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The chemical composition and microstructure of an AISI 321/Cu/Ta/Ti welded joint prepared by carbon dioxide laser is studied in this work. An analysis of the chemical composition showed that the Ta plate located between the Cu plate and Ti is the barrier for melting Ti in the welding pool. The welded joint consists of the Cu-based solid solution, austenite, and (Ta,Ti)(Fe,Cr)2 and (Ta,Ti)Сu3 intermetallic particles 10–50 µm in size. Tantalum actively interacts with the Fe-based melt. A diffusion zone consisting of β-Ti and (Ti,Ta)2Cu intermetallic particles forms near the boundary between the titanium alloy and the Ta plate. Joint fracture upon tensile tests occurs along the boundary between the (Fe + Cu) zone and Ta plate; the ultimate tensile strength is σu = 215 MPa.

The paper presents the results of an experimental study of the microstructure and microhardness of a functionally gradient material fabricated from 316L stainless steel and tungsten carbide (WC) ceramic particles by the selective laser melting method. High-quality defect-free cermet coatings with different ceramic contents were obtained. Optical and scanning electron microscopy and energy dispersive analysis show that laser processing leads to dissolution of WC ceramic particles. The produced coating has a dendritic structure and contains iron- and chromium-based carbides. The coating microhardness is in the range HV0.3 = 280 – 430.

This paper describes the experimental study of strength characteristics and the microstructure of a permanent joint of dissimilar materials (VT20 titanium alloy and V-1461 aluminum alloy), obtained by laser butt welding. Optical and electron microscopy, X-ray spectral and phase analysis, and the transmission diffraction method with the help of synchrotron radiation are all used to investigate the properties of a weld. It is shown that the laser radiation offset relative to the contact surface of dissimilar materials significantly changes the microstructure and phase composition of the intermetallic interlayer formed between the materials welded, thereby affecting the strength of dissimilar welded joints.

The influence of the laser beam parameters (power, motion velocity, and focus position) on the characteristics of the track being formed (size, elemental composition, and microhardness) is studied. If the difference in the laser radiation absorption coefficients in the heat conduction and keyhole regimes is taken into account, then the track sizes can be determined by a unified dependence on the energy parameter. The effect of the laser beam on the chemical composition and microhardness of cermet (WC-NiCrBSi) tracks is studied. Regardless of the track formation regime, these parameters are determined by a dimensionless parameter, which describes the degree of dilution of chemical substances. It is found that a track with the maximum mass fraction of tungsten and the greatest value of microhardness is formed at small values of the dimensionless parameter, which corresponds to the heat conduction regime. The microhardness of the deposited cermet structure is observed to be 4–5 times higher than the microhardness of the substrate material.

This paper presents the results of an experimental investigation of the influence of modifying nanoadditives on the structure and mechanical properties of multilayer coatings obtained by the laser surfacing of a composite powder with a strengthening phase. The powder of a nickel-based Ni–Cr–B–Si–Fe self-fluxing alloy with a strengthening phase of tungsten carbide was used as the surfacing material; and a mixture of nanosized refractory powders of titanium nitride and yttrium oxide clad with iron and chromium was used as the modifying additive. It has been established that the surfaced coating represents a complex system of phases formed in the process of melting and interaction of chemical elements of the substrate and of the surfaced powder mixture. The main component of the coating is the compound of nickel with iron of an Ni3(Fe, Cr) type. A partial dissolution of the strengthening phase occurs in the melting process depending on the concentration of the nanomodifier. In the case under consideration, the optimal amount of the modifying additive, which provides a maximum increase in the hardness and wear resistance of the composite coatings of the Ni–Cr–B–Si–Fe/WC system, is 0.1 wt % refractory TiN + Y2O3 nanopowders in the composite material.

