Search

A new approach was developed to improve strength of Al-Cu-Mg alloy laser welded joints that typically within 61–90 % of that of the base metal due to a change in the microstructure and phase composition of the weld one. This result was achieved by optimization of post weld heat treatment (PWHT) included quenching and subsequent artificial aging. For the first time, the spatial distribution and evolution of the phase composition were studied at all PWHT stages using high-resolution scanning electron microscopy and synchrotron X-ray analysis. It was found that the Al-Cu-Mg solid solution was homogenized, as well as the S(Al2CuMg) strengthening and (partly) θ(Al2Cu) phases were formed. After PWHT, ultimate tensile strength was 428 MPa, yield strength was 302 MPa, and elongation was 19.6 %, which were 99 %, 98 % and 95 %, respectively, of those of the base metal.

The process of formation of a multilevel multilayer B4C – Ti-6Al-4V cermet coating by the method of SLM is studied. The coating is characterized by presence of heterogeneous zones differing in the mechanical properties. It is shown that the use of the B4C – Ti-6Al-4V powder mixture with ceramics concentration 20 wt.% is not expedient, because it causes deficit of the metallic matrix and formation of cracks. At 10 wt.% ceramics in the powder mixture with alloy Ti-6Al-4V the wear resistance of the coating increases by a factor of 4.2.

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.

Increasing performance requirements of advanced products demands new, versatile fabrication techniques. Additive technology represents one of the most prospective fields of future production. B4C-based composites were fabricated on titanium substrate by selective laser melting (SLM) using titanium (Ti-6Al-4V) and boron carbide (B4C) powder mixture at different weight ratio (Ti:B4C = 1:0, 9:1, 8:2, and 7:3). It was shown that the use of a powder mixture В4С + Ti-6Al-4V with ceramic concentration of more than 10% of weight led to formation of cracks. The microstructure of composites was studied by optical and electron microscopy. It was shown that a heterogeneous structure was formed with regular allocation of zones inside each layer. It was established that new chemical compounds (TiB, TiB2, TiC) absent in the initial powder mixture were formed in the new structure. A significant change in microhardness is shown (for sample without ceramics—372 HV0.3, for sample 10% В4С + 90% Ti-6Al-4V—from 548 to 4214 HV0.3). It was shown that the wear loss of B4C-free sample is approximately 4.2 times higher than that of the sample with 10 wt% В4С.

One of the most promising methods of spraying protecting coating is the laser coating with strengthening phases, alloying or modifying elements. The purpose of this study is the creation of composite wear and corrosion resistant coatings by additive technology of laser coating for oil and mining industries. The possibility of obtaining complex coating with a strengthening phase is shown. Two variants of coating were considered. Variant 1: support plate made of 12Х18Н10Т stainless steel was cladded with sublayer made of Ni + Cr powder, afterwards the upper cladding layer made of Х23Н5М3ГС steel of Cr-Ni-Мn system was formed with various content of strengthening WC phase in the form of VK-12 powder. Variant 2: support plate made of carbon steel was cladded with four layers of self-fluxing cladding powder PS-12NVK-01 of Ni-Cr-Fe / WC system with addition of nanomodification of powder TiN + Y2O3 + Cr + Fe. The specialists established the dependence of microstructure, structural-phase components and micro hardness of cladded layer from the quantity of WC strengthening phase. The various content of WC strengthening phase (from 10 to 30 %) does not influence the micro hardness of the upper layer significantly – it’s average value is ≈ 700 HV The laser influence on powder mixture leads to partial deterioration of WC strengthening phase, which leads to chemical reaction of tungsten cobalt powder and stainless steеl with formation of complex intermetallic compounds and carbides. Small addition of nanosized modifier TiN + Y2O3 (0,1 % of weight) in a composite mixture with coating power PS-12NVK-01 allows increasing the hardness of protective coating by 1.4, and wear-resistance – by 2 times in comparison to the coatings with similar characteristics, obtained without nanomodifying additions.

This paper presents the results of studies of dissimilar butt laser welds of a thermally strengthened aluminum-lithium alloy of the Al-Cu-Li system and a titanium alloy of the Ti-Al-V system. The main variable parameter was the laser offset relative to the joint. Microstructure of the weld metal, the results of tensile tests as well as fractography of the fracture surfaces were shown. It was found that the microstructure of the aluminum alloy was of the dendrite type, and that of the titanium alloy was martensitic. An intermetallic layer was formed between them. The offset towards the titanium alloy plate reduced the thickness of the intermetallic layer from ∼400 μm (offset was 0) down to 2.5 and 0.7 μm (offset was 0.5 and 1.0 mm, respectively). Also, the transformation of its structure from brittle to ductile was observed. The ultimate tensile strength of the joints increased from 103 MPa (offset was 0) up to 213 and 272 MPa when offset was 0.5 and 1.0 mm, respectively. When offset was 1 mm, the weld metal failure occurred predominantly through the aluminum alloy. This indicates that the ultimate tensile strength of the intermetallic layer was higher than that of the Al-Cu-Li alloy. It is most likely that the mechanical properties of the intermetallic layer substantially depended on the composition of the alloying elements of the aluminum alloy.

