Type Of Substrate Material Research Articles

The effect of the substrate material on the value of the adhesive fracture energy, Gc: Further considerations

In a previous letter [1] it was reported that the value of the adhesive fracture energy, Gc, was dependent upon the type of substrate material which was employed for the test specimens. Even though the locus of joint failure was observed to be cohesive, approximately in the center of the adhesive layer, and the measurements were made using specimens which obeyed the requirements of linear-elastic fracture-mechanics (LEFM) tests. The results from this earlier study are given in Table I. (A single-part, heat-curing rubber-toughened epoxypaste adhesive, designed for general-purpose use, was employed to bond the following substrate materials: mild steel, aluminum alloy and CFRP (a unidirectional carbon-fiber reinforced-plastic epoxy composite). Both double cantilever beam (DCB) and tapered double cantilever beam (TDCB) specimens were employed [1, 2]. The thickness of the adhesive layer was 0.4 mm.) The results given in Table I were explained in terms of the shape and size of the plastic zone, ahead of the crack tip within the adhesive layer, changing the value of Gc. The shape and size of the plastic zone was, in turn, considered to be affected by the value of the transverse modulus, E22, of the substrates used to form the joint. However, in a recent study involving the same grade of general-purpose epoxy-paste adhesive and range of substrates [3, 4], a far more pronounced effect of the substrate material on the value of Gc was noted in the case of the CFRP joints. All tests were again valid LEFM tests, and the crack always grew cohesively, approximately through the center of the adhesive layer. (Hence, as in the previous work, any differences in the values of Gc from using the different substrates cannot be explained in terms of any changes in the interfacial adhesion as the type of substrate was varied.) The results from this second study revealed no significant differences in the values of Gc for the mild steel and aluminum alloy joints, but the value of Gc for the CFRP joints was even lower than that recorded in the first study. For the CFRP joints the value of Gc was now only 202± 23 Jm−2. (In this second study, the adhesive joints were all manufactured in the same laboratory by the same personnel, but testing was carried out by twelve different laboratories, according to a protocol [2, 4], as part of a “round-robin” series of tests on structural adhesives tested under Mode I (tensile) loading.) It was considered that the very low value of Gc recorded for the CFRP joints from this second study was far too low to be explained by the mechanics arguments advanced previously [1]. Now, in the previous study, the adhesive had always been cured under the same temperature versus time cycle of 150 ◦C for 70 min in a fan-assisted oven, whereupon the heaters were turned off and the joints allowed to cool slowly over a period of about 5 h in the oven. This relatively long curing time was employed to try to ensure that the same state of cure was experienced by the adhesive layer in all the different types of joints. Thermocouples were buried into the adhesive layer to monitor accurately the temperature of the adhesive, during the curing cycle, in combination with the various types of substrate materials. Indeed, very similar cure cycles were recorded for the different types of joints. However, it was decided to investigate the extent of cure of the epoxy adhesive in more detail by measuring the glass transition temperature, Tg, of the cured adhesive layer. This was undertaken for adhesive samples removed from the different types of joints by using differential scanning calorimetry (DSC) and employing a heating rate of 20 ◦C min−1. Samples of adhesive were therefore carefully removed from the fracture surfaces of the failed joints and these samples were then analyzed. The values of Tg were defined on the normalized heat flow endotherms as the transition half-width obtained from a second heating cycle. For the “round robin” exercise, the values of the glass transition temperatures, Tg, for the samples of adhesive taken (a) from the mild steel joints was 103.0± 0.9 ◦C, (b) from the aluminum alloy joints was 100.6± 0.6 ◦C and (c) from the CFRP joints was 87.6± 1.3 ◦C. Thus, clearly the most striking feature is the very low value for the Tg for the adhesive layer in the CFRP joints, and these joints also possessed the correspondingly very low value of Gc of 202± 23 Jm−2.

