Papers by Keyword: Microstructure

Abstract: Phase components of experimental low cost titanium alloys, their substructure and parameters, dislocation structure, features of phase formation in the metal, which differ in alloying systems, were studied using complex research methods. The stoichiometric composition of dispersed phases in the internal volumes of alloy grains was determined by diffraction patterns using transmission electron microscopy. It is shown that in the structure of titanium alloy Ti-2,8Al-5,1Mo-4,9Fe there are dispersed nanoparticles of intermetallic phases of different morphology and stoichiometric composition. These are the phases: Ti₃Al and Fe₂Ti with a size of 10…40 nm; Mo₉Ti₄ - 20…120 nm. Studies of titanium alloy Ti-1,5Fe-O showed the presence in the structure of mainly nanoparticles of oxides: Ti₃O₅ size 10…30 nm and Ti₄Fe₂O, FeTiO₅ (10…90 nm), as well as intermetallics Fe₂Ti (10…40 nm). It is established that the formation of nanoparticles of intermetallic and oxide phases in the thin plate structure of the investigated experimental low cost titanium alloys promotes the formation of the substructure with uniform distribution of dislocation density. This provides a high level of mechanical properties of alloys.

Abstract: Food-grade piping and water transportation systems extensively use dissimilar welding between stainless steel and carbon steel, where cost-effectiveness and corrosion resistance are essential consideration. However, the fusion zone of dissimilar welds often observed microstructural inhomogeneities and hardness changes, thus compromising mechanical qualities and corrosion resistance. This study was seperated in two phases to investigate and optimize dissimilar welding between carbon steel and stainless steel in both plate and pipe applications. Phase 1 studied welding A36 carbon steel plate and A304 stainless steel using gas tungsten arc welding (GTAW) with ER308L filler metal, the effect of post-weld heat treatment (PWHT) holding time on the mechanical and microstructural propertie. PWHT was performed at 650 °C for 20 and 60 minutes. The 20-minute condition yielded an optimal combination of mechanical strength and microstructural refinement, while the 60-minute condition led to grain coarsening and reduced strength. Phase 2 extended the findings to pipe welding applications, adopting the 20-minute PWHT condition. Welding was performed on dissimilar joints between A106-B carbon steel pipe and A312 TP304L stainless steel pipe (2-inch OD) using ER308L and ER309L filler metals under 99.99% argon shielding. Tensile and hardness testing indicated that welds with ER309L offered superior mechanical performance. Microstructural analysis revealed delta-ferrite and stabilized austenite in the fusion zone, with enhanced Cr and Ni concentrations contributing to improved corrosion resistance, as confirmed by electrochemical testing.

Abstract: Quasicrystalline ingots of the following compositions were obtained and studied: Al₆₃Cu₂₅Fe₁₂; Al_62.735Cu₂₅Fe₁₂Sc_0.265; Al_62.56Cu₂₅Fe₁₂Sc_0.44. It is shown that 0.01% Sc is contained in the icosahedral quasicrystalline phase (Al_65.1Cu_22.57Fe_12.33Sc_0.01). In addition to this scandium is contained in the intermetallic Al_51.45Cu_37.29Sc_8.23 (hexagonal W phase). It is established that alloying of the quasicrystalline Al-Cu-Fe alloy with scandium in the amount of 0.44 at. % significantly increases the content of the quasicrystalline icosahedral phase in ingots from 50 to 65 vol.% which leads to an increase in the microhardness of ingots. The microhardness of Al-Cu-Fe quasicrystalline ingots in the range of 20 - 400 °C is weakly dependent on temperature and amounts to 7-8 GPa. With increasing temperature, the microhardness value begins to decrease and at 720 °C reaches a value of 0.5 GPa. The study of the electrochemical characteristics of the corrosion process of quasicrystalline ingots showed that alloying of Al-Cu-Fe quasicrystalline alloy with Sc decreased the corrosion rate of non-annealed samples, and simultaneously lowered both the corrosion potential and the pitting potential.

Abstract: Relevance of the work. One of the key challenges currently faced by manufacturers of steel wire rod for welding applications worldwide is achieving maximum plasticity in the metal before delivery to hardware plants. This need arises due to the ongoing technological advancements in hardware plants and the integration of modern equipment capable of producing wire at high drawing speeds with significant degrees of unit deformation. Such processes demand high-quality raw materials (wire rod). Another crucial aspect is ensuring a high-quality surface for the welding wire, free from microcracks and hard inclusions. These defects can negatively impact the welding process by increasing metal spatter, causing electric arc instability, and leading to critical defects in welded joints, such as cavities and cracks. Rational microstructural design is a key principle in producing highly plastic wire rod for the efficient manufacturing of solid-section welding wire from low-carbon alloy steels. The presence of hard components (such as martensite, bainite, or their mixtures) in the wire rod’s structure is undesirable, as they increase the risk of metal failure during intensive cold deformation by drawing. Minimizing these hard phases remains an urgent scientific and practical challenge. The aim of the study is to determine the mechanism of martensite grains formation during slow cooling of low-carbon alloy steel grade CrMoV1Si wire rod, used for producing welding wire, from the austenitization temperature to room temperature. Material and methodology. The material used in this study was steel with the chemical composition (in wt.%) 0.08C–1.30Mn–0.54Si–1.06Cr–0.54Mo–0.24V–Fe_(balance). The samples were subjected to thermal cycles using an automated Gleeble 3800 thermal deformation simulation system. The thermal cycle involved heating the samples to the temperature required for complete austenitization, holding them at this temperature, and then continuously cooling at controlled rates of 0.20, 0.10, and 0.05 °C/s to room temperature. Metallographic analysis was conducted using an optical microscope and a scanning electron microscope. The hardness of individual structural components was measured using a microhardness tester following the standard method. The chemical composition of the phases was determined by energy-dispersive X-ray spectroscopy and Auger electron spectroscopy. Results. The study established an anomalous increase in the volume fraction of austenite shear transformation products in CrMoV1Si steel after continuous slow cooling at rates of 0.20–0.05 °C/s, at the same time, martensite had a relatively high carbon content (up to 1.6 wt.%). The authors attribute this microstructural evolution to dynamic changes in the chemical composition of individual phases during cooling, primarily due to the partitioning of carbon and other alloying elements between the α and γ phases, as confirmed experimentally. Based on the obtained results, a mechanism has been proposed for the formation of high-carbon martensite grains in low-carbon alloy steel wire rod during slow cooling from the austenitization temperature to room temperature.

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.