Sławomir Zimowski

Influence of polyetheretherketone coatings on the Ti–13Nb–13Zr titanium alloy's bio-tribological properties and corrosion resistance

Polyetheretherketone (PEEK) coatings of 70-90μm thick were electrophoretically deposited from a suspension of PEEK powder in ethanol on near-β Ti-13Nb-13Zr titanium alloy. In order to produce good quality coatings, the composition of the suspension (pH) and optimized deposition parameters (applied voltage and time) were experimentally selected. The as-deposited coatings exhibited the uniform distribution of PEEK powders on the substrate. The subsequent annealing at a temperature above the PEEK melting point enabled homogeneous, semi-crystalline coatings with spherulitic morphology to be produced. A micro-scratch test showed that the coatings exhibited very good adhesion to the titanium alloy substrate. Coating delamination was not observed even up to a maximal load of 30N. The PEEK coatings significantly improved the tribological properties of the Ti-13Nb-13Zr alloy. The coefficient of friction was reduced from 0.55 for an uncoated alloy to 0.40 and 0.12 for a coated alloy in a dry sliding and sliding in Ringers solution, respectively. The PEEK coatings exhibited excellent wear resistance in both contact conditions. Their wear rate was more than 200 times smaller compared with the wear rate of the uncoated Ti-13Nb-13Zr alloy. The obtained results indicate that electrophoretically deposited PEEK coatings on the near-β titanium alloy exhibit very useful properties for their prospective tribological applications in medicine.

Microstructure and tribological properties of low-friction composite MoS2(Ti,W) coating on the oxygen hardened Ti-6Al-4V alloy

Duplex surface treatment, which combines the oxygen diffusion hardening with a deposition of low friction MoS2(Ti,W) coating, was applied to improve the Ti-6Al-4V alloy load bearing capacity and tribological properties. The coating (3.1 μm thick) was deposited on the oxygen hardened alloy by magnetron sputtering. Microstructure characterisation was performed by scanning- and transmission electron microscopy methods, as well as X-ray diffractometry. The results of micro/nanostructural analyses performed by high-resolution transmission electron microscopy showed that the coatings are composed of MoS2 nanoclusters embedded in an amorphous matrix. Some Ti α, W, and Ti2S nanocrystals were also found in the coating microstructure. The wear resistance and friction coefficient of the hardened oxygen, as well as the coated alloy, was investigated at room temperature (RT), 300 °C, and 350 °C. The presence of the MoS2(Ti,W) coating decreases the friction coefficient from 0.85 for the oxygen hardened alloy to 0.15 (at RT) and 0.09 (at 300 °C and 350 °C) for the coated one. The coating essentially increases the wear resistance of the alloy at RT and 300 °C. It was found that the wear resistance of the coated alloy decreased significantly during the wear test performed at 350 °C.

Semiconductive friction node as a temperature sensor

When constructing micro- and milirobots, it is important to secure that structural elements perform also metrological functions. Silicon is used in microrobots, while for milirobots polymer composite materials are applied. These composites shall have the following features: metrological sensitivity, appropriate mechanic and tribologic characteristics. Strong piezoresistive properties of three- component composites: metal, resin, graphite make their utilization possible for diagnosis of temperature and stress. These properties have composites of composition in surrounding of critical concentration of percolation process. The authors undertake an effort to develop models of these thermosensitive and piezoresistive properties for friction pair microcontact.

Microstructure and properties of thick nanocomposite TiN/Si3N4 coatings on Vanadis 23 HS steel

Abstract The microstructure and selected micro-mechanical properties of a 13.4 μm thick nanocomposite TiN/Si3N4 coating deposited onto Vanadis 23 HS steel by a new gas pulsed magnetron sputtering technique were investigated. Scanning and transmission electron microscopy were employed to investigate the detailed microstructure of the coating. It was found that the coating exhibited a fully nanocrystalline structure and was composed of two zones: the outer zone with columnar structure and the inner one with equiaxed, fine columnar structure. Both zones consisted mainly of the δ-TiN nanocrystallites with a small amount of α-Si3N4 and β-Si3N4. In order to increase coating adhesion to the substrate, a graded intermediate layer consisting of three different phases (pure Cr, CrN and Cr2N) was applied. The hardness of the as-deposited TiN/Si3N4 coating was equal to 48 GPa, whereas it was equal to 40 GPa after annealing. The coatings exhibited very good adhesion to the underlying steel substrate.

