Materialwissenschaft und Werkstofftechnik最新文献

The aim of the research is to investigate the weldability of thick sections of carbon steel using submerged arc welding with varying process parameters. The experimental design for joining thick carbon steel involves manipulating input weld process parameters such as current (A), voltage (V), weld speed (mm/h), and weld electrode diameter (mm). The quality of the weld material is assessed based on transformations in microstructure, weld hardness measured by Brinell hardness number, and tensile strength (MPa). It is crucial to note that the grain structure and metallurgical behavior of other hard materials may differ significantly. The presence of carbon in the ferrite phase has led to the formation of bainite, martensite, and composites of martensite and austenite within the weld zone, as confirmed by high-resolution microscopy. The weldment‘s hardness has increased from 242.5 HV 30 in the base metal to 316.4 HV 30 in the weldment due to metallurgical alterations in the microstructure. Weld energy input emerges as the primary factor influencing weld quality. With increasing weld current and voltage, there is a corresponding increase in the joined metal, resulting in improved characteristics in the weld structure, particularly at maximal energy input and welding speed. In the context of boiler applications, understanding the weldability of thick carbon steel sections is paramount for ensuring structural integrity and longevity under high-temperature and high-pressure conditions. The optimized welding parameters identified in this study can contribute to enhancing the reliability and performance of boilers, thereby promoting safety and efficiency in industrial settings.

Synthesis of two-dimensional (2D) titanium carbide (Ti₃C₂T_x), with the name of MXene, by etching Ti₃AlC₂ (MAX) for different times 20 (v/v) % hydrofluoric acid (HF) at 40 °C was carried out. The influences of time, temperature and source of MAX on the synthesis of MXene were researched. The MXenes produced were characterized by fourier-transform ınfrared (FT-IR) spectroscopy technique, energy dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM), x-ray diffraction (XRD) and thermogravimetry (TG) instruments. Above 390 °C, MXene layers were considerably oxidizing and forming anatase and rutile phases of TiO₂ under air atmosphere. The resistance of MAX and MXene was 3.6 Ω and 116 Ω, respectively. However, the resistance of the residual part of MXene heated to 620 °C considerably increased to 17850 Ω. This behavior is another important piece of evidence showing that the MXene crystal structure has changed significantly and transformed into a new chemical structure containing anatase and rutil titanium oxide (TiO₂). The dielectric loss (ϵ’’) and alternating conductivity (δ_ac) of the MAX and MXenes were determined from their impedance measurements. The ϵ’’ and δ_ac values of MXene were compared with those of MAX. Direct curent conductivities of MAX and MXene produced for 24 h were found to be 0.016 S/cm and 0.0023 S/cm, respectively.

The research aims to forecast the mechanical performance of a hybrid woven fabric natural composite subjected to compression, utilizing the three-dimensional finite element method. A detailed finite element model of a plain woven fabric unit cell is created and analyzed for different materials like flax, basalt, and jute, and combinations of these materials (inter-yarn hybrid basalt-flax, jute-flax and basalt-jute fabrics). It is observed that fabric‘s response to compression is mainly influenced by the transverse longitudinal shear behaviour and the stiffness of the yarn cross-section. Compression of single-layer woven fabric involves yarn bending and compaction, resulting in varying fiber volume fractions in different areas due to compaction. The basalt-jute hybrid plain woven fabric outperformed other plant-based fiber fabrics with a polypropylene matrix in terms of mechanical performance under compression. Increase in yarn spacing and fabric thickness resulted in higher strain energy and displacement, attributed to changes in fiber volume fraction and crimp angle. Whereas, increasing yarn width led to a stiffer fabric due to increased contact area at the crossover region and higher bending rigidity, resulting in decreased strain energy and displacement. Importantly, this developed model can effectively simulate textile fabrics with diverse weaving patterns, material properties, and loading conditions.

Utilization of inorganic waste, if included in composite material, can be beneficial in reducing the accumulation of waste, which could help in resolving problems of disposal. beside from that, incorporating waste into composite materials also reduces the overall cost of the composites as a whole. The study examines the impact of dolomite content on the mechanical properties of the composites. Increasing the amount of dolomite in the composite significantly weakens its flexural strength, falling from 42.4 MPa at 0 % dolomite to 28.7 MPa at 15 % dolomite. Composite tensile strength also decreases by up to 25.8 % with rising dolomite dust concentration. Additionally, dolomite increases interlaminar shear strength (ILSS), with EDH15 composites showing the highest improvement. Dolomite dust in epoxy-based composites increases the hardness value from 85 HRL to 95 HRL with an increase in dolomite dust content. The erosion test perform on air jet tester shows lowest wear rate was achieved under the following conditions: 10 % dolomite dust weight, 30° impingement angle, 10 m s⁻¹ impact velocity, and 150 μm erodent size. Furthermore, scanning electron microscopy was used to examine the damaged, eroded surfaces for assumed wear mechanisms.

In this work, an investigation has been carried out on the sound absorption properties of the microperforated composites prepared by filling natural luffa fiber and synthetic luffa fiber. These composite structures are created by 3-dimensional printing of polylactic acid, which exhibits excellent biodegradability. After preparing the structure, the micro-perforation is done at the top of the composite with the help of a heated cylindrical drill. During the printing process, the infill density (printing parameter) and type of luffa fiber (natural and synthetic) have been varied to find out its effect on acoustic properties. Finally, a comparative study is carried out among natural luffa fiber and without using natural luffa fiber. The results showed excellent sound absorption of luffa filled structure compared to an unfilled structure. Out of three different infilled densities, the density of 5 % revealed a maximum amount of absorption, suggesting the potential applications of these structures in the field of sound absorption.

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.