Surface Characteristics Of Coatings Research Articles

Hard Cr2O3 coatings on SS316L substrates prepared by reactive magnetron sputtering technique: a potential candidate for orthopedic implants.

316L stainless steel (SS) implants suffer from tribological and biocompatibility problems which limit their service lifetime. In order to improve the surface properties of 316L SS for orthopedic implant applications, hard chromium oxide coatings were applied on 316L SS substrates using a reactive magnetron sputtering technique. The morphological, structural, and phase compositional analyses were conducted on the deposited coatings by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The Rockwell-C indentation tests were performed on the coated substrates to qualitatively evaluate the adhesion of coatings on the steel substrates. The surface characteristics of coatings were measured by using an optical profilometer. The mechanical properties of coatings were reported by measuring the Hardness and Young's modulus. The corrosion resistance of coated and uncoated SS substrates was compared using potentiodynamic polarization tests. An inductively coupled plasma optical emission spectrometry (ICP-OES) was employed to analyze the biocompatibility of the samples by measuring the amount of toxic Cr ions released after the immersion test. The results show that the coatings are adherent and composed of a single Cr2O3 phase with a hardness of 25 to 29GPa. The corrosion resistance of the SS has been improved by applying a chromium oxide coating. The coated SS samples have also demonstrated better wear resistance and lower friction coefficient compared to bare SS samples under a reciprocating sliding condition in saline solution. The biocompatibility of the SS has been enhanced by the Cr2O3 coating as much less Cr ions were released after immersion tests. These results indicate that the hard Cr2O3 coatings can be considered as a candidate for extending the lifetime of SS implants.

Study on Physio-chemical Properties of plasma polymerization in C2H2/N2 plasma and Their Impact on COL X

Nitrogen-containing plasma polymerization is of considerable interest for tissue engineering due to their properties on cell adhesion and mesenchymal stem cells (MSCs) response. In this study, low-pressure RF plasma of acetylene and nitrogen was used to deposit nitrogen-containing plasma polymerized coatings on several substrates. Deposition kinetics and surface characteristics of coatings were investigated in terms of RF power and gas flow ratio. OES was used to monitor the plasma process and investigate the relation between the film structure and plasma species. Presence of several bonds and low concentration of amine functional groups were determined using FTIR and Colorimetric methods. Contact angle goniometry results indicated about 30% increase in surface hydrophilicity. Stability of coatings in air and two different liquid environments was examined by repeating surface free energy measurements. Deposited films exhibited acceptable stability during the storage duration. Surface roughness measured by AFM was found to decrease with growing concentration of nitrogen. The deposition rate increased with increasing RF power and decreased with growing concentration of nitrogen. Zeta potential measurements of coatings revealed the negative potential on the surface of the thin films. Temporary suppression of collagen X in the presence of plasma coatings was confirmed by RT-PCR results.

Erosion Characteristics of Nanoparticle-Reinforced Polyurethane Coatings on Stainless Steel Substrate

Hydropower generation from the Himalayan rivers in India faces challenge in the form of silt-laden water which can erode the turbine blades and reduce turbine life. To address this issue, polyurethane coatings reinforced with boron carbide (B4C) or silicon carbide (SiC) nanoparticles on 16Cr-5Ni martensitic stainless steel substrate were used in the present investigation to improve erosion wear resistance in silt erosion conditions. Slurry erosive wear tests were carried out based on ASTM G-73 protocol at various test conditions of impact velocity, impingement angle, and erodent particle size as well as slurry concentrations as determined by the implementation of Taguchi design of experiments. Analysis of variance studies of erosion rate indicated that nanoparticle content in PU material is the single most important parameter, and interaction of impact velocity and impingement angle was also proved to be significant. The coatings with B4C nanoparticles had higher wear resistances than those with SiC nanoparticles due to higher hardness of the former. An interesting finding from the results is that there is an optimum amount of nanoparticles at which mass removal is the minimum. This observation has been explained in terms of surface characteristics of coatings as brought out by a combination of measurements including SEM images as well as roughness measurement.