This paper describes an experimental study of a temperature effect on the fracture of laser welded joints of Mg- and Cu-containing aviation aluminum alloys. The fracture of alloys and their welded joints under a uniaxial loading at temperatures of −60, 20, and 85◦C is under study. It is revealed that the strength and ultimate strain of welded joints of Cu-containing alloys decrease as temperature rises because of the formation of fixed zones of localized plastic shears. Heating and cooling suppress the Portevin–Le Chatelier effect and significantly reduce the ultimate strain of a Mg-containing alloy, even though such reduction is not observed in a welded joint. It is shown that, the maximum limiting elongation of the welded joint of a Mg-containing alloy is achieved at a negative temperature, while the formation of secondary cracks is begins during heating.

Laser welding of the 1420 alloy of the Al–Mg–Li system is experimentally studied for the purpose of its optimization. Various modes of heat treatment of fixed joints obtained by means of laser welding are considered. Heat treatment modes that allow significant enhancement of the welded joint density as compared to the as-received alloy are chosen. The ultimate relative elongation of samples after ageing is found to decrease by a factor of 3.

The influence of a thermal wake due to gas injection and due to a pulsating optical discharge (POD) on the aero-dynamic-drag force of a body in a supersonic air flow with Mach number M = 1.45 are experimentally examined. With the help of a single-component aerodynamic balance, the influence of the injected subsonic jet and the thermal wake produced by POD on the aerodynamic drag of a hemisphere-on-cylinder model was studied. It is shown that the observed aerodynamic-force reduction phenomenon can be made more pronounced by increasing the laser power and pulse repetition frequency, or by decreasing the distance between the model and the pulsating optical discharge. The maximum aerodynamic-force reduction (up to 15%) due to the thermal-wake action was observed at a maximum laser-radiation power of W = 2.3 kW and at a pulse rate of f = 90 kHz. The joint effect due to the argon jet and due to the POD caused an aerodynamic-drag force reduction reaching 30%.

The effect of thermal regimes and some technological methods (the application of intermediate compact metal inserts and nanomodifying additives) on the quality of laser-welded permanent joints of porous titanium or stainless steel plates has been experimentally studied in this work. It has been established that the formation of a high-quality defectless seam requires the use of an intermediate compact (nonporous) metal insert placed butt to butt between the edges of welded plates. In this case, the position of a focal spot should be installed at a depth equal to the thickness of a plate, i.e., on its lower surface. To form a bead joint or a joint flush to the plates to be welded together, the height of an insert must exceed the thickness of the plates. The application of nanomodifying titanium nitride based additives increases the structural dispersity and uniformity of a seam, thus producing a positive effect on the mechanical characteristics of a welded joint.

Results of experimental investigations of welded joints of high-strength aluminum–lithium alloys of the Al–Cu–Li and Al–Mg–Li systems are reported. The welded joints are obtained by means of laser welding and are subjected to various types of processing for obtaining high-strength welded joints. A microstructural analysis is performed. The phase composition and mechanical properties of the welded joints before and after heat treatment are studied. It is found that combined heat treatment of the welded joint (annealing, quenching, and artificial ageing) increases the joint strength, but appreciably decreases the alloy strength outside the region thermally affected by the welding process.

A method is proposed for creating principally new functionally graded heterogeneous materials on the basis of B4C ceramic powders with different mass fractions in the original mixture and plastic metallic additive of Ni by a combined method of cold spraying with subsequent layer-by-layer laser treatment. Mechanical properties of the resultant tracks are examined. It is shown that the track microhardness increases with increasing B4C concentration in the original mixture. The track structure is found to depend on the size of ceramic particles in the interval from 3 to 75 μm. Reduction of the B4C particle size (approximately by a factor of 2–3) inside the track owing to fragmentation under the action of the laser beam is observed for the first time.

The acoustic-emission method for inspecting flaws that form during laser bonding with the use of a CO2 continuous-wave laser with a power of up to 8 kW and characteristics that can be preadjusted prior to welding is considered. The structure of acoustic-emission signals registered in a specimen’s flawed domain has been analyzed using the wavelet transform. It has been shown that the structural coefficients of the acoustic-emission signals localized in specimen’s flawed sections become identical over time.

