Key Engineering Materials Vol. 813

Abstract: WAAM (Wire-Arc-Additive-Manufacturing) is an additive manufacturing process which uses arc welding to produce metal parts. This process is prone to heat accumulation, i.e. a progressive increase of the interlayer temperature and molten pool size, having detrimental consequences on the material properties and on the workpiece integrity. This paper investigates the effect of air jet impingement, an active cooling technique, to prevent heat accumulation, on the surfaces of WAAM workpieces. A reference test case was manufactured using traditional free convection cooling and air jet impingement. The workpiece temperature was measured using Ktype thermocouples. The manufactured surfaces were measured using a coordinate measuring machine and compared in terms of deposition efficiency, deposit height and average arithmetical deviation. The temperature results highlight that air jet impingement is effective in preventing the occurrence of heat accumulation. The surface data highlight that air jet impingement increase the deposited height and the surface waviness with a consequent decrease of the deposition efficiency.

Abstract: The leveling power of gluconate and citrate electrolytes used to obtain the Co-W and Fe-W alloys was studied. The leveling power parameter P was calculated according to the results of profilographic measurements of microprofile carried out before and after deposition of the coating on surface. It was shown that deposition of said alloys occurs with preferential coating thickness increase on microprofile peaks and low microlevelling power.

Abstract: Electron multipacting and electron cloud have been identified as being the major limiting factors for the beam quality or for the cryogenic system of high-intensity positive particles accelerators. Among conditioning operational techniques and other surface structuration techniques used to decrease the Secondary Electron Yield (SEY) of surfaces, laser surface treatment is a promising method to treat in situ and at atmospheric pressure copper surface of the vacuum chamber. Here, pulsed laser irradiation of copper in parallel lines pattern led to the local ablation and deposition of aggregates of copper particulates on the surface. Tests undertaken at CERN have shown that the modification of the surface morphology by creating roughness at different scales induces a decrease of the SEY by geometrical effects. Nevertheless, the mechanical strength and dust generation of the treated surface have not been addressed yet.In this work, a qualitative analysis of the multi-scale description of the surface morphology was carried out. Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to investigate morphological characterization such as size and shape of the particulates, chemical composition, metallographic structures and phase transformation on the laser-processed surface.SEM and FIB examinations showed that the surface morphology depends on the local laser energy irradiating the surface and especially, relatively to the ablation threshold. TEM analysis revealed chemical composition and crystalline configuration of the treated material and helped to identify the laser modified and oxidized areas. A variety of superficial structures were observed. Potential vulnerable structures have been identified as oxidized matter redeposited on the ablated near surface. Material continuity and composition play a major role in the mechanical integrity of the generated surface morphology. The adherence of the created structures was assessed analyzing the origin of the dust extracted after mechanical stress.

Abstract: The understanding of tire’s adherence with a rough surface is a common goal for several fields in the automotive sector. In fact, grip is synonym of safety and performance, playing a decisive role for braking distance and vehicle stability, fuel consumption, wear rate [1], noise generation and for the vehicle dynamics control system (e.g. ABS, TCS, AYC and other) [2]. This paper deals with tire tread grip experimental investigation and evaluation under different conditions that influence it during the sliding contact [3]. In this regard the test campaign involves the use of different tire compounds (in terms of viscoelastic characteristics), tested in several conditions: different contact pressure, sliding speed, temperature, sliding contact length and road surface. The test bench employed by the UniNa Vehicle Dynamic Research Group is an upgrade of the British Pendulum, an instrument for outdoor tribological tests on road sections. The principal sensors installed on the test bench are an encoder, for the evaluation of the sliding speed of the tire specimen, and a load cell, for the measurement of the force arising at tire/road interface in the longitudinal and vertical directions [4]. In fact, the grip shall be determined as the ratio of the longitudinal force and corresponding load on the tire. The paper's aim is the description of the experimental campaign after an accurate introduction on the test setup and an illustration of the equipment. Finally, the preliminary results and the methodologies used to process the acquired data are described.

Abstract: In this activity, customized panels for the CS deposition have been produced and aluminium has been deposited using air as a carrier gas. The custom-made panels were made with different matrix thicknesses on the surface in order to point out the influence of the fibres in the deposition and to study the feasibility and the growth of the coating. The polymer chosen for the matrix is polypropylene, widely used in the automotive sector, while for the reinforcements glass fibres have been used. Different process parameters have been examined in order to point out the influence of temperature, stand-off distance and pressure chosen, on the compaction and densification of the coating produced. In addition, morphological investigations were performed to further characterize the coatings deposited. It has been noticed that aluminium powders can be effectively deposited on polypropylene panels, leading to significantly better results when the thickness of the matrix is ​​sufficient to prevent the powders bouncing elastically on the fibres, while benefiting from the stiffening effect of the latter.

