Acicular Morphology Research Articles

Effect of Hot Working Processes on Microstructure and Mechanical Properties of Pipeline Steel

The microstructure and microhardness of X70 pipeline steel were investigated after conducting different processing routes. The microstructure was characterized using optical and electron microscopy. Scanning electron microscopy equipped with electron backscattered diffraction (EBSD) and transmission electron microscopy techniques were applied for investigation of different thermal processing treatment conditions. Mechanical properties were characterized by a microhardness tester. The results show that the microstructure mainly consists of granular bainite, acicular ferrite and a small amount of M/A constituents under hot rolling states. There are many dislocations inside the acicular ferrite. The thermal simulation experiments show that the microstructure becomes homogeneous with the increase in cooling rate. The acicular ferrite morphology becomes fine and uniform, and the content of M/A constituents increases at the same compression amount. The compression gives rise to the accumulated strain and stored energy, which accelerate the transformation of acicular ferrite and refine the microstructure of the pipeline steel. The microhardness rises with the increase in deformation ratio and cooling rate. The microstructure of the pipeline steel subjected to the isothermal quenching process is ultrafine ferrite and M/A islands. When the isothermal quenching temperature reaches 550 °C, a small amount of upper bainite appears in the microstructure. With the increase in isothermal quenching temperature, the microhardness decreases. Acicular ferrite is a better candidate microstructure than ultrafine ferrite for the pipeline steels.

Impact of Sodium Vanadium Oxide (NaV3O8, NVO) Material Synthesis Conditions on Charge Storage Mechanism in Zn-Ion Aqueous Batteries

The electrochemical charge storage of sodium vanadate (NaV3O8 or NVO) cathodes in aqueous Zn-ion batteries has been hypothesized to be influenced by the inclusion of structural water for facilitating ion transfer in the material. Materials properties considered important (morphology, crystallite and particle size, surface area) are systematically studied herein through investigation of two NVO materials, NaV3O8· 0.34H2O [NVO(300)] and NaV3O8·0.05H2O [NVO(500)], with different water content, acicular morphologies with different size and surface area achieved via post-synthesis heat treatment. The electrochemistry of the two materials was evaluated in aqueous Zn-ion cells with 2 M ZnSO4 electrolyte using cyclic voltammetry, galvanostatic cycling, and rate capability testing. The thinner NVO(300) nanobelts (0.13 mm) demonstrate greater specific capacities and higher effective diffusion coefficients relative to the thicker NVO(500) nanorods. Notably however, while cells containing NVO(500) deliver lower specific capacity, they demonstrate enhanced capacity retention with cycling. The structural changes accompanying oxidation and reduction are elucidated via ex situ X-ray diffraction, transmission electron microscopy, and operando V K-edge X-ray absorption spectroscopy (XAS), where NVO material properties are shown to influence the ion insertion. Operando XAS verified that electron transfer corresponds directly to change in vanadium oxidation state, affirming vanadium redox as the governing electrochemical process.

Preparation of Synthetic β-Wollastonite Produced from Amorphous SiO<sub>2</sub> Bamboo Leaf Ash and <i>Meretix meretix</i> Shell

The objective of this study is to produce b-wollastonite from amorphous SiO2 obtained from bamboo leaf ash (BLA) and CaO derived from meretix meretix shell (MMS) using solid state reaction. Amorphous SiO2 utilization in this work obtained by precipitation of BLA and calcined at 700 °C for 3 h, whereas CaO MMS was generated by calcination of MMS at 1000 °C for 5 h. High purity amorphous SiO2 obtained was 99.325 wt % and CaO purity obtained was 97.531 wt %. Single phase of b-wollastonite found in this study as confirmed by XRD results. The vibrations at 933.42 , 904.49, and 890.99 cm-1 were caused by the Si-O-Ca bond, which shows the bonding of b-wollastonite obtained from the FTIR. The acicular morphology of b-wollastonite with average grains size of 0.28,0.33 and 0.71 mm was obtained for the samples calcined at 900 , 1000 , and 1100 °C respectively.

