BIO-TRIBOLOGICAL PROPERTIES AND MICROSTRUCTURE OF SEMICRYSTALLINE AL2O3/PEEK COATINGS ELECTROPHORETICALLY DEPOSITED ON THE TI-13NB-13ZR ALLOY

Tribological applications of titanium alloys in orthopedic surgery and traumatology are limited due to their low resistance to wear and low hardness [1]. Therefore, in order to protect of the alloy surface and improve the performance of titanium alloys in orthopedic implants in friction and wear applications, for example, in the head and acetabulum of endoprostheses, surface treatment is necessary. Electrophoretic deposition (EPD) is a very convenient method for producing the composite ceramic-polymer coatings on metallic substrates. Polyetheretherketone (PEEK) and PEEK-based coatings have often been applied as a sliding material in bio-tribosystems because of their high wear resistance, corrosion resistance and self-lubricating capacity [2-4]. In our previous study, we successfully deposited a well-adhered PEEK coating which improved bio-tribological properties of the Ti-13Nb-13Zr alloy substrate [4]. In the present work, composite Al2O3/PEEK coatings deposited by EPD were applied for further improvement the bio-tribological properties of the Ti-13Nb-13Zr alloy. The deposits exhibited the uniform distribution of powders used for deposition. The PEEK in the as-deposited coatings had a nearly amorphous structure. Subsequent heating at a temperature above the PEEK melting point, 350 ºC, enabled homogeneous, semi-crystalline PEEK as a coatings matrix with spherulitic morphology to be produced (Fig. 1). TEM investigation revealed the presence of uniformly distributed γ-Al2O3 nanoparticles as well as agglomerates of both α-Al2O3 and γ-Al2O3 particles within the PEEK matrix. The coating thickness depended strongly on the time of EPD and equalled 45 μm, 80 μm and 120 μm after 20 s, 30 s and 60 s, respectively. Micro-scratch tests showed that all the coatings exhibited very good adhesion to the titanium alloy substrate, however, the thickest coating had the best adhesion. The composite Al2O3/PEEK coatings significantly improved the tribological properties of the Ti-13Nb-13Zr alloy, also in comparison with a polymer PEEK coated alloy. The Al2O3/PEEK coated alloy exhibited excellent wear resistance in comparison with uncoated ones and was better than the PEEK coated alloy. The coefficient of friction was reduced from 0.55 for an uncoated alloy to 0.30 and below 0.20 for the Al2O3/PEEK coated alloy in dry sliding and sliding in Ringer\u27s solution, respectively. The coatings increase the corrosion resistance of the alloy in Ringer’s solution at a temperature of 37 ºC. Please click Additional Files below to see the full abstract

Analytical electron microscopy studies of the CMSX–4 single crystal superalloy subjected to high temperature annealing

The aim of the present work is to investigate the development of the γ/γ' microstructure and the changes in chemical composition of γ and γ' phases during high temperature annealing of CMSX-4 superalloy at a temperature of 1100°C in the time range from 500 to 2500 h. The studies were performed by means of scanning electron microscopy and the modern scanning-transmission electron microscopy with Super-X EDS system of four SDD detectors. Results of scanning electron microscopy and scanning-transmission electron microscopy analyses have shown that the microstructure of CMSX-4 superalloy is unstable during ageing at high temperature and the coalescence of cuboidal γ' precipitates was observed. Energy dispersive X-ray microanalysis revealed the distribution of particular alloying elements in the γ and γ' phases and the differences in their concentration in the function of the annealing time

Analytical electron microscopy investigation of topologically close-packed phases in CMSX-4 single crystal superalloy

In this work the topologically close-packed phases precipitated during annealing of CMSX-4 single-crystal superalloy at temperature 1100°C were investigated. Microstructural analyses were carried out by means of scanning- and transmission electron microscopy as well as scanning-transmission electron microscopy in high angle annular dark field mode. Chemical composition in nanoareas was determined using energy dispersive X-ray spectroscopy. Scanning electron microscopy investigation has shown that the topologically close-packed precipitates were formed already after 50 h of annealing at temperature 1000°C. With prolongation of the annealing time up to 2500 h the change of the morphology of topologically close-packed particles from blocky to needle-like occurred. Selected area electron diffraction analysis indicated that the topologically close-packed precipitates are the orthorhombic P phase. Quantitative energy dispersive X-ray spectroscopy analysis revealed that the topologically close-packed precipitates are enriched mostly in Re and W