Technological modes of laser welding is perfected and structural and phase features of the fusion zones structure (ZC) and thermal influence (ZTI) on low carbon steel tube 10G2FBYu is studied. Mart...

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.

A metal-matrix composite based on Ti-6Al-4V – B4C with TiB, TiB2 and TiC inclusions was successfully obtained as a result of in-situ synthesis using repetitively pulsed laser radiation. For the first time, the phase composition of the obtained metal-matrix composite was studied using synchrotron radiation. A comparison of the effect of using continuous and pulsed-periodic radiation in selective laser melting on the microstructure and mechanical properties of coatings was made. The use of repetitively pulsed radiation made it possible to form more uniform structures and to improve the mechanical properties of metal-matrix coatings in comparison with the continuous mode of exposure. It has been established that the use of repetitively pulsed radiation and the formation of TiB2, TiB, TiC phases made it possible to increase the wear resistance of the formed composite by a factor of 6 in comparison with the Ti-6Al-4V metal coating.

This paper explores the structure and phase composition of laser welded joints of Al-Cu-Li alloy without and after post heat treatment (annealing, quenching, and artificial aging). Changes in the structure and phase composition of welds and the base alloy before and after heat treatment are studied using scanning electron microscopy, X-ray diffractometry, and synchrotron radiation diffraction. The investigation results have shown that the formed agglomerates of intermetallic particles are mainly represented by the Т1(Al2CuLi) phase. The change in the strength of the Al-Cu-Li alloy samples after laser welding and heat treatment is not due to the absence or presence of the strengthening Т1(Al2CuLi) intermetallic phase but rather due to the different localization of particles of this phase in the weld joint. The segregation of the phase at dendritic grain boundaries leads to a significant strength decrease, and, vice versa, its homogeneous distribution in the solid solution achieved by post heat treatment (annealing, quenching, and artificial aging) increases the strength of the laser welded samples.

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 work aims to study the effects of post heat treatment by quenching and artificial aging on the mechanical characteristics (strength, microhardness) and microstructure of laser welded joints of aluminum alloy V-1461 of the system Al-Cu-Li. Heat treatment regimes were identified in which the tensile strength, yield strength, and relative elongation of the welded specimens are respectively 92%; 91%, and 88% of the base alloy characteristics.

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.

The technological test bench has been developed and manufactured to perform the laser welding with a filler wire. Effective control of the laser radiation characteristics has been researched, and the methods of the optimal supply of the laser beam into the welding zone of the alloy 1420 with the filler wire AMg6 have been found. The optimal modes of the laser welding with and without wire have been found; they provide the X-shaped butt-end defect-free welded joint. The mechanical characteristics have been measured, the microstructure of the resulting welded joints has been studied.

The study investigates the structure and mechanical properties of laser welded X80 pipeline steel. It is found that the fusion zone has a dendritic martensite structure, and the heat affected zone exhibits ferrite-bainite structures. The fine-grained heat affected zone has a small fraction of granular bainite and regions of degenerate upper bainite consisting of parallel bainitic ferrite laths separated by martensitic-austenitic constituents and twinned martensite plates. The laser welded joint is shown to have the strength and ductility characteristics at the level of the base material. Despite an ≈2-fold decrease in the impact toughness KCV of the welded samples in comparison with the base material, the weld material demonstrates high KCV values (KCV–70°C = 170 J/cm2).

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.

The paper deals with the analysis of the effect of the thermal mechanical processing on the mechanical characteristics (elasticity and tensile strength) of the welded joints of the aluminum alloy, the system Al-Mg-Li. The microstructures of the basic alloy and welded joint before and after the thermal processing are compared by electronic microscoping. The X-ray diffraction method is used to compare the phase composition. The concentration of the strengthening phase δʹ(Al3Li) reduces in the welded joint, which results in the low mechanical characteristics. The thermal processing, namely quenching, increases the concentration of the equilibrium S1 phase (Al2MgLi) in the welded joint as compared with an unquenched joint. The elasticity of the welded joint rises significantly at the almost constant strength, the value of the relative extension lies within the range of 2.4 – 19.2 % before and after quenching, respectively. Artificial ageing applied to the welded joint after the quenching gives the structurization of the S1 phase. The full thermal mechanical processing (quenching, elastic deformation, artificial ageing) of the welded joint of the aluminum alloy (the system AL-Mg-Li) results in the tensile strength increase up to 0.95 of the basic alloy strength.

