Introduction. Spheroidal graphite (SG) iron is widely used in engineering structures due to its high mechanical properties, which are largely determined by the degree of spheroidization (nodularity) of the graphite inclusions. Conventional metallographic evaluation of nodularity provides high accuracy but is a destructive and time-consuming procedure. Therefore, there is a need for a reliable non-destructive approach for rapid quality assessment of castings, especially in small-batch foundry production. The purpose ofthis work is to develop a methodological framework for predicting nodularity and mechanical properties of SG iron castings based on ultrasonic testing. Methods. Castings of three SG iron grades (SGI400/12, 500/7, and 600/3) were manufactured according to a Taguchi L27 experimental design. The controlled process parameters were: pouring temperature (1,380-1,420 degrees C), carbon equivalent (4.0-4.6), and section thickness (5-15 mm). Ultrasonic testing was performed using a flaw detector with a 4 MHz transducer to measure the longitudinal ultrasonic wave velocity in the samples. Nodularity was determined from the ultrasonic measurements using the instrument's internal calibration and the corresponding velocity relationship. Ultimate tensile strength (UTS, 6u) and Brinell hardness were determined by standard mechanical testing methods. Multiple linear regression models were developed relating the process parameters and ultrasonic velocity to nodularity, UTS (6u), and hardness. Results and Discussion. The developed models demonstrated high predictive capability, with coefficients of determination of R2 = 0.8955 for nodularity, R2 = 0.9954 for UTS (6u), and R2 = 0.8135 for hardness. Carbon equivalent was identified as the most significant parameter affecting all responses. Ultrasonic velocity showed a clear positive correlation with nodularity and mechanical properties. Validation using metallographic analysis confirmed good agreement with ultrasonic predictions, with deviations within 2-3%. The study demonstrates that ultrasonic velocity can be effectively used to predict the microstructural and mechanical characteristics of SG iron. The developed regression models provide a simple and practical tool for non-destructive evaluation, ensuring rapid quality control in foundry production, especially for small-scale enterprises.
Traditional welding methods are rarely used to join such material pairs due to their tendency to form brittle intermetallic compounds. One of the main parameters determining the quality of the weld is the impact angle gamma. The aim of the work is to study the influence of the impact angle on the temperature-strain characteristics in the joint zone during high-velocity impact of aluminum 1050A and steel 321 plates using numerical simulation. Research methods. The smoothed particle hydrodynamics (SPH) method implemented inAnsysAutodyn 2020 R2 software was used for the simulations. In all calculations, the contact point velocity was constant at Vc = 2,500 m/s, and the impact angle varied (9.5 degrees, 12 degrees, 14.5 degrees). The Mie-Gr & uuml;neisen equation of state and the Johnson-Cook constitutive model were used to describe the properties of the materials. Results and discussion. It was found that an increase in the impact angle leads to higher pressure, temperature, and plastic strain. Specifically, temperature and plastic strain increase monotonically with gamma, whereas pressure varies non-monotonically, reaching a peak of 8.87 GPa at gamma = 12 degrees. At gamma = 12 degrees, the most uniform interface is formed, and at gamma = 14.5 degrees, an asymmetrical interface with the penetration of steel into aluminum is observed. All studied impact conditions result in local melting of aluminum while keeping the steel solid. The most favorable of the investigated impact angles, which provides a beneficial combination of pressure, temperature, and interface morphology for the 1050A/321 system at a speed of 2,500 m/s, is 12 degrees.
Introduction. Friction stir processing (FSP) is recognized as a promising method for surface layer modification of structural copper-based alloys; however, the high thermal conductivity of this class of materials significantly complicates thermal cycle management and, consequently, microstructural control. The present work is devoted to a systematic study of the effect of controlled heat removal-both air cooling and water cooling-during single-pass FSP on the structural-phase state and the resulting mechanical properties of a series of commercial copper alloys. The purpose of the study is to establish the relationship between the intensity of forced cooling, the thermophysical properties of the alloys, and the resulting grain morphology in the stir zone, which determines the level of service properties of the processed materials. Methods. The following alloys were selected as research objects: 89 Cu-9 Al-2 Mn, 93.35 Cu-6.5 Sn-0.15 P, 96 Cu-3 Si-1 Mn, and 63 Cu-37 Zn. FSP was performed in a single pass on a specialized experimental setup at ISPMSSBRASusing atool fabricated of the nickel-based superalloy ZhS6U. Active heat removal was realized by immersing the workpiece in flowing water, circulating coolant through the tool body, and directing a water jet into the contact zone; compressed air blowing was used as an alternative cooling scheme. Macro-and microstructure were investigated using optical metallography, scanning and transmission electron microscopy, X-ray diffraction analysis, and energy-dispersive spectroscopy. Mechanical properties were determined by Vickers microhardness measurements and uniaxial quasi-static tensile testing. Results and Discussion. It was established that, in all studied alloys, FSP leads to the formation of a recrystallized fine-grained structure with predominantly equiaxed grain morphology. The best process stability and the most pronounced strengthening were achieved for aluminum bronze 89 Cu-9Al-2 Mn and brass 63 Cu-37 Zn: microhardness, and ultimate tensile strength for 89 Cu-9Al-2Mn increased by 7, and 12%, respectively, and for 63 Cu-37 Zn increased by 22, and 4%, respectively, compared to the initial condition of the alloys. It was revealed that the higher thermal conductivity of the alloys necessitates an increase in axial tool force, which expands the shoulder-affected zone and forms a wide stir zone. A pronounced grain size heterogeneity along the stir zone thickness was observed: in alloys with lower thermal conductivity under water cooling, the grain size near the root of the processed zone exceeded that near the top surface by a factor of up to 16, which is explained by differences in the rate of recrystallization arrest. Higher thermal conductivity promotes the formation of a more homogeneous grain structure, especially in the absence of forced water cooling.
