Key Engineering Materials Vol. 813

Abstract: Machining process usually involves relevant wear effects on the cutting tool, producing undesirable surface features on the work-pieces. Lubricants and cooling fluids are used with the aim to minimize the wear phenomena as well as high temperatures produced during the cutting processes. However, the use of these fluids may have an adverse environmental impact. For this reason, the reduction of quantity of cutting fluids used in the machining process is a requirement in order to improve the performance and sustainability of the process. For this purpose, this work proposes an increase of the lubricant retention ability for cutting tools based on surface modification. In this research, micro-geometrical features of Carbide (WC-Co) surfaces have been modified by laser texturing techniques. A wide range of roughness topographies had been developed by changing the laser irradiation parameters of energy density of pulse (E_d) and scanning speed of the beam (V_s). Different geometries of the textured tracks (single spots, linear tracks, circular tracks) also were studied. Moreover, through specific roughness features conducted by texturing process, the retention ability of cutting fluids was modified. It was evaluated by the contact angle between liquid and solid phases. This modification allowed to increase the self-lubricant effect of the WC-Co surface. This methodology has been validated on carbide tools under lubricated machining processes. Wear effects on the cutting tool were reduced and the surface finish of the machined parts was remained at least in the same ranges as non-modified tools.

Abstract: When designing the individual subassemblies of machines or entire devices one has to draw special attention to the resistance of the elements working there, to tribological damages (mechanical, fatigue, adhesion, abrasion, hydrogen and other damages) as well as to non-tribological damages (corrosion, diffusion, cavitation, erosion, ablation and others). The main purpose of this publication was to examine the influence of the applied CrN+WC/C and WC/C protective coating deposited by PVD (Physical Vapour Deposition) method on the cavitation wear processes of construction elements working in difficult cavitation environment. Two steels were selected for detailed examinations in the conditions of cavitation wear. The first one is P265GH steel commonly used for pressure devices working at elevated temperatures, with a ferritic – pearlitic structure, and the other derives from a group of stainless steels, i.e. chromium – nickel X2CrNi18-9 (304L) steel with an austenitic structure. The tests results obtained allow to conclude that the application of special low – friction protective coatings allows to reduce costs associated with selection of engineering materials for a substrate of constructional elements working in a cavitation wear environment. P265GH steel is 4.5 times cheaper than austenitic chromium – nickel X2CrNi18-9 (304L) steel, and if a CrN+WC/C and WC/C coating is deposited in this case, this considerably extends the working time of such elements in a cavitation environment.

Abstract: In this research activity, the manufacturing of metallic coatings on polymer-based panels through the low pressure cold spray technique was studied. Aluminium particles were sprayed for the metallization and carbon fibre composite materials with thermoplastic matrix (PP, PA66) were used as substrates. Different deposition parameter combinations have been set to investigate the feasibility of the process; SEM analyses were carried out to study the coating surface morphology and the interface interaction between particle and substrate. The results showed that the CS process is an effective technique to create aluminium coatings on polymeric matrix composite materials: compact coatings can be obtained if the process parameters are properly set.

Abstract: Metallic infrastructures suffer deterioration during their service life. When the metallic component reaches a limit level of damage, it is replaced by a new one. This generates high costs of maintenance and residues management. However, the deposition of coatings by the cold spray technique would allow the repairing of these damaged components and extent their service life. In this work the effect of the spraying temperature and pressure on the mechanical behavior of 316L stainless steel coatings deposited on carbon steel by the cold-spray technique has been analyzed. Spraying gas temperatures of 800oC, 900oC and 1000oC combined with gas pressures of 50 and 60 bars were selected. Indentation stress-strain curves were determined for each spraying conditions. The results showed a significant effect of both spraying parameters on the work hardening of the coatings.

Abstract: In order to improve wear properties of thermosetting resins, potential solutions are the reduction of the adhesion between the counterparts and the improvement of their hardness, stiffness and compressive strength. These goals can be achieved with success by using appropriate inorganic fillers. Concerning this, the present work shows the possibility to increase the abrasive wear resistance of an epoxy resin filled with hard powder. The filling is made by silicon carbide powders in different content and with different particle sizes. Abrasive tests, performed by means of a pin on disc apparatus, highlight that the wear of plain and reinforced resins increases both with the contact pressure between the counterparts and the counterface roughness. Moreover, the wear resistance of the filled resins increases with the increase of content and dimensions of the filling particles.

