ICMCTF2018 Session EP: Symposium E Poster Session

Fe-Co based coatings which have a broad application in improving the surface properties have excellent wear resistance and soft magnetic properties. In this study, (FeCoNi) Si B Cu Mo coatings with high saturation magnetization and good tribological properties were prepared using lasers cladding.The different process parameters effect on the microstructure, mechanical properties of the cladding layer wereinvestigated. It was found that laser power P, scanning speed V and laser remelting technology which had a significant effect on the magnetic properties and tribological properties. The optimum process parameters were determined and the coatings showed bcc dominated microstructures. The average microhardness and friction coefficient of the coatingsreached 1032 HV_0.5 and 0.291 respectively. With the decrease of grain size, wear resistance and microhardness of coatings improved significantly. In addition, the coatings exhibited higher saturation magnetization (212emu/g), comparable magnetic properties to those of their conventionally processed counterparts.

Acknowledgements

In this study, AISI 4140 steel was boronized using solid state thermochemical boriding technique, producing a monophasic iron boride (Fe₂B) layer with a mean thickness of 49,5 μm. The microstructural and chemical characteristics were evaluated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD). To investigate the tribocorrosion behavior samples were immersed in 3,5% NaCl solution subjected to a pin-on-disk wear test and connected to a potentiostat monitoring the open circuit potential (OCP).

The results obtained show that boronized samples have an improved tribological behavior compared to unboronized samples and the evaluation of the OCP curve indicates the formation of a passivation layer during de wear test. These results can be explained by the high hardness and chemical inertness of iron boride layer.

Despite being a ceramic material widely known for its high hardness, chemical resistance and high thermal stability; TiB₂ coatings using in industrial conditions has been really limited due to the high residual stresses associated with the reduction of adhesion. Recently, several investigations have shown that the incorporation of carbon within TiB₂ coatings reduces the residual stresses, increasing the adhesion and becoming Ti-B-C coatings in excellent candidates for applications at high temperatures. In this research, Ti-B-C coatings were deposited onto M2 steel substrates by DC UBMS. Prior to the coatings deposition a plasma cleaning process was carried out both substrates and targets with a 40 sccm flow of Ar and a pressure of 3 Pa for 0.5 h. For the deposition, two targets of TiB₂ (99.9%) and graphite (99.9%) opposite each other was used. The power density of TiB₂ was fixed to 2.4 W/cm² and four different power ratio W_TiB2/W_C was made in order to varied the carbon content in the Ti-B-C coatings. Microstructural analysis by X-ray diffraction (XRD) showed h-TiB₂ crystal structure with preferential orientation (001), increasing the carbon content, the intensity of (001) peak decrease becoming the crystalline coatings in amorphous coatings. Using AFM technique, an increase in roughness and grain size was observed with higher carbon content, except for coatings with ~20%. SEM images revealed columnar, dense and homogenous structure for all coatings. A progressive decreasing in hardness and Young modulus was observed with the increasing in carbon content, hardness up to 27 GPa was reached with lower carbon content and a decreasing under 5 GPa with the higher carbon content. The Young modulus exhibited the same featured. Tribological properties of the coatings were investigated using Pin-on-disk, all coatings showed COF higher tan AISI H13 substrate, only the coatings with 36% of carbon showed COF over 0.30. respecting to the wear rate it was keep almost constant for all Ti-B-C coatings.

Due to the high material utilization and the associated resource and energy efficiency, production processes from the field of cold forging of steel are of great importance. At present, environmentally harmful lubricants have to be used to ensure process stability as well as low wear and friction. Due to environmental, economic and legislative aspects, there is an increased research potential to reduce or to completely substitute lubricants. To achieve the goal of lubricant free dry cold forging of steel, physical vapor deposition (PVD) coatings with self-lubricating properties are applied on forming tools. Promising for this application are PVD coatings on the basis of a (Cr,Al)N hard phase with embedded MoS_x which simultaneously meet the requirements of high wear resistance and friction reduction. Furthermore, a sufficient compound adhesion is needed to withstand high contact stresses up to σ = 3,000 MPa during cold forging of steel. In addition to the mechanical stresses, a thermal load up to T = 250 °C occurs during cold forging. In the presented work, three self-lubricating coatings (Cr,Al)N/MoS_x deposited with varying bias voltage were investigated. The hybrid PVD technology, consisting of direct current and high power pulse magnetron sputtering dcMS/HPPMS, was used for the coating deposition in an industrial coating unit. Two different steels AISI D2 (X155CrMoV12, 1.2379) and AISI M2 (HS6‑5‑3C, 1.3343) were used as substrate materials. The influences of the substrate material and heat treatments at T = 250 °C on mechanical, compound adhesion and tribological properties were investigated. The samples were analyzed with respect to the universal hardness HU and modulus of indentation E_IT using nanoindentation. To determine the interfacial adhesion of the compound coating/substrate, Rockwell indentation and scratch tests were carried out dependent on the heat-treatment. For the analysis of the tribological behavior, AISI 5115 (16MnCr5, DIN 1.7131) and AISI 4140 (42CrMo4, DIN 1.7225) were used as counterpart materials, since these are widely used as forming material. As closed tribometer, a Pin-on-Disc (PoD) was used at varying temperatures. In this case, the coated substrate is continuously loaded with the worn pin on the same track. As open tribometer, a newly developed Pin-on-Cylinder (PoC) was used. The particular feature of the PoC is that the pins (AISI D2) are coated and pressed by means of a defined feed along a rotating cylinder (AISI 5115 and AISI 4140). Thus, the coated pin is permanently in contact with an unworn surface of the cylinder. The contact region was studied by Raman spectroscopy before and after the tribological tests.