In this study, certain technological variants of the laser welding of alloy 1424 of the Al–Mg–Li–Zr system are considered with the purpose of obtaining the durability level of the welded joint, which is close to that of the basic metal. It is shown that, in the case of using various types of plastic deformation of the welded joint, its durability can be increased considerably to 0.85–0.95 from that of the basic metal.

Results of an experimental study of properties of joints obtained by using different regimes of laser welding of the 1424 alloy (Al–Mg–Li) are reported. The strength and structure of the welded joints are determined. The influence of various types of welded joint straining on its strength is studied. It is demonstrated that the joint strength increases in the case of plastic straining.

The quality of cutting of low-carbon and stainless steel by beams of fiber and CO2 lasers with oxygen or nitrogen being used as a process gas is compared. The cut surface roughness for sheets from 3 to 10 mm thick is determined. Domains of optimal (in terms of the minimum roughness criterion) application of lasers of various types in the space of dimensionless parameters (Peclet number and dimensionless power) are found. It is demonstrated that the CO2 laser is more effective for laser-oxygen cutting, while the fiber laser is more beneficial for cutting with the use of a neutral gas.

Results of an experimental study of the structure, the phase composition, and the mechanical properties of laser-welded joints of 3-mm thick titanium and 12Kh18N10T steel sheets obtained with the use of intermediate inserts and nanopowdered modifying additives are reported. It is shown that that such parameters as the speed of welding, the radiation power, and the laser-beam focal spot position all exert a substantial influence on the welding-bath process and on the seam structure formed. In terms of chemical composition, most uniform seams with the best mechanical strength are formed at a 1-m/min traverse speed of laser and 2.35-kW laser power, with the focus having been positioned at the lower surface of the sheets. Under all other conditions being identical, uplift of the focus to workpiece surface or to a higher position results in unsteady steel melting, in a decreased depth and reduced degree of the diffusion-induced mixing of elements, and in an interpolate connection formed according to the soldering mechanism in the root portion of the seam. The seam material is an over-saturated copper-based solid solution of alloying elements with homogeneously distributed intermetallic disperse particles (Ti(Fe, Cr)2 and TiCu3) contained in this alloy. Brittle fracture areas exhibiting cleavage and quasi-cleavage facets correspond to coarse Ti(Fe, Cr)2 intermetallic particles or to diffusion zones primarily occurring at the interface with the titanium alloy. The reported data and the conclusions drawn from the numerical calculations of the thermophysical processes of welding of 3-mm thick titanium and steel sheets through an intermediate copper insert are in qualitative agreement with the experimental data. The latter agreement points to adequacy of the numerical description of the melting processes of contacting materials versus welding conditions and focal-spot position in the system.

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.

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.

The results of studying products obtained using the laser ablation of a composite consisting of granular nanofibrous carbon impregnated by an organic-silicon compound—tetraethoxysilane-based alcogel—are presented. A continuous CO2 laser with a power of 0.6 kW was used as a radiation source; the radiation flux density was 3.4 W/cm2, the pressure in the reactor was 770–780 torr, and helium was used as the medium. The material, which was evaporated and gathered from the condenser surface and also taken from the target at the point of laser-beam impact, was studied using high-resolution electron microscopy on an electron microscope JEM-2010 with the application of local energy-dispersive X-ray microanalysis on an EDAX spectrometer. It has been found that the evaporated and condensed material contains nanostructures—nanorods ∼20 nm in diameter formed by transverse silicon carbide layers and covered by a layer of silicon dioxide. Silicon carbide particles about 15 nm in size are also revealed in the target material after its exposure to the laser beam.