Silicon carbonitride layers deposited on titanium and polyurethane by PACVD method

This work reports the results concerning formation and tribological properties of SiCxNy(H) layers deposited on Ti Grade 2 and polyurethane foil. Depending on the substrate, two variants of PACVD were used. The SiCxNy(H) layers on titanium were deposited with application of MWCVD (2.45 GHz, 2 kW). The layers on polyurethane were deposited using RFCVD (13.56 MHz, 400 W). Good adhesion between the SiCxNy(H) layers and polymeric foil was achieved by formation of a transitional C:N:H layer and incorporating Si gradient into the structure of the SiCxNy(H) layer. The chemical composition of the layers was tailored by precise control of the gaseous precursors ratios: [SiH4]/[NH3], [SIH4]/[NH3]/[CH4], [SiH4]/[CH4] or [SiH4]/[N2]/[CH4]. The structure and chemical composition of the obtained layers were subjected to further studies (FTIR, SEM/EDS). The roughness, friction coefficient and wear resistance were also measured. The results show that SiCxNy(H) layers offer attractive tribological properties which make them good candidates for various applications, including biomedical devices.

ANALYSIS OF THE TRIBOLOGICAL PROPERTIES OF TiN/Si3N4 NANOCOMPOSITE COATING IN SLIDING CONTACT WITH CERAMIC, STEEL, AND POLYMER COUNTERPART

