1,818 research outputs found
Direct current plasma spraying of mechanofused alumina-steel particles
Stainless steel particles (60 m in mean diameter) cladded with an
alumina shell (2 m thick and manufactured by mechanofusion) were sprayed
with an Ar-H2 (53-7 slm) d.c. plasma jet (I = 500 A, P = 28 kW, \rho_th = 56
%). Two main types of particles were collected in flight, as close as 50 mm
downstream of the nozzle exit: particles with a steel core with pieces of
alumina unevenly distributed at their surface and those consisting of a
spherical stainless steel particle with an alumina cap. The plasma flow was
modeled by a 2D steady parabolic model and a single particle trajectory by
using the 3D Boussinesq-Oseen-Basset equation. The heat transfer, within the
two-layer, stainless steel cladded by alumina, particle, considered the heat
propagation phenomena including phase changes. The models allowed determining
the positions, along the particle trajectory, where the convective movement
could occur as well as the entrainment of the liquid oxide to the leading edge
of the in-flight particles. The heat transfer calculations showed the
importance of the thermal contact resistance TCR between alumina and steel
NUMERICAL FORECAST OF THE MELTING AND THERMAL HISTORIES OF PARTICLES INJECTED IN A PLASMA JET
18 pagesThis work presents the numerical simulation of the melting process of a particle injected in a plasma jet. The plasma process is nowadays applied to produce thin coatings on metal mechanical components with the aim of improving the surface resistance to different phenomena such as corrosion, temperature or wear. In this work we studied the heat transfer including phase-change of a bi-layer particle composed of a metallic iron core coated with ceramic alumina, inside a plasma jet. The model accounted for the environmental conditions along the particle path. The numerical simulation of this problem was performed via a temperature-based phase-change finite element formulation. The results obtained with this methodology satisfactorily described the melting process of the particle. Particularly, the results of the present work illustrate the phase change evolution in a bi-layer particle during its motion in the plasma jet. Moreover, the numerical trends agreed with those previously reported in the literature and computed with a finite volume enthalpy based formulation
Study of the mechanical and metallurgical properties of AMDRY 9954 HVOF coated Ti-6A1-4V alloy
Ti-6A1-4V alloy is commonly used in gas turbines due to its excellent tensile and fatigue strength, corrosion resistance, and high toughness to mass ratio. In the present study, the metallurgical and mechanical properties of High Velocity Oxygen Fuel (HVOF) thermally sprayed AMDRY 9954 (Cobai.Ni32Cr21Al8Yo.5) superalloy powder on Ti-6A1-4V alloy are examined. The mechanical tests include three point bending, tensile, fatigue, indentation, and microhardness tests. The mechanical tests are applied on Ti-6A1-4V specimens (a) asreceived, (b) as-received heat treated, (c) coated then heat treated and (d) coated without heat treatment. Three-point bending tests are carried out to investigate the coating-base material interface properties and the influence of heat treatment on the interface properties. Tensile tests are performed to evaluate the adhesion of the thermally sprayed coating to Ti- 6A1-4V alloy. The fatigue tests are conducted to study the fatigue resistance behavior of the coated substrate martial under fluctuating load. Finite element method (FEM) is introduced to simulate the bending and tensile testing situations and predict the stress distribution in the workpieces. In addition, the microhardness and the indentation tests are carried out to measure the hardness and estimate the plane fracture toughness of the coating, respectively. The metallurgical characterization and surface morphology prior and after mechanical testing are investigated using SEM, optical microscopy, EDS, and XRD. It is found that heat treatment modifies the elastic modulus of the coating; in addition, tensile and fatigue performance of the specimens subjected to the heat treatment is low
Numerical investigations of thermal spray coating processes: combustion, supersonic flow, droplet injection, and substrate impingement phenomena
The aim of this thesis is to apply CFD methods to investigate the system characteristics of high speed thermal spray coating processes in order facilitate technological development. Supersonic flow phenomena, combustion, discrete droplet and particle migration with heating, phase change and disintegration, and particle impingement phenomena at the substrate are studied. Each published set of results provide an individual understanding of the underlying physics which control different aspects of thermal spray systems.A wide range of parametric studies have been carried out for HVOF, warm spray, and cold spay systems in order to build a better understanding of process design requirements. These parameters include: nozzle cross-section shape, particle size, processing gas type, nozzle throat diameter, and combustion chamber size. Detailed descriptions of the gas phase characteristics through liquid fuelled HVOF, warm spray, and cold spray systems are built and the interrelations between the gas and powder particle phases are discussed. A further study looks in detail at the disintegration of discrete phase water droplets, providing a new insight to the mechanisms which control droplet disintegration, and serves as a fundamental reference for future developments of liquid feedstock devices.In parallel with these gas-particle-droplet simulations, the impingement of molten and semi-molten powder droplets at the substrate is investigated and the models applied simulate the impingement, spreading and solidification. The results obtained shed light on the break-up phenomena on impact and describe in detail how the solidification process varies with an increasing impact velocity. The results obtained also visually describe the freezing induced break-up phenomenon at the splat periphery
Particle Injection Simulation on Cold Spray Technology