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 paper pioneers the complex experimental investigation of the metal-ceramic coating made by the additive technologies, the combination of the cold gas-dynamic spraying (CS) and following layered laser processing. The coating is made of ceramic powders WC and B 4 C, the concentration in the initial mixture of 10-70 wt.%, and metal powders based on Ti+Al, the ratio 94:6 wt.%, and Ni. The result is the strategy of the production of the heterogeneous material without pores and cracks by the consequent deposition of the powder by the CS method followed by the laser action; the thickness of the coating is 4 mm.

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 paper presents the investigations of the shape of single tracks formed by the laser cladding method and distribution of ceramic particles in them. The laser effect on the powder mixture was optimized, which resulted in the formation of pore-free clad tracks. We have found that the initial concentration of ceramics in the powder mixture influences intensively on the track geometrical shape. It is demonstrated that at the higher ceramics concentration in the clad powder, ceramic particles are oriented over the track edges.

The results of an experimental study of laser cutting of aluminum-lithium alloys using a repetitively pulsed CO2 laser with Q-switching under conditions of intense material evaporation are presented. The dependence of cut quality on the assisted gas pressure is determined. It is shown that a high-quality cut with a sheet thickness of 1.5 mm can be obtained at a gas pressure of 0.5–0.6 bar, which is significantly less compared to cutting with a continuous laser power. This makes it possible to reduce the assisted gas consumption. The dependence of cut surface roughness on the pulse repetition rate is measured.The results of an experimental study of laser cutting of aluminum-lithium alloys using a repetitively pulsed CO2 laser with Q-switching under conditions of intense material evaporation are presented. The dependence of cut quality on the assisted gas pressure is determined. It is shown that a high-quality cut with a sheet thickness of 1.5 mm can be obtained at a gas pressure of 0.5–0.6 bar, which is significantly less compared to cutting with a continuous laser power. This makes it possible to reduce the assisted gas consumption. The dependence of cut surface roughness on the pulse repetition rate is measured.

The paper presents a series of experimental works for the optimization of the thermal post-treatment process (quenching and artificial ageing) of the laser welding joints of aluminum-lithium alloy 1420 (the system Al-Mg-Li) by the temperature and time characteristics, in order to find the breaking stress, yield limit and ultimate tensile strain approaching to the respective characteristics of the main alloy, or equal to them. Low-cycle tests have been done with the thermally-treated welding joints for the pulsing stretching at various loading amplitudes at the temperatures of –60, +20, +85°С. The surface structure of ruptured welding joints with and without thermal treatment has been studied after low cycle tests at various loading amplitudes at the increased and decreased temperatures.

The present paper studies the effect of the laser radiation on geometrical and mechanical characteristics of formed tracks using the powder mixtures based on nickel alloys (60 weight % NiCrBSi) and tungsten carbide (40 weight % WC). It has been found that the mode of laser radiation highly influences the shape and mechanical characteristics (the keyhole mode or thermal-conductivity mode) in respect to the surface of the initial layer of the powder mixture. It is demonstrated that in the clad track at the thermal-conductive mode (the focusing mode Δf = ±20), the uniform distribution of ceramic parts is observed, and the maximal microhardness value is registered. It is found that the clad metal-ceramic structure has 4 – 5 times higher value of microhardness 850.4 HV0.1 than the substrate 178 HV0.1.

The effect of assist gases (argon or air) on the quality of edge surfaces of aluminum alloys cut with a pulsed Q-switched CO2 laser was experimentally investigated. Sheets of both Al-Mg-Li and Al-Cu-Li alloys with thicknesses of 1.5 and 2.0 mm were cut. It was found that the morphologies of the cut-edge surfaces were significantly different after cutting with argon and air. For the first time, the cutting process was carried out using a laser-plasma mode, when an optical discharge was maintained in an argon flow. At an argon pressure of 0.5 bar, the cut-edge surfaces were without dross and their roughness were significantly lower than that after cutting with a continuous wave laser. Severance energy levels were similar for both laser-plasma and continuous wave cutting modes.

