Obrabotka Metallov / Metal Working and Material Science

Introduction: this study examines research and development efforts aimed at developing non-asbestos brake friction composites (BFCs) to improve the safety and performance of automotive brake systems. The evolution of BFCs from asbestos-based materials to safer alternatives is studied, and an analysis is performed to develop alternative material combinations. The critical roles of key components — fibers, binders, friction modifiers and fillers — in creating durable brake friction composites for brake systems is emphasized. A composite material based on basalt fiber with calcium carbonate filler is compared to a composite material based on aramid fiber with barium sulfate filler through pin-on-disc tribological testing. Based on the test results, it is determined that the alternative composite materials show promise for application in brake systems. This work also provides a foundation for further development of eco-friendly brake friction composites by selecting optimal formulations. The present work defines an approach for subsequent research aimed at varying the components and their ratios in the creation of composite materials. This research will further improve the functionality of automotive brake systems. Purpose of the work: this research is focused on the development of non-asbestos brake friction composites (BFCs) with the goal of improving the safety and performance of automotive brake systems. Eco-friendly alternatives to asbestos are investigated, and the roles of fibers, binders, friction modifiers, and fillers are analyzed. The objective of the research is to identify optimal formulations for creating durable, sustainable brake materials, paving the way for further implementation of innovative solutions in practice. Methods of investigation: a pin-on-disc tribological method is used to evaluate wear, friction, and durability, as well as to assess the suitability of the developed materials for use in brake systems. This research is dedicated to analyzing the influence of components (fibers, binders, friction modifiers, and fillers) on the properties of friction composites for brake systems. Two compositions were experimentally studied: basalt fiber with calcium carbonate and aramid fiber with barium sulfate. Results and discussion: the results of the research demonstrate the effectiveness of using basalt fiber with calcium carbonate and aramid fiber with barium sulfate as components in friction composites for brake systems. It is shown that these materials provide high levels of wear resistance and friction performance. The potential for further optimization of compositions to improve eco-friendliness and enhance the operational properties of braking systems is emphasized. The obtained results also highlight the importance of component selection for the development of safe and sustainable brake friction composites.

Introduction: Machining hard materials and shape memory alloys (SMAs), such as NiTi, NiCu, and BeCu, using conventional techniques is challenging due to excessive tool wear and poor surface finish. Non-conventional machining methods, particularly electrical discharge machining (EDM), offer improved precision and surface quality. However, the effectiveness of EDM is contingent upon the optimization of process parameters. The purpose of this study is to optimize EDM parameters to enhance the machining performance of SMAs by considering factors such as pulse-on time, pulse-off time, discharge current, gap voltage, and workpiece electrical conductivity. Methods. In this study, the Taguchi experimental design approach was employed to analyze the influence of key process parameters on the material removal rate (MRR), surface roughness (SR), and tool wear rate (TWR). Analysis of variance (ANOVA) was then applied to identify the most statistically significant factors affecting machining performance. A multi-objective optimization method, based on utility theory, was utilized to determine the optimal EDM settings that balance MRR, SR, and TWR. The results were validated through experimental trials. Results and Discussion. The experimental results indicated that Trial 15 achieved the highest MRR of 9.076 mm³/min, while Trial 1 produced the lowest SR of 2.238 µm. The minimum TWR of 0.041 mm³/min was observed in Trial 10, which contributes to increased tool lifespan. ANOVA revealed that gap voltage was the most influential factor, accounting for 85.98% of the variation in machining performance, followed by discharge current (4.76%) and pulse-off time (2.59%). The multi-objective optimization process successfully identified parameter configurations that optimize MRR while minimizing SR and TWR. The prediction model developed in this study demonstrated high accuracy, with an R² value of 93.3% and an adjusted R² of 89.7%. Validation experiments confirmed the effectiveness of the optimized parameters, resulting in an average MRR of 8.852 mm³/min, SR of 2.818 µm, and TWR of 0.148 mm³/min. The findings presented herein confirm that careful optimization of EDM parameters significantly enhances the machining performance of SMAs, considerably improving machining efficiency and tool longevity.

Introduction. Milling stainless steel with a ball-end tool is a complex technological process that requires precise control of processing parameters to ensure high surface quality. In this regard, it is an urgent task to develop methods for predicting roughness parameters, such as Rz. The aim of this work is to develop a predictive neural network model that can estimate surface roughness when milling stainless steel using a ball-end tool. Method and methodology. The main focus is on error backpropagation and gradient descent methods, as well as hyperparameter tuning, which are necessary to prevent overfitting and underfitting of the model. Experimental studies include the analysis of both controlled variables, such as feed per tooth, angle of inclination and diameter of the tool, and uncontrolled, including coolant supply and tool wear. Results and discussions. The use of coolant for milling austenitic steel has reduced the roughness parameters Rz by an average of 14%. A strong negative correlation has been established between the dimensional wear of the tool and the parameter Rz (−0.95). At the same time, wear in the range of 2…4 μm affects an increase in the Rz parameter by 21% compared to the minimum values. The data obtained were used to train eight configurations of artificial neural networks, which were used to predict roughness using the Rz parameter. The results show that the 3-16-16-1 network configuration showed the lowest MSE (0.0313), followed by 3-20-14-1 (0.0470) and 3-64-64-1 (0.0481), respectively. In addition, these configurations also demonstrated the lowest average absolute error values, which demonstrate the average of the absolute differences between predicted and observed values (0.1014; 0.1251 and 0.1155, respectively), and the coefficient of determination, which is a statistical measure indicating the proportion of data variability explained by the model (0.9944; 0.9916; 0.9904). A comparison of the experimental data with the predictions of various models allowed us to determine the average value of the absolute differences for the models according to the parameter Ra ≈ 0.074. The study suggests approaches to training neural network models for accurate prediction of roughness parameters, which makes a significant contribution to the methods of modeling machining processes.

