A tribological study of tetrahedral amorphous carbon films prepared by filtered cathodic vacuum arc technique

In this study, a series of tetrahedral amorphous carbon films (ta-C) were deposited on silicon, W18Cr4 V high-speed and Cr18Ni9 stainless steel substrates respectively by using pulsed filtered cathodic vacuum arc system with a MEVVA source, and ta-C film’s tribological properties, including the structure, mechanical performance, adhesion, friction and wear character, were investigated. The results show: the hardness and elastic modulus of ta-C film on a high-speed substrate were reached to 76 and 453 Gpa, respectively; and the effects of substrate and film thickness on ta-C film’s friction coefficients have been studied as well; moreover, the corresponding adhesion damage mechanism and wear damage mechanism have been investigated, respectively.     

Nanoindentation of LaCrO3 thin films

Nanoindentation of LaCrO₃ thin films deposited by radio-frequency magnetron sputtering onto stainless steel substrates was performed using an XP Nanoindenter. The “as-deposited” film was amorphous but transformed to an orthorhombic LaCrO₃ perovskite structure after annealing at 1073 K for 1 h. The film thickness in the “as-deposited” state was 800 nm. Single loading/unloadings were performed in the displacement control mode on the crystalline film using different maximum displacements (50, 200, 400, and 800 nm). Therefore, the integral response of the film−substrate system was probed at different distances from the substrate. Nanoindentation experiments on LaCrO₃ perovskite films revealed sharp “pop-in” events at certain loads. Such “pop-ins”, are most likely caused by the orthorhombic-to-rhombohedral phase transition which is known to occur in a LaCrO₃ perovskite structure under pressure. However, such discontinuities have never been observed upon indentation of the amorphous “as-deposited” La-Cr-O thin films, and the pressure found to be typical of this transition in the LaCrO₃ thin films is higher than previous bulk LaCrO₃ sample studies. Mechanical characteristics of the films, such as hardness and Young’s modulus, were also measured.     

Nanoindentation Measurements of the Mechanical Properties of Ni Thin Films: Effects of Film Microstructure and Substrate Modulus

This paper presents the results of nanoindentation measurements of the hardness and moduli of normally and obliquely deposited nanocrystalline Ni films on substrates of SiO₂, Si, and bulk Ni. Following an initial characterization of film microstructure and surface topography with atomic force microscopy (AFM), the paper examines the effects of film microstructure, film thickness, and substrate modulus on the measured film mechanical properties. Obliquely deposited films are shown to have lower hardness values than normally deposited films. The measured hardness values and material pile-up are also shown to depend significantly on the mismatch between the film modulus and substrate modulus. A framework is presented for quantifying the effects of substrate modulus mismatch on basic film mechanical properties.     

Electrophoretic deposition of organically modified gibbsite nanocomposites with liquid crystalline character

A scalable synthetic approach was developed for the purpose of producing nanoplatelet composites with nacre-like structural organization. Gibbsite nanoplatelets were first synthesized and then organically modified to provide stable suspensions in organic solvents. The nanoplatelets were subsequently deposited from select organic phases using nonaqueous electrophoretic methods. The electrophoresis was carried out in the presence of organic diacrylate monomer resins that were ultimately retained to form thick (ca. 10–1,000 μm) nanocomposite films. The resulting optically transparent films exhibited a high solids loading (>40 % by volume) and a layered morphology consistent with colloidal liquid crystal systems. Following release from the conductive substrate, the deposited films were rolled, pressed, and polymerized to form bulk nanocomposites with improved strength and elastic modulus. The stratified organization of the nanoplatelets was successfully preserved throughout the processing steps. The deposition method is useful for the continuous production of bulk nanocomposites, and the resulting materials serve as a platform for further developments with alternative nanoplatelets possessing improved mechanical properties and optical transparency.     

Mechanical studies on poly(vinyl chloride)–poly(methyl methacrylate)-based polymer electrolytes

The aim of the present work is to study the mechanical properties of poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) blends based polymer electrolytes for lithium ion batteries. The introduction of PVC into PMMA is found to increase the Young’s modulus value from 5.19 MPa (in pure PMMA) to 6.05 MPa (in PVC:PMMA = 70:30). The different Young’s modulus values in PVC blends is due to the difference in the cross-linking density provided by PVC with different weight fraction values. The stress–strain analysis reveals that the mechanical strength of the polymer electrolyte system deteriorated with the incorporation of LiCF₃SO₃. The results show that the introduction of salt decreases the Young’s modulus and stress at peak values along with higher elongation at peak value. The addition of low molecular weight plasticizers to PVC–PMMA–LiCF₃SO₃ decreases the modulus and stress at peak of the complexes. To be applicable in practical applications, the mechanical strength of the plasticized films is found to improve with the addition of silica as nanocomposite filler.     

