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Nowadays, the material and energy consumption control is a major challenge in the sustainable development context. Greenhouse gas emissions, growing energy consumption and materials development costs intensified research on renewable energies, biomaterials, rationalization of consumption and preserving the environment (White & Ali, 2016; Tamali, Boumedienne and Ahmed, 2016). The rule is to align with the topical directions of scientific research which highlights the importance of the international trilogy: Materials - Energy - Environment.
Besides, thin films obtained in surfaces treatment by plasma spraying is an important manufacturing process which was and remains extensively used in industrial applications. This process is used to enhance the performance of engineering components such as coating of pistons, piston rings and shafts, and improving resistance to thermal degradation, corrosion and wear. As many are the experimentations in the process field, there is a huge interest to conduct numerical works to achieve high performance and to reduce experimental cost and efforts. Moreover, the arc plasma spraying processes are of high level complexity due to the various parameters involved in many stages.
The aim of this work falls into this objective. A scrutiny of spray jet and impact characteristics under dispersion effects of powder injection parameters will be presented to show whether injection parameters are influencing the spray stream and then the impact conditions. In a second part, a Taguchi experimental design study will be conducted to explore the weighting of some spraying parameters on the characteristics of the formed coat. Experimental design technique, which is required in the industrial practice of experiments design, has met with growing interest in engineering process. Chen et al. (1993) conducted a D-optimal experimental design to characterize the effects of the APS process parameters on in-flight particle temperature and velocity, and on the oxide content and porosity in the coatings based Alloy 625. Authors concluded that the optimum spraying conditions produced a coating with less than 4% oxide and less than 2.5% porosity. The spray distance, particle size, and current have largest effects on porosity. The particle size, current, and Ar flow rate have an influence on particle velocity and temperature.
Steeper et al. (1993) conducted an experimental study on plasma spraying of Alumina-Titania powder. The coating experiments were conducted using a Taguchi methodology. It has been concluded through the Taguchi evaluation that hydrogen flow and traverse rate were the most significant contributors to porosity. Authors concluded also that the spray distance dominated the insulator plate and tube resistance and the surface finish is influenced the most by primary nitrogen flow.
See the Nomenclature for this article in Table 1.
Table 1. | Vector Quantities |
 | Gas velocity (m/s) |
 | Particle velocity (m/s) |
 | Particle position (m) |
 | Drag force (N) |
 | Gravity force (N) |
 | Force due to additive mass (N) |
 | Thermophoretic force (N) |
 | Gravitational field (=9.81m/s2) |
| Physical Parameters |
| a | Thermal accommodation coefficient |
| Ap | Particle surface, = πdp2 |
| CD | Drag coefficient |
| Cpp | Particle specific heat (J/mol.K) |
| dinj | Injector diameter (m) |
| dp | Particle diameter (m) |
| fkn | Corrective factor related to Knudsen effect |
| fprop | Corrective factor related to boundary layer effect |
| hf | Convective heat transfer coefficient (W/m2/K) |
| Kn* | Knudsen number |
| kp | Particle conductivity (W/m2/K) |
| Le | Material latent heat of boiling (J/kg) |
| Lm | Material latent heat of melting (J/kg) |
| mp | Liquid-solid averaged particle mass (kg) |
| Nf | Modified Nusselt number |
| Prw | Prandtl number of hot gas at Tw |
| Qconv | Convective heat flux received by the particle (W/m2) |
| Qnet | Total heat flux received by the particle (W/m2) |
| Qrad | Radiative heat flux received by the particle (W/m2) |
| Re | Relative Reynolds number,  |
| Rep | Particle Reynolds number,  |
| t | Particle time (s) |
| T | Physical gas temperature(k) |
| T∞ | Local jet temperature (k) |
| Ta | Ambient temperature, 300K |
| Te | Material boiling point (k) |
| Tm | Material melting point (k) |
| Tp | Particle temperature,  |
| Tw | Particle-wall temperature |
| Xp | Volumetric melt fraction of the particle |
 | Gas density (kg/m3) |
 | Particle density (kg/m3) |
 | Gas dynamic viscosity (kg/m/s) |
 | Specific heat ratio |
| Subscripts, Superscripts and Abbreviations |
| b | Boiling |
| g | gas |
| ma | Additive mass |
| p | Particle |
| prop | Gas property |
| th | Thermophoresis |
| w | wall |
| FD | Finite Differences |
| LTE | Local Thermal Equilibrium |
| ODE | Ordinary Differential Equations |
| PSP | Plasma Spraying Process |
| ∞ | Far from particle |
 | Rate of mass vaporization |
| min | Minimum value |
| max | Maximum value |
| av | Average value |