Abstract: In this paper, we present the results of plasma nitriding treatments on austenitic stainless steel substrates previously coated with a patterned silicon oxide layer. For this purpose, masks were made by PECVD for the deposition of a silicon oxide layer on polished austenitic AISI 316L samples. For the final nitriding treatment, we used a multi-dipolar plasma providing independent substrate polarization. The interactions between expanded austenite and fixed silicon oxide mask in different shapes (circular and square dots) are observed by atomic force microscopy (AFM) on the same area before and after the nitriding treatment. After this thermochemical treatment, we obtain strong distortions of the dots, in particular at the edges of the larger size dots. The role of elastic deformation, due to the expanded austenitic phase formed by the diffusion of nitrogen under the mask is of primary importance.

Abstract: Graphene-based nanoparticles are suitable to enhance toughness related to impact, fracture and fatigue of epoxy nanocomposites to make them able to meet industrial requirements. The increase in the mechanical performance of graphene-based films is well known in the literature. This paper highlights an additional beneficial effect of graphene-based nanoparticles, which is related to the increase of the photooxidative resistance of polymeric films. Graphene Nanoplatelets (GNPs) have been incorporated, at different weight percentages, in the epoxy films. Unfilled and nanofilled films (30 ± 1.5 μm thick) have been subjected to the accelerated photo-oxidative degradation by exposing them to UV-A radiation (295–380 nm). AFM-Harmonix modulus maps at the micro and nanoscale level have been detected to investigate the effect of graphene nanoparticle on the mechanical properties of untreated and UV treated unfilled and nanofilled samples. SEM analysis has been used to analyse the effect of graphene on morphological features of the film surface. UV irradiation determines relevant damages of the mechanical properties and morphological feature of the unfilled sample. The experiments carried out on the nanofilled films show that GNPs, dispersed in the epoxy-based films, determine a strong decrease in the entity of the damages of the film surfaces.

Abstract: Aluminium alloys are covered spontaneously by a natural oxide layer, well adherent to the surface. For improving the material’s anticorrosion performance surface pre-treatments are needed in order to remove the superficial oxide and to prepare the alloy surface to subsequent treatments. The pre-treatment process involves several steps, including desmutting. The last requires the immersion of the part in an appropriate solution, typically composed of several chemicals, able to remove the oxide layer. In this work, the effect of the fluorides addition into a sulfuric acid-based solution, when used in a desmutting industrial process, was evaluated. Potentiodynamic curves, glow discharge optical emission spectrometry and contact angle techniques were used to characterize the surface of the aluminium alloy AA8006 after desmutting.

Abstract: Waste cooking oils (WCOs) are widely considered in the scientific community as potential energy vector or source for bio-lubricants. This is because of the opportunity deriving from recycling and the difficulties in disposing of waste oils. Indeed, industrial plants for WCOs treatment include bio-refineries (bio-diesel, bio-lubricants, fine chemicals...) or simple recovery systems: the former ones assume triglycerides transformation into other compounds, according to the specific commercial destination; in the latter, triglycerides are preserved and the WCO is purified from by-products, formed during cooking process, in order to sell to the market. In an era scarred by CO₂ and petroleum dependency, biodegradable products, offer many advantages. In this scenario, nanostructured additives, which are pointed out as the step forward in lubricant technology, can exploit WCOs’ derivatives for compatibilization or as reactive components allowing improvements in nanolubricant fluids. This paper proposes a Cu nanoparticle-based additive, properly surface functionalized and prepared through a “wet chemistry” approach, to be involved in tribochemical reaction with epoxidized vegetable oil. The idea was to promote the formation of tribofilm under contact, exploiting energy generated during the movement.

Abstract: Aluminum alloys are one of the main materials employed in aerospace and automotive applications. One of the problems that affect these alloys in certain application is the poor corrosion resistance that can, however, be enhanced with proper surface treatments, such as anodizing. Among these treatments, Plasma Electrolytic Oxidation (PEO) is one of the most promising and the production of PEO coatings on traditional aluminum alloy was extensively studied in literature. Recently, the production of a lot of components is going into the direction of using innovative manufacturing systems and customized components, with improved mechanical and physical properties, can be manufactured by additive manufacturing (AM) techniques. Among the AM methods, laser-based AM has an immense potential for producing fully dense metallic structures, using a variety of available metal powders and has attracted more and more attention. The resulting AM samples are characterized by different microstructures in comparison with the conventionally manufactured ones and this can cause differences also in the production of PEO coatings and other surface treatments. Objective of the present work is to produce PEO coatings on AM samples in order to increase the corrosion and wear performances of the samples. PEO coating were produced on the samples testing different parameters and the coatings were characterized, in terms of microstructure and composition, with SEM analysis. The corrosion resistance of the samples was also evaluated with electrochemical tests. The results were compared with the ones obtained on traditionally manufactured samples. PEO coatings were successfully produced on AM samples obtaining samples with good coatings thickness and improved corrosion performances compared to the untreated ones.