Vasily M. Fomin

Current status of the cold spray process

This chapter focuses on several researches undertaken in the areas—the gas-dynamics of cold spray, interaction of a high-speed particle with the substrate and bonding mechanism, and related technologies and applications. Obtaining coatings by the cold spray method involves the use of a high-velocity gas flow for the accelerating and heating of particles. The particle velocity that can be reached in a cold spray facility is limited by the gas velocity. Owing to the use of high gas pressures, long nozzles, and fine particles, the particles move with a velocity close to the gas velocity that can be increased by using gases with low molecular weights and by gas heating. This approximation implies that the gas flow in a converging/diverging nozzle is isentropic and one dimensional. The gas is perfect and has a constant ratio of specific heats. Based on isentropic computations, it is concluded that the particle temperature is almost independent of pressure, but the particle velocity increases by 15% if the pressure is doubled.

Discovery of the cold spray phenomenon and its basic features

This chapter addresses the experiments that resulted in the discovery of the cold spray process and established the basic physical principals of the process. Two aspects of the cold spray process are important for better understanding and improving the process. First is the physics of high speed particle impact to explain bonding mechanism, and second is the gas-dynamics to optimize spray parameters and provide as high particle velocity as possible. Cold spray process offers many advantages that helps in producing and repairing a wide range of industrial parts, such as turbine blades, pistons, cylinders, valves, rings, bearing components, pump elements, sleeves, shafts, and seals for many industries. Various coatings may add strengthening, hardening, wear resistance, corrosion resistance, electro-magnetic conductivity, thermal conductivity, and other properties.

Gas-dynamics of cold spray

This chapter discusses the gas-dynamics and thermal effects associated with a supersonic jet exhausting from the nozzle and its interaction with the substrate in the cold spray method. To accelerate particles, two types of nozzles are used—nozzles with circular and rectangular sections. The chapter investigates the gas-dynamics of jets exhausting from conical nozzles with circular cross sections—symmetrical-axis flows. An analysis of the features of such jets, as applied to the cold spray method, reveal that the use of nozzles with rectangular cross sections is also significant. With the same ratio of the nozzle-exit and throat cross sections, nozzles with a rectangular section can provide a wider spray beam in the direction of the smaller size of the section and a narrower beam in the direction of the larger size of the section. Such nozzles can also decrease the effect of particle deceleration in the compressed layer in front of the substrate by decreasing the thickness of the layer itself. The issues of acceleration of finely dispersed particles in supersonic nozzles and formation of flat and comparatively thin two-phase jets, which ensure high deposition efficiency over the area, are of significant interest in the process of cold spray. The chapter concludes that the particle velocity reached immediately before the impact on the substrate plays the most important role in deposition of coatings by cold spray method.

Demonstrator of continuous-detonation air-breathing ramjet: Wind tunnel data

First experimental investigations were carried out into the detonation combustion of hydrogen in a demonstrator of an original-design air-breathing ramjet while blowing with an air flow at Mach 4 to 8 in an impulse wind tunnel, and for the first time under these conditions, continuous spin and longitudinal pulsed modes of detonation combustion of hydrogen in an annular combustor were detected.

Hypersonic Short-Duration Facilities for Aerodynamic Research at ITAM, Russia

Beginning from the first wind tunnels and until 1950s, it was assumed that aerodynamic experiments can only be performed under steady conditions. Therefore, all wind tunnels were long-duration facilities where the test time was longer than the characteristic times of the examined phenomena by orders of magnitude. However, it became clear in the 1950s that the existing facilities cannot satisfy the requirements for modeling high-velocity flight conditions because of energy constraints. One way to overcome these constraints was reduction of the test time, proportionally leading to reduction of the energy necessary to perform the experiments. The main advantage of test time reduction to 1 s and less is the possibility of using new design solutions, which allow record-breaking parameters of the test gas to be reached.

