Influence of Cr Content on the High-Temperature Oxidation Behavior and Mechanism of Low-Alloy Steels.

The high-temperature oxidation behavior of low-carbon steel (AISI 1015, AISI 8617, AISI 4115) was investigated over the temperature range from 600 to 1000 °C in humid air containing 25% water vapor. Mass gain of oxidation measurement was performed to study the oxidation kinetics. The microstructure, thickness, and composition of the oxide scale formed were investigated via optical microscope (OM), scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and electron probe microanalyzer (EPMA). The oxidation process was performed from 2 to 100 min. As the oxidation time increased, the trend of mass gain per unit area switched from a linear to a parabolic law, regardless of the steel grade used. As the chromium content increased, the duration of time during which the oxidation rate followed a linear relationship decreased. In the low-alloy steel with higher chromium content, the thickness of the mixed oxide layer containing Cr increased and the oxidation rate decreased at all oxidation temperatures.

Chemical Cleaning of Magnetite Deposits on the Flow Mini-Channels of a Printed Circuit Heat Exchanger in an EDTA-Based Solution.

The dissolution behavior of magnetite deposited on flow mini-channel surfaces within a printed circuit heat exchanger (PCHE) and the corrosion behavior of a STS 316L PCHE material were investigated in an ethylendiaminetetraacetic acid (EDTA)-based chemical cleaning solution at 93 °C. The fouling in the PCHE was simulated using a water-steam circulation loop system. Most of the magnetite deposits were rapidly dissolved in the early stage of the circulation chemical cleaning. An empirical equation for estimating the dissolution percentage was derived as a function of cleaning time. The PCHE material showed excellent corrosion resistance during the chemical cleaning tests. These results indicate the fouling layers in the PCHEs can be removed efficiently by the chemical cleaning process without concern about base metal corrosion.

Quantitative approach to realization of ultrasonic grain refinement of Al-7Si-2Cu-1Mg alloy.

Ultrasonic melt treatment (UST) was applied to Al-7Si-2Cu-1Mg melt at various temperatures of 620, 650, 700 and 785 °C. MgAl2O4 particles which were often found to be densely populated along oxide films, became effectively dispersed and well-wetted by UST. Transmission electron microscopy work combined with crystallography analysis clearly indicates that MgAl2O4 particles can act as α-Al nucleation site with the aid of UST. However, with UST, grain refinement occurred only at temperature of 620 °C and the grain size increased from 97 to 351 µm with increase of melt temperature to 785 °C for UST. In quantitative analysis of grain size and MgAl2O4 particle diameter, it was found that ultrasonic de-agglomeration decreased mean particle size of the MgAl2O4 particles, significantly reducing size from 1.2 to 0.4 µm when temperature increased from 620 to 785 °C. Such a size reduction with increased number of MgAl2O4 particles does not always guarantee grain refinement. Thus, in this work, detailed condition for achieving grain refinement by UST is discussed based on quantitative measurement. Furthermore, we tried to suggest the most valid grain refinement mechanism among the known mechanisms by investigation of the relationship between grain size and particle size with variation of melt temperature.

Electrically Conducting and Mechanically Strong Graphene-Polylactic Acid Composites for 3D Printing.

The advent of 3D printing has had a disruptive impact in manufacturing and can potentially revolutionize industrial fields. Thermoplastic materials printable into complex structures are widely employed for 3D printing. Polylactic acid (PLA) is among the most promising polymers used for 3D printing, owing to its low cost, biodegradability, and nontoxicity. However, PLA is electrically insulating and mechanically weak; this limits its use in a variety of 3D printing applications. This study demonstrates a straightforward and environment-friendly method to fabricate conductive and mechanically reinforced PLA composites by incorporating graphene nanoplatelets (GNPs). To fully utilize the superior electrical and mechanical properties of graphene, liquid-exfoliated GNPs are dispersed in isopropyl alcohol without the addition of any surfactant and combined with PLA dissolved in chloroform. The GNP-PLA composites exhibit improved mechanical properties (improvement in tensile strength by 44% and maximum strain by 57%) even at a low GNP threshold concentration of 2 wt %. The GNP-PLA composites also exhibit an electrical conductivity of over 1 mS/cm at >1.2 wt %. The GNP-PLA composites can be 3D-printed into various features with electrical conductivity and mechanical flexibility. This work presents a new direction toward advanced 3D printing technology by providing higher flexibility in designing multifunctional 3D printed features.

Publisher Correction: Superplasticity in a lean Fe-Mn-Al steel.

The original PDF version of this Article omitted to state that "Jeongho Han and Seok-Hyeon Kang contributed equally to this work" in the affiliations section. This has now been corrected in the PDF version of the Article. The HTML version was correct from the time of publication.

Superplasticity in a lean Fe-Mn-Al steel.