Introduction. The wear behaviour of physical vapour deposition (PVD) hard coatings is difficult to predict because of the nonlinear relationship between coating chemistry, deposition thickness, operating temperature, and applied contact load. Multi-dimensional parameter mapping through exhaustive experimentation is both timeconsuming and costly. The purpose of the work is to implement a low-data hybrid architecture that combines Taguchi design, response surface methodology (RSM), and machine learning (ML) to predict and optimize wear performance based on a small dataset (n = 28). Methods. Three coating types-AlTiN, CrN, and TiC-were tested at temperature range of 40-50 degrees C, contact load range of 5-15 N, and coating thickness range of 2-4 & micro;m. Analysis of variance (ANOVA) was performed to identify the most influential parameter affecting wear. A predictive wear model was developed using response surface methodology. Results and discussion. ANOVA revealed that load and coating chemistry are the most influential factors affecting wear. Temperature and thickness were not found to be significant within the studied range. ARSM model was found statistically significant for predicting contact load and coating chemistry with R2 = 0.901 (Adj-R2 = 0.834, RMSE = 0.0076). Random forest (RF) had highest generalisation performance (CV R2 = 0.755) and gradient boosting (GB) had the best foverall fit (R2 = 0.913) among the ML models tested using five-fold cross-validation. SHAP analysis indicated that coating chemistry formed the major contribution, then contact load, and little temperature contribution. Gradient boosting optimisation indicated that AlTiN at 4 mu m thickness, 15 N load and 50 degrees C are the preferred settings and the expected wear rate is 0.010823 (mm3/Nm). The proposed framework demonstrates credible, interpretable wear forecasting using limitted experimental data.
Introduction. One of the key trends in modern mechanical engineering is the development of hybrid machine tool equipment that integrates mechanical and surface-thermal technological operations within a single machine platform. In the context of the Industry 4.0 paradigm and increasing demands for precision, productivity, and equipment multifunctionality, combined electrodiamond grinding (CEDG)-which combines mechanical cutting by diamond grains with electrochemical action on both the tool and the workpiece-is of particular relevance. Grinding of high-strength composite materials based on zirconium diboride (ZrB2) under conventional conditions leads to intensive clogging of metal-bonded diamond wheels and a critical loss of their cutting ability, rendering the conventional process inefficient. Despite existing results in the field of electro-diamond machining, the issues of stage-by-stage formation of the cutting relief on the wheel working surface under continuous electrochemical dressing, the mechanisms of oxide film formation on bond elements, and their functional role as solid lubricants in the contact zone remain insufficiently studied. The purpose of this work is to establish the formation mechanisms of the surface layer of a metal-bonded diamond wheel under continuous electrochemical dressing with simultaneous electrochemical anodic dissolution of the stock allowance during combined grinding of a ZrB2-based composite material, and to substantiate the prospects for integrating this technology into the concept of hybrid machine tool equipment. Methods. Experiments were conducted on a modernized PP-600F surface grinding machine equipped with two independent electrical circuits: a continuous electrochemical dressing circuit (current density 0.1-0.6 A/ cm2) and an anodic dissolution circuitfor stock removal (current density 15-30A/cm2). Diamond wheels AC6125/100M1-100%on a copper-zinc-aluminum bond were used as the tool. The working medium was a nitrite-nitrate electrolyte (3%NaNO3, 1%NaNO2, 0.5%Na2CO3). Mechanical parameters: cutting speed 35 m/s, longitudinal feed 0.5-2.5 m/min, depth of cut 0.01-0.04 mm. Surface topography of the wheel and workpiece was investigated by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). Results and Discussion. It is established that continuous electrochemical dressing ensures selective anodic dissolution of the metal bond components (primarily aluminum, copper, and zinc), forming a stable cutting relief with exposed diamond grains and intergranular cavities for electrolyte and debris accommodation. It is shown that under simultaneous operation of the dressing and workpiece etching circuits, oxide films form on the diamond grain surfaces and bond elements, functioning as solid lubricants and reducing the intensity of adhesion-diffusion interaction in the contact zone. Implementation of additional electrochemical weakening of the stock allowance reduces cutting forces and contact temperatures, preventing deformation damage to the workpiece surface layer. It is substantiated that the developed CEDG technology constitutes a technological basis for designing hybrid machine tool equipment integrating mechanical and electrochemical actions, meeting modern requirements for modularity, adaptability, and digital control. The obtained results contribute to the formation of a theoretical and methodological framework for designing next-generation hybrid metalworking systems.
