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"Misra, R"
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High strength and ductility combination in nano-/ultrafine-grained medium-Mn steel by tuning the stability of reverted austenite involving intercritical annealing
The structure–property relationship in 0.06C–5.5Mn steel subjected to different annealing temperatures and time was studied. Mn played a stronger effect on stabilizing austenite in comparison with Ni, and low-C medium-Mn steel possessed excellent hardenability. The reverse transformation of martensite to austenite occurred during intercritical annealing, and the volume fraction was first increased and then decreased on increasing annealing temperature or prolonging annealing time, indicative of change in thermal stability by element partitioning and coarsening of grain size. Correspondingly, the elongation was first increased and then decreased, consistent with the variation in the stability of reverted austenite. The yield strength was gradually decreased because of several factors, including recrystallization of α′ martensite, decreased stability of reverted austenite, and coarse grain size. The maximum product of strength and ductility was obtained on annealing at 650 °C for 10 min, which was attributed to the optimal stability of reverted austenite rather than the highest volume fraction, and tensile strength and elongation were 1120 MPa and 23.3%. The strain partitioning behavior of two phases was elucidated by analyzing Lüders straining and continuous work hardening after yield point elongation, and the deformation mechanism was strongly related to the stability of reverted austenite.
Journal Article
Nanoscale Generators for Tissue Healing: A Perspective
Electroactive components can promote tissue healing and control neuronal activity with the support of the tissue environment and offer electrical impulses and biocompatible material habitats. Due to the increasing growth of portable electronics, it is imperative to generate tiny, lightweight power supply appliances with outstanding performance and sustainable energy conversion ability. In order to deal with the energy deficiency of electronic devices, self-powered systems based nanogenerators are committed to capturing ambient energy for electronic device consumption. Nanogenerator assemblies provide a range of benefits, including adjustable shape, flexibility, affordability, and transportability. As such, they represent a novel and intriguing area for biomedical investigation. In living organisms, bioelectrical mechanisms play an integral part in regulating the functions of cells and tissues. An essential component of electroactive assemblies includes self-powered nanogenerators. In conjunction with nanogenerators, biomedicine has contributed to the invention of medical devices based on self-powered system. Currently, one of the most significant energy-based technologies to guarantee the long-term functioning of implanted biomedical devices is the accumulation of biomechanical energy in vivo. This review covers the development of nanogenerators for biomedical applications. Piezoelectric and triboelectric materials, which could foster the evolution of potential applications in the field of bone regeneration and tissue engineering, are the primary focus of this review. These materials are electrically self-sustaining generators that encourage tissue repair involving osteogenic proliferation, differentiation, and microbial sterilization. Eventually, the discussion highlights the potential future scope and challenges related to the nanogenerators.
Journal Article
A randomized synbiotic trial to prevent sepsis among infants in rural India
Sepsis in early infancy results in one million annual deaths worldwide, most of them in developing countries. No efficient means of prevention is currently available. Here we report on a randomized, double-blind, placebo-controlled trial of an oral synbiotic preparation (
Lactobacillus plantarum
plus fructooligosaccharide) in rural Indian newborns. We enrolled 4,556 infants that were at least 2,000 g at birth, at least 35 weeks of gestation, and with no signs of sepsis or other morbidity, and monitored them for 60 days. We show a significant reduction in the primary outcome (combination of sepsis and death) in the treatment arm (risk ratio 0.60, 95% confidence interval 0.48–0.74), with few deaths (4 placebo, 6 synbiotic). Significant reductions were also observed for culture-positive and culture-negative sepsis and lower respiratory tract infections. These findings suggest that a large proportion of neonatal sepsis in developing countries could be effectively prevented using a synbiotic containing
L. plantarum
ATCC-202195.
A synbiotic preparation of
Lactobacillus plantarum
and fructooligosaccharide was found to significantly reduce sepsis and infections of the lower respiratory tract in a trial involving rural Indian newborns.
Reducing sepsis in newborns
Neonatal sepsis is a major contributor to infant death rates worldwide. In this paper, the authors carry out a randomized placebo-controlled trial in the Odisha province in India. They administered an orally prescribed synbiotic preparation to newborns in 149 villages. Results from the follow up of 4,556 infants 60 days after treatment show a reduction in cases of combined sepsis and death in the symbiotic-treated group, suggesting that this is a potentially useful intervention.
Journal Article
Nanomedicine-Driven Approaches for Kartogenin Delivery: Advancing Chondrogenic Differentiation and Cartilage Regeneration in Tissue Engineering
Articular cartilage degradation and osteocartilage defects are the most prevalent concerns that vary from localized to more systemic forms of cartilage disease. However, regulating chondrogenic differentiation within the joints remains a significant challenge. Kartogenin, a small heterocyclic compound, has recently garnered considerable attention as a potential therapeutic agent, owing to both chondrogenic and chondroprotective properties for intra-articular therapy. Initially, it was created for osteoarthritis; it has also been used to address various diseased conditions, such as the regeneration of disc and bone-tendon junctions. On top of that, it preserves the equilibrium between cartilage catabolism and anabolism, while also mitigating inflammation and alleviating pain by preventing damage induced by cytokines. To modulate tissue function and cellular behaviour, it is crucial to have sustained release of ketogenic through an appropriate delivery system. A multitude of biomaterial-based carriers have been developed for the prolonged release of kartogenin. Moreover, many biological mechanisms of action of kartogenin have been identified. The most critical molecular mechanism among them is the dissociation of filamin A from core-binding factor (CBF)-β induced by kartogenin. Filamin A subsequently translocates to the nucleus, where it engages with RUNX-1 to transcribe genes implicated in the chondrogenesis of mesenchymal stem cells. This review focuses on the development of biomaterials functionalized with kartogenin, including their structure, design, physicochemical properties, biological roles, molecular mechanisms of action, and applications in tissue engineering and regenerative medicine. In conclusion, we discussed the future possibilities and challenges posed by recent advancements in kartogenin research and their potential applications in tissue regeneration.