Transcrystallization kinetics of poly(vinylidene fluoride)

We report the transcrystallinity of poly(vinylidene fluoride) on several different types of substrate materials. The supermolecular structure and its development were characterized with polarization microscopy, whereas differential scanning calorimetry was used for monitoring the isothermal and nonisothermal crystallization kinetics. Although only approximately applicable, an Avrami–Ozawa analysis of the latter yielded reliable exponents, which characterized the transcrystalline nucleation conditions, the related dimensionality of growth, and the resulting texture. The results complemented and agreed quantitatively with those of light microscopy. Several polymers, including poly(ethylene terephthalate), polytetrafluoroethylene, and polyimide, induced distinct transcrystallinity, but only a spherulitic supermolecular structure developed on glass and metallic substrates. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2130–2139, 2001

On the significance of the H/ E ratio in wear control: a nanocomposite coating approach to optimised tribological behaviour

Although hardness has long been regarded as a primary material property which defines wear resistance, there is strong evidence to suggest that the elastic modulus can also have an important influence on wear behaviour. In particular, the elastic strain to failure, which is related to the ratio of hardness ( H) and elastic modulus ( E), has been shown by a number of authors to be a more suitable parameter for predicting wear resistance than is hardness alone. There is presently considerable interest in the development of nanostructured and nanolayered coatings, due to the fact that materials with extreme mechanical properties (which are difficult to synthesise by other methods) can be created, particularly when using plasma-assisted vacuum processing techniques. Until now, scientific research has been directed mainly towards the achievement of ultra-high hardness, with associated high elastic modulus, the latter of which, conventional fracture mechanics theory would suggest, is also desirable for wear improvement (by preventing crack propagation). In this study, we discuss the concept of nanocomposite coatings with high hardness and low elastic modulus, which can exhibit improved toughness, and are therefore better suited for optimising the wear resistance of ‘real’ industrial substrate materials (i.e. steels and light alloys, with similarly low moduli). Recent advances in the development of ceramic–ceramic, ceramic–amorphous and ceramic–metal nanocomposite coatings are summarised and discussed in terms of their relevance to practical applications. We also discuss the significance of elastic strain to failure (which is related to H/ E) and fracture toughness in determining tribological behaviour and introduce the topic of metallic nanocomposite coatings which, although not necessarily exhibiting extreme hardness, may provide superior wear resistance when deposited on the types of substrate material which industry needs to use.

The structure study of thin cadmium and copper sulphide films by diffraction of synchrotron radiation

Crystalline structure and phase composition of thin CdS, Cu 2S and Cd(Cu)S films were investigated using diffraction of synchrotron radiation (SR). These films were synthesized by RPECVD using nontraditional volatile sulphur-containing precursors. The diffraction measurements were performed at the station “Anomalous Scattering”, existed at the second canal of colliding electron–positron beam accelerator VEPP-3 of Siberian center of SR (Institute of Nuclear Physics of SB RAS, Novosibirsk, Russia). It was established that these films have a high transmittance in the visible range of spectra. This type of substrate material was found to determine the structure of sulphide films. The deviation of lattice parameters of cadmium and copper sulphides in thin film state obtained on Si(1 0 0) substrates from following the parameters in bulk state probably connects with lattice mismatch of silicon substrate and hexagonal structure of growing sulphide films.

Residual stresses in spray-formed A2 tool steel

The objective of this work was to investigate the fundamental factors that govern the formation and magnitude of residual stresses in A2 tool steel fabricated using spray-forming techniques. To that effect, a finite-element method (FEM) was performed by using a commercial code, ABAQUS, to solve for the temperature and displacement fields. Moreover, the residual stresses in the spray-formed materials were measured using x-ray diffraction to compare the FEM results with experimentation. Two types of substrate material, copper and Rescor™ 780 cer-cast ceramic, were used to investigate the influence of heat conduction on residual stress in the preforms. Relatively good agreement was found between experimentation and theory. The results show that the residual stress varies greatly with the position in deposited preform and that heat-transfer coefficient at the interface of spray-formed material/substrate affects the distribution and magnitude of the residual stresses significantly.

