Melting Point of Carbon Particles behind the Gas Detonation Front

A mathematical model of gas detonation of fuel-enriched mixtures of hydrocarbons with oxygen has been formulated, which makes it possible to numerically study the equilibrium flows of detonation products in the presence of free carbon condensation. Reference data for graphite were used to describe the thermodynamic properties of carbon condensate. The calculations are compared with the known results of experimental studies in which, when detonating an acetylene-oxygen mixture in a pipe closed at one end, it is possible to obtain nanoscale particles from a carbon material with special properties. It is assumed that the melting point of such a material is lower than that of graphite and is about 3100 K. Only with such an adjustment of the melting temperature, the best agreement (with an accuracy of about 3 %) was obtained between the calculated and experimental dependence of the detonation front velocity on the molar fraction of acetylene in the mixture.

Application of intelligently controlled technologies in designing of technological processes for explosive forming of shell parts

The object of research is the processes of pulse metalworking (hydroexplosive, magnetic pulse, electrohydraulic, gas detonation forming, etc.). Among these methods of forming for the production of aircrafts engines parts from cylindrical and conical blanks, the most efficient in terms of its energy capabilities and overall dimensions is explosive. The modern level of theory and practice of metal forming processes allows, on the basis of a systematic approach and control theory, to determine the optimal parameters of plastic forming processes, select the best technical solutions, and create a precondition for the transition to complex automation. The most difficult task of metals forming methods optimizing is to find the best solution among many potentially possible ones, considering the introduced restrictions and efficiency criteria, environmental, economic, technical, ergonomic, and other requirements. The most problematic is that it is impossible to optimize the process of forming post-factum (finishing works, elimination of defects in shape and size, welding of cracks, etc. are required), therefore, when solving optimization problems, the implementation of the feedback principle is required - comparison of the value of the controlled variable, determined by the control program, with the desired value. In general, the processes of metal forming by pressure are characterized by a variety of problems of the theory of optimal control, the solution of which is carried out by methods of mathematical programming. And, although the equipment for pulse processing can have a different design, it necessarily includes structural elements that make it possible to convert the energy of the source and with its help (through the action of a solid body, transmitting medium, or field) to deform the metal of the workpiece. Due to this, in this work, it is proposed to control the quality of the obtained parts by varying the degree of deformation of the workpiece in the process of forming. The result of the work is the development of an integrated intelligent system, with the help of which it is possible to carry out the computer-aided design of almost all pulse-action processes based on the intelligent selection of suitable forming parameters.

Effects of Heat and Momentum Gain Differentiation during Gas Detonation Spraying of FeAl Powder Particles into the Water

In this paper, dynamic interactions between the FeAl particles and the gaseous detonation stream during supersonic D-gun spraying (DGS) conditions into the water are discussed in detail. Analytical and numerical models for the prediction of momentum and complex heat exchange, that includes radiative effects of heat transfer between the FeAl particle and the D-gun barrel wall and phase transformations due to melting and evaporation of the FeAl phase, are analyzed. Phase transformations identified during the DGS process impose the limit of FeAl grain size, which is required to maintain a solid state of aggregation during a collision with the substrate material. The identification of the characteristic time values for particle acceleration in the supersonic gas detonation flux, their convective heating and heat diffusion enable to assess the aggregation state of FeAl particles sprayed into water under certain DGS conditions.

Tribological wear of Fe-Al coatings applied by gas detonation spraying

Comparative tests of gas detonation (GDS) coatings were carried out in order to investigate the influence of spraying parameters on abrasive wear under dry friction conditions. The tests were carried out using the pin-on-disc (PoD) method at room temperature. The microstructure of the coatings was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM / EDS) methods. The results showed that with specific GDS process parameters, the main phases in both coatings were FeAl and Fe3Al involving thin oxide films Al2O3. The tribological tests proved that the coatings sprayed with the shorter barrel of the GDS gun showed higher wear resistance. The coefficient of friction was slightly lower in the case of coatings sprayed with the longer barrel of the GDS gun. During dry friction, oxide layers form on the surface, which act as a solid lubricant. The load applied to the samples during the tests causes shear stresses, thus increasing the wear of the coatings. During friction, the surface of the coatings is subjected to alternating tensile and compressive stresses, which lead to delamination and is the main wear mechanism of the coatings.