The demands of reusable solid lubricants with continuous lubricating properties from room temperature (RT) to 1000 °C or even higher temperatures become increasingly urgent with the development of high-tech industries, especially that of aerospace industry. In our work, chromium oxide was investigated as a primary coating because it possesses high melting point and excellent thermal stability. The chromium oxide coatings were deposited on Ni-based high-temperature alloy substrates through an arc ion plating system and then annealed at 1000 °C in air for 2 h. The effects of annealing on the structure and tribological properties in wide temperature range of Cr₂O₃ coating were researched in detail. The phase change and elements diffusion behavior of Cr₂O₃ coating annealed at 1000 °C were also discussed. Main results and conclusions are as-followed:

The hydropower industry routinely makes use of thermally sprayed coatings and solid lubricating polymer coatings in their operations to enhance the lifetime of their infrastructure, especially those components subjected to sliding wear. Often these two coating systems are used independent of one another but in this study, we examine the feasibility of a duplex coating where a self-lubricating polymer composite was infiltrated into a porous SS316 substrate. This resulted in coatings consisting of a top layer made of a self-lubricating polymer composite and a bottom layer made of a polymer composite infiltrated into a porous metallic structure. This paper presents the tribological behaviour of the polymer composite and the transition when wearing reaches the infiltrated metallic porous substrate.

Addition of graphite (Gr) to a thermoset bismaleimide (BMI) significantly reduced coefficient of friction and wear rate. An in-situ tribometer that uses a transparent sapphire hemisphere as counterfaces permits microscopic observation and video recording of the sliding contact. Interfacial sliding dynamics such as material transfer, formation of transferfilms and wear debris were examined and therefore wear mechanisms of BMI + Gr and BMI + Gr + SS316 were observed. A stable transfer film that was rich in Gr was formed when sliding on the top layer of BMI + Gr, while participation of metallic material in the sliding contact contributed to deposition of transfer film onto wear tracks and transfer film reformation. Raman spectroscopy was used to detect formation of Gr-containing tribofilms and transferfilms in the running-in and steady-state regimes. X-ray photoelectron spectroscopy (XPS) testing on the wear tracks and transferfilms revealed possible tribochemical reactions such as polymer decomposition and interaction with Gr and/or SS316 induced by sliding wear. Mechanical properties of the as-received polymer composites and worn materials were also investigated using nanoindentation.

Coatings in the material system B-C-W have been synthesized by pulsed magnetron co-sputtering of a boron carbide and a tungsten target. The bipolar co-sputtering process enables fine tuning of the composition through variation of sputtering pulse times. In the range of composition from pure boron carbide to 70 at-% tungsten content, the hardness of the coatings as determined by nanoindentation changes only little, typically in the range of 24 GPa to 28 GPa. However, in contrast to completely amorphous pure boron carbide, the x-ray diffraction pattern of B-C-W coatings exhibit broad peaks, indicative of extremely small crystalline domains that cannot clearly be attributed to a single phase for tungsten content below 50 at-%. Corresponding to a smooth transition in structure, scanning electron microscopy investigation reveals very homogeneous coatings with extremely smooth surfaces, even at a thickness of several microns. Consistently, EDX mapping reveals a very homogeneous element distribution. Thermal stability has been tested up to a temperature of 600°C in vacuum and in air. While no degradation is observed in vacuum, the oxidation rate in air depends on the tungsten content of the coatings.

In contrast to many other hard coatings, the stress level of the B-C-W layers is very low and the material seems to be rather resistant to crack propagation, as far as scratch test analysis can reveal. The coatings have been tested on cutting tools for cemented carbide cutting, where they abrade rather rapidly. However, the combination of properties still makes them interesting as hard and tough coatings.

Cp-Ti is commonly used in different applications because of its good structural properties but its low mechanical and tribological properties restricts its usage areas. Therefore, different surface modifications based on TiO₂ formation on material surface are applied to enhance its surface properties. In this study, TiO₂ films were produced on Cp-Ti substrates by sol-gel and successive ionic layer adsorption and reaction (SILAR) methods in order to compare the performance of different coating methods. The structural, morphological and mechanical features of TiO₂ films were investigated by XRD, SEM and microhardness tester. The tribological properties of films were characterized using a pin-on-disc tribotester. The electrochemical behavior of TiO₂ films were determined by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analyses. The structural and mechanical analyses showed sol-gel method caused the formation of more stable and hard film structures with good adhesion in comparison to SILAR method. For that reason, TiO₂ films produced by sol–gel method exhibited better wear and corrosion resistance than the films produced by SILAR.

The basic goal of presented investigations is comparison of feedstock powders of WC-Co-Cr type in area of its chemical and phase compositions as well as morphological parameters, size distribution and shape. Those parameters have direct transfer on technological properties of powders such as followability etc., what is essential form high velocity spraying process point of view. In this part of article the X-ray and EDS analysis of powders were made, additionally scanning electron microscopy observation was carried out too. The size distribution was analysed by laser diffraction method. Obtained data gives the possibility to comparison of powders from different sources from technological properties point of view.

The second part of paper related with microstructural characterization of coatings deposited by high velocity air fuel (HVAF) method. The standard procedure for those kind of powders was used. The gun of Kermetico of K5 type was used. The range of investigations included characterization of coatings top surface with descriptions of roughness, as well as the stress state was analysed by X-ray method. Phase analysis was made after deposition and obtained data were compared to initial phase composition of powders as well as theirs chemical compositions. In area of mechanical properties basic parameters such as hardness and fracture toughness were measured and analysed. The final part of investigations is related with characterization of tribological properties of coatings with the same chemical and phases constituent buy deposited from different feedstock materials

A publication supported under the Rector's Grant in the area of scientific research and development. Silesian University of Technology, No 11/030/RGH17/0157.