Effect of Cu strike coating on adhesion between Cu–Sn coated steel and rubber

In order to improve the adhesion between steel and rubber, a novel coating deposition technique has been developed, where steel substrate with orchestrated surface roughness was coated with double-layer coatings consisting of a thin Cu strike layer followed by a Cu–Sn layer with varying Sn compositions by immersion route. Coating surface characteristics studied using scanning electron microscope coupled with energy dispersion spectroscopy analyzer, electron probe micro analyzer, and inductively coupled plasma optical emission spectroscopy showed improvement in surface coverage with coating after employing the strike layer coating attributed to the better coating penetration in the deep roughness troughs. Peel test of the coated samples vulcanized with styrene butadiene rubber (SBR) was carried out which showed improvement in adhesion strength of the double-layer-coated samples inferring more uniform Cu-sulfide layer formation at interface due to more uniform coating coverage in these samples. Highest peel strength with uniform cohesive fracture within rubber was observed for optimum 2–3 wt% Sn content in the coatings. This result was further supported by pull-out test conducted on coated wire samples vulcanized with SBR.

Surface modification of Ti–13Nb–13Zr and Ti–6Al–4V using electrophoretic deposition (EPD) for enhanced cellular interaction

Hydroxyapatite–titanium dioxide (HAp-TiO2) nanohybrid composite was coated on Ti–6Al–4V and Ti–13Nb–13Zr substrates by electrophoretic deposition. Coating surface characteristics and biocompatibility were analysed using X-ray photoelectron spectroscopy, water contact measurement, scanning electron microscopy and fluorescence microscopy. The results indicated high degree of crystallinity and densely packed crack free morphology of the coating. The coated substrates displayed lower contact angle (Ti–13Nb–13Zr, 17·4°; Ti–6Al–4V, 22·2°) than the controls (Ti–13Nb–13Zr, 80·8°; Ti–6Al–4V, 72·6°). The cytocompatibility of the coated substrates was determined by staining the human dermal fibroblast cells with 4′,6-diamidino-2-phenylindole and imaging under fluorescent microscope. Both SEM and florescence microscope images showed comparatively enhanced cell adhesion on coated Ti–13Nb–13Zr and Ti–6Al–4V than the uncoated substrates. This difference could be attributed because of the higher wettability of Ti–13Nb–13Zr. Hence, this study provides evidence that the coating provided a better surface property for adhesion of human dermal fibroblast cells.

A comparative study between experimentally measured mechanical attributes and users’ perception of soft feel coatings: Correlating human sense with surface characteristics of polyurethane based coatings

Different soft feel coating formulations using waterborne resins composed of soft and hard polyurethane resins were prepared. The effects of resins mixtures on the soft feel properties were studied. Attempts were made to find out the correlation between users perception and experimentally measured surface characteristics of the coatings. To this end, 72 people were asked to touch the coatings in a similar testing environment and to express their feeling in order to rank them between 1 (lowest soft feel effect) and 4 (highest soft feel effect). The coatings physical characteristics were studied by tensile test, micro Vickers hardness, atomic force microscope (AFM) and friction coefficient measurement. It was shown that the mixtures of 25:75 of soft and hard resins resulted in the best soft feel effect. Users did not consider low or high hardness films as soft. Instead, those coatings having greater toughness were ranked as the best soft feel effect. Also, coatings with lower friction coefficient and lower surface roughness were preferred by users. However, the lowest friction coefficient did not result in the best soft feel appeal. In fact, the mechanical properties, surface roughness and friction coefficient were found to play as the criteria to show soft feel effect. It is thus concluded that by selecting appropriate surface characteristics of coatings related to soft feel effect, good agreement between these properties and human feeling can be made.

Friction coefficient and error test via micro-rotation mechanics model

An air pressure-loading mode incorporated into the friction apparatus is firstly applied to coatings tribology involving large load, automation, stepless and continuous loading processes. A novel measurement principle is proposed and a micro-rotation mechanics model was developed for high precision measurement of friction coefficient. By properly designing and locating two sensors real-time monitoring the normal and friction forces, the troublesome influences in friction measurement is considerably relieved which come from surface characteristics of coatings of the samples in traditional friction test processes. By calculation and analysis, the max rotation angle θmax = 0.0018° is gained, which indicates that the measurement error of the apparatus is greatly reduced. The whole system error is about 1.15% given by finite element method and indication error of the least square fitting of measurements.

