Papers by Keyword: Surface

Abstract: Final turning, which is a finishing process for obtaining components with specific precise parameters, affects the integrity of the surface and its properties, whether hardness or surface residual stresses. The synergistic effect of these factors affects the susceptibility of the material, to stress corrosion cracking. In this work, 2 types of austenitic stainless steel, namely AISI 304 and AISI 321, were turned. Tool with positive cutting geometry was used for turning. The cutting parameters that varied were the cutting speed (100 and 250 m.min⁻¹) and the tool feed (0.12, 0.2 and 0.3 mm·rev⁻¹). The depth of cut was the same for all turnings (0.8 mm). Subsequently, the prepared samples were exposed in MgCl₂ solution based on the ASTM G36 for 96 hours. After this time, the samples were analysed using SEM, where the density of surface cracks was monitored. When comparing the crack density, an increase in density was visible for AISI 304 compared to AISI 321. It was shown that with increasing cutting speed, the density of cracks increased significantly, as well as with increasing tool feed. On the cross-sections the depth and length of the cracks were analysed. Crack depth and length increased with increasing feed too.

Abstract: The article presents potentiometric (pH-metric) methods that are used to study the acid-base properties of the surface of dispersed materials of different chemical nature. It is shown that the surface of any solid body has a surface hydroxyl-hydrate layer with a set of active adsorption centers (ACA) of different chemical structure and a wide range of acid-base properties. It has been proven that potentiometric (pH-metric) methods of studying dispersed materials in suspensions allow obtaining the most complete information about surface acid-base properties.

Abstract: The process of electrolyte plasma nitriding is presented consisting in surface saturation of steels in low-temperature hydrostatic glow-discharged plasma generated in nitrogen containing liquid electrolyte. The method can be applied for strengthening of small machine parts made of carbon steels or of low-alloyed steels for increase wear and corrosion resistant of components working in corrosive and wear conditions (moisture, humidity, sand, etc.). Processes of steels surface strengthening by nitriding in low-temperature electrolyte plasma are combined with their surface alloying by a metal element (chromium, aluminum, vanadium, titanium, tungsten, molybdenum, and niobium) and also by combination of metals. Microstructure and phase composition of diffusion layers are examined; results of wear and corrosion tests are discussed.

Abstract: The paper presents the results of research on creating a high-strength cement composite using a complex additive. The optimal concentrations of additives of the Odolit-K hyper plasticizer in combination with bentonite have been determined. A significant decrease in the w / c ratio and an increase in the cement stone's strength was obtained. High-strength cement composites have been obtained with the optimal content of the complex additive. The volume-weighted average crystallite sizes were calculated using the Scherrer formula on the basis of X-ray studies. Deformation diagrams of statically loaded samples of prisms of the basic and control compositions of high-strength concrete were obtained. Deformation diagrams are investigated.

Abstract: In the last decade, a continuous increasing research activity is focused on the surface modification of natural porous materials for the efficient removal of oil contaminants from water. A continuous in-situ oil/water separation technique for oil spill cleanup had been designed using surface modified Irind mine pumice as a sorbent. Irind mine pumice is an aluminosilicate rock, with well-developed porosity, mechanical strength, high buoyancy, chemically inert and eco-friendly, therefore it must exhibit certain water-and oil absorption capacities. The modified pumice absorbs a broad variety of oils and organic solvents with high oil absorption capacity and negligible water take-up at both static and dynamic conditions. Irind mine pumice have been used with grain sizes ranging from 2.5 ... 5.0 mm. Oligomethylhydride siloxane is used as a modifier.

Abstract: This paper presents the laser surface polishing of titanium alloy (Ti6Al4V) by using a nanosecond pulse laser. Air, nitrogen and argon were employed as a shielding gas in this study, where the areal roughness (Sa) of laser-polished surface was measured and compared. The results showed that argon was the suitable assist gas for improving the metal surface without causing the oxidation. The effect of laser pulse repetition rate and scan speed on the surface roughness was also investigated in this study. The use of high repetition rate together with slow scan speed was able to reduce the surface roughness of titanium alloy. The roughness was found to be reduced by 47% when the pulse repetition rate of 500 kHz and scan speed of 50 mm/s were applied.

Abstract: The paper presents the results of experimental studies on the determination of corrosion products on the surface of reinforced concrete structures. This paper also discusses methods for creating samples with artificial electro corrosion under conditions close to real operation. The paper presents the results of testing samples using laser-inducted breakdown spectrometry (LIBS) devices.

Abstract: Industrial X-ray computed tomography (XCT) is a tool for non-destructive testing and a volumetric analysis method with the ability to measure dimensions and geometry inside a component without destroying it. However, XCT is a relatively young technology in the field of dimensional metrology and thus faces several challenges. The achievement of a high measurement resolution, which is re-quired to detect small geometrical features, depends on a variety of influencing factors. In this arti-cle, the interface structural resolution (ISR) as one of the key challenges will be investigated. The two-sphere standard called the hourglass standard allows the determination of the structural resolu-tion by evaluation of the surrounding area of an ideal point contact of two spheres after the CT re-construction in form of a neck-shaped transition. Close to the contact point of the two spheres two opposing surfaces exist. Their distances from each other increase as the distance from the contact point of the two spheres increase. The determination of the distances between the spheres’ surface allows a statement about the ISR. A new developed specimen or standard with a variable gap size consisting of calibrated parallel gauge blocks allows statements about the ISR, too. Because of the higher number of probing points of the gauge block standard the results of the determined ISR are more stable compared to the hourglass standard. This paper compares the results of the computed tomography measurements for the designed interface structural resolution standard with those of the hourglass standard.

Abstract: Dense oxide coated AZ 31 magnesium alloy surfaces were uniformly formed using a radio frequency magnetron sputtering method. The magnesium oxide thin film thickness was about 240 nm. XRD results of the film indicated that film of magnesium oxide single phase was deposited. The surface of the film was uniform and no crack was observed. The Vickers hardness measured by the nanoindenter was about Hv80 and Hv200 for the AZ31 substrate and the sample coated with the thin film, respectively. The dynamic hardness of the AZ31 substrate and the sample coated with the thin film were almost the same. In the curve at the time of pressurization, a step was observed in the sample coated with the thin film. On the other hand, many steps were observed in the data curve for the thin film deposited on the glass substrate.

Abstract: The possibility to reduce costs of the additive manufacturing (AM) technologies by using recycled powders is still an open question. The present paper aims to investigate the effect of using virgin and recycled powders on the corrosion resistance of Ti6Al4V titanium alloy additive manufactured parts. Although the study of the electrochemical behaviour of titanium parts produced by using AM is present in the literature, the corrosion resistance of samples manufactured using recycled powders is less investigated. This work would like to contribute to the deepening of this aspect. The experimental investigations have been carried out on as-built samples as well as on samples after mechanical polishing. The metallographic observations of additive manufactured samples showed a martensitic microstructure inside the prior β grain grew up as columnar structure. X-ray diffraction analysis revealed the presence of titanium oxide in rutile crystallographic phase. The electrochemical characterisation unveiled the lower corrosion resistance of the as-built additive manufactured components compared to the traditional counterpart. It also highlighted the effect due to the use of recycled powders when the bulk of the samples has been investigated.