Key Engineering Materials Vol. 799

Abstract: The effect of composite materials reinforcement by hardmetal with various size of particles (WC 710-1000 μm, recycled WC-Co 710-800 μm and pure WC 10 μm) with Fe-based matrix thermally affected by spark plasma sintering (SPS) method at temperatures 1100°C, 1200°C and 1280°C was studied. The analysis of samples cross-section was performed with SEM and EDS to illustrate distribution of elements after thermal influence. The aim of this research was an investigation of diffusion process behaviour between Fe-based matrix and WC and WC based hardmetal particles at various temperatures. Results help to identify and understand melting and solidification of grains affected at high temperature. Similar temperatures are used for surfacing and repair of worn parts and recycled tungsten carbide particles (as reinforcement) could be used during manual or plasma transferred arc welding.

Abstract: The multilayered AlCrN coating physical vapour deposited (PVD) over the stainless steel (SS) substrate was studied. Raman spectroscopy was used to determine the resistance of the coating under high temperature oxidative conditions (25–800 °C). Static oxidation tests of the AlCrN PVD coating mainly leads to the formation of Cr₂O₃ at temperatures up to 800 °C. The results of the sliding tests indicate the development of oxides layers in the wear tracks on the surface of AlCrN PVD coated samples at the room temperature, which is critically dependant on the sliding speed against Si₃N₄ counter balls. The maximum reliable sliding speeds against Si₃N₄ counter balls under applied normal load of 3 N at 20, 300/500 and 800 °C was determined to be 0.486, 0.162 and 0.054 m·s^-1, respectively.

Abstract: Ion-plasma antifriction coatings based on Ti-Cu were deposited by the method of ion-plasma sputtering in vacuum with the aim to gain a coating with a low coefficient of friction. To protect steel part from wear intermetallic, nitride and conglomerate coatings based on Ti-Cu with thickness of the coating h ≈ 2-5 μm obtained at different regimes of deposition. Thickness of the antifriction coatings and proportion of the chemical composition varied by deposition time, voltage and current of the magnetron, current of evaporators, pressure of gas in a vacuum chamber. This paper presents the results of the tribotest carried out on CSM Instruments pin-on-disk type tribometer. Comparing with uncoated samples microhardness and roughness of the coated samples increased two to three times, coefficient of friction of coated samples was twice lower.

Abstract: In this study we determined average residual stresses in hard nitride PVD AlCrN, TiAlN and TiCN coatings through simultaneous measurement of length variation in thin-walled tubular substrates and of the curvature of plate substrates. A device for measurement of the length of the tube was developed. Inside the depositing chamber the tube and the plate were fixed parallel in the relation to the axis of the rotating cathode. One batch of plate samples was produced by deposition on front surface (facing the cathode) and the other batch, by deposition on back surface (with back to the cathode). The cross-sectional microstructure and thickness of the coatings were investigated by means of scanning electron microscopy (SEM). The thicknesses of the coatings deposited on front and back surfaces of the plates and on the tube were significantly different. The values of average compressive residual stresses, determined by both methods, were very high irrespective of coating thickness. It was found that the values of compressive residual stresses in the coating were dependent on the shape of the substrate and on its position in the relation to the axis of the rotating cathode.

Abstract: Metal hollow mini-spheres (MHMS) present a basis for the creation of new structured materials due to their low weight and energy adsorption capacity. Typically, MHMS are made of steel with a high level porosity in the sphere’s wall 80-110 microns thick. Modification of the outer surface by copper coating of 20-30 microns imposed by vacuum sputtering provides several times higher electrical conductivity, lower porosity of the outer layer and smoother surface, preserving light weight and flotation properties. This modification will provide better possibilities for spheres’ consolidation by means of sintering and electric brazing and creation of new cellular structures.

Abstract: The aim of this research was to optimize the mechanically activated synthesis (MAS) technology of the Cr₃C₂-Ni powder intended for thermal spraying. The MAS production route included ball milling for 72 h (ball-to-powder ratio 20:1) and sintering under 1075 °C in vacuum for 4 h. Sintered compact was crushed, classified by sieving to obtain the fraction suitable for thermal spraying (20–45 μm). The morphology and the phase composition of the powder were analyzed by a scanning electron microscope (SEM) and X-ray diffraction (XRD). The optimal Cr:C ratio found was 7:1. The powder had an equiaxial or a slightly elongated lamellar shape, Cr₃C₂ carbides in a single powder particle had an elongated shape. The principal phases in the optimized powder were Cr₃C₂, Cr₇C₃ and Ni (Cr) solid solution. Coatings from the manufactured powder were produced by the high velocity oxy-fuel (HVOF) spraying. The abrasive wear tests were carried out according to standard ASTM G65. The wear tests showed that the sprayed coatings from the experimental powder exhibited about five times higher wear rate at abrasive wear conditions than the coatings from the reference commercial powder.

Abstract: In this study, the influence of plasma and detonation spraying techniques on the microstructure and wear behaviour of FeNiCrBSiC-20wt%CrB₂ coating was investigated. The obtained coatings were found to comprise of Fe, Ni-based solid solution matrix reinforced with mixed boride phases (Fe,Cr)₂B, (Ni,Fe,Cr)B, (Cr,Fe,Ni, Mo)B. The main microstructural differences of the plasma and detonation sprayed coatings are the morphology, the size and the distribution of hard boride particles. The tribological behaviour of coatings was examined under dry sliding conditions against Al₂O₃ ball at 20, 200 and 400 °C. The wear loss of detonation sprayed coatings was slightly lower at high temperatures while plasma sprayed coating had same wear at all temperatures. The investigation of worn surfaces revealed that abrasive and oxidative wear mechanisms are proved to be dominant for FeNiCrBSiC−20wt.%CrB₂ plasma sprayed coatings, while brittle delamination and oxidative wear are characteristic for detonation sprayed coating. The sliding wear loss of the unreinforced commercial FeNiCrBSiC plasma sprayed coating was 2-3 times higher than that of reinforced (with chromium boride) coating at high temperatures due to splat delamination.

Abstract: One of the most efficient methods of improving the durability of a product is applying different coatings to the working surface. The quality of decorative and protective coatings is determined by the quality of workpiece surface (roughness, texture, etc.), preparation of workpiece surface (contamination, presence of oxide films, degree of surface activation by ion etching), and the production methods. The article presents the results of a series of experiments in creating multi-component ion-plasma coatings by vacuum deposition on Ti-Al basis. A series of experiments aimed at obtaining single-layer coatings have been carried out using a certain pattern of sputtering in argon and nitrogen environment. The obtained coatings can have a wide variety of colors. Different properties of the created coatings including spectral characteristics, reflection coefficient at different angles of incidence of light as well as chemical composition have been studied. The energy-dispersive electron microprobe analysis revealed the dependence of coating reflection coefficient and spectral characteristics on the chemical composition.

Abstract: The paper deals with the results of a research study into Ti-Al-Si-Cr-based thin heat resistant ion-plasma coatings for titan alloy-based parts of a gas turbine engine (GTE). The research involved the use of three Ti-Al-Si-Cr-based alloys – intermetallic, with different Cr-Ti priority. The analysis of surface oxidation process in the range of 600-850°C with the help of scanning electron microscopy was performed, and the key features of coating fracture process under high-temperature oxidation conditions were identified.