Introduction. The key obstacle to the development of "smart" mechanical engineering enterprises and the implementation of untended technologies lies in the "digital divide" (i.e., the gap between fully digitized process planning and the empirical setting of tool coordinates) during the dimensional setting of CNC machine tools. The design contour of pre-production engineering (PPE) has been completely digitized, but tool setup coordinates are still calculated empirically using trial runs because there is no theory describing the behavior of the non-stationary tolerance zone for a batch of workpieces in the absolute coordinate system of the machine. Objective. To theoretically substantiate the existence and uniqueness of the absolute coordinate of a cutting tool, guaranteeing that every workpiece in the batch, starting from the very first one, is machined within tolerance under the influence of multicomponent errors. Methods. The study is based on the systems analysis of technological dimensional chains and elasticity theory. The key methodological approach is axiomatic; four basic axioms are formulated (on the batch of parts, stationarity of the machine coordinate system, non-stationarity of the tolerance zone, and the generation of geometry). These axioms serve as the foundation for rigorous proofs of subsequent theorems. Results. Based on the adopted axioms, a theorem on the existence of a stationary "0-0 boundary" in the CNC coordinate system was formulated and proven for the first time. This boundary serves as a stationary reference datum linking the position of the non-stationary tolerance zone with the rigid machine coordinate system. Its uniqueness as a condition for minimum guaranteed stock removal is proven. An equation for the balance of tolerance and multicomponent errors is derived, which is a fundamental condition for process feasibility. An "accuracy life" criterion is introduced and justified to quantitatively evaluate the safety margin of the technological system and to limit cutting parameters. Scientific novelty. For the first time, the existence of an absolute setting coordinate has been analytically proven based on a system of axioms formalizing the non-stationarity of the tolerance zone and the rigidity of a CNC system. It is shown that the "0-0 boundary" is the only point that guarantees process determinism under parametric uncertainty. Practical significance. The developed theory provides a methodological basis for creating digital twins of operations and intelligent CAM modules that automatically calculate setting parameters. This eliminates trial machining cycles, reduces the time required for the production process, and paves the way for the implementation of untended technologies in small-and medium-scale production.
Introduction. The paper is devoted to the selection and justification of rational geometric parameters for the contact surface of an annular roller used in line-by-line surface plastic deformation (SPD). The relevance of this work stems from the need to enhance the service performance of machine components while ensuring high surface quality and processing productivity. The purpose of the study is to determine a tool working profile geometry that provides maximum hardening depth and compressive residual stress levels with minimal distortion of the surface microgeometry under conditions of overlapping single deformation tracks. Methods. To solve the formulated problem, the finite element method (FEM) implemented in the ANSYS Workbench software package (Transient Structural module) was employed, using a bilinear isotropic hardening model for Steel 45 (AISI 1045). A comparative analysis of three roller profile types was performed: convex (toroidal), concave (profiled), and straight (cylindrical). During the computational experiment, the tool profile radius and the circular feed step were varied. The efficiency was evaluated based on the criteria of hardened layer depth, residual stress magnitude, and the height of plastic pile-up at the boundaries of adjacent processing tracks. Results and Discussion. It is established that the rational profile radius for the toroidal profile is 5.0 mm, and for the profiled roller - 15.5 mm. The disadvantages of the basic geometries are identified: the toroidal roller provides a hardening depth of 1.15 mm but requires small feeds (resulting in low productivity); the profiled roller allows for increased feed, but the hardening depth decreases to 0.91 mm. It is shown that the use of a modified cylindrical profile with fillet transitions enables the effect of "controlled constraint" of plastic deformation. This geometry ensures the formation of a uniform hardened layer with a depth of 1.02 mm, residual stresses of 300-320 MPa, and a micro-irregularity height of 2-5 mu m. Conclusions. The application of the developed tool makes it possible to increase the productivity of the SPD process by 5 times compared to the toroidal roller without loss of surface layer quality. The obtained results can be recommended for the design of technological tooling for the finishing and hardening treatment of critical machine components operating under cyclic loads.
Introduction. Mechanical alloying (MA) combined with spark plasma sintering (SPS) is widely used for the fabrication of high-entropy alloys (HEAs). The combination of MA and SPS effectively suppresses grain growth, largely preserving the structure obtained after mechanical activation. This enables the production of HEAs with unique properties. In this study, HEAs of the AlFeCoCrNiNbx system (where x is the molar fraction, x = 0, 0.25, 0.5, and 0.75) were fabricated by MA for 40 hours followed by SPS at 1,000 degrees C. The purpose of this work is to investigate the effect of Nb content on the microstructure and properties of the AlFeCoCrNiNbx high entropy alloy obtained via the combined MA and SPS method. Methods. Both initial powders and sintered samples were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). Microhardness and compressive properties were evaluated, and the resulting fracture surfaces were analyzed. Results and Discussion. During MA, a solid solution with a BCC lattice and a nanoscale substructure was formed in the powder of all AlFeCoCrNiNbx alloys. Alloying with a significant fraction of niobium led to the formation of a small amount of the strengthening Laves phase. Subsequent SPS promoted a phase transformation, resulting in approximately equal volume fractions of a BCC solid solution enriched in Al and Ni and an FCC solid solution enriched in Fe and Cr. Heating facilitated the precipitation of the Laves phase as secondary grains within the BCC solid solution grains. Increasing the Nb content in the alloy led to an increase in the fraction of the Laves phase. Evaluation of the mechanical properties showed that the highest plasticity is characteristic of the AlFeCoCrNi alloy; the highest strength, of the AlFeCoCrNiNb0.25 alloy; the highest hardness, of the AlFeCoCrNiNb0.75 alloy, which is attributed to the specific microstructural features and the fraction of the Laves phase in the alloy.