EPD and Characterization of Graphite Oxide/Hydroxyapatite/Sodium Alginate Coatings Incorporated with Si3N4 or CuO Nanoparticles on Titanium Biomaterials

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The descriptive epidemiology of DSM-IV Adult ADHD in the World Health Organization World Mental Health Surveys

We previously reported on the cross-national epidemiology of ADHD from the first 10 countries in the WHO World Mental Health (WMH) Surveys. The current report expands those previous findings to the 20 nationally or regionally representative WMH surveys that have now collected data on adult ADHD. The Composite International Diagnostic Interview (CIDI) was administered to 26,744 respondents in these surveys in high-, upper-middle-, and low-/lower-middle-income countries (68.5% mean response rate). Current DSM-IV/CIDI adult ADHD prevalence averaged 2.8% across surveys and was higher in high (3.6%)- and upper-middle (3.0%)- than low-/lower-middle (1.4%)-income countries. Conditional prevalence of current ADHD averaged 57.0% among childhood cases and 41.1% among childhood subthreshold cases. Adult ADHD was significantly related to being male, previously married, and low education. Adult ADHD was highly comorbid with DSM-IV/CIDI anxiety, mood, behavior, and substance disorders and significantly associated with role impairments (days out of role, impaired cognition, and social interactions) when controlling for comorbidities. Treatment seeking was low in all countries and targeted largely to comorbid conditions rather than to ADHD. These results show that adult ADHD is prevalent, seriously impairing, and highly comorbid but vastly under-recognized and undertreated across countries and cultures

Zdolność nanokompozytowych powłok węglowych do tarcia w ekstremalnych warunkach

The paper presents an analysis of the micromechanical properties of selected thin, hard anti-wear coatings of the type nc-TiN/a-C and nc-TiC/a-C, which were deposited by magnetron sputtering on a steel substrate. The load carrying capacity of the nanocomposite coatings was analysed in point contact with the use of indentation method, a scratch test, and friction test in contact with a ceramic ball. The hardness and modulus of elasticity of the coatings were determined by an instrumented indentation method using a Vickers indenter. The coating adhesion to the substrate was examined in a scratch test. Tribological tests in sliding contact with an Al2O3 ball were made at various loads to determine the limit load in which normal friction occurs. The results of tribological tests were compared with the resistance to plastic deformation index (H3/E2). It was found that the basic micromechanical parameters of coatings provide important information concerning durability and load carrying capacity. However, while predicting wear, it is also important to investigate the nature of the wear process during friction. The wear nature of the nc-TiN/a-C and nc-TiC/a-C coatings depends on the load value and the number of forced loads.W pracy przedstawiono analizę właściwości mikromechanicznych wybranych cienkich, twardych powłok przeciwzużyciowych typu nc-TiN/a-C oraz nc-TiC/a-C, które zostały osadzone metodą magnetronowego rozpylania na podłożu stalowym. Zdolność nanokopozytowych powłok do przenoszenia obciążeń analizowano w styku skoncentrowanym metodą indentacyjną poprzez testy zarysowania oraz testy tarciowe z ceramiczną kulą. Twardość i moduł sprężystości powłok określono instrumentalną metodą wciskania wgłębnika Vickersa, a adhezję powłok do podłoża zbadano w teście zarysowania. Testy tribologiczne w ślizgowym styku z kulą Al2O3 wykonano przy różnych obciążeniach w celu określenia granicznego obciążenia, w którym zachodzi tarcie normalne. Wyniki badań tribologicznych porównano ze wskaźnikiem odporności na plastyczną deformację (H3/E2). Stwierdzono, że podstawowe parametry mikromechaniczne powłok niosą ważną informację o trwałości i zdolności do przenoszenia obciążeń, jednak w prognozowaniu zużycia istotne jest również zbadanie charakteru zużycia podczas tarcia. Przebieg procesu zużywania powłok nc-TiN/a-Ci nc-TiC/a-C uzależniony jest od wielkości nacisku oraz liczby wymuszeń obciążeniowych

