Department of Metallurgical & Materials Engineering

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In this study, we investigated the effect of intermediate heat treatment (IHT) on the texture evolution and stretch formability of annealed AZ31 Mg alloy sheets during different stages of hot rolling. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) techniques were used to measure the crystallographic texture and to explain how IHT contributes to the texture evolution in hot-rolled specimens. The behavior of static recrystallization (SRX) during IHT was investigated to explain its role in weakening the basal texture in IHT specimens. Furthermore, t-EBSD was used to investigate the orientation distribution of recrystallized grains in the deformed matrix. Moreover, the effect that IHT can exert on the mechanical and Erichsen Index (IE) of annealed sheets was investigated at room temperature, and also at 100 and 200 °C. An analysis of the different IHT specimens indicated that the influence of IHT on the IE was significantly dependent on the measurement temperature. © 2021 Elsevier B.V.

World University root node

Journal of Alloys and Compounds

Effect of intermediate heat treatment during hot rolling on the texture and formability of annealed AZ31 Mg alloy sheets

Polyetheretherketone (PEEK) is a high-performance plastic with favorable physical, mechanical, chemical, and biological properties for various industrial applications. Most PEEK substrates/components are manufactured using traditional methods like milling, compression molding, injection molding, pressure sintering, and so forth. With the advent of various additive manufacturing (AM) techniques, researchers have been working on optimizing the processing parameters for AM of PEEK. Furthermore, several PEEK composites with improved properties have also been developed, and efforts have also been made to use these PEEK composites in AM. Since AM of PEEK and its composites is a relatively new area of the advanced manufacturing process, the field faces many challenges. There is a dearth of comprehensive reports on this topic. Keeping this perspective in mind, we have tried to collate the relevant information on the composites and AM of PEEK in this review. The review highlighted the influence of variation in composition on material properties and performance of PEEK and showed the correlation with AM processability of such composites. A detailed analysis of the various reports on fused deposition modeling and selective laser sintering based processing of PEEK composites is included in the review. Critical barriers to the AM of these high-performance polymer composites are pointed out. We have also included the outcome of some interesting studies about the coating of PEEK with various materials/compounds to provide a broader perspective. This review will help the researcher to design and develop additively manufactured PEEK-based structures with improved and customized properties. © 2022 Society of Plastics Engineers.

Polymer Composites

Additive manufacturing of polyetheretherketone and its composites: A review

Graphene Oxide (GO) has tremendous application potential as a functional material. However, we found GO to be extremely sensitive toward external energy in the form of heat, light, X-rays, etc. It is because the Oxygen Functional Groups (epoxide, carbonyl, carboxyl, hydroxyl, etc.) attached to the underlying monomolecular layer of carbon in GO are prone to reduction through externally supplied energy leading to the formation of reduced Graphene Oxide (rGO). Eventually, GO lacks preserving its original chemical composition, physical and chemical properties while interacting with the measurement probes. In addition, GO also undergoes a gradual reduction over a period in an ambient environment. This obvious behavior of GO compelled us to re-examine the related literature. In this report, we studied the detailed effects of various characterization tools, possible ways to minimize the side-effects while measurement, and an alternative way to use GO for its various uses. This involved the review of not only the different important parameters of the characterizing probes but also its synthesis protocols and the environment of its storing desiccator. In this direction, we report a careful set of experiments using X-ray Diffraction, X-ray Photoemission Spectroscopy, Raman Spectroscopy, UV–Visible Spectroscopy, Photoluminescence Spectroscopy, Transmission Electron Microscopy and Atomic Force Microscopy. This elucidates the precautions needed while establishing the best practices in GO synthesis and characterization for addressing the exact functional requirements related to an end application. Also, we did a similar study for reduced Graphene Oxide (rGO). © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.

Applied Physics A

Effect of characterization probes on the properties of graphene oxide and reduced graphene oxide

240th ECS Meeting (October 10-14, 2021)

Investigating the Activity of Transition Metal-NC and Metal Nitride Electrocatalysts for Nitrogen Reduction Reaction

UNS S32101 lean duplex stainless steel (DSS) has a two phase microstructure consisting of austenite and ferrite in near equal proportions. Aging at high temperature results in formation of σ phase reducing ductility and also corresponding depletion of Cr from the matrix. The effect of long term aging on the microstructure and mechanical properties is still an active area of research for lean DSSs. In the present work effect of aging at 750 °C (up to 480 h) on microstructure and mechanical properties has been systematically studied. Scanning electron microscopy (SEM) revealed that the precipitates were distributed along ferrite/austenite (δ/γ) interfaces and ferrite/ferrite (δ/δ) boundaries. Nitrides (mainly Cr2N) were observed in initial phases of aging and σ phase afterwards, mostly at longer aging times. The decrease of Ni and Mo and increase in N in UNS S32101 steel delayed the precipitation of σ, but could not avoid it completely. The room temperature absorbed impact energy of specimens decreased gradually as the aging time increased. The lowest value of absorbed impact energy was found to be 24 ± 2 J after 480 h of aging, which was only ~11% as that of solution annealed specimen. Fractography also showed that the fracture morphology changed from fibrous (ductile) to dominant brittle (which involved predominance of cleavage facets along with long, wide cracks i.e. delamination fracture) with increasing aging time. Tensile tests also showed a decrease in ductility and an increase in yield stress/ultimate tensile strength with aging time.