Influence of filler material on the microstructure, mechanical properties, and residual stresses in tungsten inert gas welded Ti-5Al-2.5Sn alloy joints

The microstructure and defects in the weld zone affect the weldment characteristics. One way to improve the microstructure and reduce the defects in the weld zone is by using a filler during welding which influences the physical, chemical, and mechanical properties of the manufactured component. In the present study, tungsten inert gas (TIG) was used to weld Ti-5Al-2.5Sn alloy using different titanium alloy fillers; Ti-6Al-4V, Ti-5Al-2.5Sn, and autogenous weldments were also produced. The welded joints were characterized in terms of their microstructure, mechanical properties, and residual stresses in its various regions. The weldment with Ti-6Al-4V as filler exhibited a higher proportion of α′ martensite in fusion zone, as compared to the welded joint with Ti-5Al-2.5Sn alloy as filler, owing to the higher proportions of β stabilizers present in Ti-6Al-4V alloy. The α’ martensite was present in basketweave and acicular morphology in all the weldments, with and without fillers. Ti-6Al-4V filler welded joint showed higher tensile strength (approximately 1144 MPa) and relatively higher hardness than Ti-5Al-2.5Sn filler welded joint (approximately 1027 MPa) and autogenous weldment (approximately 770 MPa), due to increased amount of martensite in its fusion zone. As compared to the weldment produced with Ti-5Al-2.5Sn filler, the welded joint produced without filler and with Ti-6Al-4V as a filler had more compressive residual stresses at surface (approximately 25% higher), leading to less amount of pile up after nanoindentation. This was attributed to the generation of compressive strains due to martensitic transformations in the fusion zone of both these weldments.

On the interaction of microstructural morphology with residual stress in fiber laser welding of austenitic stainless steel

The development of compressive residual stress is governed by the metallurgical transformation and associated microstructure, which in turn influences the mechanical properties of a welded structure. In the present work, the microstructural interaction with the thermo-mechanical performance of Yb-Fiber laser-welded austenitic stainless steel (SS304) is evaluated at different heat inputs and varying defocus distances. The interrelation between microstructural morphology and the typical pattern of residual stress is systematically investigated. The development of the thermal-metallurgical-mechanical model particularly considers the effect of solid-state phase transformation (SSPT) such that the model predicts the phase fraction and its influence on residual stress distribution. The present study exclusively focuses on the mechanism of residual stress generation as a consequence of dual-phase microstructural evolution during solidification. Low heat input (45J/mm) leads to a high cooling rate, excellent tensile strength, and low tensile residual stress. The finite element-based thermo-mechanical model predicts the residual stress with a maximum deviation of ±50 MPa compared to the experimental value. The Ferritic-austenitic (FA) mode of solidification results in the combination of skeletal and lathy δ-ferrite morphology. Increasing peak intensity of δ {110} with a cooling rate confirms the enhancement of δ-phase within the austenite matrix and restricts the complete transformation to the austenitic phase. A relatively high amount of δ-ferrite due to enriched Cr and lean Ni content at the dendritic core with fine or acicular morphology at a high cooling rate reduces the longitudinal and transverse residual stress significantly. Besides, the increasing trend of primary dendritic arm-size of δ-ferrite yields a gradual increase in residual stress.

Influence of natural beach mineral corundum on the wear characteristics of LM30 aluminium alloy composites

The work investigates the effect of corundum (Al2O3) reinforcement on the dry sliding wear of LM30 aluminium alloy composites. Composites with the different size range of corundum particles (fine; 1–20 μm, medium; 32–50 μm and coarse; 75–106 μm) and weight percentages varying from 5 to 20 wt% were prepared. The stir casting process was used for the fabrication of composites. LM30 billets were melted at 850 and stirred with the graphite stirrer for 3–4 min. Corundum particles were added to the melt and the molten mass was stirred for another 3–4 min. Finally, the mixture was poured into a cast iron mould. Pins of 8 mm diameter were prepared for wear test and tested against the hardened die steel disc. Optical microscopy of the composites revealed a uniform distribution of corundum particles in the matrix. The microstructure of the composite also got refined. The acicular morphology of eutectic silicon in base alloy got refined to globular for the composites leading to improvement in the hardness of the composites. Dry sliding wear analysis of the composites revealed the decrement in the wear rate of the composites over the base alloy. Similar to the wear rate, the coefficient of friction of the composites also decreased with the increase in the corundum weight percentage. Finally, the wear tracks and debris analysis of the composites revealed the underlying wear mechanisms during the dry sliding wear behavior at a low contact pressure of 0.2 MPa and high contact pressure of 1.8 MPa. The wear mechanism of the composite is dependent on contact pressure. At low contact pressure of 0.2 MPa, the abrasive type wear transformed to adhesive type at a high contact pressure of 1.8 MPa.