Introduction. Analysis of contemporary data in the fields of materials science and the application of ceramic cutting tools for machining difficult-to-machine iron- and nickel-based alloys reveals a limited amount of experimental data concerning the use of the promising Y-TZP-Al2O3 ceramic, which is based on submicron yttria-partially-stabilized zirconia and reinforced with alumina. Purpose of the work. To study the performance of RNGN 120400-01 removable cutting inserts made from Y-TZP-A12O3 ceramic during dry high-speed (200 m/min) cutting of 0.4 C-Cr (AISI 5135) steel (HRC 43…48). Research Methods. Characterization of the initial powders and the sintered ceramic, both before and after cutting tests, was performed using X-ray fluorescence (XRF) and X-ray diffraction (XRD) analyses, as well as scanning electron microscopy (SEM) in BSE mode. The physical and mechanical properties of the sintered ceramic were determined using the hydrostatic weighing method, three-point bending, and Vickers microhardness and fracture toughness measurements. Cutting tests were conducted on a high-rigidity lathe in a production shop conditions, involving dry high-speed turning of hardened 0.4C-Cr steel (AISI 5153) (HRC 43…48) in two stages. The first stage involved establishing the allowable variation limits for cutting modes (cutting speed and feed rate) and investigating the wear and failure characteristics of the cutting insert rake and flank faces. The second stage utilized ceramic cutting inserts with a chamfered cutting edge. Results and discussion. It was established that for Y-TZP-A12O3 ceramic, the use of cutting modes V > 200 m/min, S > 0.4 mm/rev, and t > 0.2 mm is not advisable due to the short service life of the cutting edge. A chamfer on the cutting edge is necessary to provide controlled edge blunting. The observed wear patterns and analysis of failure areas indicate a dominant brittle fatigue failure mechanism, caused by the thermal effects of high-speed friction combined with tangential stresses from the chip flow. It is concluded that the Y-TZP-Al2O3 ceramic composite is promising for use as a cutting tool material for dry high-speed turning of both hardened steels and, potentially, wear-resistant cast irons. Based on the conducted research and described observations, recommendations are formulated for the use of Y-TZP-Al2O3 ceramic in future studies.

Introduction. The low yield strength of austenitic stainless steels is a factor significantly limiting their industrial applications. In turn, the formation of a heterogeneous structure is a promising method for achieving a synergy of mechanical properties. At the same time, an effective way to obtain a bulk heterogeneous structure is cold radial forging. However, the underlying mechanisms for the improved mechanical properties of materials with a heterogeneous structure formed in the process of cold radial forging are currently poorly understood. Purpose of the work is to investigate the effect of a heterogeneous structure obtained by deformation and heat treatment on the mechanical properties of austenitic stainless steel 0.08 C-17 Cr-13 Ni-2 Mn-Ti. Methods. Uniaxial tensile tests were performed on specimens obtained by cold radial forging followed by heat treatment at 600–700°C, using an Instron 5882 testing machine at room temperature with a strain rate of 1.15 × 10–3 s–1. A VIC-3D visual inspection system was used to measure elongation during testing. The fine structure was examined on perforated foils with a diameter of 3 mm using a JEOL JEM-2100 transmission electron microscope at an accelerating voltage of 200 kV. Results and discussion. It was shown that, after thermo-mechanical treatment, a twin-matrix austenite structure was obtained in the center of the rod, while an ultrafine-grained structure with isolated recrystallized austenite grains of approximately 1 μm in size was obtained at the edge. It was established that a two-component axial austenite texture <001>/<111> is formed in the center of the rod, which transformed into a shear texture B/B? towards the rod surface. It was determined that the formation of a heterogeneous structure led to additional strengthening due to back stresses. It was found that, after heat treatment at 700°C, the specimen with a heterogeneous structure exhibited the highest yield strength, equal to 1054 MPa, with a relative elongation of 16%. Thus, the employed thermo-mechanical treatment may be a promising method for obtaining large-sized rod stocks from austenitic stainless steel 0.08 C-17 Cr-13 Ni-2 Mn-Ti with high mechanical properties.