The purpose of these investigations was to study the effect of heat treatment on the structure and the phase composition of laser welded joints of the Al-2.8Cu-1.7Li alloy (V-1461 grade), providing the maximum tensile strength. To study the phase composition of the weld metal, synchrotron radiation was applied using a ‘Mega Science’ facility. This enabled to assess the phase distribution across the weld metal before and after heat treatment. It was found using high-resolution scanning and transmission electron microscopy, energy dispersive X-ray analysis, and synchrotron X-ray diffractometry that the T1(Al2CuLi) and T2(Al6CuLi3) main phases had been formed in the weld metal and at the interfaces with the matrix. Ultimate tensile strength of the welded joints was about 341 MPa, which was 62% of that of the base metal. Subsequent heat treatment of the welded samples, included hardening and artificial aging, caused the homogenization of the Al–Cu–Li alloy solid solution, as well as the formation of the δ′(Al3Li) hardening phase. Also, the T1 and T2 phases were formed partially. After quenching, tensile strength of the welded joints improved and was about 85% of that of the base metal. After artificial aging, it was about 510 MPa and approached tensile strength of the base metal (93%).

The paper presents the analysis of the structural and phase composition by the methods of electronic microscopy, X-ray diffraction analysis and synchrotronic radiation of the laser welded joints for the Al-Li alloys of the systems Al-Cu-Li and Al-Mg-Li without and after the post thermal treatment. It is shown that during the welding, strengthening phases dilute in the solid solution of the welded joint, and, in the case of Al-Cu-Li alloys, they concentrate over the dendrite boundary. The optimal post heat treatment restores the structural phase composition and mechanical properties of the weld.

In this paper, the heat affected zone (HAZ) of laser welded joints of the X70 steel were studied by the transmission electron microscopy method. The effect of the initial microstructure (coarse-grained hot-rolled and fine-grained after cross-helical rolling) on the HAZ formation and the mechanical characteristics of the welded joints were shown. It was found that the microstructure in the inter-critical HAZ of the steel after cross-helical rolling was more dispersed, homogeneous, and uniform compared to that of the coarse-grained hot-rolled one due to the initial fine-grained ferrite-bainitic-pearlite microstructure and the absence of pronounced ferrite-pearlite banding in the base metal. The character of the microhardness value distribution in the HAZ of the steel after cross-helical rolling was smooth with the gradual decrease from 370 down to 185 HV as shifted towards the base metal. In the HAZ of the coarse-grained hot-rolled steel, the heterogeneous microhardness value (up to 640–670 НV) distribution was revealed. The reason was the upper degenerate bainite microstructure with high residual stresses, characterized by laths up to 2.0–2.5 μm long and a high martensitic-austenitic constituent fraction (10–16%) of a slender shape along the boundaries of bainite laths. The conclusion was drawn that one of the ways to reduce the brittleness of the laser welded joints could be using the initially fine-grained steels possessing the homogeneous (mainly bainitic) microstructure.

Characteristics of craterlike structures on the laser cut surface and their dependence on surface roughness are experimentally studied for sheet thickness of 3-16 mm. The crater size and the number of craters increase with the sheet thickness. The dependence of the number of craters on the cutting velocity is nonmonotonic and has a peak. This peak is observed at an optimal cutting velocity, which ensures the minimum roughness of the cut surface. A qualitative explanation of the observed phenomena is proposed.

The paper deals with the optimized laser welding of heterogeneous materials based on titanium and aluminum-lithium alloys. The tensile strength of resulting joints has been measured. The micro-structure of the surface of welded joint fracture has been studied. The tensile strength of the welded joint reaches 250 MPa.

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.

The work presents the experimental investigation of the laser welding of the aluminum-lithium alloys (system Al-Mg-Li) and aluminum alloy (system Al-Cu-Li) doped with Sc. The influence of the nano-structuring of the surface layer welded joint by the cold plastic deformation method on the strength properties of the welded joint is determined. It is founded that, regarding the deformation degree over the thickness, the varying value of the welded joint strength is different for these aluminum alloys.

Production of welded bimetallic structures of titanium and steel using a laser beam is a very urgent and important task in the shipbuilding, airspace and power engineering. Laser welding using an intermediate insert is one of the ways to solve this problem. In this paper, we present the results of experimental studies of formation of the structure and properties of composite insert, obtained by explosion welding, after its application at laser welding steel with titanium. A study of a four-layer composite insert obtained by explosion welding showed that it has no brittle intermetallic phases and defects in the form of cracks and pores. The boundaries between the plates to be welded in the composite insert have a characteristic wavy structure with narrow zones of mutual diffusion penetration of elements of the adjacent metals. It is established that the strength of the composite insert is comparable with the maximum strength of Grade 4 alloy, and the destruction of the product during the tensile tests in m...

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.

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.

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.