Effect of interface on the characteristics of functional films deposited on polycarbonate in dual-frequency plasma

Functional coatings are used in increasingly demanding applications that require specific optical characteristics, resistance to damage and good adhesion to different types of substrate materials, including polymers. In the present work we investigate thin films fabricated by low pressure plasma-enhanced chemical vapor deposition, using a dual-mode microwave/radio-frequency (MW/RF) plasma approach. The substrates are exposed to the principal dense microwave (MW, 2.45 GHz) plasma, while applying a RF-induced negative bias voltage. This technique provides independent control of the energy and flux of bombarding ions, and it allows one to deposit dense films at ambient substrate temperature at a high rate over large areas. We optimized the deposition process for amorphous hydrogenated silicon nitride (SiN1.3) obtained from SiH4/NH3 mixture. Using an average ion energy of about 150 eV, we obtained low-stress (<100 MPa) films with a refractive index of 1.89, at deposition rates around 30 Å/s. MW plasma pretreatments with different gases have been investigated in order to further enhance adhesion of the SiN1.3 coatings on polycarbonate (PC) substrates—the highest adhesion, determined by the microscratch- and the adhesive-tape peel tests, was found when PC was pretreated in N2 plasma. The adhesion is related to the thickness and chemical structure of the interface. In fact, spectrophotometry and x-ray photoelectron spectroscopy analysis suggest the presence of a graded interface region, up to 40 nm thick, part of which contains Si–C, Si–O–C, and Si–N–C chemical links.

Structural order in thin a-Si:H films

Hydrogenated amorphous silicon (a-Si:H) films were grown in an rf-plasma deposition system on various substrates. The thickness of the films ranged from 11 to 579 nm. The structural properties of the films were studied by means of ex situ Raman spectroscopy. The width of the transverse-optic peak in the Raman spectrum was used as a measure for the amount of bond-angle variation in the films. In contrast to earlier reports, it is found that bond-angle variation in glow-discharge-deposited a-Si:H does not depend on the film thickness, nor on the type of substrate material.

Production of polycrystalline diamond films by d.c. glow discharge CVD

Abstract Polycrystalline diamond films on various substrates (W, Mo, Si, Si 3 N 4 , SiC and WCo) have been grown by the CVD method in a d.c. glow discharge plasma. The diamond crystal nucleation density was studied as a function of the substrate temperature in the range from 700 to 1100 °C. The experiments at constant discharge parameters have revealed the increase in the diamond nucleation density as the substrate heating temperature decreased. The diamond crystal density varied from 10 3 cm −2 at 900 °C to 10 8 cm −2 at 700 °C. An increase in the diamond nucleation density with decreasing synthesis temperature was observed on all types of substrate material.

Hairy carbon electrodes studied by cyclic voltammetry and battery discharge testing

Hairy carbon is a new material developed by growing submicron carbon filaments on conventional carbon substrates. Typical substrate materials include carbon black, graphite powder, carbon fibers and glassy carbon. A catalyst is used to initiate hair growth with carbonaceous gases serving as the carbon source. To study the electrochemical behavior of hairy carbons, cyclic voltammetry and discharge testing were conducted. In both cases, hairy carbon results surpassed those of the substrate materials alone.

Aeroservoelastic DAP missile fin development

The development of an active aeroservoelastic missile fin using directionally attached piezoelectric (DAP) actuator elements is detailed. Several different types of actuator elements are examined, including piezoelectric polymers, piezoelectric fiber composites and conventionally attached piezoelectric (CAP) and DAP elements. These actuator elements are bonded to the substrate of a torque plate. The root of the torque plate is attached to a fuselage hard point or folding pivot. The tip of the plate is bonded to an aerodynamic shell which undergoes a pitch change as the plate twists. The design procedures used on the plate are discussed. These include an optimization of the actuator element orientation, substrate material type and thickness, as well as a determination of the optimum elastic axis location. A comparison of the various actuator elements shows that DAP elements provide the highest deflections with the highest torsional stiffness. A torque plate was constructed from 0.2032mm thick DAP elements bonded to a 0.127mm thick AISI 1010 steel substrate. The torque plate produced static twist deflections in excess of ±3º. An aerodynamic shell with a modified NACA 0012 profile was added to the torque plate. This fin was tested in a wind tunnel at speeds up to 50ms-1. The static deflection of the fin was predicted to within 6% of the experimental data.