Optical and mechanical properties of diamond like carbon films deposited by microwave ECR plasma CVD

Diamond like carbon (DLC) films were deposited on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapour deposition (CVD) process using plasma of argon and methane gases. During deposition, a d.c. self-bias was applied to the substrates by application of 13·56 MHz rf power. DLC films deposited at three different bias voltages (−60 V, −100 V and −150 V) were characterized by FTIR, Raman spectroscopy and spectroscopic ellipsometry to study the variation in the bonding and optical properties of the deposited coatings with process parameters. The mechanical properties such as hardness and elastic modulus were measured by load depth sensing indentation technique. The DLC film deposited at −100 V bias exhibit high hardness (∼ 19 GPa), high elastic modulus (∼ 160 GPa) and high refractive index (∼ 2·16–2·26) as compared to films deposited at −60 V and −150 V substrate bias. This study clearly shows the significance of substrate bias in controlling the optical and mechanical properties of DLC films.     

Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin film annealed at different temperatures

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by sol–gel method. The effect of annealing temperature on microstructure, ferroelectric and dielectric properties of PZT films was investigated. When the films were annealed at 550–850 °C, the single-phase PZT films were obtained. PZT films annealed at 650–750 °C had better dielectric and ferroelectric properties. The sandwich composites with epoxy resin/PZT film with substrate/epoxy resin were prepared. The annealing temperature of PZT films influenced their damping properties, and the epoxy-based composites embedded with PZT film annealed at 700 °C had the largest damping loss factor of 0.923.     

An efficient biomimetic process for fabrication of artificial nacre with ordered-nanostructure

The authors developed an efficient biomimetic process to fabricate inorganic/organic nanocomposites with clay nano-platelets being the mineral and polyimide being the organic constituency. Samples with thickness of 10–200 μm were produced in a very short time using a centrifugal deposition process. This process resulted in an ordered nanostructure with alternating organic and inorganic layers. The mechanical properties were comparable to that of lamella bones, with a tensile strength of 70–80 MPa, Young's modulus of 8–9 GPa and hardness of about 1–2 GPa. The composite films could be lifted from the substrate and stacked to form bulk material for biomedical applications such as bioactive dental materials or bone replacements. This approach represents a milestone in the development of bulk-form layered inorganic/organic nanocomposites.     

Microtensile tests of mechanical properties of nanoporous Au thin films

The mechanical properties of nanoporous Au (NPG) thin films were investigated by uniaxial microtensile tests. Such mechanical parameters as Young’s modulus, tensile strength, and breaking strain were obtained from the recorded force–displacement curves. Through observations on the microstructure and fracture surface morphology of the samples after the tension tests by a scanning electronic microscope (SEM) and an optical microscope, we analyzed the physical mechanisms underlying the mechanical behavior of NPG thin films. It was found that the NPG films exhibit mechanical properties distinctly different from its bulk counterpart.     

Abrasion resistance and mechanical properties of high-volume fly ash concrete

The abrasion resistance and mechanical properties of concrete containing high-volume fly ash (HVFA) were investigated. Sand (fine aggregate) was replaced with 35, 45, and 55% of Class F fly ash by mass. The water to cement ratio and the workability of mixtures were maintained constant at 0.46 and 55 ± 5 mm respectively. Properties examined were compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and abrasion resistance expressed as depth of wear. Test results indicated that replacement of sand with fly ash enhanced the 28-day compressive strength by 25–41%, splitting tensile strength by 12–21%, flexural strength by 14–17%, and modulus of elasticity by 18–23% depending upon the fly ash content, and showed continuous improvement in mechanical properties up to the ages of 365 days. Replacing fly ash with sand significantly improved the abrasion resistance of concrete at all ages. Strong correlation exists between the abrasion resistance and each of the mechanical properties investigated.     

Microstructural characteristics and mechanical properties of magnetron sputtered nanocrystalline TiN films on glass substrate

Nanocrystalline TiN thin films were deposited on glass substrate by d.c. magnetron sputtering. The microstructural characteristics of the thin films were characterized by XRD, FE-SEM and AFM. XRD analysis of the thin films, with increasing thickness, showed the (200) preferred orientation up to 1·26 μm thickness and then it transformed into (220) and (200) peaks with further increase in thickness up to 2·83 μm. The variation in preferred orientation was due to the competition between surface energy and strain energy during film growth. The deposited films were found to be very dense nanocrystalline film with less porosity as evident from their FE-SEM and AFM images. The surface roughness of the TiN films has increased slightly with the film thickness as observed from its AFM images. The mechanical properties of TiN films such as hardness and modulus of elasticity (E) were investigated by nanoindentation technique. The hardness of TiN thin film was found to be thickness dependent. The highest hardness value (24 GPa) was observed for the TiN thin films with less positive micro strain.     