In this work, the friction and wear of a hard TiN/Si3N4 nanocomposite coating in sliding contact with Al2O3 ceramic, 100Cr6 steel, and PTFE polymer balls were analysed. The coating was deposited on Vanadis 23 high-speed steel by a new gas pulsed magnetron sputtering technique. Studies of micromechanical properties indicate very high hardness of the coating equal to 49 GPa with simultaneous very good adhesion to the substrate confirmed in the scratch test. Based on the tribological studies in an unlubricated ball-on-disk contact, the coefficient of friction and specific wear index of the coating and balls were determined. In the friction cooperation, the most advantageous pair of coating and counterpart was an association of TiN/Si3N4 coating with a ceramic Al2O3 ball. In this combination, the wear index of the coating was 5.3·10 -6 mm3/Nm, whereas the value of the wear index of the ball was 0.04·10-6 mm3/Nm. According to our investigation, this is the best pair among the tested materials that can be used in friction nodes under a high load. The analysis of the wear mechanism for individual pairs was based on microscopic examination of wear tracks. Słowa kluczowe: nanokompozytowe powłoki, rozpylanie magnetronowe; tarcie; odporność na zużycie; supertwardość. Streszczenie W niniejszej pracy dokonano analizy tarcia i zużycia twardej powłoki nanokompozytowej TiN/Si3N4 podczas współpracy z kulami ceramicznymi Al2O3, stalowymi 100Cr6 i polimerowymi PTFE. Powłoka została osadzona na próbkach z ulepszonej stali szybkotnącej Vanadis 23 metodą rozpylania magnetronowego sterowanego impulsami ciśnienia gazu. Badania właściwości mikromechanicznych wykazały bardzo dużą twardość powłoki wynoszącą 49 GPa i jednocześnie bardzo dobrą adhezję do podłoża potwierdzoną w próbie zarysowania. Na podstawie badań tribologicznych w niesmarowanym styku ślizgowym typu kula/tarcza wyznaczono współczynnik tarcia oraz wskaźnik zużycia objętościowego powłoki i kul. Najkorzystniejsze pod względem odporności na zużycie zarówno powłoki, jak i przeciwelementu było skojarzenie powłoki TiN/Si3N4 z kulą Al2O3. W tym skojarzeniu wskaźnik zużycia powłoki był równy 5,3·10 -6 mm3/Nm, a kuli 0,04·10-6 mm3/Nm. Skojarzenie to jest najlepsze spośród badanych par i może znaleźć zastosowanie do wysoko obciążonych węzłów tarcia. Analizę mechanizmu zużycia dla poszczególnych skojarzeń wykonano w oparciu o badania mikroskopowe śladów zużycia. * AGH University of Science and Technology, Faculty of Mechanical Engineering and Robotics, Al. A. Mickiewicza 30, 30-059 Krakow, Poland, e-mail: zimowski@agh.edu.pl. ** AGH University of Science and Technology, Faculty of Metals Engineering and Industrial Computer Science, ul. Czarnowiejska 66, 30-059 Krakow, Poland, e-mail: tmoskale@agh.edu.pl. *** Lodz University of Technology, Institute of Materials Science and Engineering, ul. Stefanowskiego 1, 90-924 Lodz, Poland, e-mail: bogdan.wendler@p.lodz.pl. INTRODUCTION The significant increase in the popularity of tribological coatings has been observed over the last few decades. This is especially evident in such areas as the automotive industry or aviation, where the role of coatings of a high wear resistance is of immense importance, or in biomedical engineering, where the materials have to meet the additional requirements of biocompatibility and corrosion resistance. Therefore, numerous research institutes are incessantly working on the development of new coating materials or on the improvement of the existing ones [L. 1–4]. Among numerous types of wear-resistant coatings, special attention should be 126 ISSN 0208-7774 T R I B O L O G I A 4/2017 given to the nanostructured ones with multilayer structure including the superlattices as well as to the composite coatings. Contemporary nanomaterials can be divided into three classes according to their hardness (H): hard nanocomposites (20 ≤ H < 40 GPa), superhard (40 ≤ H < 80 GPa), and ultrahard (H ≥ 80 GPa) [L. 5]. Modification of transition metal (Me) nitrides by introducing such elements as Al, Si, Cr, W, or Zr results in the formation of a composite structure and the improvement of composite strength. The concept of crystalline-amorphous nanocomposite coating production (presented inter alia by S. Veprek [L. 6–9]) is an interesting way to improve coating hardness by grain refinement. These coatings consist of nanocrystalline (nc-) nitrides, carbides, borides, silicides, or transition metal oxides surrounded by amorphous (a-) matrix, e.g. Si3N4, BN, C, C:H. In such coatings, the dislocation movement is blocked by nanocrystallites (less than 10 nm in size) and by thin layers of amorphous matrix surrounding the nanocrystallites, which reinforce the composite [L. 6, 8]. In order to obtain such advanced coatings, deposition techniques are still being developed to better control coatings’ nanostructure [L. 3, 10, 14–16]. Selection of an appropriate coating for a specific application requires knowledge of phenomena that occur in the tribological contact. This knowledge allows one to predict the wear behaviour of components of kinematic pairs and determines the impact on the stability, reliability, and the correct operation of the device. The preselection stage is essential in the selection process of the coating. However, this preselection must be based on appropriate knowledge of the friction and wear mechanisms of the kinematic pair, as well as on other material properties of both elements relevant to their application. In this paper, the friction and wear of hard TiN/ Si3N4 nanocomposite coatings deposited by magnetron sputtering technique were analysed during dry sliding against ceramic, steel, and polymer counterparts.

Modern Self-Lubricating Coatings for Automotive, Aviation and Spacecraft Industry

