Papers by Keyword: Metal Deposition

Abstract: Cold spray additive manufacturing (CSAM) is a promising process for producing metallic layers on different substrates, using powders as a feedstock material. The metallic powders are deposited through pressured gas that reaches supersonic velocities. Due to the low heat input required, as the powders remain in solid-state, this technology is particularly suitable to coat thermo-sensitive materials such as composites. Moreover, the absence of melting allows design freedom, allowing to build complex structures on the substrates, layer by layer. In this scenario, machine learning techniques can be crucial to improve the quality and understanding of this manufacturing process. The aim of this work is to predict the deformation and penetration of a particle upon impact using machine learning techniques in order to assess the properties of the coating. A univariate linear regression method was chosen to verify the feasibility of Theory Guided Machine Learning (TGML) techniques to predict the characteristics of the coating. The training dataset was obtained from both experimental data and computational data. It was confirmed that TGML could be a good route to pursue in order to optimize this process.

Abstract: Cold spray (CS) is a low-temperature process that can be used for the metallization of temperature-sensitive materials, such as polymers or polymer matrix composites, so coupling the lightweight of polymers with the wear resistance, physical properties and hardness of metals. The study of the cold spray of metal particles applied to polymers is still in its early stage and the deposition mechanisms underlying the process are not thoroughly understood yet. Moreover, numerical studies of cold spray of metal-to-polymer are almost completely absent in literature. Therefore, aiming to fulfill this gap of knowledge, the scope of this work is to develop a numerical FE model capable of predicting the impact and the adhesion of a micron size metallic particle onto a polymeric substrate. The results from the model were compared with the experimental outcomes found in literature to establish the effectiveness of the model that was used as a powerful tool to better understand the bonding mechanisms and all the related phenomena ruling the CS process of metal-to-polymer.

Abstract: The article presents the simulation of part distortion during laser metal deposition and a comparison of its results with the deposition performed in experiment. A numerical methodological approach to simulation is viewed which involves dividing the deposited material into primitive solids and further heating and cooling of each primitive solid along the deposition trajectory instead of simulating a moving heat source.

Abstract: Nickel aluminum bronze (NAB) castings possess favourable combinations of strength and resistance to corrosion, biofouling and cavitation/erosion, and so have long been used in naval applications. Nonetheless, in seawater environments NAB castings are susceptible to selective phase corrosion and so such components periodically require either replacement, which is very costly, or repair. However, repairs involving traditional, high heat input welding operations can lead to distortion and microstructural changes that unacceptably degrade NAB corrosion performance, and so repairs are not commonly performed. In the present work, cold spray is explored as an alternative for NAB (alloy CuAl9Fe5Ni5) repair without excessive distortion or base metal degradation, and preliminary results of its performance reported. Suitable cold spray parameters have been determined using an iterative approach by analyzing deposits in terms of microstructure, porosity and adhesion to the substrate. It is intended that these parameters will later be used to create simulated repairs which can be more thoroughly characterized for strength, toughness and corrosion performance.

Abstract: High pressure cold spray has been showing increasing promise and application for structural repairs and coating applications where wrought like strengths are required. For example, numerous applications have been developed for repairing high cost and long lead time parts for the aerospace and defense market, such as aircraft skin panels, titanium hydraulic lines, aluminum valve actuator internal bores, hardened and chromed steel shafts, gas turbine engine parts, magnesium castings, and many more. These processes also have direct application in commercial markets like transportation and heavy industry. In particular, parts with lead times in excess of 12 months have been successfully repaired and re-introduced into service. This saves not only the direct cost of the part, but also returns the system to service much sooner. Additional benefits of field application with a hand-held nozzle assembly are also possible, particularly for power plants, refineries, and other large industrial plant operations. Cold spray consequently has a tremendous opportunity to enhance manufacturing sustainability by repairing parts that previously could only be replaced and recycled. It is environmentally friendly, as there are no toxic fumes or other harmful emissions from cold spray. Furthermore, because parts are being repaired and refurbished rather than replaced, there is tremendous cost, energy, and overall environmental benefit, making cold spray a “green” technology and an excellent technology for enhancing the long-term sustainability of high value assets.

Abstract: A 1000 hour hydrotreating experiment was performed to investigate the hydrotreating behavior of heteroatom compounds (first stage) and HDM catalyst deactivation (second stage) using Venezuela De-Asphalted Oil. The effect of reaction severity on impurities removal was the expected one, the deeper the hydrotreating degree, the higher the conversion of impurities. The Characterization of spent HDM catalyst shows that the content of coke deposition on spent HDM catalyst is only 4 wt% while that of metal is more than 30 wt%. Vanadium compounds in DAO with less diffusion resistance can deposit inside of the HDM catalyst grain. Lower coke formation also retard the HDM catalyst by keeping the diffusion pores and active cites. The removal of asphaltenes largely improved the stability of the HDM catalyst.

Abstract: The anatase nano-TiO2 was modified by metal ion-doping to improve its photocatalystic activity. Then the modified nano-TiO2 was used in coating as a formaldehyde degradation material and antibacterial materials. The test results showed that modified nano-TiO2 photocatalytic properties was significantly improved whose formaldehyde degradation rate reached 85% and bacteriostatic rate was more than 99%. Then the photocatalytic theory and the antibacterial theory of modified nano - TiO2 were analyzed.

Abstract: High-strength steels are used in several critical aerospace applications such as aircraft landing gear, primary structure and engine components. These steels, such as the AISI 4340 assessed here exhibit small critical crack sizes, and when they suffer in-service damage from impact or corrosion, repairing the damage is particularly challenging. One potential repair method is using laser assisted metal deposition (LAMD or ‘laser cladding’ LC), to rebuild the damaged region or the grinding depression remaining after the damage has been removed. The critical situations where these materials are used makes it essential that repairs do not introduce any degradation, such as microcracking, that could lead to failure in service. In this trial, 420 grade stainless steel cladding powder was used to produce a clad layer with both high strength and good corrosion resistance. The cladding was performed under various powder mass flow rates, traverse speeds, and laser powers. The clad thickness and the depth of the fusion zone varied, as expected, with all the cladding conditions. It was found that there was very little porosity, and importantly, no evidence of microcracking under any cladding condition. There were some small defects near the clad boundary, apparently associated with each clad pass. The absence of microcracking is a promising result, and the research will be continued to assess the effect of microstructure and defects on performance of the repaired plates.

Abstract: A novel technique has recently been presented for depositing metal layers onto a SAM. This is demonstrated here for Pd and Pt deposits on a mercaptopyridine (4-PyS) SAM. The SAMcovered Au(111) electrode is immersed into the metal-ion-containing solution without potential control. As a result, metal ions, e.g., Pd(II) (respectively Pt(II)) adsorb on the surface by forming a complex with the pyridine species. Subsequently, the electrode is transferred to a metal-ion-free solution, where the adsorbed metal ions are reduced electrochemically to its zero-valent state. Upon reduction, monoatomic high metal islands were observed in STM. Angle resolved XPS measurements show unequivocally that the reduced metal resides on top of the SAM.