Journal of Materials Engineering and Performance最新文献

As the primary alloying element in 7075 aluminum alloy, Zn content directly influences its microstructure and mechanical properties. This study investigates the microstructure and mechanical properties of 7075 aluminum alloys with three different Zn concentrations (5.17, 5.50, and 5.88 wt.%) in both as-cast and homogenized states. The phase evolution during homogenization was analyzed using optical microscopy (OM), scanning electron microscopy (SEM), x-ray diffraction (XRD), and other techniques. The results show that as Zn content increases, the morphology of the T-AlZnMgCu phase in the as-cast microstructure changes from spherical to a network structure and segregated toward the grain boundaries. The grain size of the alloy gradually decreases, with the morphology transitioning from dendritic to petal-like cellular dendrites, eventually becoming equiaxed grains. During the homogenization process, the spherical T-AlZnMgCu phase transforms into the S-Al₂CuMg phase and dissolves completely into the matrix. However, the transition time for the network T-AlZnMgCu phase to convert to the S-Al₂CuMg phase is longer. It continuously absorbs Cu, forming coarse and insoluble Al₇Cu₂Fe phases that tend to agglomerate at grain boundaries, ultimately shortening the time needed for alloys with varying Zn contents to reach peak mechanical properties. Additionally, as Zn content increases, mechanical properties decrease, reflecting a reduced homogenization process window with higher Zn concentrations. This provides a theoretical foundation for the precise control of enhancing the performance of 7075 aluminum alloy.

The hot deformation behavior and microstructure evolution of an Al-Mg-Zn-Sc-Zr alloy under isothermal compression at temperatures ranging from 400 to 475°C and strain rates ranging from 0.001 to 1 s⁻¹ were investigated. Based on the true stress–true strain curves, the flow stress increased with strain, reached a maximum, then decreased and eventually stabilized. An eighth-order strain-compensated Arrhenius model was proposed to predict the flow stress, with an activation energy of Q = 212.54 kJ mol⁻¹, a correlation coefficient of 0.9873 and an average relative error of 5.894%. EBSD analysis indicated that the temperature and strain rate significantly affected the dynamic recrystallization (DRX) behavior of the alloy. The synergistic effect promoted the formation of both continuously and discontinuously recrystallized grains and facilitated the DRX process. Consequently, a large number of fine-sized, low-dislocation and well-oriented DRX grains were generated in the alloy. Based on the hot processing map and microstructural evolution analysis, the optimal hot working parameters for the alloy were determined to be 460-475°C and 0.001-0.005 s⁻¹.

Laser-assisted machining (LAM) is a new type of machining that achieves high efficiency and low damage when processing engineering ceramics from difficult-to-machine materials. Si₃N₄ ceramics are utilized in various critical components within the aerospace, automotive manufacturing, and medical fields. LAM technology has been demonstrated to enhance the performance, reliability, and service life of these ceramics by improving surface quality and reducing defects. To understand the mechanism behind the surface formation of Si₃N₄ ceramics, laser-assisted turning, conventional turning, and laser-assisted turning experiments were conducted on Si₃N₄ ceramic materials, employing numerical modeling, temperature field simulation, and experimental investigations. Following the simulation, the laws governing laser radiation are examined. The temperatures derived from the simulations are in line with those obtained from laser illumination. Laser irradiation has been demonstrated to effectively repair defects in ceramic surfaces by reducing defect depth and forming a protective oxide film through oxidation reactions. This process can be utilized to repair ceramic surfaces at high temperatures, where oxidation reactions and thermal stresses are prevalent. A study was conducted to examine the surface roughness and morphology of conventional turning, oxidized turning, and laser-assisted turning using EDS spectroscopy. The results of the study indicated that an oxide film is generated on the surface after high-temperature heating to attach to the substrate surface. Based on the surface roughness Sa = 5.797 m for conventional turning, the surface roughness for laser-assisted turning was Sa = 1.893 m, which is an improvement of 67.34%. The generation of continuous-shaped chips after the experiment showed that plastic removal was evident. During machining, laser-assisted turning reduces the turning force and significantly improves the tool life, according to an analysis of cutting force and tool damage. This study reveals the method to remove the surface of Si₃N₄ ceramics.