Influence of the substrate material on the effectiveness of coatings in metal cutting

Considerable studies concerning metal cutting in the past have been devoted to tungsten carbide tools and their coatings. As a result, a wide range of carbide substrates has been developed for more than 30 kinds of hard coatings or combination of coatings, ranging from single layer to as much as 13 layers of coatings in multi-layer coated tools. Some of these technological “spill-overs” helped in the evolution of another new generation of cutting-tool materials, namely coated cermets, which not only use less of strategic raw materials such as tungsten and cobalt, but also exhibit excellent wear properties such as good resistance to diffusion wear and the ability to retain a higher hardness at elevated temperatures. A comparison, based on CNC lathe turning, was made of these two types of substrate materials, namely carbides and cermets, coated with some of the more common hard coatings such as TiN, TiC, TiCN, and Al 2O 3 using physical vapour deposition (PVD). The results are analysed and discussed.

Measurement of the Adhesive Force between Particles and a Substrate by Means of the Impact Separation Method. Effect of the Surface Roughness and Type of Material of the Substrate.

In order to study the effect of surface roughness and substrate material type on the adhesion of particles, measurements were made using the pendulum impact separation method using a variety of powders and substrates. Two methods were used to attach powder particles to a substrate : the free falling method and the fluidized method. When the powders were deposited on a substrate by free falling (with negligible force), the force of adhesion to the substrate with a rough surface was less than the adhesion to the smooth surface substrate. The degree of reduction in adhesive force increased as the shape of sample powder more closely resembled a sphere. When the powders were attached to a substrate under a fluidized state, a remarkable increase in adhesive force was observed in organic powder/polyvinyl chloride (PVC) systems. This is probady due to the electrostatic force produced by the collision and/or friction of particles to the PVC sheet.

Au/Si interface: Experiments on substrate influence

We have studied the influence of amorphous and crystalline substrate materials, such as a-Si and a-Si:H, as well as c-Si(111), (100), and hydrogen implanted c-Si(111) on the outdiffusion of Si through an evaporated Au thin film, and its subsequent oxidation in atmosphere. Using Auger electron spectroscopy depth profiling we observed that the SiO2 layer thickness d formed on top of the Au film strongly depends on the type of substrate material giving most enhanced Si outdiffusion from amorphous ones. The metastable phase AuxSi is detected on both interfaces between the Au/Si and the SiO2/Au layers. A temperature independent ratio, dH/d ≊ 2, is observed for the oxide layer thickness of substrates with and without hydrogen. This is a surprising result, which indicates the influence of nonthermodynamic effects, probably related to the surface structure of the semiconductor substrates and a strong influence of hydrogen. A model of the layer structure is developed, which permits the calculation of diffusion activation energies resulting in qHD ≂ qD ≂ 1.0 (eV) for the diffusing species on substrates with and without hydrogen, respectively.

Three‐dimensional nonstationary calculation of Quasi‐phase‐matched guided‐wave, second‐harmonic generation using weighted‐index method

AbstractA three‐dimensional (3‐D) nonstationary analysis method is proposed for the quasi‐phase‐matched (QPM) second‐harmonic generation in an optical waveguide with a periodic domain‐inversion structure. In this method, a 3‐D modeling of a waveguide‐type QPM is made possible by combining the mode coupling theory with the weighted‐index method (WIM) which is a highly accurate approximate analysis method for an optical channel waveguide. As an example of application, the effect of the channel dimensions on the conversion efficiency is studied for a proton‐exchanged LiNbO3 waveguide with a rectangular‐shaped inverted domain. The actual domain‐inversion shape is expected to be different, depending on the type of substrate material and inversion process. The present method is also applicable to an arbitrary inverted‐domain shape. Hence, the method is considered to be extremely useful for an actual device design.