Computational Fluid Dynamics (CFD) is a useful tool when it comes to research in the fields of Aerodynamics, Turbomachinery, and is used in several other fields of research. CFD is an important tool in the engineering industry because it allows for understanding and evaluation of a new design, this can lead to advancements in developing a more efficient and effective design. This tool helps in the understanding of the flow phenomena and how it can interact with its surroundings. One of the main reasons in the use of CFD is to reduce the cost of testing a design by running simulations, whereas creating an experimental apparatus to test a design would lead to a higher cost. A CFD analysis can be done on coating technologies to evaluate their performance and behavior. Coating technology has a wide variety of applications such as: oxidation protection, corrosion protection, aid in repairs, and thermal protection. One of the most researched coating technologies is Cold Spray Technology, this technology is relatively new and has many unique characteristics. Cold spray is used to manufacture coatings in the solid state, fully preserving the feedstock material properties. This coating is done by the compression of the carrier gas in a converging section of the nozzle, followed by a diverging section where the thermal energy is converted into kinetic energy, thereby speeding up the particles to their desired velocity and creates a non-thermal coating on the substrate. This thesis is focused on the proper procedure that must be taken to create and run a simulation on the injection of particles into a cold spray nozzle. This procedure is broken down into the study of physics models, the desired mesh that must be analyzed and evaluated to obtain adequate simulations and results. These simulations will be able to demonstrate the behavior of the particles as they travel through the cold spray nozzle, thus being able to compare different carrier gases and evaluate which would perform better with the particles. The studies performed were done by using different meshing densities using the k- Omega turbulent models provided in StarCCM+ solver. Validation is very important to ensure that the results are adequate. The validation step was done by comparing the simulations ran to the simulations done by Muhammad Faizan Ur Rab. By comparing the simulations we are able to validate the studies
Simulation of Gas Dynamic Cold Spray Process
The utilization of computational fluid dynamics (CFD) as a study tool in the aerodynamics and turbomachinery industry reinforces efficiency in the design of aircraft or for understanding the flow through pipes. CFD offer tools to model different geometries and perform a more extensive study of the flow phenomena. This gives the opportunity to model a variety of geometries and analyze their behavior under different operating conditions. A similar approach can be applied to coating technologies. Coating technologies play an essential role in the manufacturing industry. Their ability to form layers of specific materials onto engineering components to enhance mechanical and physical properties has numerous applications. The applications include corrosion protection, repair, and thermal protection, etc., In recent years, CFD simulations are increasingly used in Cold Spray Technology which is a relatively new and novel coating technology used to manufacture coatings in the solid state fully preserving feedstock material properties. This thesis is conducted mainly to verify the results of changing the cold spray nozzle profile shape. However, this study presents the theoretical and practical aspects of Cold Spray process modeling, discusses various numerical analysis research areas, and determines the significant parameters to be considered while developing a custom cold spray setup and exhibits analysis based correlations. The simulations were performed on some meshes of different density using the k- Omega turbulent model in StarCCM+ solver. To assess the modeling requirements including mesh, numerical algorithm, and turbulence model, it is critical to validate the calculations against the experimental data. Hence, the numerical results were compared with Muhammad Faizan Ur Rabâs simulation results [25], and they were in good agreement
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High Strain Rate Dynamic Response of Aluminum 6061 Micro Particles at Elevated Temperatures and Varying Oxide Thicknesses of Substrate Surface
Cold spray is a unique additive manufacturing process, where a large number of ductile metal micro particles are deposited to create new surface coatings or free-standing structures. Metallic particles are accelerated through a gas stream, reaching velocities of over 1 km/s. Accelerated particles experience a high-strain-rate microscopic ballistic collisions against a target substrate. Large amounts of kinetic energy results in extreme plastic deformation of the particles and substrate. Though the cold spray process has been in use for decades, the extreme material science behind the deformation of particles has not been well understood due to experimental difficulties arising from the succinct spatial (10 Όm) and temporal scales (10 ns). In this study, using a recently developed micro-ballistic method, the advanced laser induced projectile impact test (α-LIPIT), the dynamic behavior of micro-particles during the collision is precisely defined. We observe single aluminum 6061 alloy particles, approximately 20Όm in diameter, impact and rebound off of a rigid target surface over a broad range of impact speeds, temperatures, and substrate oxide film thicknesses. Through observation of the collisions, we extract characteristic information of the dynamic response of particles as well as the relationship with various parameters (e.g. surrounding temperature, particle diameter, oxide thickness, and impact velocity). By impacting a polished aluminum 6061 alloy substrate we are able to mimic the collision events that occur during cold spray deposition. The connection between the temperature increase and the oxide thickness plays a role in theorizing the cause of unexpected phenomena, such as increased rebound energies at higher temperatures. Highly-controlled single particle impacts results, are provided to calibrate and improve computational simulations as well. This, in turn, can provide insight into the underlying material science behind the cold spray process
Youngâs Modulus and Residual Stresses of Oxide-Free Wire Arc Sprayed Copper Coatings
Conventional thermal spraying processes are almost exclusively carried out in an air atmosphere, resulting in the oxidation of the particle surfaces and interfaces within the coating and between the substrate and coating. Furthermore, the initial process of surface activation conventionally takes place in an air atmosphere, preventing an oxide-free interfacial transition. Consequently, the application of spraying materials with high oxygen affinity represents a major challenge. To overcome these issues, the present study utilized silane-doped inert gases to create an environment in which the oxygen concentration was equivalent to the residual oxygen content in an extreme high vacuum. By transferring the corundum blasting and coating process (wire arc spraying) to this environment, materials with a high oxygen affinity can be applied without oxidation occurring. For industrial use, this is an interesting prospect, e.g., for repair coatings, as the homogeneity of the composite is improved by a non-oxidized coating. Using the example of arc-sprayed copper coatings, the microstructure and mechanical properties of the coatings were analysed. The results showed that the oxide-free, wire arc sprayed copper coatings exhibited an improved wetting behaviour resulting in a significant reduction of the coating porosity. Moreover, the improved wetting behaviour and led to an increase in the bonding rate and apparent Youngâs modulus. Contrary to expectations, the residual stresses decrease although relaxation mechanisms should be inhibited, and possible reasons for this are discussed in the paper
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