Introduction. Nickel-based alloys such as Inconel 625 are widely used in the aerospace industry due to their high heat resistance and corrosion resistance. However, their machining is complicated by the low thermal conductivity of the material, its tendency to work hardening, and accelerated tool wear. The advent of additive technologies makes it possible to obtain blanks close to the final shape, but the machinability of such materials has not been sufficiently studied, especially taking into account the anisotropy of properties caused by synthesis conditions. In this regard, the study of cutting forces, the explanation of chip morphology, and the description of the causes of tool wear during milling of additively manufactured Inconel 625 is an urgent task. Methods. The samples were obtained by electron beam additive manufacturing (EBAM) from Inconel 625 wire. Milling was carried out with uncoated cemented carbide end mills. The cutting forces were recorded using a three-component dynamometer Kistler mod. 9257BA. The microstructure, chip morphology, and tool wear were studied by scanning electron microscopy using energy-dispersive analysis and X-ray diffraction analysis. Results and discussion. It has been found that in conventional milling, the cutting forces increase linearly with increasing feed rate. The cutting speed of 23.8 m/min reduces cutting forces compared to 11.9 m/min, but leads to an increase in chip length and deterioration of its removal. Machinability anisotropy is revealed: the cutting forces along the synthesis direction exceed the corresponding values when milling transversely across, which correlates with a higher yield strength in the longitudinal direction. The chip length increases with increasing feed rate and cutting speed, reaching 1.55 mm under maximum conditions, while the chips lose their coiled shape and become cracked. The dominant wear mechanism is adhesion-fatigue wear, confirmed by the presence of WC particles on the rake surface of the chips and the formation of Cr23C6 and NiW phases on the cutting edges. Oxidative wear does not play a significant role. X-ray diffraction analysis showed a decrease in the initial crystallographic texture in the chips and on the machined surface, as well as a broadening of the peaks, indicating severe plastic deformation. Conclusions. Rational milling parameters have been determined (cutting speed from 11.9 to 23.8 m/min, feed rate of no more than 200 mm/min, depth of cut up to 1 mm, width of cut up to 7 mm), ensuring tool operability. An increase in the feed rate to 250 mm/min leads to catastrophic failure of the cutting edges. The results obtained can be used to develop technological recommendations for the subtractive machining of parts made of additively manufactured Inconel 625 (EBAM).
Introduction. To extend the service life of components exposed to abrasive particles during operation, wear-resistant coatings are applied to their working surfaces using powder spraying or various surfacing methods. One of the simplest and most accessible surfacing techniques is arc surfacing in air. To improve the productivity of this process, flux-cored wire is used instead of stick electrodes. Subject. This paper describes the technology for producing a composite powder for flux-cored wire manufacturing, and presents the equipment used for wire fabrication and arc coating surfacing. The purpose of the work is to investigate a composite powder synthesized from a mechanically activated mixture of ferrotitanium (FeTi35Si5) and carbon black (soot), as well as the wear-resistant coatings deposited by arc surfacing onto a steel 0.09 C-Mn-2 Si substrate using a low-carbon steel 0.08 C-Al wire with a composite powder core. Methods. The powder and the arc-surfaced coatings were characterized by optical metallography, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) for elemental composition analysis, and X-ray diffraction (XRD). The surfaced coatings were tested for abrasive wear according to GOST 23.208-79, and the microhardness of both the powder and the coatings was measured. The composite powder used as the core filling in the flux-cored wire was obtained by crushing sintered cakes - the products of reaction synthesis in a mechanically activated powder mixture offerrotitanium (FeTi35Si5) and carbon black, processed in an Activator-2S ball mill. Specialized equipment was used for flux-cored wire fabrication and for electric arc surfacing. Results and Discussion. According to XRD analysis, the powder synthesized from the mechanically activated ferrotitanium-carbon black mixture contains two phases: titanium carbide (TiC) and alpha-iron (ferrite). Metallographic examination revealed that the synthesized powder exhibits a structure characteristic of an iron-matrix composite reinforced with nanosized carbide particles. The coating surfaced using the flux-cored wire has the same phase composition, but with a reduced titanium carbide content. The coating features a martensite-like microstructure, exhibits 4.5 times higher hardness and 2.5 times higher abrasive wear resistance compared to a coating surfaced with a solid 0.08 C-Al steel wire (without powder filling). Conclusions. Electric arc coatings surfaced with flux-cored wire filled with an iron-matrix composite powder exhibit high hardness (6,629 +/- 498 MPa) and abrasive wear resistance (158 +/- 11 mg/h) due to the martensitic structure of the surfaced layer, which is additionally reinforced by micron-sized titanium carbide particles. During surfacing, the submicron titanium carbide particles present in the composite powder structure undergo complete dissolution, enriching the weld pool with carbon and promoting martensitic transformation upon cooling.