Abstract: The investigation of the corrosion resistance of Ti6Al4V alloy components produced by additive technology is still lacking in the literature. This paper aims to study the electrochemical behaviour of Ti6Al4V components fabricated by laser powder-bed fusion additive manufacturing process. The metallographic analysis was carried out by an optical microscope. The electrochemical behaviour has been evaluated in 3.5 wt. % of natural aerated NaCl aqueous solution by potentiodynamic polarization test. The results have been compared to a conventionally manufactured Ti6Al4V component. The typical martensitic structure has been shown by the additive manufactured sample. As expected, the metallographic analysis revealed a martensitic microstructure. The electrochemical tests carried out on the surface of the as-received additive manufactured specimen showed an influence of its morphology on the values of passive current density, higher than that recorded for the conventionally manufactured sample, used as the control. After mechanical polishing, the electrochemical tests were repeated on the "bulk" of the samples. The open circuit potential values were higher than the value recorded for the conventionally manufactured sample. The conditions of the additive process affect the corrosion resistance of the components due to the roughness of the surface and to the microstructure created.

Abstract: Ti6Al4V coatings were cold sprayed onto the same bulk alloy at standard conditions, using 800 °C as gas temperature, and a set of new conditions, using 1100°C as gas temperature, which improved coatings performance. Some of these coatings, processed with innovative parameters, were heat treated to promote adhesion and reduce porosity. Scratch tests were performed using a nanoindenter Agilent G200 and the effect of both normal load and scratch velocity were explored. The different mechanisms responsible of wear were evaluated, identifying ploughing and cutting as the main abrasion mechanisms. The wear rate measured in the standard coating was the highest, indicating that this material could not be used to repair the bulk component. However, the abrasion resistance measured in the coatings sprayed at 1100°C was similar to that found in the bulk substrate. Therefore, cold spray could be used for repairing using the new conditions evaluated in this work.

Abstract: Silver-gold alloy catalyst for ketones hydrogenation in liquid-phase using NaBH4 as hydrogen source is reported. AgAu alloy nanoparticles are synthesized from common inorganic precursors and mild experimental conditions. To favour the dispersion of the sample in the mixed-aqueous reaction solution a ligand exchange with citric acid was promoted. This citric acid modified AgAu catalyst, thanks to the synergistic effect of Au and Ag, allows for the selective hydrogenation of ketones with to maximum isopropanol yields of 99.7 % within 8 min and shows an excellent reusability after 7 run.

Abstract: Additive Manufacturing by means of laser irradiation of powder bed is receiving increasing interest in many industrial fields thanks to a number of benefits including the opportunity of producing complex, accurate components with optimized physical and mechanical features. Depending on the application, specific surface properties in terms of texture and roughness are required. Therefore, this paper is aimed to investigating the effects of the building parameters and the exposure strategies on the resulting surface aspect and roughness. Indeed, different patterns are expected on the exposed surface as a consequence of the values of laser operating power, scanning speed and hatch spacing. The results in terms of roughness and surface geometry are discussed with reference to current standards. Suggestions are provided to guide the reader in selecting the proper processing conditions based on the expected surface features.

Abstract: In this work an influence of cold spray nozzle displacement parameters on the properties of copper-silicon carbide cold spray deposits is considered. In particular the influence of nozzle traverse speed and distance between deposited tracks on the coating porosity and behavior during compressive tests was analyzed. It was shown that cold spraying at low nozzle traverse speed leads to formation of thick tracks with quasi-triangular cross-section. As a consequence, the particle impact angle on the sides of spraying track increases that. Thus, the particle deformation at impact on the track periphery becomes insufficient and local porosity value rises. Increase of nozzle traverse speed allows increasing coating density and mechanical properties due to amelioration of particle deformation conditions. Compressive tests revealed significant anisotropy of mechanical properties of copper-silicon carbide cold spray deposits. In particular, compressive strength measured in vertical direction (perpendicular to the substrate) was significantly higher than one measured in horizontal plane (parallel to substrate). This anisotropy could be explained by the orientation of particle deformation pattern during impact.