Characteristics of microwave planar transmission lines using superconducting oxide films

AbstractIt is expected that the superior high‐frequency characteristics, such as low loss and low dispersion, of superconducting oxides are applied to microwave circuits. However, low‐loss superconducting oxide films can only be fabricated on limited types of substrate materials using present technologies. Therefore, the dielectric constant, dielectric loss, and thickness of substrate materials place severe limitations on the circuit design and the propagation characteristics.This paper discusses the attenuation constants, characteristic impedances, and wiring density of three fundamental planar transmission lines, namely, stripline, microstrip line, and coplanar waveguide fabricated on substrate materials MgO and LaAlO3. This discussion is based on the TEM and quasi‐TEM analysis procedures. The thin films with low surface resistances have been fabricated on MgO and LaAlO3. It is concluded that the microstrip line is suitable for fabricating a low‐loss transmission line and the coplanar waveguide on a low dielectric constant substrate is suitable for high‐density wirings.Also measured were the characteristics of the half‐wave transmission line resonators of these three transmission line configurations, which are made of EuBa2Cu3Ox thin films on an MgO substrate. The attenuation constant of 50 Ω, 50‐μm wide coplanar waveguide is 9.7 × 10−3 Np/m (8.4 × 10−2 dB/m) at 3.9 GHz and 28 K. This value is two orders of magnitude lower than that of the copper transmission line.

Temperature transients on engine combustion chamber walls—IV. Application of the finite-difference model to surface thermocouples and wall deposits

The FD computational code developed in Part I ( Int. J. Mech. Sci. 33, 775 (1991) [1]) has the capability of handling composite walls having different material layers. This characteristic of the FD model is used to study the effects of thermocouple thickness and material type, as well as substrate material type on surface thermocuple readings. Later, the effects of wall deposits on surface thermocouple readings and engine heat transfer are explained.

Additional approximate formulas and experimental data on micro-coplanar striplines (MMICs)

Approximate design formulas and experimental data of micro-coplanar striplines for high-packing-density MMICs are given. These formulas are applicable to three types of substrate materials: GaAs, plastics, and alumina with different dielectric constants.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Recent Developments in Laser Melt/Particle Injection Processing

Investigations into crack formation in particle injected surfaces and into microstructural evolution during cladding were some of the recent developments in laser melt/particle injection processing. Both surface modification techniques involved blowing powder particles into a melt pool formed by a laser beam. When the particulate materials were metal carbides composite surface layers were formed and the thermal stresses that developed during cooling of the carbide injected layer resulted in the formation of microcracks. It was found that modest levels of preheating were sufficient to prevent cracking and that cracking was eliminated mainly by the reduction in thermal stresses and not by modifications in microstructure. With lower melting alloy powders clad overlays were formed. It was found that the limited mixing between the clad material and the substrate resulted in complex macrostructures containing fluid-flow driven segregation bands. The degree of microstructural in-homogeneity depended upon the type of substrate material and had a direct influence on the soundness of the cladding.

Effects of substrate temperature and substrate material on the structure of reactively sputtered TiN films

Stoichiometric TiN films were reactively magnetron sputtered in an Ar- N 2 atmosphere. The films were deposited at various substrate temperatures in the range 200–650°C onto two types of substrate material, high speed steel and stainless steel. The microstructure of the films obtained was investigated by the use of a transmission electron microscope and the morphology was studied in a scanning electron microscope. Measurements of the hardness were also performed. The analysis of the microstructure shows that the growth of the film is markedly influenced by the substrate material. In particular, the high speed steel substrates were found to have a considerable influence on the microstructure. The vanadium carbide particles in these steels, which have a good lattice match to TiN, stimulate a localized epitaxial growth to occur on these carbide particles. This results in a microstructure consisting of large grains surrounded by small grains. The shape of the large grains is influenced by the temperature. In the development of these large grains cracks and/or voids occur in and around the grains at substrate temperatures above 400°C and the hardness drops by about 20%. No large grains were found on films deposited onto stainless steel and their hardness increases slightly with temperature. High hardness for films deposited onto the high speed steel substrate at temperatures above 400°C can also be obtained if a substrate bias is used. Ion bombardment during film growth suppresses the formation of the large grains with voided or cracked boundaries because of a continuous renucleation process. The formation of the different microstructures is discussed in terms of surface energy minimization and thermally activated processes as surface and grain boundary migration.

The influence of the lattice misfit on the growth of CuGaSe2 Epitaxial Films on {100}‐oriented GaAs and GaP Substrates

AbstractCuGaSe2 epitaxial layers were prepared on GaAs and GaP {100}‐oriented substrates by flash evaporation technique and characterized by RHEED. Different epitaxial relationships have been found for growth on the different types of substrate material. The orientation is determined by the minimum misfit.