Introduction. The development of a new class of non-magnetic corrosion-resistant materials with constant elastic properties over a wide temperature range - i.e., exhibiting Elinvar effect - is a pressing challenge in the transition to advanced intelligent manufacturing technologies and robotic systems. To address this challenge, it is necessary to develop a process chain for producing ingots of stable (3-titanium alloys with Elinvar effect. Achieving a stable recrystallized structure of the alloys over a wide temperature range also appears promising. Such advances will enable the use of this class of materials in the fabrication of elastic elements intended for oscillatory measuring systems in aerospace and other high-tech applications. Purpose. This study aimed to investigate the feasibility of producing a recrystallized (3-phase structure in Ti-Nb-Zr, Ti-Nb, and Ti-Mo alloys exhibiting a new type of Elinvar behavior using thermomechanical processing methods. To achieve this purpose, the following tasks were accomplished: (1) production of ingots of stable p-titanium potentially Elinvar alloys Ti-22Nb-15Zr, Ti-4ONb, Ti-45Nb, Ti-5ONb, Ti-12.6Mo, Ti-15Mo, and Ti-2OMo (at.%); (2) development of a processing sequence capable of forming a recrystallized equiaxed (3-phase structure without traces of other phases, given that the new type of Elinvar behavior is structurally insensitive; and (3) investigation of the structural and phase state of alloys with potentially natural Elinvar behavior, and elucidation of the relationship between grain size and alloying element content. Methods. The objects of the study were ingots of Elinvar alloys Ti-22Nb-15Zr, Ti-4ONb, Ti-45Nb, Ti-5ONb, Ti-12.6Mo, Ti-15Mo, and Ti-2OMo (at.%). The ingots were smelted in an electric arc furnace with a tungsten electrode. The samples were then subjected to thermomechanical processing according to the following schedule: longitudinal hot rolling (true logarithmic strain e = 0.3), homogenization annealing, longitudinal cold rolling (true logarithmic strain e = 0.67), and post-deformation annealing. Annealing was performed at 1,000 degrees C for 30 minutes in an argon atmosphere, followed by water quenching. The structural and phase state of the samples was investigated using optical and electron microscopy, X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The average grain size was determined using the linear intercept method. Results and discussion. Stable 3-titanium Elinvar alloy ingots were obtained. They are characterized by a high degree of chemical homogeneity and compliance with the specified composition throughout the cross-section. It was found that the proposed thermomechanical processing route for these alloys leads to the formation of a single-phase recrystallized structure consisting of equiaxed (3-phase grains. Grain sizes are shown to vary from 22.6 + 1.4 to 68.1 + 3.7 & micro;m. In binary alloys of the Ti-Nb and Ti-Mo systems, a decrease in grain size is observed with an increase in the Nb and Mo content. Specifically, for the Ti-Nb system, the grain size decreased from 57.8 + 3.3 & micro;m to 22.6 + 1.4 & micro;m with an increase in niobium content of 10 at.%. For the Ti-Mo system, the grain size decreased from 68.1 + 3.7 & micro;m to 34.4 + 2.0 & micro;m with an increase in molybdenum content of 7.4 at.%. The formation of a recrystallized equiaxed (3-phase structure throughout the ingot volume during combined thermomechanical processing confirms the potential for industrial application of these alloys.
Introduction. The metal-composite technology (MCT) for manufacturing tool bodies using an "SLM shell + metal-polymer composite material (Metal-polymer/MPCM)" enables the implementation of curvilinear coolant/lubricant supply channels and reduces the additively manufactured metal volume; however, the quality of filling thin-walled cavities is critically determined by the level of gas porosity of the filler. Gas porosity degrades the thermal conductivity and load-bearing capacity of the MPCM, reduces the stability of filling in critical zones near the SLM shell wall and adjacent to the channels, and increases properties dispersion and the risk of defects during tool operation. The purpose of the work is to experimentally establish the relationship between MPCM gas porosity and residual pressure under vibro-vacuum degassing and to justify a technologically preferable vacuum range for application in MCT tool bodies. Methodology. The study was carried out using a vibro-vacuum setup comprising a preliminary degassing chamber and a casting chamber with low-frequency vibration. Standard MPCM samples were produced for each vacuum condition. Porosity was evaluated using an adopted scoring scale based on microscopy (analysis of pore distribution, clustering, and characteristic defect sizes). Results and discussion. The experiment revealed a stable nonlinear (V-shaped) trend: as pressure decreases from atmospheric to approximately 450 Pa, the average porosity score monotonically decreases and reaches a minimum in the 400-350 Pa range (1-2 points). Further vacuum intensification below 300 Pa leads to vigorous gas evolution and foaming ("boiling"), accompanied by a sharp increase in defectiveness (up to 3-5 points). Conclusions. The identified optimal vacuum range of 400-350 Pa is recommended as a compromise between effective removal of entrapped gas and avoidance of the foaming, ensuring reproducible filling quality of MPCM within SLM shells in MCT tool-bodies manufacturing.
Introduction. The purpose of this study is to evaluate the technological potential of using oxide activating fluxes in the novel FB-TIG and FZ-TIG methods to improve penetration efficiency and weld quality in carbon and low-alloy steels. This paper attempts to analyze and review the published literature concerning various hypotheses that explain the high penetration achieved using activating fluxes. Materials and Methods. Low-alloy steel samples with thicknesses ranging from 3 to 10 mm were used in this study. Fine flux powders were pre-dispersed in acetone. The flux was carefully applied with a brush to the upper surface of the plate over half of its length. The other half of the plate was left without flux to perform conventional TIG welding for comparison. Bead-on-plate welds were made without the addition of any filler material. Several parallel weld passes were deposited with sufficient spacing to avoid thermal interference. The arc current was varied in the range of 80-250 A, while the welding speed was kept constant at 100 mm/min. The welding voltage was set to 15-16 V. Heat input was calculated using the standard expression, assuming a heat transfer efficiency of 0.8. High-purity, industrial-grade argon was used as the shielding gas at aflow rate of 20 L/min. A standard optical microscope was used for metallographic examination, and a camera was used to record the welding process. Results and Discussion. The studies have shown that penetration depth primarily depends on such welding parameters as arc length (mm), welding current (A), and travel speed (mm/s). The depth-to-width (D/W) ratio is high for the FB-TIG method; moreover, surface appearance and slag detachability are improved. The influence of the acidic or alkaline nature of the flux on weld geometry and surface appearance is analyzed. Acid fluxes provide a smoother weld surface than alkaline oxide fluxes. Welding with activated FB-TIG and FZ-TIG using SiO2 flux increases the penetration depth and the depth-to-width ratio by factors of 1.5-1.7, respectively, compared to conventional A-TIG welding.
