A Novel Modeling Method to Study the Oxide Layer Effect on Metallic Bonding in Cold Gas Dynamic Spray Process

In this study; a new physically-based finite element approach is proposed to model and predict the superficial oxide layer removal and the occurrence of localized metallic bonding during particle impacts. The process physics; based on explosive welding theory and experiments; and method implementation is presented. Prediction of critical velocity of copper is obtained and compared to experimental data to validate the model. Moreover; the model is also able to show the bonding locations at the interface between particles and substrate. The predicted bonding locations are consistent with experimental data from literature for several metals.

Cold Gas-Dynamic Spray for Catalyzation of Plastically Deformed Mg-Strips with Ni Powder

Magnesium hydride (MgH2) has received significant attention due to its potential applications as solid-state hydrogen storage media for useful fuel cell applications. Even though MgH2 possesses several attractive hydrogen storage properties, it cannot be utilized in fuel cell applications due to its high thermal stability and poor hydrogen uptake/release kinetics. High-energy ball milling, and mechanically-induced cold-rolling processes are the most common techniques to introduce severe plastic deformation and lattice imperfection in the Mg/MgH2. Furthermore, using one or more catalytic agents is considered a practical solution to improve both the de-/rehydrogenation process of MgH2.These treatments are usually dedicated to enhance its hydrogen storage properties and deduce its thermal stability. However, catalyzation of Mg/MgH2 powders with a desired catalytic agent using ball milling process has shown some disadvantages due to the uncontrolled distribution of the agent particles in the MgH2 powder matrix. The present study has been undertaken to employ a cold gas-dynamic spray process for catalyzing the fresh surfaces of mechanically-induced cold-rolled Mg ribbons with Ni powder particles. The starting Mg-rods were firstly heat treated and forged 200 times before cold rolling for 300 passes. The as-treated ribbons were then catalyzed by Ni particles, using cold gas-dynamic spray process. In this catalyzation approach, the Ni particles were carried by a stream of Ar gas via a high-velocity jet at a supersonic velocity. Accordingly, the pelted Ni particles penetrated the Mg-substrate ribbons, and hence created numerous micropores into the Mg, allowed the Ni particles to form a homogeneous network of catalytic active sites in Mg substrate. As the number of coating time increased to three times, the Ni concentration increased (5.28 wt.%), and this led to significant enhancement of the Mg-hydrogen storage capacity, as well as improving the de-/rehydrogenation kinetics. This is evidenced by the high value of hydrogen storage capacity (6.1 wt.% hydrogen) and the fast gas uptake kinetics (5.1 min) under moderate pressure (10 bar) and temperature (200 °C). The fabricated nanocomposite MgH2/5.28 wt.% Ni strips have shown good dehydrogenation behavior, indicated by their capability to desorb 6.1 wt.% of hydrogen gas within 11 min at 200 °C under 200 mbar of hydrogen pressure. Moreover, this system possessed long cycle-life-time, which extended to 350 h with a minimal degradation in the storage and kinetics behavior.

Fused Filament Fabrication of ONYX-Based Composites Coated with Aluminum Powders: a Preliminary Analysis on Feasibility and Characterization

Polymer-based AM methods are the most mature additive technologies for their versatility and variety of products obtainable. The addition of fibre reinforcement can also confer to the manufactures produced good mechanical properties. Unfortunately, several applications are still precluded because polymers cannot guarantee appropriate electrical conductivity, erosion resistance and operating temperature. Aiming to overcome these issues, the metallization of the surfaces emerges as a possible solution. Unfortunately, thermoplastic polymers exhibit thermosensitive behaviour and run the risk of being damaged when traditional metallization techniques, which require the melting of metal powders which will act as a protective coating. For this reason, studies have focused on Cold Gas Dynamic Spray, an additive manufacturing technology, which exploits kinetic energy to favour the adhesion of metal particles rather than the increase in temperature. In this work, a first attempt is made to verify the feasibility of cold spray coatings on 3D printed composite substrates, produced by means of Fused Filament Fabrication (FFF) technique. FFF technology allows the deposition of two different types of filaments by using a double extruder. These composite fibres within 3D printed parts manage to give the object a resistance comparable to that of a metal part with lower production cost and a high degree of automation. These structures, made of ONYX, a Nylon matrix in which short carbon fibres are dispersed, and reinforced with long carbon fibres, are designed to better fit the CS deposition. Aluminium coatings have been produced and a characterization campaign has been carried on.

A numerical analysis of compressive residual stresses in cold gas dynamic spray (CGDS) deposition method

This study presents a finite element approach of a numerical model to investigate the profile of the deformed sprayed particles and the compressive residual stresses analysis at the interfacial zone of particle and substrate impact using cold gas dynamic spray (CGDS). The Lagrangian approach was used to analyze, in details, the material deformation behavior during impact, contact problems of single-particle impact process and the outputs of equivalent plastic strain and temperature to achieve a qualitative understanding of cold gas dynamic spray contact process of cold sprayed particle on the substrate. The evolution of residual compressive stresses during impact was also analyzed for multiple-particles impact process using the Lagrangian approach. It can be observed that the compressive residual stresses increase by increasing the preheating temperature and particle initial impact velocity.