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The paper contains experimental researches of the creation of the functionally-gradient heterogeneous materials based on metal-ceramic powders using the laser cladding method. Optimal conditions have been found for the creation of qualitative additive monolithic layers, the layer has minimal roughness and no pores, metal-ceramic coatings regarding the laser action parameters and coating composition, deposition technique, ceramic powder size and metal binder. Experimental data have been gathered on the morphology and microstructure of the clad layers versus the coating composition and laser action parameters.

The paper presents the results of experimental investigation of the effect of the beam polarization on the quality of the oxygen-assisted laser cutting of steel by a CO2-laser. Under consideration is the effect of the laser cutting parameters by the beam with the linear polarization on the cut surface roughness. It is founded that the minimal roughness is reached when the electric field vector is perpendicular to the cutting speed vector. It is concluded that the absorbed power distribution imposes the essential influence on the surface quality, and that the radiation heating of side walls is important to have lower roughness. Obtained results enabled to present probable reasons of the worse surface quality of the metals cut by a fiber laser than the ones cut by a CO2-laser.

Analysis of the laser cut surface morphology remain topical. It is related with the fact that the surface roughness is the main index of the cut quality. The present paper deals with the experimental study of the relatively unstudied type of defects on the laser cut surface, dimples, or craters. According to the measurement results, amount of craters per unit of the laser cut surface area rises as the sheet thickness rises. The crater diameter rises together with the sheet thickness and distance from the upper sheet edge. The obtained data permit concluding that the defects like craters are observed predominantly in the case of thick sheets. The results agree with the hypothesis of crater formation as impact structures resulting from the melt drops getting on the cut channel walls upon separation from the cut front by the gas flow.

The effect of an optical pulsed discharge created by CO2-laser with an average power of up to 2.2 kW on the aerodynamic drag of a model in a supersonic air flow is experimentally investigated. Experiments were carried out in a supersonic wind tunnel MAU-M (diameter of the nozzle outlet dc = 50 mm) on the modes M = 1.36, Re1 = 1.4– 3.8*107 1/m. To ensure a stable optical breakdown, a jet of argon gas was introduced into the focusing region of the laser beam. As a result, a decrease in the aerodynamic force acting on the model was obtained. This decrease was 15% when a subsonic flow of argon was introduced into the main flow and another 15% when optical pulsed discharge was organized.

In the present work, a combined method is considered for the production of a metal-matrix composite coating based on Ni and B4C. The coating is created by consistently applied methods: cold spray and laser cladding. The conditions of obtaining cermet layers are investigated depending on the parameters of laser cladding and cold spray. It is shown that the laser track structure significantly changes in accordance to the size of ceramic particles ranging 3–75 µm and its concentration. It is shown that the most perspective layers for additive manufacturing could be obtain from cold spray coatings with ceramic concentrations more than 50% by weight treated in the heat-conductivity laser mode.

In the present work, a combined method is considered for the production of a metal-matrix composite coating based on Ni and B4C. The coating is created by consistently applied methods: cold spray and laser cladding. Main focus of this work aimed to microstructure of coatings, element content and morphology of laser tracks. At this stage, the authors focused on the interaction of the laser unit with the substance without affecting the layer-growing technology products. It is shown that coating has deformed particles of nickel and the significantly decreased content of ceramic particles B4C after cold spray. After laser cladding there are no boundaries between nickel and dramatically changes in ceramic particles.

The results of an experimental study of laser-oxygen cutting of low-carbon steel using fibre and CO2 lasers are generalised. The dependence of roughness of the cut surface on the cutting parameters is investigated, and the conditions under which the surface roughness is minimal are formulated. It is shown that for both types of lasers these conditions can be expressed in the same way in terms of the dimensionless variables – the Peclet number Pe and the output power Q of laser radiation per unit thickness of the cut sheet – and take the form of the similarity laws: Pe = const, Q = const. The optimal values of Pe and Q are found. We have derived empirical expressions that relate the laser power and cutting speed with the thickness of the cut sheet under the condition of minimal roughness in the case of cutting by means of radiation from fibre and CO2 lasers.

The microstructure of WC/Co hard alloys after surface laser treatment is studied. It is established that during the laser treatment of the hard alloys, the chemical interaction between the components of the WC/Co powder mixture occurs in the samples’ surface according to the reaction 3Co+3WC→(Co; W)3C+2C. High cooling rate during the laser treatment allows preserving the products of this reaction, i.e. graphite inclusions and complex carbide (Co; W)3C to room temperature.

