Polished Stainless Steel Substrates Research Articles

Properties of nano-crystalline LiMn 2O 4 thin films deposited by pulsed laser deposition

Properties of LiMn 2O 4 thin films deposited on polished stainless steel substrates at 400 °C and 200 mTorr of oxygen by pulsed laser deposition have been characterized by electrochemical measurements and physical analyses. The film was mainly composed of nano-crystals less than 100 nm. A maximum specific capacity of 141.9 mAh/g cycled between 3.0 and 4.5 V with a current density of 20 μAh/cm 2 has been achieved. The film exhibited an excellent cycling stability up to 500 cycles. The low charge-transfer resistance at high potentials as revealed by AC impedance resulted in high charge/discharge potential and more capacity. The effect of overdischarge was limited and Jahn–Teller effect was overcome to a significant extent in this nano-crystalline film. Ex situ XRD, Raman and XPS provided supporting evidence in the changes in structure, reactivity and cycling stability of nano-crystalline LiMn 2O 4 film cathodes under different charge/discharge states and cycling tests. SEM images also revealed the stability of the surface topography after a long-term cycling test.

Errors in resolved modulus during nano-indentation of hard films on soft substrates: A computational study

A systematic computational study was performed in which hard films perfectly bonded to relatively soft substrates of the same modulus were indented using a sharp conical tip. Maximum indentation depths h max up to film thickness t were considered; resolved modulus was obtained from Oliver–Pharr analysis of unloading curves. Despite the elastic matching between film and substrate, it was found that for depths of penetration h on the same order of film thickness t, the resolved modulus exhibits a significant (>50%) decrease relative to input values. This is attributed to a ‘plastic hinge’ in the substrate that strongly affects pile-up around the indenter, as well as the volume of material that ‘springs back.’ Results shown for elastic-perfectly plastic systems suggest the importance of further parametric study. For discussion, results are compared with experimental results of rapidly quenched, small-volume Ni structures (‘splats’) on polished stainless steel substrates, where similar modulus decrease was observed.

Effect of a gold–palladium coating on the long-term adhesion of human osteoblasts on biocompatible metallic materials

Our ambition for several years is to study the in vitro interface between human bone cells and biomedical metals in order to improve dental and orthopaedic implant's surface. The long-term adhesion of human osteoblasts cultured on pure titanium, titanium alloy and stainless steel substrates presenting 4 different surface morphologies and 2 different roughness amplitudes (obtained by sand-blasting, acid-etching, electro-erosion and polishing) was quantified from 24 h to 21 days. The half part of the samples was sputter-coated with gold–palladium. The coating by a nanometric gold–palladium layer influenced differently the long-term adhesion of human osteoblasts as a function of the composition of the substrate. This influence was either positive, neutral or negative but was significantly demonstrated only three times. In all the three cases, the coating improved the long-term adhesion of osteoblasts. Consequently, it appears that a gold–palladium coating could be a good way to improve cell adhesion, and perhaps tissue adhesion, on metallic surfaces with low biocompatibility like polished stainless steel substrates or acid-etched pure titanium substrates.

Growth of zinc oxide nanostructures

Zinc oxide (ZnO) nanowhiskers have been prepared using a multilayer ZnO(50 nm)/Zn(20 nm)/ZnO(2μm) structure on a polished stainless steel (SS) substrate by high rate magnetron sputtering. The formation of uniformly distributed ZnO nanowhiskers with about 20 nm dia. and 2 to 5 μm length was observed after a postdeposition annealing of the prepared structure at 300–400° C. An array of highlyc-axis oriented ZnO columns (70–300 nm in dia. and up to 10 μm long) were grown on Si substrates by pulsed laser deposition (PLD) at a high pressure (1 Torr), and Raman studies showed the activation of surface phonon modes. The nanosized powder (15–20 nm) and nanoparticle ZnO films on glass substrate were also prepared by a chemical route. Nanowhiskers showed enhanced UV light detection characteristics, and the chemically prepared ZnO nanoparticle films exhibited good sensing properties for alcohol