Introduction. One of the most significant phenomena in every industrial sector is friction and wear, which inevitably occurs when there is relative motion between similar or dissimilar materials. A substantial portion of global energy production is estimated to be expended in overcoming friction and wear, making them critical factors in energy efficiency and sustainability. Recently, advances in materials science, lubrication technologies, and innovative design approaches have facilitated a significant reduction in friction and wear, leading to considerable energy savings and extended component lifespan. Polytetrafluoroethylene (PTFE), among other materials, has revolutionized the tribological field, emerging as a highly effective synthetic polymer. This is attributed to its exceptional properties, including a low coefficient of friction, chemical inertness, thermal stability, non-stick characteristics, and biocompatibility. These unique properties make PTFE an ideal material for various industrial applications, spanning from aerospace to biomedical sectors. The purpose of work. This study aims to conduct a comprehensive numerical and experimental investigation into the tribological properties of PTFE-based composites. The materials selected for investigation include pure PTFE, PTFE with 25% carbon (C) filler, and PTFE with 20% glass filler. Testing was performed using stainless steel (SS 304) as the counterbody. Tribological testing and subsequent evaluation were conducted under dry sliding friction conditions, considering key parameters such as load, sliding speed, and temperature. Response surface methodology (RSM) was employed to develop an empirical model, utilizing experimental data to predict the wear resistance of these materials. Empirical models were developed to understand the influence of process parameters on wear behavior and to optimize operating conditions for minimizing material loss. Method of investigation. Archard's wear model was used as the theoretical framework for predicting volume loss and specific wear rate based on numerical simulations. The wear coefficient (K) was determined through experimental testing and used as an input parameter in the numerical models. Numerical simulations were developed using the finite element analysis (FEA) software ANSYS, enabling the simulation of complex tribological interactions between the composite materials and the counterbody. A central composite rotatable design (CCRD) within the framework of RSM was used to structure the experiments. The experiments were conducted under dry sliding friction conditions using pin on disc tribometer. The input parameters for the experiments were load (ranging from 15 N to 200 N), sliding speed (ranging from 400 rpm to 1000 rpm), and temperature (ranging from 60 °C to 200 °C). Each experiment was conducted for a sliding distance of 5 km to ensure sufficient wear for analysis. A total of 20 experiments were performed for each material, providing a comprehensive dataset for statistical analysis and model validation. Result and discussion. The results of the study highlight the effectiveness of numerical simulation in predicting the wear resistance of PTFE-based composites under dry sliding friction conditions. Experimental investigations reveal that pure PTFE exhibits low mechanical strength, leading to a high wear rate, whereas PTFE with carbon and glass fillers demonstrates improved wear resistance characteristics. The addition of carbon to PTFE enhances the composite's performance by forming a stable transfer film on the counterbody, while the addition of glass promotes increased hardness and, consequently, reduced material loss. Empirical models developed using response surface methodology (RSM) confirm that the applied load on the pin is the most significant parameter affecting wear, followed by sliding speed and temperature. Numerical simulations based on Archard's wear model exhibit good agreement with experimental data, validating the accuracy of the numerical simulations. This research contributes to a deeper understanding of the application of PTFE-based composites in extending the service life and enhancing the reliability of industrial products.

Introduction. Shape memory alloys based on TiNi possess a set of properties, including biocompatibility, corrosion resistance, low density, high specific strength, thermal stability, shape memory effect, and superelasticity. A significant number of studies are currently dedicated to various deformation methods of processing such materials, aiming to enhance their mechanical properties and shape memory characteristics. One such method is plastic deformation with the simultaneous application of pulsed current. Since the shape memory properties in TiNi-based alloys are due to the presence of thermoelastic martensitic transformations, the combined effect of deformation and current on these transformations is of particular interest. The purpose of this work is to investigate the characteristics of thermal and deformation-induced martensitic transformations in Ti50.0Ni50.0 and Ti49.2Ni50.8 alloys during rolling with simultaneous application of pulsed current. Research methods. The paper analyzes samples of Ti50.0Ni50.0 and Ti49.2Ni50.8 alloys after rolling with pulsed current at a density of 100 A/mm², a pulse duration of 100 μs, a pulse ratio of 10 to various strain levels (ε=0; 0.4; 0.8; 1.2). The study of the staging of martensitic transformations was carried out using differential scanning calorimetry at a heating/cooling rate of 10 °C/min in the temperature range of −150 to +150 °C. The phase composition was studied by X-ray diffraction analysis using Cu-Kα radiation at U=40 kV and I=40 mA in the angular range of 2θ=15 to 100 ° with a step size of Δθ = 0.05° and an exposure time of 5 s. Results and discussion. The results show that current-assisted rolling leads to the manifestation of a two-stage direct martensitic transformation during cooling in both alloys. Furthermore, increasing the strain level broadens the temperature range of the R-phase existence. The possibility of stabilizing the high-temperature austenitic B2 phase in the Ti49.2Ni50.8 alloy, as well as the emergence of a cyclically occurring deformation-induced “martensite-austenite-martensite” transformation in the Ti50.0Ni50.0 alloy, are demonstrated. Possible mechanisms for these features are discussed.