Cold spraying is increasingly attracting attentions from both scientific and industrial communities due to its unique ‘low-temperature’ coating build-up process and its potential applications in the additive manufacturing across a variety of industries. The existing studies mainly focused on the following subjects: particle acceleration and heating, coating build-up, coating formation mechanism, coating properties, and coating applications, among which particle acceleration and heating can be regarded as the premise of the other subjects because it directly determines whether particles have sufficient energy to deposit and form the coating. Investigations on particle acceleration and heating behavior in cold spraying have been widely conducted both numerically and experimentally over decades, where many valuable conclusions were drawn. However, existing literature on this topic is vast; a systematical summery and review work is still lack so far. Besides, some curtail issues involved in modeling and experiments are still not quite clear, which needs to be further clarified. Hence, a comprehensive summary and review of the literature are very necessary. In this paper, the gas flow, particle acceleration, and heat transfer behavior in the cold spray process are systematically reviewed. Firstly, a brief introduction is given to introduce the early analytical models for predicting the gas flow and particle velocity in cold spraying. Subsequently, special attention is directed towards the application of computational fluid dynamics technique for cold spray modeling. Finally, the experimental observations and measurements in cold spraying are summarized.

Gas Flow, Particle Acceleration, and Heat Transfer in Cold Spray: A review

Kinetic spray process has been applied to various industrial fields such as automotive, aviation, and defense industries due to its availability to produce high-performing coating layer. However, since the properties of kinetic-sprayed coating layer are significantly affected by the microstructures of deposit, the microstructures of the deposit should be controlled to acquire advanced coating layer and, accordingly, deep understanding of microstructural evolution must be achieved before controlling the microstructure of the coating layer. This paper gives an overview of contents related to the microstructure of kinetic-sprayed deposition. The most powerful influencing factors in microstructural evolution of kinetic-sprayed coating layer are instant generation of thermal energy and high-strain, high-strain-rate plastic deformation at the moment of particle impact. A high-density coating layer with low porosity can be produced, although some micro-cracks are occasionally induced at the interparticle boundary or at the inner region of the particles. Also, a microstructure which is distinct from the inner particle region is created in the vicinity of the particle-particle or particle-substrate interface region. However, almost no crystal phase transformation or chemical reaction is induced since the deposited particles are not heated directly by a thermal energy source.

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Microstructure of Kinetic Spray Coatings: A Review

Formation of coating and tribological behavior of kinetic sprayed Fe-based bulk metallic glass

Effect of injection pressure on particle acceleration, dispersion and deposition in cold spray

Carrier gas is known as the medium to inject the cold sprayed powders into the main driving flow inside the nozzle. Hence, the properties and conditions of carrier gas should be of great importance to the particle motion behaviour and then particle deposition process. In this study, the effect of carrier gas temperature on the particle acceleration and deposition in cold spray process was investigated by both numerical and experimental methods. It is found that the supersonic driving gas flow and the consequent particle acceleration behaviour are significantly influenced by the carrier gas temperature, more specifically, higher carrier gas temperature results in higher particle impact velocity. In addition, because the carrier gas has additional heating effect on the powder particles before injection, the final impact temperature also increases with the carrier gas temperature, which leads to the reduction in the critical velocity. The increase in particle impact velocity and reduction in critical velocit...

Significant influence of carrier gas temperature during the cold spray process

A Superior Sensor Consisting of Porous, Pd Nanoparticle–Decorated SnO2 Nanotubes for the Detection of ppb-level Hydrogen Gas

Highly selective acetone sensor based on Co3O4-decorated porous TiO2 nanofibers

A cold spray process is a relatively new process that uses high velocity metallic particles for surface modifications. Metallic powder particles are injected into a converging-diverging nozzle and accelerated to supersonic velocities. Gas accelerates in the throat of the nozzle and reaches a maximum speed at the nozzle exit. Due to compression shocks just outside the nozzle, the gas jet has an irregular shape. Experiments on the expansion ratio and the length ratio of the nozzle, particularly in terms of their relation to the gas pressure, temperature and nozzle length, were conducted for the purpose of reducing the shockwave [1].

Effect of the expansion ratio and length ratio on a gas-particle flow in a converging-diverging cold spray nozzle

Ultrasensitive Hydrogen Sensor Based on Porous-Structured Pd-Decorated In2o3 Nanoparticle-Embedded Sno2 Nanofibers

Synergistic effect of Pd and Fe2O3 nanoparticles embedded in porous NiO nanofibers on hydrogen gas detection: fabrication, characterization, and sensing mechanism exploration

Sung-Han Park

Papers

A Superior Sensor Consisting of Porous, Pd Nanoparticle–Decorated SnO2 Nanotubes for the Detection of ppb-level Hydrogen Gas

Highly selective acetone sensor based on Co3O4-decorated porous TiO2 nanofibers

Effect of the expansion ratio and length ratio on a gas-particle flow in a converging-diverging cold spray nozzle

Ultrasensitive Hydrogen Sensor Based on Porous-Structured Pd-Decorated In2o3 Nanoparticle-Embedded Sno2 Nanofibers

Synergistic effect of Pd and Fe2O3 nanoparticles embedded in porous NiO nanofibers on hydrogen gas detection: fabrication, characterization, and sensing mechanism exploration