Microstructure and tribological properties of magnetron sputtered nc-TiC/a-C nanocomposite

In this study, nanocomposite nc-TiC/a-C coatings were deposited on polished stainless steel substrates and silicon wafers by co-sputtering of graphite and titanium targets at a low temperature of 150 °C. Atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to investigate the morphology and structure of the coatings. The hardness and tribological properties were assessed using Nanoindentation and Tribometer. The coatings consisted of two phases: nanocrystalline of TiC embedded in amorphous matrix of a-C. With Ti content of less than 8 at.%, the coating appeared X-ray amorphous. As Ti increased to 16 at.%, nanocrystalline phase (nc-TiC) was detected. The crystallite size was in the range of 5 to 16 nm as Ti increased from 16 to 48 at.%. The maximum hardness of 31 GPa was obtained at 36 at.%Ti. In dry tribotests against stainless steel ball, the coefficient of friction was less than 0.24 as Ti was less than 36 at.%, but abruptly increased to 0.39 as Ti reached 42 at.%. Extremely low coefficient of friction of 0.046 was obtained with oil lubrication.

Evaporated-gas-induced splashing model for splat formation during plasma spraying

The effect of surface adsorbates on splat formation during thermal spraying is examined by controlling substrate adsorption. Splats are formed on a polished flat stainless steel substrate surface by plasma spraying. The adsorption state of the substrate is controlled with different organic substances of different boiling points and different preheating temperatures. The droplet materials used are aluminum, nickel, and Al 2O 3. Three kinds of organic substances used are xylene, glycol and glycerol, which are brushed on the surface of the substrate before spraying. It is revealed that when preheating temperature of the substrate is lower than the boiling point of the organic adsorbates on the substrate surface, the splashing occurs during droplet flattening which results in the formation of the splats with an irregular morphology. However, when the preheating temperature exceeds approximately 50 °C over the boiling point of the organic adsorbates and evaporates all organic substance adsorbed on the surface, the regular disk type splats are formed which corresponds to no occurrence of the splashing during splatting. It is clearly shown that the existence of the evaporable adsorbates on the substrate surface influences significantly the splatting and consequently the splat morphology. On the basis of the result, the evaporated-gas-induced splashing model is proposed to explain the occurrence of splashing during splatting of a spray molten droplet and the formation of the reduced splat. The effect of preheating temperature of a substrtae surface on water adsorption and desorption characteristics in ambient atmosphere is disscussed from the point of view to create a clean surface and regular disc splat.

Structure and magnetism of electrodeposited ZnSe–Co granular films

Abstract ZnSe–Co granular films have been electrodeposited under potentiostatic condition on polished stainless steel substrates. X-ray diffraction and transmission electron microscopy measurements indicate the formation of polycrystalline granular films with Co particles dispersed in an ZnSe matrix without evidence of intermediate compound formation. Magnetic measurements reveal low values of coercive field and remanence, indicating that the overall magnetic response of the deposited films is determined by multidomain nanosized particles.

Structural Characterization of [(1-x) SrBi 2 Nb 2 O 9 − (x) Bi 3 TiNbO 9 ] for Ferroelectric Applications

Bismuth-layered-structure materials with (Bi 2 O 2 ) 2+ layers intervening with pseudo perovskite blocks (M n m 1 R n O 3n+1 ) 2 m , where n = 1,2,3,4,5, M is mono, di, or trivalent ions such as Ba, Sr, Bi, Pb; R is tetra, penta-, or hexavalent ions such as Ti, Ta, Nb, show interesting ferroelectric and dielectric properties. Aurivillius phase [(1-x) SrBi 2 Nb 2 O 9 m (x) Bi 3 TiNbO 9 ] family of material has been synthesized by a chemical solution method, and thin films were deposited by spin coating. The samples were characterized by x-ray diffraction, Raman spectroscopy and scanning electron microscopy. The study reveals that a complete solid solution is formed for all compositions. Thin films deposited on ITO coated polished stainless steel substrate showed ferroelectric response.

