Volf Leshchynsky

Air gas dynamic spraying of powder mixtures : Theory and application

The radial injection gas dynamic spray (RIGDS) technology of powder coatings deposition was considered for this work. A coating was created by injecting powders with variable compositions into a supersonic air jet and depositing powder on the substrate. This study describes the preliminary analysis of an air gas dynamic spray method realized by a portable RIGDS apparatus with a radial injection of powder. Attention was given to shock compaction processes during the coating structure formation and examples of powder mixtures utilization in RIGDS. It was shown that the operational parameters of supersonic powder-gas jet have a significant influence on the coatings microstructure, thus defining the high performance of the coating. Compaction and bonding of particles were analyzed.

Localisation of deformation in cold gas dynamic spraying

One of the main specific features of the cold spray process is localisation during particle impact deformation. The resultant adiabatic shear instability is the phenomenon that is known to play a major role in the particle/substrate and particle/particle bonding and coating structure formation during the cold spray process. In this article, the cold spray process is numerically simulated as an impact between a single spherical particle with the substrate, and comparison with experimental results for Armco iron and stainless steel particles is made. To describe a deformation behavior of the two materials at high strain rates, the Johnson–Cook model has been chosen. The results indicate that the model accurately captures the grain distortion in the impact zone for both materials. This approach provides valuable information on the characterisation of the strain localisation at the particle/substrate interface.

Retraction Note to: Structure and Mechanical Properties of Thick Copper Coating Made by Cold Spray

The main purpose of this study was to form cold-sprayed copper coatings on A 516 low carbon steel, which is considered a prospective material for manufacturing used nuclear fuel containers. The 3 mm-thick Cu coatings were formed using the high pressure cold spray method with Nitrogen as the propellant gas. The deformation of copper particles during the deposition process was studied. The obtained SEM images of the Cu layer-A 516 low carbon steel substrate interface cross sections demonstrated that the Cu layer at the substrate interface had a dense microstructure with localized jet-metallic mixing areas. The Cu particles were deformed considerably more severely in this layer than in the consequently deposited upper layers. The steel substrate underwent severe deformation due to the impact of Cu particles. The mutual severe deformation of Cu particles and steel substrate resulted in a considerable increase of adhesion strength up to 120 MPa. The structure of coatings and coating-substrate interface was studied.

Low-Pressure Cold Spray (LPCS)

The Chapter “Low-Pressure Cold Spray” presents a description of basics of LPCS technology, bonding mechanisms, temperature effects and LPCS localization processes. To illustrate the main aspects of LPCS system parameters determination, the numerical simulation and experimental data are presented. The emphasis is placed on the proper development of the cold-sprayed metal matrix composite coatings and their structure and properties, which are of paramount importance to the success of LPCS. Processes such as bonding, hardening and softening of the coating materials during cold spraying and coating structure formation at following heat treatment (sintering) are dealt with from the theoretical as well as practical aspect.

Coat spraying with use of the cold spray method

In this article, physical phenomena accompanying the process of cold spraying as well as principles of bonding particles with a surface were analysed. Moreover, the basic process parameters as well as the construction of actual spraying devices were shown. Numerous advantages of the method and its applications in the industry were presented.

In-line Ultrasonic Array System for Monitoring Dynamic of Coating Forming by Cold Spray Process

This study attempts to test the viability of studying the cold spray process using acoustic methods, specifically testing during the actual spray process itself. Multiple composites studied by flat and multi channel transducers as well as actual online measurements are presented. It is shown that the final thickness as well as the dynamics of buildup can be evaluated (including plotting rates of buildup). Cross sections of the coating thickness are also easy to obtain and show true profiles of the coating. The data can also be used to generate real estimates for nozzle speed and spray diameter. Finally comparisons of real thickness and acoustically estimated thickness show a close linear relationship with the y intercept seeming to depend on the composition. The data clearly shows that online acoustic measurement is a viable method for estimating thickness buildup.

Portable, low pressure cold spray systems for industrial applications

Publisher Summary Widespread adoption of the Cold Spray [“CS”] technology implies, as the next logical step, its application in the industrial environment. Therefore, the development of a portable low pressure CS system is of fundamental importance. Of special practical interest is establishing the relationship between the operating parameters of a portable CS machine and the resultant micro-structure of the formed spray coatings. To obtain high quality coatings, the configuration of a portable CS system and the spray process parameters have to be selected thoroughly. Due to the number of CS process parameters, it is inevitable that a certain degree of trial and error is required to optimize the spray process for each specific coating–substrate combination. This chapter presents some specific characteristics related to a portable, low pressure system. These characteristics are subsequently compared with those of established high pressure CS systems. One can observe a substantial difference between the velocities of the gas and the particle. This variation is taken into account when the parameters of the powder-laden jet are calculated.