Microstructure evolution and surface characteristics of NiP and CrN composite coatings under phosphate glasses molding process

The NiP, CrN, NiP/CrN multilayer, and NiPCrN multicomponent composite coatings were fabricated by magnetron co-sputtering. Simulation of molding process on various coating systems was conducted against phosphate glass. The 50 mol.% P 2O 5–50 mol.% ZnO glass was chosen for the molding process due to its low glass transition temperature, T g, around 400 °C and significant reaction at a high temperature. Phase evolution and surface characteristics of the coatings in the as-deposited and hot-pressed states were analyzed. Smooth surface morphology with a low roughness value below 5.0 nm was observed for the coatings under the hot pressing process. Grain growth and precipitation of the coatings were retarded under loading. Glass sticking behavior occurred in the NiP coating, while severe delamination of NiPCrN multicomponent composite coating was found. On the other hand, single layer CrN and NiP/CrN multilayer coatings showed superior surface and anti-sticking properties against phosphate glasses after the simulated molding process. The feasibility of NiP, CrN, and related composite coatings for phosphate glass molding is discussed.

높은 도착효율을 가지는 회전형 정전 도장기기의 개발

A new electrostatic rotary atomizing painting equipment using air turbine was developed for high transfer efficiency. Based on the overall design requirements of painting equipment, basic design specifications of the equipment parts such as air turbine and atomizing disk are defined from the present conceptual design model. Air turbine is designed with the section profile of NACA airfoil, and its internal flow field is analyzed by commercial CFD code. Atomizing disk is designed to achieve the ligament type spray of paint with the use of visualization technique. Various experiments and tests are conducted to investigate the spray and the transfer characteristics of newly-designed painting equipment, and the measurement results are compared with the those of conventional painting equipments. The comparison results show the present painting equipment is superior to the conventional ones in the aspects of transfer efficiency and coating surface characteristics.

Enhanced osteoblast adhesion on hydrothermally treated hydroxyapatite/titania/poly(lactide- co-glycolide) sol–gel titanium coatings

Sol–gel processing was used to coat titanium substrates with hydroxyapatite (HA), TiO 2, and poly( dl-lactic-glycolic acid). Coating surface characteristics were analyzed with XRD, EDS, AFM, SEM, and water contact angle measurements which indicated that the coatings had a high degree of crystallinity and good resistance to cracking. Coatings were also evaluated by cytocompatibility testing with osteoblast-like cells (or bone-forming cells). The cytocompatibility of the HA composite coatings prepared in the present in vitro study was compared to that of a traditional plasma-sprayed HA coating. Results showed that osteoblast-like cell adhesion was promoted on the novel HA sol–gel coating compared to the traditional plasma-sprayed HA coating. In addition, hydrothermal treatment of the sol–gel coating improved osteoblast-like cell adhesion. Since osteoblast adhesion is a necessary prerequisite for subsequent formation of bone, these results provided evidence that hydrothermally sol–gel processed HA may improve bonding of titanium implants to juxtaposed bone and, thus, warrants further investigation.

Influence of abrasion on the surface characteristics of thermally sprayed hydroxyapatite coatings

The surface condition of hydroxyapatite thermal sprayed coatings can be measured in terms of smooth melted and unmelted regions. Both these areas collectively contribute to abrasion resistance of a coated implant. The purpose of this work was to determine the influence of abrasion on the surface characteristics of coatings. Coatings with three degrees of roughness ( R a of 7, 10 and 24 μm) were produced by thermal spraying. These coatings were subjected to abrasion in a pin-on-disk test. It was found that the majority of weight loss occurs within the first minute of the abrasion. Raised areas from the coating are removed and the bone analogue pin spreads amongst the elevated areas to produce a smoother coating. Further, abrasion is dependent upon the applied load. Small loads produce a smaller or negligible increase in coating loss, however, a higher load is able to displace more material from the coating surface. It is expected that the coating loss from plasma sprayed coatings amounts to a value of less than 3 wt% during the insertion into bone. Modification of the coating surface from abrasion is dependent upon the surface roughness of the coating.