We report a study of the wave structure formed by an optical discharge plasma upon the absorption of repetitively pulsed CO{sub 2} laser radiation in a supersonic (M = 1.36) air flow. Experimental data are presented on the configuration of the head shock wave and the geometry and characteristic dimensions of breakdown regions behind a laser plasma pulsating in the flow at a frequency of up to 150 kHz. The data are compared to calculation in a point explosion model with allowance for counterpressure, which makes it possible to identify the relationship between laser radiation and supersonic flow parameters that ensures quasisteady- state energy delivery and is necessary for extending the possibilities of controlling the structure of supersonic flows. (interaction of laser radiation with matter)

CO2-laser welding of 12Kh18N10T stainless steel and a VT1-0 titanium alloy with the use of a composite insert obtained by means of explosive welding of four sheets (VT1-0 titanium, high-purity tantalum, M1 copper, and 12Kh18N10T steel) is experimentally studied. After mechanical processing, the insert is placed between the welded steel and titanium sheets. Butt-end welding of the steel and titanium sheets with the steel and titanium sides of the insert, respectively, is performed by a laser beam. Metallographic and spectrographic investigations are performed; mechanical properties of the resultant composite are tested. After thermal processing, the composite is found to break over the copper layer, which has a strength of 417 MPa.

Processes of cutting stainless steel by ytterbium fibre and CO2 lasers have been experimentally compared. The cut surface roughnesses for 3- and 5-mm-thick stainless steel sheets are determined. The absorption coefficient of laser radiation during cutting is measured. It is established that the power absorbed by metal during cutting by the CO2 laser exceeds that for the ytterbium laser (provided that the cutting speed remains the same). The fact that the maximum cutting speed of the CO2 laser is lower than that of the ytterbium fibre laser is explained.

It has been experimentally shown that mechanical Q-switching in CO2 lasers with convective cooling and a self-filtering resonator can be used to provide stable generation of repetitively pulsed radiation at repetition frequencies up to 120 kHz. At low repetition frequencies, the peak power is only limited by the time of Q-switching, which must be smaller than the characteristic duration of the first generation peak. At higher frequencies (40–120 kHz), the observed decrease in the peak power with increasing frequency is caused by limitations related to relaxation processes, i.e., to the rates of population of the upper laser level and depopulation of the lower laser level.

We present the results of investigation of the parameters of an optical pulsed discharge (OPD) and their relation with gasdynamic parameters of a supersonic flow and with characteristics of laser radiation. For the first time the discrete objects are detected in the OPD by an optical method, namely, low-density caverns moving along with the flow. The propagation velocity of the thermal track arising in a supersonic flow under the action of the OPD is measured. It is found that at a pulse repetition rate of 90 – 120 kHz the caverns unite into a single plasma jet.

Re-sults of experimental studies of nano-sized refractory compounds impact on structural and mechanical characteristics of a joint obtained by CO 2 laser welding of metal plates are presented. Introduction of small quantity of specially prepared refractory nanoparticles with size less than 100 nm is shown to impact the alloy crystallization process, form fine-dispersed globular structure at its solidification. This results in increase of mechanical and operational properties of the weld seam.

The results of laser welding of an Al-Mg-Mn and two Al-Mg-Li alloys with different lithium contents which used in the aircraft industry are presented in this paper. Microstructure, phase composition and mechanical properties of the welds were investigated. A fundamental difference in the processes of formation of structural-phase compositions in the weld metal of these alloys was found.

The paper presents the investigation of the laser welding of the alloy Al-Cu-Li and titanium alloy Ti-Al-V, as well as the analysis of the post=processing on the strength properties of welded joints. Macro- and micro-structure of the joints have been studied. The resulting heterogeneous welded materials have been post-processed. The mechanical characteristics of the welded joints have been determined before and after the thermal processing.

The microstructure, hardness property and wear resistance coatings of WC, Ni-Cr and Fe powders deposited by laser cladding at varying processing parameters were investigated. The results of the present study revealed the prospects of multilayer cladding of R6M5 high-speed tool steel (analogy of M2 steel) onto low-alloy steel with the use of a laser beam. Controlling thermal cycles of laser cladding, it is possible to obtain a clad coating made of high-speed steel having the structure of high-alloy austenite martensite mixture with disperse inclusions of carbides up to 10 mm thick, i.e., it is actually possible to create bimetal structures. The wear resistance of the laser-clad self-fluxing PG-10N-01 (Ni-Cr-B-Si-C) alloy increases by a factor of 5 due to additional hardening by cast tungsten carbide with spherical particles. As a result, it becomes higher than the wear resistance of high-speed steel by more than a factor of 3.

