Materialwissenschaft und Werkstofftechnik最新文献

This study investigates the effects of different processing methods on the chemical composition of thermoplastic polyurethanes, focusing on isocyanates and extractable oligomers. Using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and gas chromatography/mass spectrometry (GC/MS), seven commercially available thermoplastic polyurethane samples are analyzed as unprocessed granulate, injection-molded, and 3D-printed parts. Diffuse reflectance infrared Fourier transform spectroscopy analysis enables direct identification and quantification of isocyanates. In two polyester-based materials, substantial isocyanate contents were detected after processing. In both cases, the concentrations exceeded the w = 0.1 % threshold defined by REACH Regulation (EU) 2020/1149 for monomeric diisocyanates, thereby underscoring the regulatory significance of processing-induced changes. Gas chromatography/mass spectrometry analysis complements these results by indirectly but quantitatively detecting the formation of oligomers during processing via methylene diphenyl diisocyanate. The highest isocyanate content determined was w = 1.16 % in an injection-molded sample. The comparison of both methods shows their complementary significance in isocyanate detection. The study highlights the importance of choosing the correct processing parameters and analytical techniques to ensure thermoplastic polyurethane integrity and reduce undesirable changes in material composition.

This study investigates the densification behavior and mechanical properties of LM26 aluminum alloy powder subjected to various compaction pressures in powder metallurgy. The powder's flowability and compressibility were evaluated using the angle of repose, Carr's index, and Hausner ratio, confirming its suitability for compaction processes. Particle characterization through dynamic light scattering, energy-dispersive x-ray spectroscopy, field emission scanning electron microscopy, and x-ray diffraction revealed insights into particle size, elemental composition, morphology, and crystalline phases. Green density, determined by mass-to-volume ratio, ranged from 77.45 % to 96.02 % at pressures of 100 MPa–550 MPa, with a notable linear relationship between applied pressure and density. The Panelli and Ambrosio Filho model best described the compressibility behavior. Mechanical testing showed significant increases in Vickers hardness, reaching 42.89 HV 0.2 for cube specimens at 550 MPa and 44.12 HV 0.2 for cuboid specimens at 250 MPa. Flexural strength reached a peak of 30.44 MPa at 250 MPa, highlighting the benefits of higher compaction pressures. Weibull distribution analysis confirmed the uniformity and reliability of hardness and strength characteristics, reinforcing the applicability of powder metallurgy for structural applications.

This study investigated the resistance spot welding performance of 1.5 mm thick Mg-6Sn-1Ca and Mg-7Sn-1Ca magnesium alloys, focusing on the effects of welding current (12 kA to 16 kA) on tensile properties, hardness, fracture morphology, microstructure, and nugget diameter. Optical microscopy and scanning electron microscopy were employed for characterization. The results indicate that the Vickers hardness of Mg-6Sn-1Ca was highest in the nugget zone, followed by the heat affected zone, and lowest in the base metal, with the overall hardness peaking at 14 kA. For Mg-7Sn-1Ca, the hardness was highest in the base metal and lowest in the nugget zone at 12 kA to 14 kA, while at 16 kA, the nugget zone hardness became the highest and the base metal hardness the lowest. Both alloys exhibited brittle fracture characteristics, with coarse grains in the heat affected zone and finer grains in the nugget zone, while the base metal consisted of fine equiaxed grains. As the welding current increased, the grains in the nugget zone coarsened, and the nugget diameter reached its maximum at 14 kA, decreasing at 16 kA. This research provides a foundation for optimizing the resistance spot welding process of dissimilar magnesium alloys.

Titanium-6 aluminum-7 niobium alloy, known for its excellent biocompatibility, mechanical strength, and corrosion resistance, is an important choice for bone implants. Through selenium dioxide modification and the preparation of a micro-arc oxidation-gelatin composite film, a gelatin layer approximately 1 micrometer thick was formed, with some micropores exposed. Electrochemical tests indicated an increase in corrosion current density, while contact angle tests showed improved wettability of the film. In vitro mineralization experiments demonstrated higher hydroxyapatite deposition capacity of the composite film, indicating significantly enhanced bioactivity and mineralization performance.

