core–shell silica-coated Co₂B CNP (Composite nanoparticles) were performed for the first time with a nanoindenter in the load range 30–300 μN. The CNP modulus is comparable with the bulk material (E_CNP = 159–166 GPa), but the hardness is as much as 5 times higher (～4.5 ± 1.0 GPA). Both modulus and hardness (to a lesser extent) are found to increase with the applied pressure. The paper first addresses the limitations of ordinary contact analysis intended for single-phase NP, and then presents a hybrid Oliver–Pharr strategy suitable for CNP, where numerical modeling overcomes issues related to anisotropy and heterogenety of the composite nanostructure that hinder the direct application of basic contact models. An alternative regression-based approach for estimating modulus and hardness is also considered for comparison. The importance of the model selection for the contact area A for accurate modulus and hardness results is emphasized. Besides typical Hertzian, geometrical and cylindrical area models, a new one is formulated from a “rigid-sphere” approximation, which turned out to perform best and consistently in this study, on a par with the cylindrical model. Finally, evidence of the magnetic nature of CNP and, unexpectedly, reverse plasticity is provided.     

Mechanical behavior of diamond matrix composites with ceramic Ti3(Si,Ge)C2 bonding phase

Polycrystalline diamond, PCD, compacts are usually produced by high pressure–high temperature (HP–HT) sintering. This technique always introduces strong internal stresses into the compacts, which may result in self-fragmentation or graphitization of diamond. This may be prevented by a bonding phase and Ti₃(Si,Ge)C₂ was so investigated. This layered ceramic was produced by Self Propagating High Temperature Synthesis and the product milled. The Ti₃(Si,Ge)C₂ milled powder was mechanically mixed, in the range 10 to 30 wt.%, with 3–6 μm diamond powder (MDA, De Beers) and compacted into disks 15 mm in diameter and 5 mm high. These were sintered at a pressure of 8.0 GPa and temperature of 2235 K in a Bridgman-type high pressure apparatus. The amount of the bonding phase affected the mechanical properties: Vickers hardness from 20.0 to 60.0 GPa and Young's modulus from 200 to 500 GPa, with their highest values recorded for 10 wt.% Ti₃(Si,Ge)C₂. For this composite fracture toughness was 7.0 MPa m^1/2, tensile strength 402 MPa and friction coefficient 0.08. Scanning and transmission electron microscopy, X-ray and electron diffraction phase analysis were used to examine the composites.     

The mechanical properties of a nanocrystalline Al2O3/a-Al2O3 composite coating measured by nanoindentation and Brillouin spectroscopy

In this work, ellipsometry, Brillouin spectroscopy and nanoindentation are combined to assess the mechanical properties of a nanocrystalline Al₂O₃/a-Al₂O₃ composite coating with high accuracy and precision. The nanocomposite is grown by pulsed laser deposition at either room temperature or 600 °C. The adhesive strength is evaluated by nanoscratch tests. In the room temperature process the coating attains an unusual combination of compactness, strong interfacial bonding, moderate stiffness (E = 195 ± 9 GPa and ν = 0.29 ± 0.02) and significant hardness (H = 10 ± 1 GPa), resulting in superior plastic behavior and a relatively high ratio of hardness to elastic modulus (H/E = 0.049). These features are correlated to the nanostructure of the coating, which comprises a regular dispersion of ultrafine crystalline Al₂O₃ nanodomains (2–5 nm) in a dense and amorphous alumina matrix, as revealed by transmission electron microscopy. For the coating grown at 600 °C, strong adhesion is also observed, with an increase of stiffness and a significant enhancement of hardness (E = 277 ± 9 GPa, ν = 0.27 ± 0.02 and H = 25 ± 1 GPa), suggesting an outstanding resistance to wear (H/E = 0.091).     

Effect of tungsten carbide nanoparticles on mechanical properties and sinterability of B4C-WC nanocomposites using pressureless sintering method

The effect of tungsten carbide (WC) nanoparticles on sinterability and mechanical properties of boron carbide is investigated in this study. Boron carbide, being one of the hardest materials nowadays, has a variety of applications in wear-resistant components such as cutting tools. The low strength and low fracture toughness property of this material is the drawback in its application. Production of high density boron carbide is a problem due to its covalent bonds, low plasticity, surface energy and self-diffusion ratio, high resistance to slide in the grain boundaries etc… Boron carbide samples containing 5,10,20 and 30 vol.% WC were manufactured by firstly cold press and then sintering at three elevated temperatures of 2150 °C, 2200 °C and 2250 °C. It observed that addition of WC nanoparticles results in increase in mechanical properties and density of boron carbide. The highest increase is in the 30 vol.% sample with sintering temperature of 2250 °C were the density is improved by 23%, hardness by 33%, Young's modulus by 53%, and fracture toughness by 38% compared to pure boron carbide.