Transmission electron microscopy study of rapid solidification of plasma sprayed zirconia – part II. Interfaces and subsequent splat solidification

Transmission electron microscopy (TEM) is used to investigate the first two splat layers of a plasma sprayed yttria stabilized zirconia (YSZ). Sample preparation by modified wedge polishing technique and results for the first splat were presented in the first part of this paper. The second part focuses on two different interfaces present in the microstructure, rough substrate effects on first splat solidification, and finally on solidification of the second splat layer. The interface between plasma sprayed ceramic and metal substrate as well as the interface between two subsequent splats were examined by conventional and high resolution TEM. The presence of a thin layer of native oxide on polished and preheated stainless steel substrates was established. Such an interface appears to promote very good adhesion of YSZ. The effect of liquid flow on the solidified microstructure of the second and subsequent splats was clearly demonstrated. The top surface of the first solidified splat acts as an excellent nucleation site for a subsequent splat and causes epitaxial growth of columnar grains in subsequent splats.

Growth, microstructure, and microhardness of W/Mo nanostructured multilayers

Artificially modulated W/Mo multilayers on polished stainless-steel substrates with modulation wavelength Λ ranging from 4.0 to 60.0 nm and total film thickness of 2.0 μm were prepared by magnetron sputtering. X-ray diffraction (XRD) and cross-sectional transmission electron microscopy showed that though the polycrystalline films exhibited coherent interfaces, the interfaces have a wave-like appearance due to the different orientations of individual crystals. The interplanar spacings of the W and Mo layers determined by the XRD method in W/Mo multilayers varied with the modulation wavelength. The mechanical properties of these films were investigated by a low-load microhardness indentation technique. The maximum hardness enhancement is about 51% higher than the value calculated from the role of mixtures at wavelength Λ=10.0 nm. The Koehler’s modulus difference model and Cahn’s coherent stress model have been used to estimate the hardness enhancement of W/Mo multilayers. From the comparison of theoretical calculation results with experimental dates, it is obvious that the combination of the two models can explain the hardness enhancement in W/Mo multilayers.

Poly-Si thin-film transistors on steel substrates

We report the successful fabrication of poly-Si thin-film transistors (TFTs) on stainless steel substrates. The TFTs were fabricated on a 500 μm thick polished stainless steel substrate using furnace crystallized amorphous Si deposited by PECVD. These devices typically have threshold voltages of 8.6 V, linear effective mobilities of 6.2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V/spl middot/s and subthreshold slopes of 0.93 decade/V. This work demonstrates the feasibility of poly-Si TFTs on stainless steel substrates and identifies some critical issues involved in poly Si processing on stainless steel. This will enable the fabrication of arrays with integrated drivers on a cheap, flexible and durable substrate for various displays and other large area array microelectronic applications.

Impact of High Velocity Cold Spray Particles

This article presents experimental data and a computational model of the cold spray solid particle impact process. Copper particles impacting onto a polished stainless steel substrate were examined in this study. The high velocity impact causes significant plastic deformation of both the particle and the substrate, but no melting was observed. The plastic deformation exposes clean surfaces that, under the high impact pressures, result in significant bond strengths between the particle and substrate. Experimental measurements of the splat and crater sizes compare well with the numerical calculations. It was shown that the crater depth is significant and increases with impact velocity. However, the splat diameter is much less sensitive to the impact velocity. It was also shown that the geometric lengths of the splat and crater scale linearly with the diameter of the impacting particle. The results presented will allow a better understanding of the bonding process during cold spray.