Thermo-hydrogen refinement of microstructure to improve mechanical properties of Ti–6Al–4V fabricated via laser powder bed fusion

This paper describes the main results from an investigation into the consequences of thermo-hydrogen refinement of microstructure (THRM) after laser powder bed fusion (LPBF) of Ti–6Al–4V on the evolution of microstructure and mechanical properties using a set of experimental techniques. Porosity fraction, grain structure, phases, and crystallographic texture per phase are characterized using micro X-ray computed tomography, microscopy, and neutron diffraction. A hierarchical structure of acicular α-phase morphology formed inside the prior β grains by fast cooling during LPBF transforms into fine-grained globular microstructure by THRM, which facilitates homogeneous nucleation and growth of the low temperature phase with some retained β phase. Moreover, hydrogenated material during THRM has low activation energy for diffusion, which in conjunction with the surface energy of pores causes densification of the material, thereby closing porosity formed during LPBF. Such significant microstructural changes induced by the THRM treatment cause brittle material created by LPBF to become ductile. Significantly, the strength and ductility produced by THRM exceed the minimums set forth by the ASTM B348 standard for Ti-6Al-4V. Moreover, the treatment improves fatigue strength of the material. In particular, it improves the endurance limit and reduces the scatter in the measured fatigue strength data. Performance characteristics of the material can be further optimized for specific application requirements by tailoring microstructures using the LPBF and THRM processes.

Sodiation mechanism via reversible surface film formation on metal oxides for sodium‐ion batteries

AbstractLong term galvanostatic charge/discharge cycling of oxygen deficient, carburized and self‐organized titanium dioxide (TiO2) nanotubes (NTs) in sodium ion (Na) batteries (SIBs) are subject to a significant self‐improving charge storage behavior. Surface reactions upon sodiation of carburized NTs form acicular surface films that can be reversibly cycled. We show that, alongside organic species from the decomposition of the electrolyte, mainly inorganic compounds, such as Na2O2 and Na2CO3, are the main constituents. These components possess a characteristic acicular morphology. Na2O2 is found to form upon sodiation and converted to NaO2 upon desodiation. This, in combination with its pseudo‐capacitive charge storage characteristics, explains the excellent rate capability measured for TiO2‐x‐C NTs. The observed high reversibility of this surface chemistry is also essential for the fast kinetics and the high capacity retention found in the system. Our findings point to a more general Na‐ion storage mechanism, that is potentially relevant to other transition metal oxides also.

Impact of sodium vanadium oxide (NaV3O8, NVO) material synthesis conditions on charge storage mechanism in Zn-ion aqueous batteries.

The electrochemical charge storage of sodium vanadate (NaV3O8 or NVO) cathodes in aqueous Zn-ion batteries has been hypothesized to be influenced by the inclusion of structural water for facilitating ion transfer in the material. Materials properties considered important (morphology, crystallite and particle size, surface area) are systematically studied herein through investigation of two NVO materials, NaV3O8·0.34H2O [NVO(300)] and NaV3O8·0.05H2O [NVO(500)], with different water content, acicular morphologies with different size and surface area achieved via post-synthesis heat treatment. The electrochemistry of the two materials was evaluated in aqueous Zn-ion cells with 2 M ZnSO4 electrolyte using cyclic voltammetry, galvanostatic cycling, and rate capability testing. The thinner NVO(300) nanobelts (0.13 μm) demonstrate greater specific capacities and higher effective diffusion coefficients relative to the thicker NVO(500) nanorods. Notably however, while cells containing NVO(500) deliver lower specific capacity, they demonstrate enhanced capacity retention with cycling. The structural changes accompanying oxidation and reduction are elucidated via ex situ X-ray diffraction, transmission electron microscopy, and operando V K-edge X-ray absorption spectroscopy (XAS), where NVO material properties are shown to influence the ion insertion. Operando XAS verified that electron transfer corresponds directly to change in vanadium oxidation state, affirming vanadium redox as the governing electrochemical process.