Introduction. To reduce the number of defects and improve the mechanical properties of components fabricated by wire arc additive manufacturing (WAAM), the application of deformation hardening operations during the synthesis process is promising. Wave deformation hardening enables the formation of a deep hardened layer, which is particularly important for hybrid WAAM processes where subsequent heating of the upper layers can lead to softening of previously deposited layers. Akey parameter determining the effectiveness of wave deformation hardening is the temperature at which the synthesized material is subjected to the deformation hardening. The purpose of this study is to analyze the influence of the product temperature on the efficiency of wave deformation hardening for several advanced structural materials produced by the WAAM method. Methodology. The experiment involved the synthesis of samples, followed by furnace heating to a predetermined temperature (0.04C-19Cr-9Ni, 0.3C-1Cr-1Mn-1Si, 0.18C-1Cr-1Mn-1Si, and 0.09C-1.7Cr-1Mn-0.6Mo-1Ni-0.8Ti-0.015N: 300-900 degrees C; for the 97Al-3Mg alloy: 100-500 degrees C), after which they were subjected to hardening. To evaluate the effectiveness of the method, microhardness (Vickers) profiles were measured as a function of depth through the hardened layer. Results and discussion. The study revealed a characteristic optimal temperature range for each material within which wave deformation hardening provides the maximum strengthening effect. For austenitic steel 0.04C-19Cr-9Ni, the greatest increase in hardness (up to 52%) was achieved when treated at 700 degrees C, attributed to the increased ductility of austenite and possible deformation-induced martensitic transformation; above 800 degrees C, recrystallization begins, reducing the effect. For medium-alloyed steels 0.3C-1Cr-1Mn-1Si, 0.18C-1Cr-1Mn-1Si, and 0.09C-1.7Cr-1Mn-0.6Mo-1Ni-0.8Ti-0.015N, the optimal range was 400-600 degrees C, with a maximum hardness increase of 34-50%; in this region, dynamic polygonization and carbide dispersion hardening actively occur, while recrystallization dominates at higher temperatures. For aluminum alloy 97Al-3Mg, the effective range was 100-300 degrees C, with an increase in hardness of up to 24%, corresponding to the recovery condition; at 400-500 degrees C, the hardness drops below the initial value due to complete recrystallization. The depth of the hardened layer exceeded 3 mm for steels and reached 8 mm for the aluminum alloy, significantly greater than achieved by conventional surface plastic deformation methods. An anomalous behavior was identified for steel 0.09C-1.7Cr-1Mn-0.6Mo-1Ni-0.8Ti-0.015N: after a decrease in hardness at 700-800 degrees C, an increase in hardness was observed at 900 degrees C, explained by secondary hardening due to the dissolution of coarse carbides and the precipitation of fine particles during cooling. The obtained data are in good agreement with known tempering and recrystallization temperatures for the materials studied. The results enabled the formulation of practical recommendations for selecting wave deformation hardening temperature conditions for integration into hybrid WAAM processes, depending on the material class, ensuring maximum improvement in both hardness and hardened layer depth for additively manufactured components.
Introduction. Manufacturing steel or carbide dies is an expensive process, significantly impacting the cost of powder metallurgy products, especially in pilot and small-scale production. Apromising direction is the use of additive manufacturing for tooling fabrication and the application of alternative, less expensive binders for cemented carbides. The purpose of this work is to investigate the feasibility of using additive manufacturing for forming die blanks from WC-15 Co and WC-5 Fe-5 Ni-5 Co cemented carbides and to conduct a comparative analysis of their phase composition, microstructure, density, hardness, fracture toughness, strength, and wear resistance. Methods. Die components (dies and punches) made of WC-15 Co and WC-5 Fe-5 Ni-5 Co alloys were fabricated by cold pressing of granulated powders in dies obtained by photopolymer 3D printing (Water-Wash Resin 2.0, layer height 20 mu m), followed by vacuum sintering at 1,400 degrees C. A comparative analysis was performed to evaluate the density, phase composition, microstructure, hardness, strength, fracture toughness, and microabrasive wear resistance of the obtained materials. Using the experimental cemented carbide dies, SNUM-120408 cutting inserts made of WC-6 Co cemented carbide were produced by cold pressing and sintering at 1,450 degrees C. The insert dimensions were compared with the requirements of GOST 19052-80, GOST 19042-80 and a commercial counterpart. Results and Discussion. The fundamental feasibility of manufacturing large-sized cemented carbide die components (weighing up to 210 g) using photopolymer tooling has been experimentally confirmed. The relative density of the components was 99.1% for WC-15 Co and 98.3% for WC-5 Fe-5 Ni-5 Co, which is slightly lower than that of reference samples pressed at higher pressure in a steel die. It is shown that replacing the cobalt binder with a medium-entropy Fe-Ni-Co binder suppresses WC grain growth (average grain size: 1.18 mu m vs. 1.40 mu m). This, together with the higher hardness of the binder, results in increased alloy hardness (1,070 HV vs. 1,010 HV) and a 10% reduction in the microabrasive wear rate. The manufactured dies produced cutting inserts whose geometric parameters (cutting edge length, thickness, corner radius) and physical and mechanical properties comply with the requirements of GOST 19052-80 and GOST 3882-74 and are comparable to commercial counterparts. Conclusion. The proposed approach, combining low-cost photopolymer 3D printing for tooling fabrication with the use of a medium-entropy Fe-Ni-Co-bonded cemented carbide, enables the efficient production of functional cemented carbide dies for small-scale production. The WC-5 Fe-5 Ni-5 Co cemented carbide, exhibiting higher hardness and wear resistance, is a promising alternative to the standard WC-15 Co cemented carbide for these operating conditions.