The Influence of Electrophoretic Deposition Parameters and Heat Treatment on the Microstructure and Tribological Properties of Nanocomposite Si3N4/PEEK 708 Coatings on Titanium Alloy

Nanocomposite Si3N4/PEEK 708 coatings were successfully fabricated on the Ti-6Al-4V alloy substrate by electrophoretic deposition (EPD) and post-EPD heat treatment. The addition of chitosan polyelectrolyte into ethanolic-based suspensions enabled the cathodic co-deposition of ceramic and polymeric particles. Zeta potential measurements allowed the elaboration of stable suspensions. The selection of the optimal EPD voltage and time enabled uniform coatings to be obtained. Heating above the PEEK melting point and cooling with a furnace or in water resulted in the formation of dense coatings with semi-crystalline or amorphous polymer structures, respectively. Both coatings with a thickness in the range of 90–105 µm had good adhesion and scratch resistance to the substrates, despite the presence of relatively high degrees of open porosity. The coatings improved the tribological properties of the titanium alloy. However, a strong relationship between the polymeric matrix structure and wear resistance was observed. Semi-crystalline coatings proved to be significantly more wear resistant than amorphous ones

Analiza właściwości mechanicznych i tribologicznych polieteroeteroketonu w postaci monolitycznej i powłoki

W pracy dokonano analizy porównawczej właściwości mikromechanicznych oraz tribologicznych polieteroeteroketonu (PEEK) w postaci monolitycznej i powłoki. Powłoka PEEK 708 została osadzona metodą elektroforezy na płaskim podłożu ze stopu tytanu. Właściwości mikromechaniczne zostały zbadane metodą indentacyjną przy użyciu wgłębnika Vickersa oraz w teście zarysowania. Na podstawie badań wyznaczono twardość Vickersa (HV), moduł sprężystości (E), twardość zarysowania (HS) oraz odporność na mikrouszkodzenia (MMR). Właściwości tribologiczne zdefiniowano poprzez współczynnik tarcia (fs i fw), który wyznaczono zarówno w teście zarysowania oraz podczas tarcia w układzie typu kula–tarcza. Wyniki badań wskazują, że pomimo niedużo większej twardości Vickers’a (HV) powłoki PEEK 708 (HV = 350 MPa, HS = 300 MPa) względem monolitycznego PEEK (HV = 300 MPa, HS = 210 MPa), występuje niemal 40% różnica w ich twardościach zarysowania (HS). Z przeprowadzonej analizy wynika, że metody wyznaczania parametrów mikromechanicznych oraz tribologicznych stosowane dla materiałów monolitycznych PEEK sprawdzają się w badaniach powłok polimerowych PEEK. W określonych warunkach badań nie stwierdzono wpływu materiału podłoża na otrzymane wyniki dla powłoki PEEK 708.In this work, a comparative analysis of the micromechanical and tribological properties of polyetheretherketone (PEEK) in bulk and coating form was performed. The PEEK 708 coating was applied on a Ti6Al4V titanium alloy flat specimen using the electrophoretic deposition method. The micromechanical properties were determined through indentation tests performed using the Vickers method and scratch tests. Based on research work, the Vickers hardness (HV), elastic modulus (E), scratch hardness (HS), and Micro Mar Resistance (MMR) were determined. The tribological properties were defined by the coefficient of friction (fs and fw), which was obtained in scratch tests and ball-on-disk tests. The results of this research indicate, despite the slightly higher Vickers hardness (HV) of the PEEK 708 coating (HV = 350 MPa, HS = 300 MPa) relative to PEEK bulk (HV = 300 MPa, HS = 210 MPa), that there is an almost 40% difference between the scratch hardness (HS) values of these PEEK forms. It appears from the result analysis in this paper that testing methods to determine the micromechanical and tribological properties of PEEK in monolith form can be used for both PEEK coatings. Under certain test conditions, the impact of the substrate properties on the results of the PEEK 708 coating was not found