Solid State Phenomena Vol. 320

Abstract: TiAl intermetallics can be considered an alternative for conventional nickel superalloys in the high-temperature application. A TBC (Thermal Barrier Coatings) with ceramic topcoat with columnar structure obtained using EB-PVD (electron beam physical vapour deposition) is currently used to protect TiAl intermetallics. This article presents the new concept and technology of TBC for TiAl intermetallic alloys. Bond coats produced using the slurry method were obtained. Si and Al nanopowders (70 nm) were used for water-based slurry preparation with different composition of solid fraction: 100 wt.% of Al, 50 wt.% Al + 50 wt.% Si and pure Si. Samples of TNM-B1 (TiAl-Nb-Mo) TiAl intermetallic alloy were used as a base material. The samples were immersed in slurries and dried. The samples were heat treated in Ar atmosphere at 1000 °C for 4 h. The outer ceramic layer was produced using the new plasma spray physical vapour deposition (PS-PVD) method. The approximately 110 μm thick outer ceramic layers contained yttria-stabilised zirconium oxide. It was characterised by a columnar structure. Differences in phase composition and structures were observed in bond coats. The coatings obtained from Al-contained slurry were approximately 30 μm thick and consisted of two zones: the outer contained the TiAl₃ phase and the inner zone consisted of the TiAl₂ phase. The second bond coat produced from 50 wt.% Al + 50 wt.% Si slurry was characterised by a similar thickness and contained the TiAl₂ phase, as well as titanium silicides. The bond coat formed from pure-Si slurry had a thickness < 10 μm and contained up to 20 at % of Si. This suggests the formation of different types of titanium silicides and Ti-Al phases. The obtained results showed that PS-PVD method can be considered as an alternative to the EB-PVD method, which is currently applied for deposition a columnar structure ceramic layer. On the other hand, the use of nanopowder for slurry production is problematic due to the smaller thickness of the produced coating in comparison with conventional micro-sized slurries.

Abstract: Basic titanium alloys are successfully used in modern aviation GTE (gas turbine engine). They are used for parts of a compressor and partly in low pressure part of turbine (intermetallic Ti-Al alloys) due to their high specific strength and at the same time low density, high corrosion resistance but can be used only up to 700 °C. The paper deals with the results of heat resistance testing at 750 °C of Ti-Al-(X)+N based thin ion-plasm multilayers coatings, with different priority of monolayers- intermetallic, conglomerate or nitride for gas turbine engine (GTE) blades from titanium alloys. All coatings showed high resistance during the test, with a maximum efficiency 42.8 of coating with a priority of conglomerate after 30 hours of testing.

Abstract: Plasma Spray Physical Vapour Deposition (PS-PVD) method was designed for production of ceramic layer on nickel superalloys. In typical process before deposition the base material is heated by plasma up to 900 °C. In present article the yttria stabilized zirconia (YSZ) was deposited on low melting point materials: 2017A-type aluminium alloy and Cu-ETP copper. The influence of power current, process time and powder feed rate on structure and thickness of obtained coatings was analysed. During first deposition process the overheating of Al-sample was observed and as result the power current was decreased to 1600 A. In the next experimental the approx. 5 mm thick dense coating was formed. During experimental processes of YSZ deposition on copper the thickness of coating increased from approx. 5 to 22 mm. The copper-oxide layer was formed under ceramic layer. The microscopic assessment showed the difficulties in formation of columnar ceramic layer on use base materials. The obtained coating was characterized by dense structure as a result of lower plasma energy during process. The increasing of power current is not possible in the case of overheating of base material.

Abstract: The testing of thin colored coatings based on urethane acrylate composition is a technologically advanced, highly specialized and complex process. For decorative pigmented coatings color stability is crucial quality parameter. The photo chemically curable polymer films were prepared by addition of 3 different radical initiators (KTO, TPO, TPO-L) to aliphatic urethane acrylate composition with various pigments (solid and fluorescent). Coating color change were evaluated in UV chamber (with luminous intensity 130 mw spectrum λ_max = 405 nm) after 1 h, 48 h and 72 h. Color measurements were performed according to the CIEL*a*b* color standard to evaluate their stability over time. It was found that pigmented coatings have higher risk of yellowness than clear coatings. Also fluorescent pigments containing red has tendency to yellow after UV light exposure. The influence of the photoinitiator on the color stability were inconsiderable.

Abstract: This study aimed to compare the X3CrNiMo17-13-3 stainless steel based plasma transferred arc (PTA) cladded hardfacings, reinforced with the in-situ synthesized Cr and Ti carbides. Carbon black and either pure Cr, pure Ti, or TiO₂ were utilized as reinforcement precursors (the respective hardfacings are further referred to as Cr+C, Ti+C and TiO₂+C). The pre-placed mixtures of matrix and reinforcement precursor powders were remelted by the plasma transferred arc, applying the preliminarily optimized process parameters (95 A, 22 – 24 V, 0.2 mm/s). As a reference, the unreinforced stainless steel hardfacing was used. The carbide reinforcement was successfully in-situ synthesized in all the hardfacings. The Cr + C hardfacing exhibited the largest average hardness (556 ± 29 HV1), while the TiO₂ + C hardfacing had the largest average Young’s modulus (156.3 ± 19.7 GPa). The Cr + C and Ti + C hardfacings demonstrated the 2.3 and 2.1 times higher resistance to abrasive wear than the reference hardfacing. The TiO₂ + C hardfacing showed 1.5 times lower wear resistance than the reference hardfacing presumably due to a lack of the reinforcement and a lower strain hardening ability.