Introduction. In aerospace engineering, thin-walled titanium spherical pressure vessels for high-pressure helium storage are manufactured by welding two precision-machined hemispheres. The geometric accuracy of the spherical surfaces and weld edge preparation determine leak tightness and service life under operating pressures up to 34 MPa and temperatures down to-196 degrees C. Due to their low stiffness, thin-walled hemispheres make machining critically dependent on locating charts, clamping forces, and cutting conditions. In the context of Industry 4.0 and the growing demand for hybrid equipment that integrates mechanical and surface-thermal operations, the development of modular robotic cells providing multifunctional machining with fewer re-clamping operations and increased flexibility has become highly relevant. However, existing design methodologies often fail to account for the multitasking nature, the complexity of preliminary studies, and the requirements for modularity and flexibility. The purpose of this work is to develop a machining process for thin-walled titanium hemispheres of spherical pressure vessels using computer simulation that ensures compliance with spherical surface accuracy and weld edge preparation requirements, and to improve machining efficiency by minimizing deformation risk, reducing the number of re-clamping operations, and shortening process planning time when integrating the process into a modular robotic cell. Methods. Design and manufacturing requirements for the hemispheres were analyzed; cutting conditions were calculated taking into account the specific features of the titanium alloy Ti-6Al-4V machining; equipment was selected through a comparative assessment based on production efficiency criteria; and the proposed process was verified in the SprutCAM computer-aided process planning (CAPP) system, considering equipment kinematics. Results and Discussion. Surface finish and accuracy requirements were established: Ra 0.8 & micro;m for the inner spherical surface and Ra 3.2 & micro;m for the outer spherical surface. A process route sheet was developed to minimize re-clamping operations and reduce the risk of thin-walled shell deformation. Based on production efficiency criteria, the DN Solutions PUMA VTS 1214M vertical turn-mill center was selected, enabling combined turning and milling operations in a single setup, consistent with integral machining on a CNC lathe platform. A locating chart using a special ring-type axial clamping fixture was developed and visualized. Machining simulation confirmed the feasibility of the process route, correct setup planning, and the absence of tool-workpiece-fixture collisions, and indicated the potential for rapid process implementation. Conclusions. The results contribute to the development of theoretical foundations and conceptual approaches for designing hybrid machine tools that integrate mechanical and surface-thermal processing operations.
Introduction. Due to the wide application of pure alpha titanium in critical products, the intensification of its machining by cutting is an urgent task. Existing studies focus mainly on alloyed alloys, while the features of high-speed dry milling of pure alpha-Ti are not well understood. The aim of this work was to investigate the influence of milling modes on the wear of a CVD-coating (Al2O3/TiCN+TiN) on carbide inserts, chip morphology and deformation processes in the surface layer of Ti Grade 2 alloy. Methodology. The experiments were carried out using parallel milling in the range of cutting speeds v = 100-300 m/min, feed rates f = 50-100 mm/min and depths of cut a & rcy; = 0.2-0.4 mm without coolant. The condition of the cutting edges and the morphology of the chips were investigated using SEM and EDX. Xray diffraction analysis was used to assess deformation changes. The data were processed using correlation and regression analysis methods. Results and discussion. It has been found that with increasing cutting speed, adhesion processes and thermomechanical stresses are intensified, leading to local scraping and delamination of the CVD coating on the rake surface. At a speed of 300 m/min, there is significant material buildup, forming an unstable built up edge. The study of the chips revealed a transition from continuous to elemental form. A strong negative correlation (r = -0.81) between the cutting speed and the height of protrusions (h3) on the chip was found, as well as a moderate positive influence of the depth of cut on the continuity coefficient (r = 0.55). The results obtained are relevant for the optimization of high-speed dry machining of pure titanium products used in cryogenic engineering and heat exchangers. Conclusions. The dominant wear mechanisms are adhesion and thermomechanical degradation of the coating. The critical mode leading to intensive buildup is a combination of v = 300 m/min, f = 100 mm/min, a & rcy; = 0.4 mm. To reduce wear, it is recommended to control heat dissipation by optimizing cutting speed and depth of cut.