Journal Article
The determining role of pre-annealing on Mn partitioning behavior in medium-Mn-TRIP steel: experimental and numerical simulation
The influence of the pre-annealing on Mn partitioning behavior was investigated for hot-rolled Fe–0.095C–6.93Mn–1Al–1.07Si medium-Mn-TRIP steel. Unlike the fully martensitic microstructure before one-step intercritical annealing, a mixed microstructure of preexisting ferrite, austenite and martensite was obtained prior to the final annealing in two-step annealed steels. The microstructure observation showed that lath-type austenite existed in the martensitic matrix, blocky and granular austenite occurred at the boundaries of primary austenite/preexisting ferrite or martensite/preexisting ferrite after two-step annealing. Based on the numerical simulations of the second annealing process, the preexisting austenite further grew rapidly without nucleation, while some secondary austenite nucleated at the martensitic lath boundaries and then grew into martensite at a relatively sluggish rate. Moreover, significant Mn partitioning with a special “bimodal distribution” feature was detected in the preexisting austenite, resulting in the formation of martensite/austenite constituents. Compared with the case of one-step heat treatment, an excellent combination of strength (1145 MPa) and ductility (39%) was obtained in the steel with pre-annealing, which was ascribed to the occurrence of martensite/austenite islands and positive TRIP effect over a wide strain range.
Journal Article
Fracture toughness behavior of low-C medium-Mn high-strength steel with submicron-scale laminated microstructure of tempered martensite and reversed austenite
Fracture toughness was studied in terms of crack-tip opening displacement (CTOD) in low-C medium-Mn high-strength steel at both room temperature and − 40 °C, and excellent fracture toughness was obtained. The critical CTOD values (δ) and crack extension (∆a) followed the relationship: δ = 0.01343 + 0.62315∆a0.47531 and δ = 0.07391 + 0.48466∆a0.60103 at room temperature and − 40 °C, respectively. With the decrease in test temperature from room temperature to − 40 °C, the corresponding δ when ∆a = 0.2 mm (δ0.2) was reduced from 0.30341 to 0.25813 mm, and intersecting point in the crack extension resistance curve with a 0.2-mm passivation line (δQ0.2BL) was reduced from 0.42132 to 0.33941 mm. The large fraction of high misorientation boundaries between tempered martensite effectively hindered the crack propagation and increased the fracture toughness. Furthermore, the submicron-scale complex laminated microstructure of tempered martensite and reversed austenite refined the effective fracture grain size, which inhibited crack propagation and led to high fracture toughness. Also, the excellent fracture toughness is attributed to strain-induced martensite transformation of reversed austenite in the small plastic deformation zone ahead of the crack tip, which absorbed the strain energy, relaxed the local stress concentration, suppressed the crack propagation, and enhanced the fracture toughness.
Journal Article
Nanoscale spheroidized cementite induced ultrahigh strength-ductility combination in innovatively processed ultrafine-grained low alloy medium-carbon steel
We describe here innovative processing of low alloy medium-carbon steel with a duplex microstructure composed of nanoscale spheroidized cementite (Fe
3
C) in an ultrafine-grained (UFG) ferritic steel. After multi-pass rolling and intermittent annealing at 550 °C for 300 s, the obtained UFG-1 steel showed an average ferrite grain size of ~430 nm, containing nanoscale spheroidized cementite (Fe
3
C) particles with an average size of ~70 nm. On annealing at 600 °C for 300 s, the average size of ferritic grains was increased to ~680 nm and the average size of spheroidized Fe
3
C particles increased to ~90 nm, referred as UFG-2 steel. Tensile tests indicated that UFG-1 steel had high yield strength (
σ
y
) of 1260 MPa, and ultimate tensile strength (
σ
UTS
) of 1400 MPa. These values are higher than that of UFG-2 steel (
σ
y
= 1080 MPa and
σ
UTS
= 1200 MPa), suggesting that the strengthening contribution is a cumulative effect of decrease in ferrite grain size and nanoscale cementite. The incoherent interfaces between nanosized particles and the matrix acted as a strong barrier to dislocation motion. The study underscores that nanosized precipitates not only provide strength but also contribute to ductility, which is very encouraging for improving the ductility of medium-carbon steels.
Journal Article
On Various Aspects of Decomposition of Austenite in a High-Silicon Steel During Quenching and Partitioning
Using a Gleeble thermomechanical simulator, a high-silicon steel (Fe-0.2C-1.5Si-2.0Mn-0.6Cr) was laboratory hot-rolled, re-austenitized, quenched into the
M
s
–
M
f
range, retaining 15 to 40 pct austenite at the quench stop temperature (
T
Q
), and annealed for 10 to 1000 seconds at or above
T
Q
in order to better understand the mechanisms operating during partitioning. Dilatometer measurements, transmission electron microscopy, and calculations showed that besides carbon partitioning, isothermal martensite and bainite form at the partitioning temperature. While isothermal martensite formation starts almost immediately after quenching with the rate of volume expansion dropping all the time, the beginning of bainite formation is marked by a sudden increase in the rate of expansion. The extent of its formation depends on the partitioning temperature following TTT diagram predictions. At the highest partitioning temperatures martensite tempering competes with partitioning. Small fractions of bainite and high-carbon martensite formed on cooling from the partitioning temperature. The average carbon content of the austenite retained at room temperature as determined from XRD measurements was close to the carbon content estimated from the
M
s
temperature of the martensite formed during the final cooling.
Journal Article
