Materialwissenschaft und Werkstofftechnik最新文献

Crevice corrosion behavior of 304 stainless steel and B30 copper-nickel alloys in sodium chloride solution containing different concentrations of thiosulfate ion (S₂O₃²⁻) were studied by wire beam electrode. The increase of thiosulfate ion concentration promotes the crevice corrosion of 304 stainless steel. However, the crevice corrosion is inhibited due to excess thiosulfate ions. The local corrosion intensity inside and outside the crevice also formed an inversion at the chloride ion (Cl⁻)/thiosulfate ion concentration ratio. When coupled 304 stainless steel and B30 copper-nickel alloy occurs crevice corrosion, 304 stainless steel outside the crevice acts as the cathode and B30 copper-nickel alloy acts as the anode at the initial stage. The active dissolution of 304 stainless steel inside and outside the crevice jointly promoted the crevice corrosion of B30 copper-nickel alloy at the later stage. The crevice corrosion mechanisms of 304 stainless steel and B30 copper-nickel alloy are also discussed.

Four-dimensional bioprinting incorporates the notion of time with three-dimensional bioprinting as the additional dimension and offers the prospect of constructing detailed and essential biological frameworks. It has been considered the future of biomedical applications, namely tissue engineering, wound repair, drug delivery systems, etc. Through the adoption of stimulus-responsive materials, Four-Dimensional bioprinting is an excellent way to construct dynamic, three-dimensional-structured biological constructs that morph their shape in reaction to varied stimuli. A new frontier in tissue engineering, i.e. four dimensional bioprinting, refers to the operational development and maturation of cell-loaded printed structures over time. This review article is concerned with the idea of four-dimensional bioprinting and the latest advances in smart/intelligent materials, which can be activated by various stimuli to create biomimetic constructs and materials, along with brief insights into biomedical applications. These advancements have significant possibilities for biomedical research while also offering promising future prospects.

Cement industries, pivotal in concrete production, remain a global environmental concern due to their impact on sustainability. Traditional concrete exhibits robust compressive strength but lacks in tension strength, often resulting in cracks. Addressing this, well-dispersed fibers play a crucial role in mitigating crack formation. Reinforcement strategies, transferring tensile loads to the material, are pivotal for enhancing concrete's overall strength. Geopolymers emerge as a sustainable alternative, potentially reducing greenhouse gas emissions associated with cement production. With the prospect of replacing Portland cement, geopolymers, including fly ash, ground granulated blast furnace slag, and silica fumes, aim to minimize carbon footprints. This research optimizes the workability and mechanical properties of self-compacting geopolymer concrete by adjusting binding materials, molarity, superplasticizer, curing temperature, and fibers. Concrete alternatives like self compacting geopolymer concrete are resource- and waste-efficient since they compress under their own weight. Composite geopolymers with fiber reinforcing are widespread. Microstructural, mechanical, and physical qualities are explored in fiber reinforced geopolymer concrete research publications by fiber type. Self-compacting geopolymer concrete is more environmentally friendly and resource-efficient than ordinary concrete, according to this study. Geopolymer composites are improved by studying fiber reinforced self compacting geopolymer concrete with different fiber reinforcements.

High-frequency pulse gas tungsten arc (GTA) welding was explored for 3 mm thick 304HCu with direct current electrode negative (DCEN) polarity at different pulse frequencies from 100 Hz to 1500 Hz. For a fixed set of optimized welding parameters, the depth of penetration increased with increasing pulse frequency, which was attributed to arc constriction during the high frequency pulsing. Optical and scanning electron microscopy were performed for the microstructural characterization of the welds. Full penetration welds produced at 1000 Hz and 1500 Hz had a fine dendritic structure with mechanical properties better than the conventional gas tungsten arc weld.

This study investigated the impacts of fibre stacking sequence and sodium hydroxide treatment on the mechanical properties of sustainable sisal/ramie hybrid vinyl ester composites. Fourier transform infrared analysis (FTIR) revealed significant chemical changes in treated fibres, including increased fibre purity due to the removal of hemicellulose and portions of lignin, resulting in more hydroxyl groups. These changes enhanced the interaction between fibres and the matrix, thereby improving the mechanical properties of the composites. Among various stacking sequences, the ramie/sisal/sisal/ramie (C6) configuration exhibited the highest Shore-D hardness (61.2 D), tensile strength (30.83 MPa), and tensile modulus (0.84 GPa), attributed to the strategic placement of ramie layers in load-bearing positions. This configuration also demonstrated superior flexural strength (63.33 MPa) and flexural modulus (2.02 GPa) due to the balanced distribution of stress between the matrix and fibres. Scanning electron microscopy (SEM) images confirmed that alkali treatment improved fibre-matrix adhesion, reducing defects such as fibre pullout and matrix cracks. The findings highlight that both fibre stacking sequence and alkali treatment play a crucial role in enhancing the mechanical performance of natural fibre composites, making them suitable for applications demanding high strength and durability.

Titanium aluminum niobium-based alloy is one of the most promising high-temperature structural materials in aerospace field, whose phase transformation mechanism has been extensively studied. In this paper, the lamellar O-phase of Ti-22Al-23Nb-1Mo-1Zr alloy is found being transformed to B2-phase at ambient temperature by high-pressure torsion. Further x-ray diffraction investigation shows that such transformation is related to the accumulation of lattice strain in the O-phase. When the lattice strain in the O-phase accumulates to an upper limit, the O-phase will be transformed into the B2-phase by shear transformation. Finally, the mechanism of phase transformation is discussed.

A failure investigation was conducted on a 321 stainless steel corrugated flexible hose in a reforming plant. Several of these flexible hoses failed while in service after being subjected to elevated temperatures and unexpected shutdowns. Visual inspections showed various surface deposits, and energy-dispersive spectroscopy elemental analysis detected the presence of chlorine, sodium, potassium, and sulfur, which are indicative of stress corrosion cracking and possible caustic stress corrosion cracking. Optical and scanning electron microscope imaging showed that the cracks were typically stress corrosion cracking-type with a branched pattern, initiating from the inner surface and propagating intergranular to the outer surface. Coarse and elongated δ-ferrite islands in the heat-affected zone were identified as crack propagation pathways. The average hardness measurements were approximately 240 HV0.5 ± 3 HV0.5 for the base metal, 257 HV0.5 ± 3 HV0.5 for the heat-affected zone, and 265 HV0.5 ± 3 HV0.5 for the weld metal. These variations, influenced by welding process parameters such as cooling rate, made the heat-affected zone a potential failure region in the flexible hose. The root causes of the failure of the flexible hoses were determined to be improper service conditions in terms of temperature control, unexpected shutdowns, and insufficient control of welding process parameters.