Materials Today Communications

Effect of isothermal aging at 750 °C on microstructure and mechanical properties of UNS S32101 lean duplex stainless steel

Laser powder bed fusion additive manufacturing (LPBF-AM) of a low-alloy, high-performance AF-9628 steel results in exceptionally high strength and good ductility. The reasons for such mechanical properties are investigated through detailed microscopy performed at several length scales. Thus, the characterization of melt pool, porosity, grain morphology, phases, and dislocations is performed in the as-printed material. The as-printed material consists of only 0.004 vol% of uniformly distributed porosity, single-phase martensitic laths with an average lath size of ≈2.5 μm, the absence of carbides indicating interstitial trapping of C atom, and high dislocation density in the martensitic laths. Experimental data through microscopy are then fed in analytical models for calculating strengthening contributions from various strengthening mechanisms. Calculated yield strength agrees well with experimentally determined value, and therefore, activation of various strengthening mechanisms is established in as-printed AF-9628. © 2020 Wiley-VCH GmbH

Advanced Engineering Materials

Microstructure–Property Correlation in a Laser Powder Bed Fusion Processed High-Strength AF-9628 Steel

Abstract: Characterization of microstructure and grain boundary character distribution (GBCD) during iterative thermo-mechanical processing (TMP) of 316L stainless steel were done using electron backscatter diffraction (EBSD). Results from EBSD scans were analyzed in terms of the fraction of special boundaries, their deviation from ideal misorientation, connectivity of random high-angle grain boundaries, and grain size. In order to understand the efficacy of the iterative processing route leading to a well-connected twin boundary network, additional analysis was done in terms of twin-related domain statistics and triple junction distribution. Results from these analyses show that initial iteration results in a microstructure with insufficient twin boundary density, and a poor twin boundary network. Although the next iteration leads to a small increase in twin statistics, it also does not significantly improve the statistics of favorable grain boundaries and their network. However, the fourth iteration of the processing results in a large improvement in both the population and distribution of favorable grain boundaries. All the subsequent iterations were found to result in microstructural deterioration in terms of both population and network of these grain boundaries. Based on the analysis, role of underlying mechanisms such as strain-induced grain boundary migration and static recrystallization in the effective optimization of GBCD was analyzed. The present research gives important insights into these mechanisms and their control during TMP in order to achieve an engineered microstructure. Graphic abstract: [Figure not available: see fulltext.]. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.

Journal of Materials Science

New perspectives on twinning events during strain-induced grain boundary migration (SIBM) in iteratively processed 316L stainless steel

Scientific reports

Coexisting commensurate and incommensurate charge ordered phases in CoO

To realize long-cherished dreams of employing inorganic graphene cousins such as boron nitride (BN) and molybdenum disulfide (MoS2) for large area coating applications, e.g., miniaturized electronic chips, radio wave devices, energy storage, LEDs, and solar cells, scalable synthesis pathways are presently being hunted with unprecedented curiosity to obtain large-scale 2D exfoliated sheets. Modified Hummers’ method provides an apt alternate and has already been established for graphene. However, it currently faces limitations in scalable production of BN and MoS2 as the nature of binding in their crystallographic lattice as well as their interactions with the solvents are different in these materials’ vis-a-vis graphene. Therefore, intensely focused efforts are needed to optimize synthesis parameters to produce scalable quantities of these advanced materials at an economical cost. By hybridizing BN with MoS2, for example, one can maneuver the material’s dielectric functionality, such as frequency bandwidth where it functions. In this report, we present a facile synthesis of BN and MoS2 via modified Hummers’ synthesis. While the fixed BN:KMnO4 precursor ratio of 1:6 was considered to obtain 2D BN, it (MoS2:KMnO4) was altered, i.e., 1:6, 1:5, and 1:4, for obtaining MoS2 sheets. Interestingly, while precursor ratio 1:6 resulted in average lateral dimension ~100 nm, precursor ratio of 1:4 yielded lateral dimensions ~500 nm as evidenced from TEM measurements. Solvothermal (200 °C for 2 h) reduction was carried out for both BN and MoS2 to remove the surface functionalities employing reducing solvent DMF. We obtained few-layer crystalline atomic sheets of BN and MoS2. While inter-atomic distance in 2D BN was measured to be ~1.5 A° as evident from HRTEM imaging, E2g vibration mode ~ 1360 cm−1 was recorded in Raman spectroscopy. While HRTEM imaging reveals that average inter-atomic (Mo-S) distances in MoS2 atomic sheets was obtained to be ~2.41 A°, two distinct MoS2 Raman modes, viz., E2g ~ 404 cm−1 and A1g ~385 cm−1, were witnessed. Microwave blending of 2D MoS2 with 2D BN resulted in significant modulation of dielectric behavior. While the modified Hummers’ synthesis for BN and MoS2 will be a boon in disguise for several dream applications envisaged earlier, it may inspire future generations of devices and sensors with novel functionalities, it is believed. © 2021, Qatar University and Springer Nature Switzerland AG.

Emergent Materials

Chemical exfoliation synthesis of boron nitride and molybdenum disulfide 2D sheets via modified Hummers' method

This short review paper examines the uniqueness of metastable high entropy alloys (HEAs) that transform during plastic deformation. The linkages among alloy design induced metastablilty, processing induced “high enthalpy states” and evolving deformation micromechanisms are intriguing. One key aspect is the adaptive nature of deformation mechanisms because of activation of different micromechanisms during plasticity. This activation of deformation micromechanisms is attributed to transformation-induced plasticity in γ-f.c.c. phase and the evolving nature of c/a ratio in the ε-h.c.p. phase during deformation. As a result, metastable HEAs have good strength-ductility synergy and exceptional fatigue strength. © 2021, The Minerals, Metals & Materials Society and ASM International.