Abstract: The results of an experimental study of damage for the structural material MoNiCa (it is high-strength cast iron VCHTG – patent of the Republic of Belarus № 15617) on sliding friction and mechano-sliding fatigue are analyzed in the report. Tests of the mechanical system shaft (a sample with a working part diameter of 10 mm made of 0.45 % carbon steel) - an insert (a prismatic counter sample with a cross section of 10 ´ 10 mm made of MoNiCa) were carried out. The kinetics of the change in average wear at 8 local points along the perimeter of the dangerous area of the sample is given for contact loads F_N from 20 to 92 N of the mechanical system under study with MoNiCa inserts without heat treatment and with heat treatment. The test results of the system under study are also presented in the form of sliding friction and mechano-sliding fatigue curves in coordinates of the contact load F_N – the number of cycles N until the limit state.

Abstract: In this manuscript surface roughness, coefficient of friction (COF) and tensile properties of a post-consumer cotton fabric are evaluated. Fabric roughness, COF, effective tensile force and breaking force measured by optical profilometer, CETR tribometer and Instron tensile machine, respectively. The results proved that COF could rely on fabric pattern. Moreover, microscopically roughness influences on friction and tensile properties due to surface defects. It was found that increase in roughness of textile cotton relates to increase of number of random directional fibers. These fibers intensify friction and reduce tensile properties. The reduced values of tensile (140.49 N), breaking (123.23 N) and effective tensile force (251.43 N) of warp direction are greater than values of tensile (79.54 N), breaking (67.97 N) and effective tensile force (179.69 N) of weft direction. These effects can lower cutting performance of post-consumer textile.

Abstract: The present case-study was aimed at evaluating and comparing the frictional properties (friction and wear) of alternative concepts for a shaft-bushing component in comparison to the actually used benchmark system. Through the use of a specially designed shaft-bushing tribology labor-sized test setup in combination with a high-precision modular tribometer, the overall performance of alternative concepts were evaluated and compared. Benchmark shafts consisted of nitro-carburized and oxidized bearing steel and benchmark bushings were made of sintered steel. The investigated alternative concepts consisted of shafts with a different thermal pre-treatment against benchmark bushings; benchmark shafts against surface modified bushings; and lubricated benchmark bushings (instead of lubricated shafts) with two different lubrication times before testing. For each concept under study, 3 performance tests were performed in order to assess the reproducibility of the results obtained. The most promising alternative component concepts identified through this labor-sized model screen test were then field tested by IMS Gear and the obtained results were in accordance with the labor test results.

Abstract: Polytetrafluoroethylene (PTFE) is characterized by outstanding non-stick properties and very low friction coefficients under tribological load. However, PTFE is incompatible with almost all other polymers exhibits cold flow and a low wear resistivity. However, PTFE can be modified e.g. in the presence of air by using high-energy radiation to achieve carboxylic acid fluorid- (-COF), carboxyl- (-COOH) functional groups and persistent perfluoroalkyl (peroxy) radicals. The hydrophilic functional groups of radiation-modified PTFE can be used to generate a chemically covalent coupling with other monomers/polymers (e.g. polyamides) via addition reactions. Another approach to get a chemical bonding of modified PTFE is the use of radicals for the covalent attachment of olefinic groups (e.g. in oils) through radical reactions. It is already known that the dispersion of modified PTFE in synthetic oils at elevated temperatures results in very stable PTFE-oil dispersions, which have improved tribological properties and are compatible with metals.The aim of this study is the development of novel tribologically effective materials based on radiation-modified PTFE, oil and polyamide 66 (PA66). In the first synthesis step, a chemical coupling between selected oils and various types of PTFE was performed. The bonding was proved by fourier-transform infrared spectroscopy (FTIR) after removing oil excess and further extraction of insoluble residue. Additional electron spin resonance measurements (ESR) showed that the linkages mainly resulted from radical reactions. The second processing step was the chemical coupling of PA66 and oil-modified PTFE by reactive extrusion. In order to get an idea about the influence of the chemical bonding of both lubricants with the polymer matrix on the mechanical material properties compared to origin PA66, multipurpose test specimens according to ISO 3167 were prepared by injection molding. It was found, that even bigger amounts of bonded lubricants did not deteriorate the mechanical characteristics in a significant manner. Finally, initial tribological testing of the novel materials was carried out by using a block on ring tribometer test set up. The antifriction and wear behaviour, as well as the transfer film thickness, were analyzed subsequently.

Abstract: Composites based on birch plywood by-product: plywood sanding dust (PSD) and mixtures of virgin (vHDPE) and recycled high density polyethylenes (rHDPE) physical mechanical properties (tensile, flexural strength and modulus, impact strength and microhardness), water resistance and fluidity of the composite melts, were evaluated. These studies showed the possibility of usage of presented mixtures for preparing of qualitative WPCs containing 50 wt.% PSD. It was observed that the melt flow index values decrease with an increase of the content of rHDPE in polymer matrix. DSC measurements showed the diminishing of melting temperature and melting heat of vHDPE by adding of rHDPE. The tensile strength and modulus of composites decrease about 25 – 30 % but frexural strength and modulus have no changes. In the contrary impact strength and microhardness of the samples increased with an increase of additives of rHDPE. Water uptake kinetics of all composites were similar and the total amount of absorbed water after 850 h of the soaking was 12 – 13 %. The optimal content of recycled HDPE in the composites could be 25 – 30 wt.%. In general presented studies showed successful possibilities of the use of additives of rHDPE to vHDPE to produce cheaper WPCs which have no worse guality. Moreover the chosen type of rHDPE in the some cases can compete with investigated vHDPE matrix.