Superplastic alloys exhibit extremely high ductility (>300%) without cracks when tensile-strained at temperatures above half of their melting point. Superplasticity, which resembles the flow behavior of honey, is caused by grain boundary sliding in metals. Although several non-ferrous and ferrous superplastic alloys are reported, their practical applications are limited due to high material cost, low strength after forming, high deformation temperature, and complicated fabrication process. Here we introduce a new compositionally lean (Fe-6.6Mn-2.3Al, wt.%) superplastic medium Mn steel that resolves these limitations. The medium Mn steel is characterized by ultrafine grains, low material costs, simple fabrication, i.e., conventional hot and cold rolling, low deformation temperature (ca. 650 °C) and superior ductility above 1300% at 850 °C. We suggest that this ultrafine-grained medium Mn steel may accelerate the commercialization of superplastic ferrous alloys.Research in new alloy compositions and treatments may allow the increased strength of mass-produced, intricately shaped parts. Here authors introduce a superplastic medium manganese steel which has an inexpensive lean chemical composition and which is suited for conventional manufacturing processes.

Design for Fe-high Mn alloy with an improved combination of strength and ductility.

Recently, Fe-Mn twinning-induced plasticity steels with an austenite phase have been the course of great interest due to their excellent combination of tensile strength and ductility, which carbon steels have never been able to attain. Nevertheless, twinning-induced plasticity steels also exhibit a trade-off between strength and ductility, a longstanding dilemma for physical metallurgists, when fabricated based on the two alloy design parameters of stacking fault energy and grain size. Therefore, we investigated the tensile properties of three Fe-Mn austenitic steels with similar stacking fault energy and grain size, but different carbon concentrations. Surprisingly, when carbon concentration increased, both strength and ductility significantly improved. This indicates that the addition of carbon resulted in a proportionality between strength and ductility, instead of a trade-off between those characteristics. This new design parameter, C concentration, should be considered as a design parameter to endow Fe-Mn twinning-induced plasticity steel with a better combination of strength and ductility.

Drawing circuits with carbon nanotubes: scratch-induced graphoepitaxial growth of carbon nanotubes on amorphous silicon oxide substrates.

Controlling the orientations of nanomaterials on arbitrary substrates is crucial for the development of practical applications based on such materials. The aligned epitaxial growth of single-walled carbon nanotubes (SWNTs) on specific crystallographic planes in single crystalline sapphire or quartz has been demonstrated; however, these substrates are unsuitable for large scale electronic device applications and tend to be quite expensive. Here, we report a scalable method based on graphoepitaxy for the aligned growth of SWNTs on conventional SiO2/Si substrates. The "scratches" generated by polishing were found to feature altered atomic organizations that are similar to the atomic alignments found in vicinal crystalline substrates. The linear and circular scratch lines could promote the oriented growth of SWNTs through the chemical interactions between the C atoms in SWNT and the Si adatoms in the scratches. The method presented has the potential to be used to prepare complex geometrical patterns of SWNTs by 'drawing' circuits using SWNTs without the need for state-of-the-art equipment or complicated lithographic processes.

Results of Total Knee Arthroplasty with NexGen LPS-flex Implant Using Navigation System (Brain Lab): Results with a 5-year Follow-up.

PURPOSE: To evaluate the clinical and radiological results of patients that underwent total knee arthroplasty (TKA) with a NexGen LPS-Flex implant using a Navigation system (Brain Lab). MATERIALS AND METHODS: Between January 2001 and December 2005, 55 knees in 46 patients which used the NexGen LPS-Flex implant with a Navigation system (Brain Lab) for primary TKA were clinically and radiologically evaluated after a minimum follow-up of 5 years. Evaluation included preoperative and postoperative range of motion (ROM), Knee Society Score (KSS), tibio-femoral angle and postoperative complications. RESULTS: Knee ROM was increased from 118.9° preoperatively to 126.9° at the last follow up. In addition, the preoperative flexion contracture improved from 6.5° to 1.8° postoperatively. The mean KSS and functional score were improved from 59.8 and 51.2 to postoperative scores of 86.4 and 85.2 respectively. The rate of appearance of radiolucency in X-ray was 21.8%. One case of superficial skin infection and one case of aseptic loosening were noted as complications but, did not require a revision surgery. CONCLUSIONS: TKA with NexGen LPS-Flex implant using Navigation system (Brain Lab) showed satisfactory improvement in pain and function, but more long term follow up will be needed to complete verification.

Amorphous-to-crystalline phase transformation of thin film rubrene.

We report on the amorphous-to-crystalline phase transformation of rubrene thin films. The crystallization of the organic thin films displays disk-like domains whose nucleation and growth follow phase transformation kinetics well-established for inorganic materials under certain time and temperature conditions. We understood that the crystallization of amorphous rubrene thin film shows site-saturated nucleation behavior while the crystalline growth involves both diffusion and interface-controlled kinetics displaying spherulitic disk growth behavior. The activation energy of the transformation kinetics was about 0.78 eV on hexamethyldisilazane-functionalized SiO(2) substrate as mostly consumed at the growth process. The crystallization kinetics changes with the film substrate; more hydrophobic substrate induces a lesser number of crystalline nuclei while causing faster growth of those nuclei.