Ismail Ozdemir

The use of advanced aluminum-based bimetal bearings is critical for addressing modern automotive demands such as downsizing, higher loads, and improved fuel efficiency. Traditional roll bonding methods, widely employed for manufacturing bimetal bearings, face significant limitations when applied to next-generation aluminum alloys due to their complexity, cost, and inflexibility. This study evaluates thermal spray techniques, specifically cold spray (CS) and high-velocity air fuel (HVAF) deposition, as alternative manufacturing methods for aluminum-based bimetal bearings. Cold spray trials showed that the AlMn1Cu bond coat achieved > 88% deposition efficiency (DE) at 500-600 °C, while the AlZn5SiCuMgBi top coat reached only 32.69% at 650 °C. The lower DE of the top coat is attributed to its higher hardness and the presence of preexisting intermetallic phases (e.g., Bi ₂ Mg ₃ ), which are only partially reduced during deposition and may undermine particle bonding. Experimental comparisons between HVAF and cold spray (CS) coatings revealed significant differences in mechanical and tribological performance. HVAF coatings exhibited superior hardness of 151 HV compared to cold spray, which had 94.5 HV, indicating a more robust and potentially wear-resistant surface. In terms of wear behavior, HVAF demonstrated lower wear depth of 83.3 µm and volume loss of 0.137 mm ³ , which are 21.5% and 22.5% lower, respectively, compared to cold spray, which had wear depths of 106.1 µm and volume loss of 0.1767 mm ³ . These results reflect the denser microstructure and improved bonding achieved by HVAF. Additionally, friction coefficient (COF) measurements showed that HVAF with a COF of 0.5 outperformed cold spray with a COF of 0.625, further emphasizing its superior tribological properties.

The purpose of this study is to investigate the influence of copper content and cutting parameters on the microstructure, hardness, machinability, and cutting-force behavior of sand-cast Al–Cu alloys under minimum quantity lubrication (MQL) conditions. In this study, workpieces obtained using the sand mold casting method were tested using the minimum quantity lubrication (MQL) method on a lathe. Five different test specimens were produced by adding copper to aluminum. The microstructures were examined via optical microscope, and hardness values were determined using Brinell hardness. Due to significant production and energy costs, the MQL method was preferred for metal cutting. Cutting forces generated during the process were measured using a dynamometer and analyzed in terms of feed rate, cutting velocity, and workpiece material using a full factorial analysis. Additionally, wear mechanisms on the cutting tool were determined using scanning electron microscope (SEM) images and Energy Dispersive Spectrum (EDS) analysis. The lowest hardness value was 34 HB in pure aluminum, while the highest was 95 HB in Al-8Cu alloy. Cutting forces increased with feed rate across all samples and decreased with higher cutting velocity. The highest cutting force (216.03 N) and feed force (26.90 N) were found in the Al-8Cu alloy, whereas the lowest cutting force (54 N) and feed force (6.07 N) were in pure aluminum. SEM and EDS analysis revealed flank wear and adhered aluminum on the cutting tools. Regression analysis verified that cutting velocity is the most critical factor influencing cutting and feed forces, with material type and feed rate also playing significant roles. Regression and ANOVA analyses consistently identified cutting velocity as the dominant factor affecting cutting and feed forces, followed by material type and feed rate.

Polymer matrix composites (PMCs) have emerged as critical materials in lightweight engineering applications due to their excellent mechanical properties and design versatility. However, their inherent limitations in electrical and thermal conductivity necessitate metallization, particularly for applications such as lightning strike protection (LSP) and electromagnetic interference (EMI) shielding. Cold spraying, a low-temperature metallization technique, addresses the shortcomings of conventional methods by enabling the deposition of dense, oxide-free, and highly conductive coatings with minimal damage to the composite substrate. This review provides a comprehensive overview of advancements in metallization techniques, with a focus on cold spraying, to enhance the electrical and thermal performance of PMCs for LSP and EMI shielding. The combination of PMCs with conductive materials presents an innovative approach to achieving lightweight, corrosion-resistant, and efficient LSP and EMI shielding solutions, offering significant advancements in surface functionalization. Future research directions include the exploration of hybrid metallization strategies and the integration of cold spraying with additive manufacturing, highlighting their potential to create multifunctional and high-performance PMC-based systems. Additionally, emerging trends such as novel or smart materials, optimization of cold spray processes through advanced modeling, and the translation of these innovations into industrial applications are discussed.

Reinforced PTFE materials can be designed to show high mechanical stability against harder materials under sliding wear conditions. Especially bearing metal-reinforced PTFE is of high practical interest. In this class of materials, bronze-filled PTFE was reported to obtain high wear resistance, a low coefficient of friction (COF), and excellent self-lubrication properties in sliding conditions. In the statistical approach of this work, PTFE composites reinforced with 25 vol%, 40 vol%, and 60 vol% bronze particles were evaluated against pure PTFE regarding wear behavior under varied wear test parameters, i.e., material, normal load, and sliding speed. Wear tests were planned to use a standard orthogonal array based on the Taguchi design method. An analysis of variance test was utilized to quantify the effects of test parameters on the wear behavior of the bronze/PTFE composites and pure PTFE. According to the variance analysis, the material type has the largest influence on the COF and the specific wear rate (SWR) under test conditions of this work. Both COF and SWR were found to be influenced by the material type (29.83% and 96.16%), the normal load (33.34% and 0.95%), and sliding speed (9.14% and 1.28%). The lowest SWR and COF values were achieved at the optimum wear test conditions where the wear test parameters were 1 m/s sliding speed (A4B2C2) at PTFE + 60 vol.% bronze reinforced composite 50 N application load and 0.32 m/s sliding speed (A4B3C1) at PTFE + 60 vol.% bronze reinforced composite 100 N application load, respectively.