Introduction. Modern mechanical engineering is characterized by the increasing application of heat-resistant alloys for critical components in aerospace and defense equipment. The machining of promising molybdenum alloys, such as Mo-30TiC, is particularly challenging due to their high heat resistance, abrasiveness, and the anomalous behavior of their mechanical properties at elevated temperatures. Existing technological solutions developed for nickel-based alloys often prove ineffective, highlighting the relevance of research in this area. Purpose of the work is to develop rational machining conditions and strategies for the milling of the heat-resistantMo-30TiC alloy, aimed at increasing tool life and ensuring the required surface quality. Methodology. Experimental studies were conducted on an Okuma MB-46BE machining center using carbide end mills from various manufacturers. The influence of geometric tool parameters (rake angle, cutting edge radius, and presence of a negative land) and cutting conditions (cutting speed, feed rate, depth of cut) on flank wear and surface roughness was investigated. Process monitoring was performed using optical microscopy and surface profilometry. Results and discussion. Optimal geometric tool parameters were determined: a rake angle of 0 degrees, a cutting edge radius of 0.5-1 mm, and a negative land width of 0.05 mm. Two distinct machining strategies were developed: a standard cutting strategy (Vc = 50-72 m/min, fz = 0.03-0.04 mm) for high-quality finishing, and a high-productivity power cutting strategy (Vc = 12-17 m/min, fz = 0.08-0.1 mm). The Karcan 99508003 and CNCINSMS15.Z5.08.19.63.38.R05 end mills demonstrated superior tool life. It was shown that the progression of tool wear leads to an exponential increase in the variance of surface roughness parameters Ra and Rz. Conclusions. The proposed set of technological solutions enables effective machining of the Mo-30TiC alloy, providing control over tool wear and achieving the specified surface quality. The results of this work are of practical importance for manufacturing enterprises specializing in the machining of difficult-to-cut materials.
Introduction. Ti-6Al-4Vis one of the most commonly used alpha+beta titanium alloys in various industries due to its excellent specific strength and corrosion resistance. Additive manufacturing (AM) processes enable the production of Ti-6Al-4Vparts with complex geometries. However, defects and microstructural inhomogeneity in the fabricated parts can adversely affect their mechanical properties. Purpose of the work. The purpose of this study is to investigate the microstructure and mechanical properties of Ti-6Al-4Vparts. The defect density and inhomogeneity in the microstructure and mechanical properties of parts fabricated by selective laser melting (SLM), electron beam melting (EBM), and spark plasma sintering (SPS) were examined. The inhomogeneity in mechanical properties, specifically hardness, was quantified. Furthermore, the effects of a laser remelting strategy on microstructural homogeneity were studied. Research methods. Ti-6Al-4Vparts were fabricated using additive manufacturing processes, namely SLM and EBM. Parts were also produced via the SPS method. A laser remelting strategy (scanning each layer three times) was applied during the SLM process. The effects of laser remelting on defects, microstructure, and mechanical properties were studied and compared with standard SLM (scanning each layer once), EBM, and SPS. Results and discussion. A lamellar alpha/alpha ' microstructure was observed in the SLM samples, both in the as-built and remelted conditions (denoted as SLM and SLM-RM, respectively). The hardness of the SLM sample (335 HV) was found to be higher than that of the SPS sample (305 HV). Application of the remelting strategy in SLM led to an increase in hardness and improved its homogeneity. The average size and shape irregularity of porosities in the SLM samples were analyzed; it was observed that surface porosity decreased with the implementation of the remelting strategy. Laser remelting significantly influences the performance of the SLM process. The results demonstrate that these synthesis processes yield Ti-6Al-4Valloys with distinct microstructural and mechanical properties.
Introduction. Investigating the statistical relationships between milling parameters and surface roughness requires a correct selection of the sample size, as amplitude parameters and form parameters respond differently to data limitations. The reliability of correlation-regression analysis depends on meeting the assumptions of normality and the stability of the estimates, making the determination of the minimum number of observations essential for constructing reliable surface roughness models. The purpose of this work is to develop a methodology for estimating the minimum sample size required to build statistically significant correlation-regression models that describe the relationship between the technological parameters of the milling process and surface roughness characteristics, ensuring statistical reliability of the results and enabling accurate prediction of machined surface quality. Methodology. The normality of the surface roughness parameter distributions after milling was assessed using the Shapiro-Wilk, Anderson-Darling, and Pearson's chi-squared tests. Multicollinearity among the technological factors was analyzed using the variance inflation factor (VIF), while the adequacy of the regression models was verified using the mean absolute error (MAE) and root mean square error (RMSE) metrics. The minimum required sample size was determined by considering statistical test power and Fisher's z-transformation. Results and discussions. The analysis of pairwise correlation coefficients revealed that amplitude roughness parameters exhibit stable relationships even at n = 16, while profile shape parameters (Rsk, Rku) are characterized by weak or negative correlations and require a substantially larger sample size. The constructed matrix of the minimum number of observations confirms that for a number of relationships, especially those involving Rsk, hundreds of measurements are necessary, which justifies the selection of the most informative parameter combinations. Increasing the sample size to n = 128 reduces estimation bias, stabilizes the correlations for amplitude parameters, and reveals a weakening of the relationships for Rsk and Rku. Rank correlation analysis confirmed a monotonic dependence between Rz and Rt and the independence of Rsk from amplitude characteristics. The verification of the normality of the distributions and the absence of multicollinearity among the factors ensured the validity of the constructed regression models, which demonstrated high accuracy and consistent error behavior.