Molecular dynamics study of Laplace pressure in solid-state nanostructures

The paper provides a comprehensive molecular dynamics study of nanostructures compressed by a system of surface atoms to analyze their surface tension. Surface tension is here understood as phenomena resulting from the presence of surface atoms. All main properties of nanostructures are conditioned by a highly developed surface. The number of surface atoms and their energy are comparable to those of bulk atoms.It is shown that at cryogenic temperatures, spherical solid-state clusters of size up to 10 nm reveal excess pressure. This pressure owes to compression of the clusters by surface atoms.The molecular dynamics study of thermodynamic properties of the nanostructures demonstrates that the increase in pressure in clusters of size from 2 to 9 nm with temperature is due to the gas component and the slope on the temperature dependence of thermal pressure does not depend on the cluster size. It is also shown that the surface tension coefficient decreases with an increase in temperature. A theoretical expression for this dependence is derived suggesting that there exists a certain Laplace temperature at which compressive pressure in a cluster is balanced by thermal gas pressure.

A Few-Parameter Equation of State and Its Application to the High-Velocity Interaction of Solids

A simple caloric model of the equation of state is proposed to describe thermodynamic properties of solid materials with the phase transitions being ignored and with the minimum possible number of parameters as the initial data. Thermal oscillations of the crystal lattice are described by the Debye approximation. The values of the parameters on the zero isotherm are calculated analytically from the generalized form of the Gruneisen function. Thermodynamic characteristics are calculated in wide ranges of densities and pressures. Two-dimensional problems of a high-velocity impact of a reactor of a nuclear power plant with the Earths surface propulsion system are solved. The destruction problem of a nuclear power plant of space power installation at space debris impact in orbit (impact velocity of 16 km/s) are solved.

Energy balance of laser-oxygen cutting of thick steel sheets with minimal roughness

In our previous work we found experimentally the scaling laws for the oxygen-assisted laser cutting of low-carbon steel of 5 – 25u2005mm. No dross and minimal roughness of the cut surface were chosen as criteria of quality. Formulas were obtained to determine the optimum values of the laser power and cutting speed for the given sheet thickness. In the present paper, the energy balance of the oxygen-assisted laser cutting is studied experimentally at these optimum parameters. The absorbed laser energy and heat conduction losses and cut width were measured experimentally, and then the energy of exothermic reaction of oxidation was found from the balance equation. To define the integral coefficient of absorption, the laser power was measured on the cutting channel exit during the cutting. The heat conduction losses were measured by the calorimetric method. It has been established that the absorbed laser energy, oxidation energy, thermal losses and melting enthalpy related to a sheet thickness unit, do not depend...

The Investigation of Nano‐dimensional Alloys Thermodynamic Properties

The question on the nanothermodynamics creation haven’t solved in the science. In this connection this paper is devoted to the investigation of thermodynamics properties of nano length scale materials. In particular it is presented the results of calculation of thermodynamical properties of pure copper and its alloy with silver. It is taken the main magnitudes, allowing to get the state equation of nanostructures. And the chief result of the work is the development of the way of research of thermodynamical properties of nanostructure and the way of getting the state equation.

Cold spray equipments and technologies

This chapter provides an overview of cold spray equipments and technologies. The main elements of the cold spray setup are: the spraying unit consisting of a prechamber and a supersonic nozzle, a powder feeder, a gas heater, a source of a compressed gas, a spraying chamber with a motion system, and a system for monitoring and controlling spray parameters. The two technologies presented are—spraying electro-conductive corrosion-resistant coatings, and spraying metal-polymer coatings. The Institute of Theoretical and Applied Mechanics of Siberian Branch of the Russian Academy of Sciences (ITAM SB RAS) has developed the technological process and equipment, which allows applying a thin (0.05–0.2 mm) but strong layer of copper, nickel, or zinc onto the operating surface of the tip by cold spraying, which eliminates conditions that favor electrochemical corrosion.