The applications of nanocomposites in aerospace, automotive and biomedical sectors are rapidly expanding, but challenges in understanding their deformation behavior persist, necessitating further study as current research remains in a nascent stage. This work examines the machinability of Mg-Al₂O₃ nanocomposites, driven by their high strength-to-weight ratio and cost-effectiveness. Despite the increasing interest in nanocomposites, very few studies have examined the machinability of Mg-Al₂O₃ with varying reinforcement levels. Moreover, the combined influence of machining parameters, cutting inserts and reinforcement volume remains underexplored, representing a significant gap in literature. Turning experiments were performed using varying nano-Al₂O₃ reinforcements (2.5, 5%), cutting tool inserts (WC, PCD), speeds (71, 133 and 173 m/min) and feeds (0.12, 0.14 and 0.16 mm/rev) under dry conditions. Results showed that increasing cutting speed reduced the cutting force by 52.3% for WC and 28.4% for PCD inserts, primarily due to thermal softening. PCD tools lowered cutting force by 23.6% compared to WC, indicating superior tooling and wear resistance. Higher reinforcement (5% Al₂O₃) increased the cutting force by 22% at low speeds but improved the surface roughness by 35% at high speeds. PCD inserts achieved a 69.9% Ra reduction at 5% reinforcement, while WC showed a 58.9% improvement. PCD tools achieved optimal results with continuous chip formation at high speeds, while WC tools performed better with lower reinforcement and speed. Reinforcement levels and cutting speeds critically influenced chip morphology and the material removal mode (brittle versus ductile). Overall, better machining performance was achieved using PCD inserts at a cutting speed of 173 m/min and feed of 0.12 mm/rev, where cutting force was minimized, and surface roughness improved by nearly 70%. WC inserts were most effective at moderate speeds (133 m/min) and lower reinforcement levels (2.5% Al₂O₃), with stable forces and acceptable surface finish.

Friction Stir Extrusion is solid-state recycling process which enables the direct extrusion from waste materials, reducing energy consumption and enhancing the metallurgical quality of the extruded parts. In this study, a thorough analysis was conducted on various geometries of the extruded parts, process parameters and setups: the direct and inverse traditional hot extrusion and the Friction Stir Extrusion processes. Moreover, a comprehensive evaluation of all the components contributing to the energy demand of both the traditional hot extrusion process and the Friction Stir Extrusion was conducted. To accomplish this, the same simulation model was developed and adapted for each process, extracting the data to evaluate the energy consumption related to axial thrusts, rotational forces in Friction Stir Extrusion, and preheating in traditional extrusion. Through the comparison of the obtained results, it was possible to discern the specific geometries, setups, and parameter combinations for which Friction Stir Extrusion demonstrates superior energy efficiency in contrast to traditional extrusion and vice versa. The study’s findings suggest that the Friction Stir Extrusion offers significant advantages over traditional recycling methods, enabling the production of high-quality extruded parts with reduced energy consumption, only if some certain conditions were considered. In particular, only when comparing the same extruded mass (7 g) for both technologies, Friction Stir Extrusion proved to be significantly more energy efficient in all scenarios, as only half (for lower descent tool feed) and a quarter (for higher descent tool feed) of the specific energy of the traditional extrusion process is required to complete the process. Furthermore, the identification of optimal process parameters and setups, as well as the analysis of bonding phenomena, provides valuable insight into the effective implementation of the process in the aluminum recycling industry.

The adhesion force is a critical factor in MEMS (micro-electro-mechanical systems) technology, especially in the micro-assembly process using microgrippers. Given the diminutive size and weight of MEMS devices, the contact force between the surfaces of MEMS components can lead to several problematic scenarios during the assembly procedure, such as the undesirable adhesion of the MEMS surface components. This can negatively affect the assembly procedure and result in incorrect positioning of microparts. Therefore, reducing the adhesion force is essential for enhancing micro-assembly. This research aimed to explore the impact of angularization of the interstitial layer and the last layer on surface morphology, surface roughness parameters, and adhesion using the glancing angle deposition method. To achieve this, six samples were simultaneously layered with varying experimental angles of 0, 30, 45, 60, 75, and 85 degrees for the deposition of thin films. These films comprised a titanium interstitial layer and the main layer Ag-Pd (0.9 wt.%)-Cu (1.0 wt.%). Following the glancing deposition, the morphology of the films was examined using SEM, while the layer roughness and adhesion force were determined using AFM. The findings of this study revealed that increasing the angle of the referenced layer resulted in an initial increase and subsequent decrease in both the grain height and surface roughness of the silver alloy. The tests showed that the angle of 85 degrees corresponded to the lowest level of adhesion observed in both experiments. In conclusion, it can be inferred that adjusting the angulation of the Ti interstitial layer in relation to the angulation of the last layer of the silver alloy results in improved grain size distribution, increased grain height, and enhanced regularity in surface adhesion behavior.