Chemical beam vapor deposition combined with the use of shadow masks is a versatile technique to deposit patterned multifunctional (in terms of thickness levels and chemical composition) oxide thin films. In this paper, the methodology and the results related to thin film patterning are presented through a use case where such thin films are used as identity tags for connected devices. The system relies on the reading of one or more material properties of the tag affixed to the object that must be combined with a secure authentication protocol. The measured properties have a twofold dimension: first ones are deterministic and based on submillimeter scale patterns (i.e. they can be predicted knowing exact deposition conditions of the tag) while the others are totally random due to unpredictable sub-micrometric growth patterns. This allows the tags to be either exploited as a standard unique identifier (with enrollment) or based on a twin tag comparison (considering only deterministic properties). Due to the large number of deposition parameters and properties associated to each tag, they are unique, unclonable and secured from reverse engineering. A first reading prototype based only on film transmission reading at different wavelengths is also presented.

The Ni_1-xZn_xFe₂O₄(x=0.2,0.3,0.4) ferrite doped with 2 wt.-% Y-type Ba₂Co₂Fe₁₂O₂₂ was prepared by conventional solid phase reaction method. The x-ray diffractometer, scanning electron microscope, vibrating sample magnetometer and magnetic flux density-magnetic field analyzer were utilized to investigate their structural, morphological and magnetic properties, respectively. The x-ray diffractometer and scanning electron microscope analysis show that the sample has uniform grain distribution, high overall density and small porosity. The magnetic property test shows that the permeability, saturation magnetization, and magnetic loss of the samples changed accordingly with higher values of x, while the magnetic loss is minimized when x = 0.3. The effect of different zinc contents on the magnetic properties of Y-type Ba₂Co₂Fe₁₂O₂₂ doped samples is studied systematically, which provides theoretical support and experimental basis for the optimal design and application of high performance soft magnetic ferrite.

Recent advancements in material science have advanced high-entropy alloy (HEA) composites through sophisticated solid-state processing techniques, achieving remarkable mechanical properties for lightweight applications. Methods like non-equilibrium solidification, magnetic field-assisted processing, and laser shock peening have enhanced dispersion strengthening, yielding composites with a 35 % increase in yield strength and 40 % improved hardness compared to traditional aluminum alloys. Integrating micro/nanoscale reinforcements - such as 5 vol.-% graphene nanoplatelets or 2 wt.-% carbon nanotubes - with aluminum matrices via mechanical ball-milling and ultrasound-assisted exfoliation ensures uniform dispersion, reducing clustering by 60 %. Machine learning algorithms optimize processing parameters, improving particle distribution homogeneity by 25 %. Dispersion strengthening, driven by 10 nm – 50 nm particles, impedes dislocation motion, boosting wear resistance by 30 %. Biomimetic liquid-state processing, mimicking nacre-like structures, and responsive nanoparticles enable adaptive responses, enhancing fatigue life by 20 %. These advancements facilitate applications in aerospace, biomedical, and energy sectors, promising transformative impacts. Continued research into sustainable synthesis and hybrid nano composites will further elevate material performance, redefining technological capabilities in material science.

Utilizing construction waste as reinforcement in polymer composites is becoming more popular these days. In the current research, composites with varying amounts of red brick dust in an epoxy matrix are developed. The mechanical characteristics of these composites have been assessed. As the filler content increases, a progressive rise in impact strength and microhardness values is noted. However, as compared to neat epoxy, epoxy-red brick dust composites show a slight reduction in tensile and flexural strength. A maximum hardness of 30.82 HV 2 and impact strength of 25.7 kJ/m² are obtained by adding 30 wt.-% of red brick dust to the epoxy matrix; nevertheless, the tensile and flexural strengths are determined to be 23.37 MPa and 10.37 MPa, respectively. The impact strength of neat polymer increased by 43.57 % with an addition 30 wt.-% filler. Simple linear regression is used to compare the results of mechanical properties. The machine learning simple linear regression model's projected outcomes closely match the mechanical values. Mechanical behaviors of the composites are also investigated with the help of Digimat software and compared with the investigational results. It has been noted that the experimental results are in excellent agreement with the numerically predicted values.

This study examined how welding speed affected the mechanical characteristics and microstructure of carbon dioxide gas-shielded welding joints made of 2 mm thick DP780 high-strength steel. The findings indicate that acicular ferrite makes up the majority of the weld zone, while slate bainite and slate martensite are found in the coarse and fine grain zones. The degree of recrystallization in the weld zone has a trend of rising and then falling with increasing welding speed. The welded joint's elongation was 13.4 % and its tensile strength was 713.32 MPa at the ideal welding speed of 430 mm·min⁻¹. The welded connection had a maximum microhardness of 352.2 HV 1. Tensile fracture surfaces show second-phase precipitated particles that affect mechanical properties.