Bogdan Wendler

The effect of hydrogen in lubricated frictional couples

The tribological experiments under circumstances of hydrodynamic and elastohydrodynamic lubrication, the immersion test in lubricating oil as well as the exposure test to the environment have been performed to elucidate the effect of hydrogen on soft and hardened surface layers. The occurrence of the effect of hydrogen tribosorption in lubricated frictional nodes has been confirmed. This effect proceeds at a different rate and in a different way for nitrided surface layers (and homologous layers), on the one hand, and for other soft or hardened surface layers on the other. The most probable mechanisms of the tribosorption for both the cases mentioned above have been presented and the significance of that phenomenon for the theory as well as for practical operation has been discussed.

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.

Micromechanical and Tribological Properties of Nanocomposite nc-TiC/a-C Coatings

The nanocomposite coatings composed of nanocrystalline TiC grains embedded in hydrogen free amorphous carbon a-C matrix (nc-TiC/a-C) were deposited by magnetron sputtering on the two substrates, oxygen hardened Ti-6Al-4V alloy and heat treated VANADIS 23 steel. The Ti-6Al-4V alloy was oxygen hardened by plasma glow discharge. Micro-mechanical and tribological properties as well as coating adhesion to the substrates were investigated. Micro/nanostructure of the coatings and the substrates were examined using scanning- and transmission electron microscopy methods as well as X-ray diffractometry. Nano-, microhardness tests performed for the coated materials showed average hardness 13.4-14.7 GPa and modulus of elasticity 160 GPa. Scratch test revealed good adhesion of coatings to the both substrates. The nanocomposite coatings significantly improved tribological properties of the titanium alloy and steel, increased wear resistance and decreased friction coefficient.

Comparison of Shot Peening and Nitriding Surface Treatments under Complex Fretting Loadings

Considered as a plague for numerous industrial assemblies, fretting associated with small oscillatory displacements is encountered in all quasi-static contacts submitted to vibrations. According to the sliding conditions, fretting cracks and/or fretting wear can be observed in the contact area. On the other hand an important development has been achieved in the domain of surface engineering during the past three decades and numerous new surface treatments and coatings are now available. Therefore there is a critical challenge to evaluate the usefulness of these new treatments and/or coatings against fretting damage. To achieve this objective, a fast fretting methodology has been developed. It consists in quantifying the palliative friction, cracking and wear responses through a very small number of fretting tests. With use of defined quantitative variables, a normalized polar fretting damage chart approach is introduced. Finally, to evaluate the performance of the assemblies after these protective surface treatments under complex fretting loadings, an original sequence of partial slip and gross slip sliding procedure has been applied. It has been demonstrated that performing of a very short sequence of gross slip fretting cycles can critically decrease the resistance of the treated surfaces against cracking failures activated under subsequent partial slip loadings.

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.

Oxidation resistance of nanocrystalline microalloyed γ-TiAl coatings under isothermal conditions and thermal fatigue

γ-titanium aluminide a promising structural material for automotive and aircraft applications at high temperatures suffers from poor gas corrosion resistance. It has been proved in this work by means of microthermogravimetry and SEM, EDS, EBSD and X-Ray diffraction carried out and under isothermal conditions and thermal cycling that a great improvement of the oxidation resistance of this material can be achieved due to magnetron sputtered coatings of γ-TiAl with vatious additions (Ag, Cr, Mo, Nb, Si or Ta) or their combinations. The oxidation rate of some of these coatings is four orders of magnitude smaller than that of the bare γ-TiAl substrate.

Hard coatings durability under fretting wear

Fretting wear, defined as a small displacement amplitude oscillatory motion between two solids in contact, is usually induced by vibrations. In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent from catastrophic consequences. Moreover, a reliable selection of surface treatment is of great interest for industrial applications. In this work fretting tests were carried out on different PVD hard coatings (TiN, TiC, TiCN, VC, TiC/VC, (TiC/VC)x2) under wide range of normal loadings and displacement amplitudes. A ball-against-flat specimen arrangement has been analyzed under gross slip fretting regime. The coatings durability criterion based on local dissipated energy has been developed and related to the friction process. The wear depth extension is referred to the cumulated density of friction work dissipated during the test. An averaged cumulated density of dissipated friction energy is successively introduced to rationalize the coating lifetime. The critical dissipated energy density related to the coatings durability has been determined for each analyzed coating and the critical number of fretting cycles has been established. Taking into account this critical value an Energy Density—Coating Endurance chart has been proposed where the coating duration is predicted as a function of the pressure, the displacement amplitude and the friction coefficient. Nevertheless, some divergence has been observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The investigated hard coatings are compared independently of the loading conditions and its thickness. Finally the global procedure to establish the coatings durability has been presented.

Creation of thin TaC or TiC layers on steels

Abstract An indirect method (a hybrid in comparison with the known physical and chemical vapour deposition methods) for the creation of hard transition metal carbide layers is presented which consists in vacuum annealing of thin carbide-forming metal layers on high carbon steel substrates. A phenomenological diffusion model for the layer/substrate system which fits the experiment well is also presented.

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.