Papers by Keyword: Microstructure

Abstract: To address the long cycle, high cost, and low efficiency of traditional Aluminum Foam Sandwich preform preparation, this study employs Friction Stir Welding to fabricate preforms with uniform powder mixing. Integrated experimental-simulation approaches reveal the formation mechanism. Temperature field analysis via infrared thermography and Fluent simulation confirms a peak temperature of 522°C at 2000 r/min rotation speed, generating an 85°C/mm thermal gradient and expanding the >450°C zone to 1.8 times the shoulder diameter. Concurrently, flow field modeling demonstrates intensified vortex flow at 2000 r/min, with tracer particles verifying uniform TiH₂/Al₂O₃ dispersion and onion ring radius expansion under 50 mm/min welding speed. Microstructural characterization identifies optimal joint quality through refined nugget zone grains averaging 1.3 μm and porosity below 2% at parameters of 2000 r/min rotation speed, 50 mm/min welding speed, 3 mm spacing, and 0.1 mm reduction. These results establish a methodology for regulating preform structural uniformity.

Abstract: This study investigates the effect of Sr (0.1, 0.15, and 0.2 wt.%) modification on the microstructure and morphological evolution of the in-situ Al-15%Mg₂Si-4.5%Si composite. The composites are developed via Low superheat casting (LSC) technique, at the onset of gravity, and subsequently characterized through optical microscope, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electron Probe Microprobe Analysis (EPMA), and XRD texture analysis. It is found that, with the increase of Sr content in the Al-15%Mg₂Si-4.5%Si composite, the morphology of primary Mg₂Si particles changes from irregular dendritic and hopper structure to nearly perfect cubic morphology. The addition of 0.2 wt.% Sr reduces the average primary magnesium silicide (Mg₂Si) particle size from ~56 µm to 36 µm and the Al grain size from ~63 µm to ~44 µm, indicating significant refinement. The XRD texture analysis through Orientation Distribution Function (ODF) reveals that the cubic texture and rotated cubic texture are the predominant orientations for Al and Mg₂Si phases, respectively. However, the composite modified with 0.2 wt.% Sr exhibits a weak texture and more random grain distribution, highlighting the role of Sr in reducing grain size and promoting uniformity. These findings underscore the potential of Sr addition to enhance the microstructural and mechanical properties of Al-15Mg₂Si-4.5Si composites for advanced applications.

Abstract: In recent years, high-entropy alloys (HEAs) have attracted significant attention owing to their remarkable physical properties such as high strength. It has also been reported that HEAs have a high potential as biomaterials. Bcc-type bio-HEAs possess high strength and biocompatibility equivalent to those of pure titanium. Bio-metallic materials require a low Young's modulus, similar to that of natural bone, but the Young's modulus of bio-high entropy alloys has not yet been clarified. Therefore, this study elucidates the relationship between microstructure control and Young's modulus in titanium-based bio-HEAs. The TiNbTaZrMo-based bio-HEAs were composed of two bcc phases. These two phases correspond to dendrite and interdendrite structures, respectively. In this study, it was found that by varying the volume fractions of these two phases, it is possible to control the Young's modulus.

Abstract: The design flexibility afforded by additive manufacturing, commonly known as 3D printing, is broadening the industrial applications of high-entropy alloys (HEAs). The 3D-printed CrMnFeCoNi HEA (or Cantor alloy) exhibits a unique combination of strength and ductility, attributed to its multifaceted deformation mechanisms. While the deformation behavior of this alloy under monotonic loading has been extensively studied, its cyclic plasticity, which is crucial for fatigue performance, remains a relatively underexplored area. To address this gap, the current work investigates the deformation microstructure of a CrMnFeCoNi HEA fabricated using laser-beam powder bed fusion. Electron backscatter diffraction (EBSD) is employed to characterize the surface microstructural changes. The results reveal the simultaneous activation of multiple slip systems in the region near the fatigue crack, which induces grain rotation. Additionally, the activation of twinning-induced plasticity plays a significant role in accommodating the cyclic plastic strain.

Abstract: The microstructural evolution of the WZ73 magnesium alloy (Mg-7.4Y-3.8Zn-0.4Zr) was systematically investigated during finishing heat-treatments following twin-roll casting and hot rolling at equivalent strain rates of 17 s⁻¹ and 50 s⁻¹. Hot rolling at 500 °C was performed to achieve a logarithmic strain of 0.7 (thickness reduction from 5.3 mm to 3 mm). Higher strain rates during hot rolling enhanced dynamic recrystallization (DRX), resulting in refined microstructures, whereas lower strain rates promoted the formation of lamellar long period stacking ordered (LPSO) phases. Subsequent heat-treatments at 200 °C to 550 °C for up to 24 hours revealed temperature-dependent microstructural transformations. At 500 °C, complete recrystallization occurred with minimal grain growth, while 550 °C caused grain coarsening, partial grain boundary melting, and morphological changes of the LPSO phase from lamellar to spherical and rod-like structures. Notably, at temperatures above 500 °C, prior hot rolling had limited influence on microstructure. The microstructure and phase evolution were characterized using optical and scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD).