Escherichia coli templated iron oxide biomineralization under oscillation.

Motility is significant in organisms. Studying the influence of motility on biological processes provides a new angle in understanding the essence of life. Biomineralization is a representative process for organisms in forming functional materials. In the present study, we investigated the biomineralization of iron oxides templated by Escherichia coli (E. coli) cells under oscillation. The formation of iron oxide minerals with acicular and banded morphology was observed. The surface charge of E. coli cells contributed to the biomineralization process. The surface components of E. coli cells including lipids, carbohydrates and proteins also have roles in regulating the formation and morphology of iron oxide minerals. As-prepared mineralized iron oxide nanomaterials showed activity in photocatalytic degradation of methylene blue as well as in electrocatalytic hydrogen evolution reaction. This study is helpful not only in understanding motility in biological processes, but also in developing techniques for fabricating functional nanomaterials.

New understanding about the relationship between surface ignition and low-carbon iron ore sintering performance

Surface ignition is the first and also the important step for iron ore sintering, which provides the initial source of energy to trigger the whole reactions. This investigation mainly focused on revealing the relationship between surface ignition and sintering performance, and elucidated the deep mechanism. Results indicate that the quality of sinter in the surface layer can be effectively improved by adjusting the ignition parameters. The preferred ignition parameters include ignition temperature of 1050 °C, ignition duration of 1 min and heat preservation of 1−2 min. The function mechanism of improved sinter quality is attributed to the increased high temperature duration for minerals melting, the enlarged melting zone, and the decreased cooling velocity. These changes facilitate the formation of enough adhesive phase of calcium ferrite, more of which generated in acicular morphology with high mechanical strength. Optimizing the ignition process reduced the solid fuel consumption due to the improved sintering performance, which then decreased the emission of NO and SO2. The research findings are of great significance for providing a guide for the design of desirable ignition system and making further contributions to energy conservation and emission reduction during sintering.

Microstructure and tensile properties of A356 alloy with different Sc/Zr additions

Addition of rare earth elements for improving the tensile properties of aluminum alloys has attracted great attention. In this study, a systematic analysis on the microstructure and tensile properties of A356–0.13Ti alloys with different contents of scandium (Sc) and scandium/zirconium (Sc/Zr) after solution and aging treatment process was carried out. The addition of Sc/Zr into A356–0.13Ti alloys can greatly refine the grain size and modify the deleterious coarse eutectic Si structure and harmful acicular iron-containing phase morphology. As a result, the maximum value of strength (298 MPa) and ductility (elongation of 8.4%) are acquired by co-addition of Sc/Zr after solution and aging treatment process, which indicates that the tensile properties of A356 alloy are greatly enhanced by the synergistic effect of co-addition of Sc/Zr.

Fe-oxides in jasperoids from two gold districts in Nevada: Characterization, geochemistry, and (U-Th)/He dating

This study examines the whole-rock geochemistry, Fe-oxide texture and crystal morphology, and Fe-oxide (U-Th)/He date variation of jasperoids, as well as the relationships between these characteristics, in order to evaluate jasperoids as an indicator for gold mineralization. Jasperoid samples with a range of textures, appearances, and expected gold concentrations were collected from two gold districts in Nevada: the northern Carlin trend (Gold Quarry Mine), and the Battle Mountain district (Marigold Mine; Battle Mountain prospect). In our jasperoid samples, whole-rock concentrations of Au are positively correlated with As, Ag, Pb, Sb, U, W, and Tl. The following Fe-oxide textures are associated with anomalous gold concentrations: disseminated, submicron crystals; feathery and acicular crystal morphologies; concentric zonation from hematite to goethite; and botryoidal textures. Calculated closure temperatures for the (U-Th)/He system in observed jasperoid Fe-oxide morphologies within our dataset range from 26 to 136 °C, indicating variable susceptibility to He diffusion at near-surface conditions. Fe-oxide (U-Th)/He dates range from 29.4 ± 0.5 Ma to 0.11 ± 0.01 Ma, displaying intra- and intersample variation. We attribute the date variation to multiple factors including He implantation, parent isotope exchange, and He loss through closure temperature sensitivity and alpha-ejection. The intra- and intersample variation within the Fe-oxide (U-Th)/He dates limits our ability to make geologic interpretations. Our case study identifies important limitations of the (U-Th)/He method in jasperoids and provides insight on how He date variation might be avoided in future studies.

