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Suspension plasma spraying has aroused much research efforts over the two last decades to describe and understand the in-flight mechanisms of suspension plasma processing by developing advanced diagnostics and models. This research field has highlighted the intricate and prevailing dependence of the coating properties, and especially the rich variety of attainable microstructures, on the thermal and dynamic histories of the submicron particles in the plasma jet. This paper gives an overview of the major key points to control from the plasma torch operation up to the coating build-up. The main diagnostics methods are examined and the most advanced models as well. The perspectives focus on the key issues to improve the basic understanding of the in-flight phenomena. They also insist on a necessary multiscale approach to combine the diagnostics and the models in order to form relevant data flows for machine learning algorithms and better process prediction and reliability. [ABSTRACT FROM AUTHOR]

The research on high-velocity air-fuel (HVAF)-sprayed CrC-based materials has mostly focused on conventional CrC-25NiCr composition. In this paper, two alternative compositions (CrC-50NiCrMoNb and CrC-37WC-18NiCoCrFe) were sprayed with high-velocity oxy-fuel (HVOF) and HVAF spray processes to evaluate the material behavior during spraying and to provide characterization of the microstructures and mechanical properties of the coatings. For comparison, coatings from the CrC-25NiCr composition were sprayed with both processes. Spray diagnostics were carried out to obtain average particle velocity and temperature for each material and process combinations. The measured average in-flight particle data were 1800 °C and 700 m/s for HVOF process, and 1450 °C and 900 m/s for HVAF process. Characterization of the coating microstructures was carried out by scanning electron microscopy and X-ray diffraction. In addition, the carbon content of the feedstock powders and sprayed coatings was measured with carbon analyzer. The results show that carbide rebounding or selective deposition of particles with higher metal matrix content is the dominating reason for carbide loss during HVAF spraying, while carbide dissolution is an additional source for the HVOF spraying. Higher particle velocities and controlled temperature measured for the HVAF process produced dense coatings with improved toughness and more homogenous coating structure. [ABSTRACT FROM AUTHOR]

This paper investigates a novel single cathode plasma column design consisting of a patented arc constrictor and its impact on process stability, versatility, and component life. The design aims to minimize the re-strike of arc, increase the arc length enabling high voltage and low amp operation as well as the use of ternary gas combination to increase the enthalpy. The arc unsteadiness and dynamic behavior are investigated through the fluctuations of electrical signals. Further, the particle velocity and temperature have been characterized by commercial diagnostics systems. The takeover/steady mode appears to be the typical operational mode of the plasma jet in this design. Low amplitude and high frequency fluctuations resulted in steady particle characteristics. Further, the design allowed the gun to operate at very high plasma velocities reaching the characteristics of an HVOF jet. The significance of the design is demonstrated through operational flexibility and stability. [ABSTRACT FROM AUTHOR]

An integrated investigation approach for temperature measurement and control of plasma sprayed coating is presented in this paper. It is based on infrared (IR) pyrometry combined with specific robot scanning trajectories. The temperature evolution was continuously detected and recorded during preheating, spraying, and cooling stages. Then the two specific factors, periodic average temperature and periodic standard deviation, were adopted to evaluate the temperature variation and the fluctuation of the thermal cycle relevant to one spraying period. These two factors were successful in describing the temperature variation during experimental processing sets. Moreover, the influence of processing parameters of Z-type robot spray trajectory, including spray distance, scanning velocity, and scanning step on coating temperature is experimentally researched and explained reasonably by comparing the two factors. [ABSTRACT FROM AUTHOR]