Materialwissenschaft und Werkstofftechnik最新文献

This study focused on developing microstructural, thermal, and radiation shielding changes in Al₅₀Si₂₅B₂₅ powders using mechanical alloying techniques. Based on the x-ray powder diffraction data, the crystallite size and microstrain of the 100-hours milled powder were calculated as 0.25 nm and 50.33 %, respectively. The solubility of silicon in the α-aluminium matrix increased with longer mechanical alloying duration. Transmission electron microscope analyses further showed that the alloy particulates had an average size of 3 μm and an average grain size of 0.226 nm. The radiation shielding properties of the Al₅₀Si₂₅B₂₅ powders indicated that the Linear Attenuation Coefficient value increased from 0.0554±0.1689 cm⁻¹ to 1.0632±0.2425 cm⁻¹ with an increase in the thickness of the Al₅₀Si₂₅B₂₅ alloy. This work successfully demonstrated the potential of mechanical alloying techniques to enhance the microstructural and thermal properties of Al₅₀Si₂₅B₂₅ powders. It highlighted their effectiveness in providing radiation shielding capabilities when varying the thickness of the alloy.

The tempering process can increase the mechanical properties of the material, such as hardness and impact strength, as well as enhance the corrosion resistance. Therefore, the selection of appropriate tempering time and cooling environment is crucial. This study aims to investigate changes in properties such as hardness, tensile strength, corrosion resistance, and microstructure of AA5083-H111 alloy after a brief tempering process (30 minutes, 45 minutes and 60 minutes) at 320 °C, followed by cooling in air and water environments. The study found that tempering time and cooling environment significantly affect the mechanical properties and corrosion rate. The results show that samples labeled as S30 and S60 have the highest hardness and impact strength, but the best corrosion resistance is achieved in the S60 sample. This study demonstrates that even after a limited-term tempering process, the mechanical properties and corrosion resistance of AA5083-H111 alloy can be improved. This information is crucial data for use in the production and application of alloys. The findings of this study could have important implications for the production and application of AA5083-H111 alloy in industries such as aerospace, automotive, and marine engineering.

The lifespan of the guide rail is a bottleneck restricting the operational life of electromagnetic railguns. A well-designed arc extinguishing device can reduce the arcing erosion caused by residual currents within the guide rail. The CuW alloy is widely used in the high-pressure arc extinction field due to its excellent electrical and thermal conductivity, high strength, and hardness. Based on the theory of equilibrium state arc plasma, a finite element model of the air arc-CuW electrode coupling in the arc extinction device was established to study millisecond-level arc initiation, evolution, extinguishing characteristics, and distribution patterns under extreme and harsh operational conditions with a current input of 110 kA. The highest temperature in the arc column region was found to exceed 50,000 K. The study elucidated the influence of arc extinction device parameters on arc evolution, breakdown time, and breakdown voltage. Consequently, it established that the R70 spherical electrode exhibits optimal arc extinguishing characteristics. The aim of this research is to provide theoretical support for optimizing the arc suppression device. Additionally, experiments on high-speed and high-current arc extinction device discharges were conducted to validate the finite element analysis results regarding arc diffusion patterns and electrode erosion.

The electrical discharge machining is very successful and generally recognized for producing complicated shapes and small openings with exceptional precision. The objective of this study is to assess the impact of different electrical discharge machining parameters on the attributes of the machining process. The evaluation of the machining process was conducted based on the workpiece‘s material removal rate, the rate at which the electrodes wear, and the level of surface roughness. Simultaneously achieving a high material removal rate, low electrode wear rate, and high surface roughness is not possible with a specific combination of approaches due to their contradicting nature. Frequently, it is necessary to independently apply many measures instantaneously in order to assess their impact on various responses. This research investigates the machining of high carbon high chromium steel making use of electrical discharge machining with aluminum, copper, and graphite electrodes. The study focuses on the impact of different current intensities on the rate of material removal, electrode wear, and surface roughness. The experimental results demonstrate that the highest material removal rate (mm^cubicmin⁻¹) is achieved at a current density of 12 A when using a copper electrode (54.67), as opposed to aluminum electrode (22.91) and graphite electrode (29.43).

In the present work, grain-refined WE43 magnesium alloy was produced by friction stir processing to investigate the in vitro degradation behavior targeted for temporary bone implant applications. Friction stir processing resulted in significant grain refinement (from 46±4.2 μm to 16.1±5.4 μm) as observed from microstructural studies. Increased wettability was observed from the contact angle measurements in grain-refined WE43 alloy. The corrosion behavior of the base alloy and the grain refined alloy assessed by potentiodynamic polarization tests demonstrated the influence of the smaller grain size and decreased intermetallics on enhancing corrosion resistance. Immersion studies carried out in simulated body fluids for one week indicated a quick development of the protective magnesium hydroxide on the surface of grain-refined WE43 alloy compared with the base alloy. The deposition of the mineral phases from the immersed solution on the surface of the samples was studied by scanning electron microscopy and x-ray diffraction analysis to assess the effect of microstructure on the biomineralization. Promisingly, grain refined WE43 exhibited relatively excellent mineral deposition which further helped to control the degradation of the alloy. The weight loss measurements of the samples from the immersion tests were also in good agreement with the electrochemical test results. Hence, the results demonstrate the promising role of grain refinement by friction stir processing in tailoring WE43 magnesium alloy with better degradation behavior for temporary bone implant applications.

This paper presents the parametric investigation and optimization of various chemical treatment parameters that affect the mechanical performance of the green composite. The injection moulding method was used to produce the green composites using flax fibre (FF) and polylactic acid (PLA). The chemical parameters chosen to investigate their effects are chemical type (sodium hydroxide, sodium carbonate, and potassium hydroxide), chemical concentrations (1 %, 2 %, and 3 % (w/v)), and duration for fibre treatment (2 h, 4 h, and 6 h). The mechanical performance of the green composites was assessed by evaluating the various properties namely strength, modulus, and elongation under tensile, share, flexural, and compression loading conditions. The morphological study was also performed to examine the failure behavior of the composite after mechanical testing. The effect of fibre length (2 mm, 3 mm, 4 mm, 5 mm, and 6 mm) and fibre loading (10 wt.%, 20 wt.%, and 30 wt.%) on the performance of the flax fibre (FF)/polylactic acid (PLA) composite was also investigated. The fibre dispersion, fibre orientation, and fibre length retention were investigated to assess the characteristics of fibre during injection moulding of the developed flax fibre (FF)/polylactic acid (PLA) composite.

The corrosion behavior of Q345qNH steel and Q420qNH steel in simulated industrial atmospheric environment medium was studied by periodic immersion+infrared aging corrosion experiment. The results show that the corrosion type of both samples is uneven comprehensive corrosion, and the rust layer formed in the later stage of corrosion is relatively dense. But average corrosion rate of Q345qNH steel is always lower than that of Q420qNH steel, and the ratio of I_α-FeOOH/I_γ-FeOOH in rust layer is always higher. Compared with Q420qNH steel, Q345qNH steel has fewer surface pits but deeper local pits. The self-corrosion potential of Q345qNH steel increases obviously, the resistance of the rust layer is larger, and protection to the matrix is stronger. This is because the formation of a large number of corrosion microcells induced by fine lamellar sorbite tissue that uneven distributed in Q420qNH steel, which increases the corrosion rate and makes corrosion uneven, while the larger pearlitic group in Q345qNH steel increases the local corrosion rate. However, the higher chromium/carbon ratio in Q345qNH steel promotes the conversion of lepidocrocite to goethite and inhibits the cathode reaction in the infrared drying stage, improving the density and stability of the rust layer.