Modern engine bearing materials encounter the challenge of functioning under conditions of mixed lubrication, low viscosity oils, downsizing, start–stop engines, potentially leading to metal-to-metal contact and, subsequently, premature bearing failure. In this work, two types of polymer overlays were applied to the bearing surface to compensate for extreme conditions, such as excessive loads and mixed lubrication. Two different polymer overlays, created through a curing process on a conventional engine bearing surface with an approximate thickness of 13 µm, were investigated for their friction and wear resistances under a 30 N load using a pin-on-disc setup. The results indicate that the newly developed polymer overlay (NDP, PAI-based coating) surface has a coefficient of friction (COF) of 0.155 and a wear volume loss of 0.010 cm³. In contrast, the currently used polymer overlay (CPO) in this field shows higher values with a COF of 0.378 and a wear volume loss of 0.024 cm³, which is significantly greater than that of the NDP. It was found that, in addition to accurately selecting the ratios of solid lubricants, polymer resins, and wear-resistant hard particle additives (metal powders, metal oxides, carbides, etc.) within the polymer coating, the effective presence of a transfer film providing low friction on the counter surface also played a crucial role.

This meta-analysis study aimed to survey the antecedents of turnover intention regarding employee development. From this perspective, developmental feedback, competence development, professional development, training and development, development opportunities, and career development variables were added to the meta-analysis. Moreover, some other antecedents were listed in the review part of this study. Twenty-three suitable studies were brought together for this meta-analytical review. The findings of this study are useful for managers striving to improve their strategies and policies to reduce turnover intention.

Aluminium matrix composites (AMCs) represent an important group of high-performance materials. Due to their specific strength and a high thermal conductivity, these composites have been considered for the large-scale production of brake discs. However, preconditioning the friction surfaces is necessary to avoid severe wear of both the brake discs and the brake linings. This can be achieved through controlled friction against commercially available brake-lining materials and the formation of transfer or reactive layers (tribosurfaces). Homogeneous tribosurfaces allow for nearly wear-free brake systems under moderate brake conditions. In this work, preconditioning was carried out with a pin-on-disc tester, aiming for the fast creation of homogeneously formed and stable tribosurfaces. The influence of surface microedges perpendicular to the direction of friction on the machined AMC surfaces on the build-up speed and homogeneity of the tribosurfaces was investigated. The microedges were generated using ultrasonic-vibration-superimposed face turning. Thereby, the vibration direction corresponded to the direction of the passive force. For research purposes, the distance of the microedges was changed by varying the cutting speed and feed. The experiments were carried out using AMC disc specimens with a reinforcement content of a 35% volume proportion of silicon carbide particles. Machining was realised with CVD-diamond-tipped indexable inserts. The evaluation of the generated surfaces before and after preconditioning was achieved using 3D laser scanning microscopy and scanning electron microscopy. It was demonstrated that ultrasonic-vibration-superimposed face turning effectively generated microedges on the AMC surfaces. The results show that larger distances between the microedges enhanced the formation of stable tribosurfaces. Thus, the tribosystem’s steady state was reached quickly. Therefore, the benefits of AMC-friction-surface microstructuring on the generation of tribosurfaces under laboratory conditions were proven. These findings contribute to the development of high-performance AMC brake systems.

Dental implant fracture is closely connected to the stress buildup surrounding the implant system during static loading. In areas where the cross-section of the implant rapidly changes or where the geometry of the implant system has discontinuities, stress concentrations arise. Therefore, the implant’s design is crucial in preventing early failure of the implant system, including fracture, screw loosening, and increased leakage, in addition to reducing stresses at the implant–abutment interface. In the current work, three-dimensional (3D) models of mechanically connected Ti6-Al-4V implant systems in various dimensions were constructed. Finite element analysis (FEA) was used to conduct a stress study of the created implants under actual acting force static loading conditions in accordance with ISO 14801. In the created models, design elements including implant screw type, thickness, and taper angle of abutment were modified in order to increase the longevity of the implants. The results show that the equivalent stress level was dramatically reduced from 596.22 MPa to 212.72 MPa in the implant model, which exhibits a more homogeneous stress pattern under static loading conditions. By increasing the implant wall thickness from 0.15 mm to 0.40 mm in the region adjacent to the abutment, the stress levels, especially at the internal screw, were significantly reduced. Also, the design modification in Model B, establishing contact between the abutment and the upper part of the conical surface of the implant, resulted in a decrease in stress in the internal screw. Thus, enhanced homogeneity in stress distribution not only improves the harmony between the implant and surrounding tissues, thus increasing patient comfort and reducing the risk of complications, but also holds promise for the development of new implants capable of withstanding the forces encountered in the oral environment due to the relatively smoother stress transmission observed in this model.

Dental implant fracture is closely connected to the stress buildup surrounding the implant system during static loading. In areas where the cross section of the implant rapidly changes or where the geometry of the implant system has discontinuities, stress concentrations arise. Therefore, the implant's design is crucial in preventing early failure of the implant system, including fracture, screw loosening, and increased leakage, in addition to reducing stresses at the implant-abutment interface. In the current work, three-dimensional (3D) models of mechanically connected Ti6Al4V implant systems in various dimensions were constructed. Finite Element Analysis (FEA) was used to conduct a stress study of the created implants under actual acting forces static loading conditions in accordance with ISO 14801. In the created models, design elements including implant screw type, thickness, and taper angle of abutment were modified in order to increase the longevity of the implants. The results show that the equivalent stress level is dramatically reduced from 596.22 MPa to 212.72 MPa in the implant model, which exhibit more homogeneous stress pattern under static loading conditions. Furthermore, the relatively smoother stress transmission observed in this model holds promise for the development of new implants capable of withstanding the forces encountered in the oral environment.