Abstract: Glass containers are manufactured by pressing or blowing a hot glass gob (700-1200°C) onto a metallic mould. Beside forming the glass, moulds are heat exchangers for cooling down the glass final product. To this goal, moulds are made of cast iron or copper-nickel alloy due to their thermal properties. If copper-nickel (nickel aluminium bronze) is the most efficient material, cast iron is mainly used for economic purposes. To enhance the properties of the cast iron mould, cold spray coating of a copper-nickel alloy is investigated. Optimization of the parameters process such as spraying temperature (800-1000°C), pressure (40-50bar) and gun’s travel speed (200-400mm/s) lead to a dense and well-bonded “bronze” coating on cast iron. Microstructural analysis is performed thanks to Optical Microscope, Scanning Electron Microscope, Electron BackScattered Diffraction, X-Rays Diffraction and microhardness tests. Finally, a simple thermal experiment has been designed for demonstrating thermal performances of the coating-substrate couple.

Abstract: This work aimed to develop new S355-based structural steels with enhanced marine corrosion resistance while preserving mechanical properties. Two alloying strategies (Cu/Ni and Al/Cr) were investigated. Conventional and new steel samples were produced and characterized for microstructure, mechanical properties, and corrosion. The new steels showed similar or improved mechanical properties. Potentiodynamic polarization tests indicated stabilization of the oxidation process in the new steels. Laboratory accelerated corrosion tests on painted specimens revealed reduced blistering at paint film defects for some new steels compared to conventional steel. Ongoing research includes evaluating painted specimens in a real offshore environment using an advanced floating laboratory

Abstract: The effect of grain size on the initiation behavior of exfoliation corrosion in cold-rolled Mg-14mass%Li-3mass%Al alloy was examined. Exfoliation corrosion initiated after 30 minutes in the coarse-grained structure (279μm), whereas it was delayed to 60 minutes in the fine-grained structure (75μm) and further to 75 minutes in the ultrafine-grained structure (39μm). This delay is attributed to the suppression of shear band formation and localization during cold rolling with decreasing grain size, which enhances the uniformity of surface reactions in the corrosive environment and promotes faster and denser formation of the protective film at the early stage. Accordingly, the improved condition of the initial corrosion film is considered the primary factor responsible for the delayed onset of exfoliation corrosion.

Abstract: The use of Fe-Si electrical steels in transformer and electrical motor cores requires the material to be cold rolled into thin sheets, as this process efficiently achieves the final dimensions while ensuring desirable magnetic and mechanical properties. For Fe-6.5 wt%Si, hot rolling of this alloy goes well. However, direct cold rolling of the Fe-6.5 wt% Si alloy cause metal cracking due to its inherent brittleness behavior. In this work, we are interested in evaluating the effect of the quenching medium after annealing at 1000°C/1h on the formation of B2 and DO3 ordered phases, which are the main sources of brittleness in the alloy, and on the alloy's mechanical properties. The results show that the quenching in ice-brine reduces the hardness of the material to around 340 HV, with the presence of a cooling rate gradient for each quenching medium, which then causes a micro-hardness gradient. Is shown that an ordering gradient is at the origin of such a harness variation. The size of the ordered domains observed by TEM and the volume fraction of ordered phases measured by XRD decrease after quenching in ice brine, and goes from a continuous form (smoot bending) for quenching in liquid nitrogen to a point form. It is concluded that, the choice of a quenching medium that efficiently removes heat from the sample without changing its physical state can limit the formation of ordered phases in Fe-6.5 wt%Si electrical steel.

Abstract: The effects of common electric arc furnace (EAF) impurities, including copper (Cu), nickel (Ni), molybdenum (Mo), and chromium (Cr), were investigated in low-carbon steels. These steel scrap originating tramp elements can influence the microstructures and mechanical properties of steel products. Tramp elements containing test materials were thermo-mechanically rolled to achieve yield strengths between 400–450 MPa with different cooling routes. Various methods of microstructure characterization and mechanical testing were utilized to study the resulting steels. Additionally, thermo-mechanical simulations were conducted using Gleeble 3800 equipment to gather information about flow stress properties. The results indicate that with a lower cooling rate, the microstructure is not significantly affected by tramp elements, however strength levels can be increased and elongation properties decreased, mostly due to the solid solution strengthening effect of impurities. In water-quenched steels, the addition of tramp elements can alter the final microstructure morphology, increasing the ultimate tensile strength but simultaneously improving the ductility. Flow stress is not significantly affected by tramp elements in the temperature range of 950–1050 °C.