Effect of niobium alloying on the microstructure, phase stability and mechanical properties of CoCrFeNi2.1Nbx high entropy alloys: Experimentation and thermodynamic modeling

A systematic study was carried out to understand the effect of Nb addition on the microstructure, phase stability, and mechanical properties in a series of cast and aged CoCrFeNi2.1Nbx (x = 0, 0.2, 0.4, 0.74) high entropy alloys (HEAs). The base alloy without Nb addition showed a fully face-centered cubic (FCC) phase, whereas Nb addition was found to promote the formation of the hexagonal Laves phase. The cast HEAs were further aged at temperatures varying from 800 °C to 1200 °C. Aging of the different Nb alloyed HEAs at 800 °C and 1000 °C resulted in the precipitation of D019 structured ε-phase having fine acicular morphology. In contrast, the HEAs aged at 1200 °C did not reveal the presence of ε precipitates. These experimental observations were critically assessed with the thermodynamic predictions. The fine precipitate network in the CoCrFeNi2.1Nb0.2 and CoCrFeNi2.1Nb0.4 HEAs improved the hardness and tensile strength considerably. However, the CoCrFeNi2.1Nb0.74 HEA showed considerable embrittlement due to the presence of a high fraction of the Laves phase. Present results indicated considerable potential of achieving superior mechanical properties in these cast HEAs even without involving thermo-mechanical processing.

Influence of the mode of laser welding parameters on microstructural morphology in thin sheet Ti6Al4V alloy

The transients and gradients generated due to localized heating and cooling by a laser source governs the thermal-metallurgical-mechanical performance of the welded structure. An attempt is made to investigate the significance of the pulse parameter over continuous mode in Yb-fiber laser welding of 800 μm thin Ti6Al4V alloy. The full-depth of penetration with minimum weld width is achieved at the lowest heat input of 12 J/mm for the pulse laser. The behaviour pattern of the thermal history is critically assessed with the aid of FE based heat transfer model and corresponding relation with evolved microstructural morphologies are systematically investigated. Several stages of transformation occurred in the weld zone such as α-phase dissolution, β-transus in the heating cycle, and diffusionless β→α'/α martensitic transformation during the cooling cycle are well explained by thermal history. A relatively high amount of α'-martensite is observed in the pulse laser welding whereas the transformed β-phase fraction gradually reduces further away from the weld line. Blocky plate-shaped α'-martensite within the coarseβ-grain boundary is apparent at higher heat input (26–80 J/mm), whereas acicular morphology within the fineβ-grain boundary is observed at a low heat input of 12–19 J/mm. The dimensional variation of α'-lath at the fusion zone has a significant influence on strength. Weld metal containing very fine α'-lath have comparable strength to that of the base metal. The images of the fractured surface shows the dimples as well as microspores in continuous mode, whereas combinations of large and small dimples are observed for pulse mode of welding. The level of contamination is examined by surface discoloration technique and found to be the highest for the heat input of 80 J/mm.

In-depth analysis of intragranular acicular ferrite three-dimensional morphology

Precipitation of intragranular acicular ferrite (IAF) is the principle means for increasing the strength of steel. This study investigated the three-dimensional morphology and growth behavior of IAF. Focused ion beam, confocal laser scanning microscopy and electron backscattered diffraction revealed that IAF had a plate-like morphology with numerous pits and defects when precipitated at 750 °C for 1 min and was needle-like with a smooth surface when precipitated at 700 °C for 1 min. Furthermore, sub-grains were observed within the IAF. This study elucidates more on the theoretical data of the IAF 3D morphology and provides novel insights into IAF.