Deposition of TiN films on Co–Cr for improving mechanical properties and biocompatibility using reactive DC sputtering

This study reports the deposition of TiN films on Co–Cr substrates to improve the substrates’ mechanical properties and biological properties. In particular, the argon to nitrogen (Ar:N₂) gas flow ratio was adjusted to control the microstructure of the TiN films. A Ti interlayer was also used to enhance the adhesion strength between the Co–Cr substrate and TiN films. A series of TiN films, which are denoted as TiN-(Ar/N₂)1:1, Ti/TiN-(Ar/N₂)1:1, and Ti/TiN-(Ar:N₂)1:3, were deposited by reactive DC sputtering. All the deposited TiN films showed a dense, columnar structure with a preferential orientation of the (200) plane. These TiN films increased the mechanical properties of Co–Cr, such as the critical load during scratch testing, hardness, elastic modulus and plastic resistance. In addition, the biological properties of the Co–Cr substrates, i.e. initial attachment, proliferation, and cellular differentiation of the MC3T3-E1 cells, were improved considerably by deposition of the TiN films. These results suggest that TiN films would effectively enhance both the mechanical properties and biocompatibility of biomedical Co–Cr alloys.     

Study of the effect of thermal annealing on high k hafnium oxide thin film structure and electrical properties of MOS and MIM devices

The effect of rapid thermal annealing on structural and electrical properties of high k HfO₂ thin films is investigated. The films were initially deposited at pre-optimized sputtering voltage of 0.8 kV and substrate bias of 80 V in order to get optimized results for oxide charges and leakage current as a MOS device. The film properties were investigated for optimum annealing temperature in oxygen and optimum rapid thermal annealing temperature in nitrogen respectively to get the best electrical results as a MOS device structure. The film thickness, composition and microstructure is studied by Laser Ellipsometry, XRD and AFM and the effect of thermal annealing is shown. The electrical I–V and C–V characteristics of the annealed dielectric film were investigated employing Al-HfO₂-Si MOS capacitor structure. The flat-band voltage (V _fb) and oxide-charge density (Q _ox) were extracted from the high-frequency C–V curve. Dielectric study were further carried out on HfO₂ thin films having metal–insulator–metal (MIM) configuration over a wide temperature (300–500 K) and frequency (100 Hz to 1 MHz) range.     

Synthesis and characterizations of CdS nanorods by SILAR method: effect of film thickness

In this investigation, we have successfully synthesized CdS nanorods by simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. The effect of film thickness on the physico-chemical properties such as structural, morphological, wettability, optical, and electrical properties of CdS nanorods has been investigated. The XRD pattern revealed that CdS films are polycrystalline with hexagonal crystal structure. SEM and TEM images showed that CdS film surface are composed of spherical grains along with some spongy cluster and an increase in film thickness up to 1.23 μm causes the formation of matured nanorods having diameter 150–200 nm. The increases in water contact angle form 105° to 130° have been observed as film thickness increases from 0.13 to 1.23 μm indicating hydrophobic nature. The optical band gap was found to be increased from 2.02 to 2.2 eV with increase in film thickness. The films showed the semiconducting behavior with room temperature electrical resistivity in the range of 10⁴–10⁶ Ω cm and have n-type electrical conductivity.     

Analysis of indentation-derived effective elastic modulus of metal-ceramic multilayers

A numerical study was undertaken to study the elastic property of metal-ceramic multilayered composites derived from indentation testing. The model system features alternating thin films of aluminum (Al) and silicon carbide (SiC), free from any effect due to the underlying substrate. The anisotropic composite elastic response was obtained by simulating overall loading of the multilayer structure. Finite element modeling of instrumented indentation was then employed to calculate the indentation-derived modulus using the unloading portion of the load–displacement curve. The results from indenting the homogenized composite (with the built-in multilayer property) and from indenting the real multilayers (with Al and SiC layers explicitly accounted for) were compared. It was found that an indentation depth beyond approximately 8–10 initial layer thicknesses is sufficient to yield a valid composite elastic response. The effective modulus thus obtained is representative of the out-of-plane modulus of the multilayer composite.     

