Journal of Metastable and Nanocrystalline Materials Vol. 34

Abstract: A chemically heterogeneous Fe-0.95C-1.8Si-1.5Mn-0.65Cr-0.34Mo-0.6Al-1.51Cowt.% steel was isothermally heat treated in the temperature range of 200-250 to produce nanostructured bainite. Observations using optical microscopy and field emission scanning electron microscopy revealed that the microstructures consisted of nanosized bainitic ferrite plates in a matrix of retained austenite, which was confirmed by X-ray diffraction analysis. The influence of chemical heterogeneity on the development of nanobainite structure was also examined. It was found that the ferritic constituent nucleates preferentially in the substitutional-solute-lean regions, leaving coarse blocks of untransformed austenite in the substitutional-solute-rich regions. A yield strength of 165511MPa and an ultimate tensile strength of 194121MPa were obtained after isothermal transformation at 250 for 16h while the ductility of the material was 40.8%. This low ductility was attributed to the instability of large regions of austenite retained untransformed in the substitutional-solute-rich regions. An unexpectedly high hardness of 800HV30 was obtained following transformation at 200 for 44h.

Abstract: The insertion of bainite as a total or partial substitute for martensite is a promising option concerning the combination of high strength and toughness, properties mainly sought after by the aerospace and high technology industries. High-carbon, carbide-free bainitic steels are obtained through thermomechanical processing, with a final microstructure consisting of bainitic ferrite and retained austenite. The presence of carbides in these steels can reduce fracture toughness when compared to conventional quenched and tempered steels. This article aims to correlate the microstructure and impact resistance of four high carbon steel alloys with varying contents of Nickel, Silicon, and Manganese, which were austenitized at 870 °C and austempered at 280 °C at 12-hour intervals, 24 hours, 72 hours, and 168 hours. Thus, the microstructural characteristics, their morphological and kinetic aspects were determined, evaluating the mechanical properties from Rockwell C hardness tests, where commonly in the four alloys there is a decrease in the hardness values, due to the stress relief that occurred during the treatment of austempered, causing the bainitic microstructure to have larger lath shapes, causing a drop in hardness values in the impact test. For the fractographic analysis of the samples using scanning electron microscopy (SEM), the analyses showed three stages of the phase transformation: martensitic microstructure; multiphase microstructure composed of bainitic ferrite, martensite, and retained austenite; microstructure formed by bainitic ferrite and retained austenite, due to the stasis of the bainitic reaction. The alloys obtained lower rates of energy absorption in the initial times (from 24 hours) due to the instability of the austenite which consequently generated an increase in the energy absorption capacity, obtained from the energy dissipated by the impact of the Charpy test the effect called plasticity. Transformation-induced (TRIP) phenomenon causing when austenite becomes martensite, thus favoring increased ductility. Finally, it was observed that alloy (a), with lower content (%) of nickel, has a predominance of brittle fracture, as a microcleavage mechanism resulting from a combined action of a failure micromechanism. For alloy (c) with higher nickel content (%), the predominant fracture is also of the brittle type, with the presence of small microcavities common to the alveoli. The other important point to be considered is the influence of the treatment time, which does not interfere in the failure mechanism, remaining fragile until the end for alloy (a), alloy (b), and alloy (c).

Abstract: In order to study the manufacturing process of diamond wire saw with magnetized baseline, we established a geometric model of the distribution of magnetic force lines around the magnetized baseline, assumed that the abrasive particles were suspended around the baseline, and analyzed the force of the baseline on the abrasive particles. Without considering the pretreatment of wire saw, the physical model of sand loading process was established. The influence of baseline magnetization on the preparation efficiency and performance of wire saw was analyzed by SEM, EDS, XRD, microscope and Gauss meter. The results show that: after baseline magnetization, it has magnetism and produces force with abrasive particles; baseline magnetization can attract abrasive particles, effectively shorten the sanding time and improve the preparation efficiency of wire saw; using the above process to prepare wire saw can ensure high durability and increase the preparation efficiency by three times.

Abstract: The influence of functionalised multi-wall carbon nanotubes (f-MWCNTs) on the conductivity of conducting polymer poly (3,4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) was explored by using various concentrations of MWCNTs to create a nanocomposite (MWCNT/PEDOT:PSS) matrix. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction and Fourier transform infrared spectroscopy were employed to examine the structural and morphological features of the produced nanocomposite thin films. The electrical conductivity of f-MWCNT and (PEDOT:PSS/MWCNT) nanocomposites was determined using a two-point probe (lab view 2018). Results showed that the conductivity was enhanced from 6.7 s/cm for PEDOT:PSS (0.01 wt.%) f-MWCNT to 36.6 s/cm for PEDOT:PSS (5 wt.%) f-MWCNT and then decreased to 11.72 and 3.14 s/cm for 7 and 10 wt.%, respectively.

Abstract: The adsorption studies of coomassie brilliant blue (CBB) on alginate-chitosan nanoparticles (ACNPs) have been carried out by synthesizing alginate-chitosan nanoparticles and dropping with sodium tripolyphosphate and CaCl₂. CBB before and after adsorbed were analyzed using a UV-Vis spectrophotometer. Nanoparticle characterizations were done using infrared spectrophotometer (FT-IR), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Alginate-chitosan nanoparticles obtained were ivory white powder that has a rough surface with an average size of 50.62 nm. Investigation also showed that the ACNPs were able to adsorb CBB with an optimum adsorption capacity 53.25 mg/g at pH 2, the contact time of 90 min, and the initial concentration 100 ppm of adsorbate. The adsorption process of CBB followed pseudo-second order kinetics and the Dubinin-Radushkevich isotherm model.