Specimens of “titanium-titanium” and “titanium-12X18H10T steel” welded joints that were obtained using laser radiation were investigated. When “titanium-12X18H10T steel” welded joints were formed, a copper plate was used as the intermediate insert. The digital computer radiography method using phosphorous image plates was used to study specimens; images were read out from image plates using an HD-CR 35 laser reader produced by Durr NDT. Fuji SR and Kodak SO-170 image plates were used in the experiments. The relative contrast sensitivity of X-ray images of specimens that was obtained experimentally was 1–1.5% at exposures that were two to three times lower than for conventional radiography on an X-ray film. Defects with openings of > 0.1 mm were detected.

The characteristics of a free supersonic air jet with a diameter of 10 mm and Mach numbers within 1.7–3.7 have been studied in the presence of energy supply via pulsed optical discharge generated by a periodic-pulsed mechanically-Q-switched CO2 laser. The coefficient of laser radiation absorption by optical discharge plasma in supersonic air jet has been studied and it is established that this parameter can reach 60%. It is demonstrated for the first time that a threshold density of air corresponding to sharp growth in the absorption efficiency amounts to 1.8–2 kg/m3 and is independent of the Mach number in airflow. Distributions of the gasdynamic parameters (including dynamic pressure and temperature) in supersonic air jet with energy supply via optical discharge have been determined.

This paper presents the results of studies of carbon nanostructures obtained by the laser ablation of a nanofibrous carbon formed in the process of a catalytic decomposition of hydrocarbons in the presence of high-percentage catalysts containing the iron subgroup of metals. A continuous CO2 laser with a radiation density of 3.4 W/cm2 was used in the experiments. The target was placed on a cooled copper substrate in a helium medium under a pressure of 770–780 torr. Upon the impact of laser radiation, the carbon evaporated and, further, condensed on the surface of a special condenser. The samples were collected from the condenser surface and the target in the radiation-exposed area. The products were studied by high resolution transmission electron microscopy using a JEM-2010 electron microscope. A number of samples underwent a local energy dispersion X-ray microanalysis on the EDAX spectrometer. Multilayer nanotubes of diameters 14–40 nm and lengths of up to 2 μm have been found in the evaporated and condensed carbon materials. It was established that part of the nanotubes was filled by the catalyst metal. Interestingly, in the target area exposed to the radiation, the initial material comprising carbon nanofibers with the structure of inserted cones transformed into carbon nanotubes (CNTs) with an average cross-section size of 20 nm.

Results of experimental determination of the energy balance in oxygen laser cutting of sheets 5–16 mm thick by a CO 2 laser in the operation regime of high-quality cutting with the minimum possible degree of surface roughness are presented. Oxygen is used as an assisting gas. For sheets 5, 10, and 16 mm thick, the energy power fluxes, which are involved into the energy balance equation, normalized to the unit thickness of the sheet are found to be independent of the latter and to have close values.

We have experimentally proved the applicability of hot-wire anemometer method to measure fluctuations at low pressures and gas flow rates when medium is no longer considered as continuous. Use of individual calibration at working conditions serves to apply standard technique for determination of sensitivity coefficients of hot-wire probes. Additional investigations are necessary to take into account influence of Knudsen number and, possibly, other parameters in heat transfer law presented as criterial dependence of Nusselt number on Reynolds number. Hot-wire measurement of mean velocity distribution and their fluctuations in the flow-through path of electric-discharge CO2 laser have been performed. The level of velocity fluctuations in the vicinity of anode is high that is caused by the zone of interacting flows from the ventilators rotating in opposite directions forming in the symmetry plane. Placing of the damping screen between the ventilator and air gap allows decreasing fluctuations intensity to the acceptable level. It has been ascertained that the vortex shedding with high intensity of fluctuations which influence is noticeable in significant part of air gap is formed in the wake behind the streamlined cathode. However, pulsation level in the proper gap does not exceed permissible values.

Operation of the diametrical disc fan was studied experimentally at low (5–50 torr) pressures in air. The effect of a drastic decrease in volumetric flow rate of the fan was revealed at pressures below 40 torr (flow rate crisis), what does not correlate with published data. The critical value of dimensionless parameter corresponding to flow transformation and formation of a closed flow inside a fan was determined and proved experimentally.