Creation of Bioceramic Coatings on the Surface of Ti–6Al–4V Alloy by Plasma Electrolytic Oxidation Followed by Gas Detonation Spraying

In this work, bioceramic coatings were formed on Ti6Al4V titanium alloy using a combined technique of plasma electrolytic oxidation followed by gas detonation spraying of calcium phosphate ceramics, based on hydroxyapatite. Plasma electrolytic oxidation was carried out in electrolytes with various chemical compositions, and the effect of electrolytes on the macro and microstructure, pore size and phase composition of coatings was estimated. Three types of electrolytes based on sodium compounds were used: phosphate, hydroxide, and silicate. Plasma electrolytic oxidation of the Ti–6Al–4V titanium alloy was carried out at a fixed DC voltage (270 V) for 5 min. The sample morphology and phase composition were studied with a scanning electron microscope and an X-ray diffractometer. According to the results, the most homogeneous structure with lower porousness and many crystalline anatase phases was obtained in the coating prepared in the silicate-based electrolyte. A hydroxyapatite layer was obtained on the surface of the oxide layer using detonation spraying. It was determined that the appearance of α-tricalcium phosphate phases is characteristic for detonation spraying of hydroxyapatite, but the hydroxyapatite phase is retained in the coating composition. Raman spectroscopy results indicate that hydroxyapatite is the main phase in the coatings.

Gas mixture explosion as a tool for generating impulsive disturbances

The work is devoted to the development of a device for generating impulsive perturbations in soil massifs. It is proposed to use the explosion energy of a high-pressure acetylene-oxygen gas mixture as a source of impulse perturbations. Applying the standard method of measuring mechanical stresses and using piezoelectric sensors, it is obtained the stress fields occurring in the soils when an explosion of the gas mixture takes place. It is revealed that the dependences of the maximal stresses in the soil massif on the relative distance to the source, when the gas charge under high pressure acts, are the power functions. The exponents of power functions approximating these experimental dependences are obtained. The attenuation of the maximal radial stresses with the distance is considered for the two cases when the charges filled with gas mixture under low and high pressure act. The comparison of these cases indicates their similarity. In the paper it is also performed the analysis of modern methods of using explosive and non-explosive sources for seismic wave generation during investigations in the search geophysics. The existing structural sources of seismic waves used in the seismic exploration are analyzed in detail. The disadvantages and advantages of explosive and non-explosive impulsive sources of seismic waves are indicated. Among the advantages of the proposed wave sources it is worth noting their low price and mobility. There is no need to obtain special permits for their use. The obtained results allow one to expand the field of gas detonation application. In particular, it can be used as an alternative source of seismic waves. The proposed method is promising for training in search geophysics and in the study of properties of soil massifs.

An All-Atom Simulation Study of Gas Detonation Forming Technique

The high-speed forming process is the key to attaining difficult and irregular profiles on ductile materials. In the present work, we proposed the all-atom model of the gas detonation forming process, wherein molecular dynamics (MD) simulations were performed on the aluminum workpiece at different loading speeds similar to the various pressure values in the process. The deformation response of an aluminum workpiece for a wide range of loading speeds, 0.1–8 Å/ps, was investigated. The dome-height, failure patterns, and formability of the aluminum workpiece were examined for these loading speeds. We obtained an inverse relationship between the formability of the aluminum workpiece and the applied loading speed. Moreover, in this work, the influence of the different percentage of defects in the workpieces on the mechanical behavior was investigated. We observed that at lower speeds (< 2 Å/ps), the deformation is observed throughout the workpiece starting from the point of contact in the middle and that is contrary to the deformations observed due to the higher loading speed where localized deformations occur due to creation of slipping planes. We also found that the internal voids lead to the rearrangement of atoms to facilitate the movement of slipping planes leading to better formability compared to the no-void workpieces. This work helps to get a fundamental understanding of deformation behavior in the high-speed forming process with and without defects in the aluminum workpiece at the nanoscale.