This paper deals with the investigation of the influence of copper on the structure-phase composition and strength of laser-welded connections of aluminum alloys of the system Al-Cu-Mg, Al-Cu-Mg-Li, Al-Cu-Li. The microstructure, mechanical characteristics and chemical composition of the welded joints have been investigated. It is founded that the laser welding results in the reduction of copper concentration in the solid solution and growth of this concentration on the dendritic boundary.

The paper presents the results of analysis of the laser welding and epy following thermal treatment influence on the phase transitions and strength characteristics of aluminiumlithium alloy of the system Al-Mg-Li. The influence of the welded joints after-treatment (quenching and artificial ageing) on the structural and phase composition has been studied for different modes. It is shown that the quenching procedure changes the microstructure of the basic alloy and welded joint, and the mechanical characteristics in the alloy and welded joint were successfully equalized, so the sample composition was maximally homogenized.

In the present work, the effects of laser beam welding and post-weld heat treatment on the phase composition and mechanical properties of the 1424 alloy (Al–Mg–Li) joints were investigated. Holding the joints at a certain temperature was followed by quenching and artificial aging. The structural studies were carried out using electron microscopy, conventional X-ray diffractometry, and synchrotron radiation diffractometry. The heat treatment conditions were optimized to favor the formation of strengthening phases in the welds, the presence of which imparted mechanical strength to the joints. For the first time, 1424 Al alloy joints with a weld strength of σuts = 500 MPa have been obtained; this value of strength was achieved by applying post-weld annealing followed by quenching and artificial aging.

The results of investigations of laser welded joints between titanium and titanium and titanium and 12Cr18Ni10Ti stainless steel are presented. It is shown that in welding of the specimens of VT1-0 titanium alloy in cooling from the high-temperature β-region, the structure of the metal of the welded joint is characterized by two typical morphological features: large polyhedral grains of the ‘transformed’ β-phase and the plate-shaped intragranular structure of the α-phase. The material failed through the parent metal and the failure was ductile. Welding of the titanium alloy with the austenitic stainless steel through a copper interlayer is accompanied by the formation of an intermediate layer based on intermetallic phases with the thickness of 100–150 μm on the side of the titanium alloy.

The paper presents the experimental investigation of the creation of complex composition corrosion-resistant coatings with low abrasive wear which are used in oil industry, by the method of laser cladding additive technology. Availability of the additive laser cladding of the complex composition corrosion-resistant coatings with a strengthening phase is shown. Optimal conditions for the cladding layers creation regarding the laser radiation parameters and radiation direction are found. The changes in micro-hardness, micro-structure and structure-phase components are established against the strengthening phase content in the upper clad layer. Different content of the strengthening phase in the upper layer from 10% to 30% does not change the micro-hardness of the upper layer and is on the average 700 HV. The laser irradiation of the powder mixture containing the strengthening phase results in the partial rupture of the WC strengthening phase. Hence the chemical interaction of the tungsten-cobalt powder mixt...

The structure and mechanical properties of welded joints of VT23 titanium alloy received by methods of laser and electron beam welding with subsequent thermomechanical treatment (TMP1 and TMP2) including ultrasonic mechanical forging are investigated. X-ray structure analysis, scanning electron and transmission electron microscopy have revealed the features of phase structure, microstructure and fractography of welded joints after electron beam and laser welding with subsequent ultrasonic mechanical forging. Application of ultrasonic mechanical forging of welded joints produced by electron beam and laser welding has allowed increasing fatigue life of samples of welded joints after laser welding from 6369 to 19 569 cycles and from 54 616 cycles to 77 126 cycles for electron beam welding. Thus, the application of ultrasonic mechanical forging can significantly raise fatigue and mechanical characteristics of welded connections.

As a result of optical and pneumometric measurements is defined the flow shock wave structure that is formed by the optical breakdown, due to focused repetitively pulsed CO2 laser radiation when entering perpendicular to a supersonic (M = 1.36, 1.9) air flow direction. The dynamics of the bow shock formation in front of the energy input area is shown, depending on the frequency of energy impulse sequence. A flow structure is defined in the thermal wake behind pulsing laser plasma as well as wake’s length with low thermal heterogeneity. A three-dimensional configuration of the energy area is defined in accordance with pneumometric and optical measuring results. It is shown that Pitot pressure decreases in thermal wake at a substantially constant static pressure, averaged flow parameters weakly depend on the energy impulse’s frequency in range of 45-150 kHz.