Splat formation and cooling of plasma-sprayed zirconia

The aim of this paper is to show, through investigations of splat formation, the influence of particle parameters at impact and of the substrate temperature on thermomechanical properties of plasma-sprayed zirconia coatings. During plasma spraying, the flattening of particles on the substrate was studied using either a linescan test or a system integrating two fast two-colour pyrometers. The size and shape factor distribution of the collected lamellae on polished stainless steel substrates as well as their cooling rate can thus be determined. A one-dimensional splat cooling model is used to predict the splat-substrate thermal contact resistance for each spraying condition. Fine (22–44 μm) and coarse (45–90 μm) cuts of fused and crushed yttria-stabilized zirconia (YSZ) were sprayed with an r.f. plasma torch and a d.c. plasma torch to obtain a range of impact velocities (50–200 ms −1). The polished ( R a ∼ 0.05 μm for steel and R a ∼ 0.2 μm for plasma-sprayed YSZ) or grit blasted or as-sprayed ( R a > 0.5 μm) substrates were kept either below 100 °C or above 300 °C. The main results obtained are the following. Almost perfect lenticular shaped splats with thermal contact resistance R th < 10 −7 m 2KW −1 are obtained for smooth, non-oxidized hot substrates ( T > 150 °C). Cooling rates of 22–45 μm particles propelled at 200 ms −1 in a d.c. torch are approximately 10 9 and 10 8 Ks −1 on 304 stainless steel and YSZ substrates respectively. The splat behaviour is similar on rough hot non-oxidized substrates. Thicker splats with lower degrees of flattening have lower cooling rates, owing to the surface asperities. The thermal contact with the substrate is also excellent. As soon as the substrate is cold ( T < 150 °C) or hot but oxidized (oxide layer thickness greater than 40 nm), the splats are very distorted with fingers of splashed material at their periphery, and their contact with the substrate is rather poor ( R th > 10 −6 m 2KW −1). Adhesion-cohesion measurements are in good agreement with results obtained on the splats. The coating adhesion increases with preheated substrates (300–500 °C). When the particles are fully molten, adhesion is highest on hot substrates and for high particle impact velocities. The larger particles (45–90 μm) are not completely melted and are less adherent to the substrate. However, for both particle size distributions, when preheating the substrate, especially up to 500 °C, the preheating time has to be limited to 90–120 s in order to limit the thickness of the resulting oxide layer. When the preheating time increases over 120 s, the adhesion of the coating decreases.

Dependence of tribological properties on deposition parameters for non hydrogenated amorphous carbon films produced by magnetron sputtering

Amorphous carbon films have been deposited on various substrates by direct current (DC) magnetron sputtering from a graphite target in an argon discharge. The composition and physical properties of films (mass density, morphology, electrical resistivity, residual stresses) were investigated as functions of the argon pressure and negative substrate bias voltage. The friction properties of 2 μm thick carbon films deposited on polished stainless steel substrates at various argon pressures and substrate bias voltages were determined by alumina ball-on-disk tribological tests performed in dry air under a load of 4.9 N with a sliding velocity of 10 m min −1 for 10 5 cycles. The tribological behavior and friction performance of carbon coated disks are discussed in connection with the deposition parameters and physical properties of non hydrogenated amorphous carbon films.

Dependence of tribological properties on deposition parameters for non hydrogenated amorphous carbon films produced by magnetron sputtering

Amorphous carbon films have been deposited on various substrates by direct current (DC) magnetron sputtering from a graphite target in an argon discharge. The composition and physical properties of films (mass density, morphology, electrical resistivity, residual stresses) were investigated as functions of the argon pressure and negative substrate bias voltage. The friction properties of 2 μm thick carbon films deposited on polished stainless steel substrates at various argon pressures and substrate bias voltages were determined by alumina ball-on-disk tribological tests performed in dry air under a load of 4.9 N with a sliding velocity of 10 m min −1 for 10 5 cycles. The tribological behavior and friction performance of carbon coated disks are discussed in connection with the deposition parameters and physical properties of non hydrogenated amorphous carbon films.