The lubricating and cooling performance is important role in the reduction of high temperature in the cutting zone. The nanofluid significantly improves the heat transfer capacity and lubricating performance of the base fluid. In the present work, the lubricating and grinding performance of water-based copper oxide (CuO) nanofluid under minimum quantity lubrication (MQL) for AISI D3 material grinding was evaluated under different conditions of lubrication. The macro- and micro-evaluation parameters were considered for finding the lubricating performance of nanofluid at the wheel/workpiece contact interface. The experimental finding shows improvement of surface grinding process by CuO nanofluid using 0.2 volume% concentrations under MQL. The coefficient of friction is reduced by 29.94%, tangential force by 22.22%, temperature at the wheel/workpiece contact interface by 17.42%, surface roughness by 15.69%, and specific energy by 23.41% compared to MQL grinding. The scanning electron microscope images of debris and workpiece surfaces confirmed the lubricating effect of nanofluid and the efficiency of the nanofluid MQL process. Moreover, nanofluid MQL serves the purpose of environment-friendly machining and to produce economical quality production using small quantity of nanofluid.

Utilization of fly ash as a matrix in composite systems offers a low-cost alternative to costlier ceramics. Ash is a waste material obtained from thermal power plants. It endangers our environment. The objective of the work is to utilize these wastes for developing a useful product. For the preparation of the composite, a powder metallurgy route is adopted. Sets of composites are prepared using fly ash and k-feldspar in different proportions. Developed products have been characterized with respect to structural, mechanical, electrical and dielectric properties. The highest reissuance of the composite has been obtained for the composition of 60% fly ash and 40% potassium feldspar (k-Feldspar). X-ray diffraction analysis marks the formation of the mullite phase. SEM micrograph reveals a glassy matrix with dispersion of crystalline phase and a few small pores. Vickers hardness value for the optimized composite is determined to be 212.87. Electrical resistance is measured by two probe methods. The highest resistance of the developed product is determined to be 33.17 giga-ohms. Frequency-dependent dielectric permittivity is estimated. Results indicate a higher permittivity value within a lower frequency region. This happens due to space charge polarization. Dielectric loss is higher in low frequency region and is lower at high-frequency regions. At a frequency of 10 MHz, the dielectric loss tangent is estimated to be 0.07. AC conductivity increases exponentially with frequency at room temperature. The developed material poses high resistance and good dielectric value suitable for electrical applications.

Steel recycling helps to preserve natural resources, reduce CO₂ emissions, and lower manufacturing costs. One side effect of recycling is that the massive use of steel scrap leads to increased concentrations of tramp elements, which can modify mechanical properties of final products. Therefore, critical concentrations of such elements and their effects on properties must be established. In this study, the influence of 0.02-0.09 wt.% Mo on the microstructure, texture and mechanical properties have been investigated for extra-low carbon (ELC) steel. It is found that although the microstructure and texture of this steel after 80% cold rolling are similar in samples with different concentrations of Mo, the rate of recrystallization, average recrystallized grain size and the area fraction of the γ-fiber in the annealing texture decrease with increasing Mo content. Analysis of a partially recrystallized microstructure indicates that frequencies of nucleated grains having either orientations along the γ-fiber or random orientations are higher than the frequency of grains having orientations along the α-fiber. Furthermore, it is found that hardness and strength of fully recrystallized samples increase, while n- and r-values decrease with increasing Mo content. The results obtained suggest that the presence of up to 0.02 wt.% Mo can be tolerated in recycled ELC steel for applications where high drawability is required.

The present study examined the effects of consolidation method and temperature on the microstructure, density and mechanical properties at room temperature of 21-4N austenitic steel. Mechanical alloying was initiated with ferro-alloys such as Fe-Cr, Fe-Mn, and Fe-Ni, followed by consolidation through vacuum hot pressing (VHP) and spark plasma sintering (SPS). VHP was conducted at two distinct temperatures, namely 1150 and 1200 °C, for a duration of 90 min., while SPS was carried out at these temperatures for 15 min. In both the cases, 60 MPa load was applied for consolidation. The maximum relative densities obtained were 88.4 and 91.8% for VHP and SPS samples, respectively, at 1150 °C. The same were found to be higher at 1200 °C, but VHP showed a higher density of 97.3% when compared to SPS density of 95.2%. VHP samples have shown an average grain size of 3.4 µm along with grain boundary carbide precipitates, while SPS samples have shown a grain size of 1.6 µm without any presence of carbides. SEM analysis of the fracture surface indicated the presence of dimples and micro-void coalescence in VHP samples. On the other hand, SPS samples have shown predominantly intergranular fracture. As a result, the material consolidated by VHP exhibited a yield strength and elongation of 548 MPa and 17%, respectively.