Effects of direct aging on near-alpha Ti–6Al–2Sn–4Zr–2Mo (Ti-6242) titanium alloy fabricated by selective laser melting (SLM)

This study reported for the first time the selective laser melting of Ti–6Al–2Sn–4Zr–2Mo (Ti-6242), a near-α titanium alloy specifically designed for high-temperature services. The microstructural stability under standard aging (595 °C/8 h) was assessed after fabrication. With increasing laser scan speeds, an increase of relative density to 99.5% was observed, followed by a dramatic decrease to around 95.7%. The arithmetic mean roughness value (Ra) evolved consistently with the density, achieving the lowest value at the laser scanning speed of 950 mm/s. The as-built sample consists mainly of martensitic α′ colonies separated by prior-β grain boundaries. Martensites partially decomposed into α laths and nano β precipitates after aging treatment, but still retained initial acicular morphologies. Despite the stress relief during aging treatment, the hardness still increased from 410 HV of the as-built sample to 450 HV. The as-built and aged Ti-6242, respectively, exhibited a maximum room-temperature tensile strength of 1437 MPa and 1510 MPa, while the ductility was reduced from 5% to 1.4%. The nanotwins within martensites contribute significantly to the relatively high ductility of the SLMed sample. The aging-induced reinforcement is mainly attributed to the precipitation hardening effects of nanosized β-phase particles.

Influence of Intercritical Temperature on the Microstructure and Mechanical Properties of 6.5 Pct Ni Steel Processed by Ultra-fast Cooling, Intercritical Quenching and Tempering

A novel treatment comprised of ultra-fast cooling, intercritical quenching and tempering is proposed to modify the microstructure and improve the mechanical properties of low-concentration Ni-containing steel (6.5 pct Ni steel). The influence of intercritical temperature on the microstructure and mechanical properties has been systemically investigated. The results reveal that a mixed microstructure of alloy-depleted intercritical ferrite and alloy-enriched fresh martensite and retained austenite is obtained after intercritical quenching. Moreover, reversed austenite is formed at the grain boundaries of fresh martensite and retained austenite during subsequent tempering. Furthermore, the increase in intercritical temperature promoted the formation of lath-like fresh martensite, leading to the refinement of intercritical ferrite and the formation of secondary acicular reversed austenite. When the intercritical temperature was increased to 670 °C and 700 °C, reversed austenite exhibited sufficient stability at − 196 °C because of the fine-grained structure and acicular morphology. Finally, an optimal combination of strength and cryogenic toughness has been achieved by intercritical quenching from 700 °C. The obtained high yield strength can be ascribed to the decrease in the amount and size of intercritical ferrite, whereas excellent cryogenic toughness can be attributed to the increase in fine-grained stable acicular reversed austenite and decrease in effective grain size.

Effect of Ti2Cu precipitation on antibacterial property of Ti-5Cu alloy.

To instill pure Ti with an antibacterial effect, Cu was added by metallurgical alloying to produce Ti-5 wt% Cu alloy (Ti-5Cu alloy). The precipitation of the likes of Ti2Cu in a Ti-Cu alloy is one of the factors that influences its antibacterial property. However, in the present study, Ti-5Cu alloy precipitates with different microstructures were obtained by applying heat treatment at different temperatures and for different durations. After the heat treatment, metallographic, microstructure, and element analyses were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS). The antibacterial property of the Ti-5Cu alloy was assessed by the plated-count method using Escherichia coli (E. coli). The microstructure analysis revealed that the solution-treated alloy had no precipitation, while the aged alloy contained precipitations of intermetallic Ti2Cu compound. The aged alloy exhibited better antibacterial performance as the duration of the aging treatment increased. The optimal heat treatment for Ti-5Cu was found to be aging at 700 °C for 4 h, at which point the nucleation formation of the Ti2Cu particles would assume an acicular morphology. These acicular precipitates exhibit a high Cu content which, in turn, influences the antibacterial performance.

Natrophosphate and kogarkoite precipitated from alkaline nuclear waste at Hanford

The Hanford Site, near Richland, Washington in the U.S.A., is implementing a treatment process for liquid radioactive waste. This study determined the mineralogy of existing soilids in the process feed tank, both bulk fine material and large aggregates. The large particulate was cemented kogarkoite (Na3SO4F) and natrophosphate (Na7F(PO4)2·19H2O). The bulk material was also natrophosphate and kogarkoite with trace amounts of gibbsite and Na–C–O-bearing species that are likely sodium oxalate or sodium carbonate. The kogarkoite had an acicular morphology, which has not been observed previously in waste or geological samples.