A series of nanocomposite, self-lubricating coatings designed for dry friction at different temperatures based on amorphous carbon or amorphous MoS2 or amorphous MoO3 matrix was deposited by magnetron sputtering onto high-speed (HS) steel or Ti6Al4V alloy substrates and characterized with use of LM, SEM, TEM and HRTEM microscopy as well as with use of several other techniques. The nanocomposite nc-MeC/a-C(:H) carbon-based coatings (where Me=Cr or Ti or W) were composed of different nanocrystalline phases of a given transition metal of a size of several nanometers embedded in an amorphous hydrogenated or hydrogen-free carbon matrix. The nanocomposite MoS2(Ti,W) coatings were composed of Tiα or Wα or TiS2 nanocrystallites of 3 nm ÷ 10 nm diam. embedded in a semi-crystalline MoS2 matrix with MoS2 clusters of 3 nm÷8 nm diam. The magnetron sputtered MoO3 based coatings after deposition were composed of Ag nanocrystallites of 50 nm÷100 nm diam. embedded in an amorphous fractal-type matrix composed of MoO3 clusters of different size from very small to relatively great ones (not exceeding, however, 400 nm diam.). These amorphous clusters after 3 hours annealing in the ambient atmosphere under normal pressure at 300 °C transform into nanocrystalline MoO3 ones or after same annealing at 450 °C into crystalline silver molybdate Ag2MoO4 ones. The coatings preserve their resistance to wear and their low friction coefficient to approximately 250 °C in case of carbon-based coatings or to 350 °C in case of MoS2-based ones or to 550 °C in case of MoO3-based coatings. Several mechanical and tribological chracteristics of the coatings are given in the paper as well.

Surface Modification of Titanium by Plasma Assisted Chemical Vapor Deposition (PACVD) Methods

One way of obtaining new materials with different properties is to modify existing ones to improve their insufficient properties. Due to the fact that many of the useful properties of materials, including wear and corrosion resistance, friction coefficient and biocompatibility, depend on the state of the surface, modern surface engineering methods are especially helpful. They involve the deposition of the layers with tailored chemical composition and structure. In terms of medical applications, amorphous or nanocrystalline layers containing carbon, nitrogen, silicon and hydrogen appear to be the most suitable. They combine the beneficial properties of silicon carbide SiC and silicon nitride Si3N4, and thus exhibit a strong resistance to oxidation at high temperatures, high modulus of elasticity, low friction coefficient and wear resistance. However, silicon carbonitride compound is not stable thermodynamically in normal conditions and therefore it must be obtained by non-conventional synthesis. One of such method is Plasma Assisted Chemical Vapour Deposition (PACVD). The authors of this paper anticipate that the modification of titanium surface by SiCxNy(H) layers make them proper for use as materials for long-term contact with human body. It contains results of research on titanium Ti Grade 2 surface modification by deposition amorphous carbon layers doped with nitrogen (a-C:N:H) and silicon carbonitride layers SiCxNy(H). What is more, for IR analysis, in the same plasmochemical methods process obtain layers on monocrystaline silicon (001)Si. The layers were synthesis by PACVD with plasma generated by radio waves (RFCVD, 400 W, 13.56 MHz) for a-C:N:H layers and microwaves (MWCVD, 2 kW, 2.45 GHz) for layers containing silicon, carbon, nitrogen and hydrogen. During deposition process metallic surface were ion-etching by argon plasma. The layers were obtained from reactive gas mixture containing CH4, N2 or NH3 for a-C:N:H layers and CH4, SiH4, N2 or NH3 for silicon carbonitride compound. In this process argon was used as an inert gaseous. Process conditions allowing obtaining good adhesive layer to the metallic substrate were specified. Obtained systems were subject for further research. Chemical composition of the materials were studied by SEM / EDS techniques with application ETD and BSED detectors. Compared images registered for titanium before surface modification and surfaces covered by a-C:N:H or SiCxNy(H) layers. More information about layers structure provided FTIR spectroscopy. Spectra FTIR was register transmition for (001)Si-layer and reflective for titanium-layer systems. Assessed the impact of different kind of substrate on the layers deposited structure. Operational properties of synergic layer-titanium systems were evaluated in the measurements of tribological parameters. This tests shown that silicon carbonitride layers have the lowest friction coefficient and the highest resistance to wear. Furthermore, it was possible, on the basis of the obtained result, to indicate directions the surface modifications ensuring optimization on their usable properties as medicine and another industries. In previous authors paper the layers were investigated in the aspect of possible application in medicine.