Microstructure and tribology of ion-mixed Fe/Ti/C multilayers on AISI 304 stainless steel

A multilayered Fe/Ti/C structure consisting of eleven alternating sublayers, four Fe, four Ti and three C, was ion mixed on an AISI 304 stainless steel substrate with 400 keV Xe 2+. Complete mixing was observed after an irradiation of 1 × 10 17Xe/cm 2 at 550°C. Electron diffraction revealed the formation of the compounds TiC and Fe 3C and a small amount of an amorphous phase. Some samples were given a second irradiation with 5 × 10 15Xe/cm 2 at 0°C. The phases present following the second irradiation were TiC, α-Fe and an amorphous phase. Tribological and nanoindentation measurements revealed that both types of samples possessed similar hardness and friction properties. The ion mixed samples possessed an increased hardness and a decreased friction coefficient relative to untreated polished stainless-steel substrate. However, the wear life of the hot ion mixed sample was consistently longer than the wear life of the sample processed at both 550 and 0°C. These results are explained by differences in adhesive wear which result from differences in the chemical reactivity of the phases formed during ion beam processing.

Distinguishing thin film and substrate contributions in microindentation hardness measurements

Microhardness measurements were carried out on silicon, boron, boron nitride, and nickel films deposited on polished stainless steel substrates. A titanium diboride film on a sapphire subsubstrate was also examined. It is shown that a log–log plot of indentation size versus applied load (the Meyer plot) reveals the point at which the substrate begins to influence the hardness measurements. The ratio of indentation depth to film thickness at the critical point varied from 0.06 to 0.4 depending on both film and substrate hardness. The microhardness numbers differ from those calculated from data in the composite (film plus substrate) region by proposed formulas.

Microstructure and magnetic properties of BCC/FCC-mixed phase films prepared by sputtering from stainless steel targets

A new type of magnetic recording disk composed of a substrate and a recording layer both made from stainless steel has been proposed. The ferromagnetic and nonmagnetic stainless steel films needed for the recording layer and the underlayer, respectively, were deposited by sputtering the composite targets with SUS304 stainless steel plates and nickel chips as the first step in the preparation of these disks. Since films with a nickel content of 25-30 wt.% and FCC-phase crystal structure are nonmagnetic, they may be suitable as the underlayer to be deposited on the mechanically polished stainless steel substrates. On the other hand, since films with a nickel content of 15-20 wt.% and BCC/FCC-mixed-phase crystal structure have a high coercive force up to 200 Oe and a moderate saturation magnetization of 500 emu/cm/sup 3/, they may be suitable for the recording layer. >

Temperature compensation of amorphous silicon strain gauges

The applied potential of amorphous silicon as a strain gauge material has been investigated. Measurements of the gauge factor, K, were carried out on a-Si/a-SiN x thin-film structures deposited from a glow discharge plasma on polished stainless steel substrates. The conductance changes of phosphorus-doped a-Si under uniaxial strain lead to room temperature K values between −20 and −40, depending on the potential applied to the substrate. The control of K by the field effect makes it possible in principle to compensate for the temperature coefficients of the gauge factor.

Electrochemically measured porosity of magnetron sputtered TiN films deposited at various substrate orientations

TiN layers were deposited by magnetron sputtering on polished stainless steel substrates, the position of which was changed in steps from parallel to perpendicular relative to the target surface. Substrate target distance was varied between 25 and 50 mm. Bias current density and substrate temperature at the beginning of deposition were also varied. The porosity of the films deposited under these circumstances was measured by an electrochemical method. The double layer capacity electrolyte/TiN film is a measure of the porosity and the true surface area of the deposited film. Dense films were deposited in all substrate positions when the starting temperature was around 300 °C and the bias current densities were above 2 mA/cm2. With bias current densities below 1 mA/cm2 or no bias and a position of the coated plane perpendicular to the target surface, the true surface of the film is enlarged to 500 times that of the geometrical area of the substrate used. The structural changes responsible for the increase in the porosity are shown in scanning electron microscope (SEM) micrographs.