Structure and Time-Dependent Mechanical Behavior of Highly Oriented Polyethylene

The structures of polyethylene films and film fibers, having different orientation degrees and prepared by orientational crystallization and orientational drawing, have been investigated by electron microscopy and X-ray diffraction and specific features of the supermolecular structures and differences in the mechanical properties of the samples obtained by these methods have been discovered. Thermomechanical tests have also shown that samples prepared by the two techniques demonstrate different behavior on heating. The time-dependent behavior of the mechanical properties – tensile strength and elastic modulus – have been studied. The phenomenon of slow relaxation of the elastic modulus has been observed for the samples obtained by orientational drawing. It is shown that a long-term decrease in the elastic modulus can be attributed to the presence of structural elements capable of relaxation due to a weak connection between them, their small sizes, and the inhomogeneity of the sample deformation during orientational drawing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation and thermoelectric properties of BP films on SOI and sapphire substrates

The chemical vapor deposited (CVD) BP films on Si(100) (190 nm)/SiO _x (370 nm)/Si(100) (625 μm) (SOI) and sapphire (R-plane) (600 μm) substrates were prepared by the thermal decomposition of the B₂H₆–PH₃–H₂ system in the temperature range of 800–1050 °C for the deposition time of 1.5 h. The BP films were epitaxially grown on the SOI substrate, but a two-step growth method, i.e., a buffer layer at lower temperature and sequent CVD process at 1000 °C for 1.5 h was effective for obtaining a smooth film on the sapphire substrate. The electrical conduction types and electrical properties of these films depended on the growth temperature, gases flow rates and substrates. The thermal conductivity of the film could be replaced by the substrate, so that the calculated thermoelectric figure-of-merit (Z) for the BP films on the SOI substrate was 10⁻⁴–10⁻³/K at 700–1000 K. Those on the sapphire substrate were 10⁻⁶–10⁻⁵/K for the direct growth and 10⁻⁵–10⁻⁴/K for the two-step growth at 700–900 K, indicating that the film on a sapphire by two-step growth would reduce the defect concentrations and promote the electrical conductivity.     

Preparation and characterization of biomimetically and electrochemically deposited hydroxyapatite coatings on micro-arc oxidized Ti–13Nb–13Zr

Surface properties and corrosion resistance analyses of Ti–13Nb–13Zr coated by an oxide film (obtained by micro-arc oxidation at 300 V) or an oxide/hydroxyapatite (HA) film are reported. HA films were biomimetically or electrochemically deposited on the alloy/oxide surface, and their properties compared. Both the biomimetic and the electrochemical method yielded rough and globular apatite surfaces (10–20 μm globules for the former and 1–2 μm for the latter). As inferred from XRD data, the electrochemical method yielded more biologic-like HA films, while the biomimetic method yielded films containing a mixture of calcium phosphate phases. Coated Ti–13Nb–13Zr samples were immersed in an aerated PBS solution and continuously analyzed during 49 days. Considering that, after immersion, the biomimetically deposited films presented smaller variations in thickness and morphology and higher electric resistance (determined by electrochemical impedance spectroscopy), they clearly provide significantly better protection to the Ti–13Nb–13Zr alloy when in PBS solution.     

Zinc oxide nanoparticle-polymeric thin films for dynamic strain sensing

Piezoelectric transducers are becoming increasingly popular for dynamic strain monitoring due to their small form factors and their ability to generate an electrical voltage drop in response to strain. Although numerous types of piezoelectric thin films have been adopted for strain sensing, it has been shown that piezo-ceramics are expensive, brittle, and can fail during operation, while piezo-polymers possess lower piezoelectricity and mechanical stiffness. Thus, the objective of this study is to develop a piezoelectric thin film characterized by high piezoelectricity (i.e., high dynamic strain sensitivities) and favorable mechanical properties (i.e., being conformable to structural surfaces yet stiff). First, zinc oxide (ZnO) nanoparticles are dispersed in polyelectrolyte solutions, and the excess solvent is evaporated for thin film fabrication. The amount of ZnO nanoparticles embedded within the films is varied to yield seven unique sample sets with ZnO weight fractions ranging from 0 to 60%. Upon film fabrication, specimens are mounted in a load frame for monotonic uniaxial testing to explore the films’ stress–strain performance and to subsequently determine their mechanical properties (namely, modulus of elasticity, ultimate strength, and ultimate failure strain). Finally, film specimens are also mounted onto cantilevered beams undergoing free vibration due to an applied initial displacement. The generated voltages in response to induced strains in the beams are recorded, and the piezoelectric performance and dynamic strain sensitivities for the different weight fraction films are calculated and compared. Commercial PVDF thin films are also employed in this study for performance comparison.     

Processing and compression testing of Ti6Al4V foams for biomedical applications

Open cell Ti6Al4V foams (60% porosity) were prepared at sintering temperatures between 1,200 and 1,350 °C using ammonium bicarbonate particles (315–500 μm) as space holder. The resulting cellular structure of the foams showed bimodal pore size distribution, comprising macropores (300–500 μm) and micropores (1–30 μm). Compression tests have shown that increasing sintering temperature increased the elastic modulus, yield and compressive strength, and failure strain of foams. The improvements in the mechanical properties of foams prepared using smaller size Ti64 powder with bimodal particle distribution were attributed to the increased number of sintering necks and contact areas between the particles. Finally, the strength of foams sintered at 1,350 °C was found to satisfy the strength requirement for cancellous bone replacement.