Browsing by Subject "Stainless steel"

Now showing 1 - 7 of 7

Open Access
Excitonic enhancement of nonradiative energy transfer to bulk silicon with the hybridization of cascaded quantum dots
(AIP, 2013) Yeltik A.; Guzelturk, B.; Hernandez-Martinez, P. L.; Akhavan S.; Demir, Hilmi Volkan
We report enhanced sensitization of silicon through nonradiative energy transfer (NRET) of the excitons in an energy-gradient structure composed of a cascaded bilayer of green- and red-emitting CdTe quantum dots (QDs) on bulk silicon. Here NRET dynamics were systematically investigated comparatively for the cascaded energy-gradient and mono-dispersed QD structures at room temperature. We show experimentally that NRET from the QD layer into silicon is enhanced by 40% in the case of an energy-gradient cascaded structure as compared to the mono-dispersed structures, which is in agreement with the theoretical analysis based on the excited state population-depopulation dynamics of the QDs. © 2013 AIP Publishing LLC.
Open Access
In vitro biocompatibility of plasma-aided surface-modified 316L stainless steel for intracoronary stents
(Institute of Physics Publishing, 2010) Bayram, C.; Mizrak, A.K.; Aktürk, S.; Kurşaklioǧlu H.; Iyisoy, A.; Ifran, A.; Denkbaş, E.B.
316L-type stainless steel is a raw material mostly used for manufacturing metallic coronary stents. The purpose of this study was to examine the chemical, wettability, cytotoxic and haemocompatibility properties of 316L stainless steel stents which were modified by plasma polymerization. Six different polymeric compounds, polyethylene glycol, 2-hydroxyethyl methacrylate, ethylenediamine, acrylic acid, hexamethyldisilane and hexamethyldisiloxane, were used in a radio frequency glow discharge plasma polymerization system. As a model antiproliferative drug, mitomycin-C was chosen for covalent coupling onto the stent surface. Modified SS 316L stents were characterized by water contact angle measurements (goniometer) and x-ray photoelectron spectroscopy. C1s binding energies showed a good correlation with the literature. Haemocompatibility tests of coated SS 316L stents showed significant latency (t-test, p < 0.05) with respect to SS 316L and control groups in each test. © 2010 IOP Publishing Ltd.
Open Access
Influence of tool wear on machining forces and tool deflections during micro milling
(Springer, 2016) Oliaei, S. N. B.; Karpat, Y.
Tool wear on the cutting edges of micro end mills is an important issue affecting process outputs such as tool deflections and surface roughness, especially when difficult-to-cut materials such as titanium alloys, stainless steel, etc. are machined at micro scale. An understanding of the interactions between tool wear, machining forces, tool deflections, and surface roughness is important in order to maintain component quality requirements. However, in literature, the number of studies concerning tool wear in micro end mills is limited. The goal of the paper is to better understand tool wear patterns (flank wear, edge rounding) of micro end mills and their relationship to machining parameters. In this study, first, the influence of tool wear on micro milling forces and surface roughness parameters is analyzed and favorable micro milling process parameters are identified. It is shown that, when machining with worn end mills, forces are affected by the tool wear patterns. Then, the influence of increased milling forces due to tool wear on tool deflections and tool breakage is studied using both experimental techniques and finite element analysis. The finite element model-based tool deflection and tool breakage predictions are validated through experiments. The results of this study can be used in process parameter selection in pocket micro milling operations and tool condition monitoring systems.
Open Access
Liquid-phase sintering of medical-grade P558 stainless steel using a new biocompatible eutectic additive
(Elsevier, 2012-02-02) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, M.; Mashhadi, S. B.; Okyay, Ali Kemal
One of the effective approaches to reduce residual pores in powder metallurgy parts is activated liquid-phase sintering process using proper additives. In this work, for the first time, a new biocompatible additive (Mn-11.5 wt.% Si, a eutectic alloy) is experimented for liquid-phase sintering of nanocrystalline/amorphous P558 stainless steel powders. It is realized that by increasing the sintering aid content and temperature, the density is effectively increased: a sharp densification progress when the sintering temperature increases from 1000 °C to 1050 °C and a slower densification rate when it exceeds 1050 °C. This preliminary study opens up the development of high-density medical-grade stainless steels produced by powder metallurgy, where suitable additives can lower sintering temperature and time, which is promising for retarding grain growth and commercial applications.
Open Access
Microstructural characterization of medical-grade stainless steel powders prepared by mechanical alloying and subsequent annealing
(Elsevier, 2013) Salahinejad, E.; Hadianfard, M. J.; Ghaffari, M.; Amini, R.; Mashhadi, S. B.; Okyay, Ali Kemal
The harmful effect of nickel ions released from conventional stainless steel implants has provided a high level of motivation for the further development of nickel-free stainless steels. In this paper, the microstructure of medical-grade nickel-free stainless steel powders, with the chemical composition of ASTM F2581, is studied during mechanical alloying and subsequent annealing. Rietveld X-ray diffraction and transmission electron microscopy evaluations reflect nanocrystallization, austenitization and amorphization of the powders due to mechanical activation. It is also realized that annealing of the as-milled powder can develop a single austenitic structure with nanometric crystallite sizes, implying a considerable inherent resistance to grain growth. This study demonstrates the merit of mechanical alloying and subsequent annealing in the development of nanostructured medical-grade stainless steels.
Open Access
Nanocomposite glass coatings containing hexagonal boron nitride nanoparticles
(Pergamon Press, 2016) Çamurlu, H. E.; Akarsu, E.; Arslan, O.; Mathur, S.
Glass coatings composed of SiO2-K2O-Li2O, containing non-modified and fluorosilane modified hexagonal boron nitride (hBN) nanoparticles, were prepared on stainless steel plates through sol-gel spin-coating method. Coatings were examined by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), atomic force microscopy (AFM) and thermo-gravimetric analysis (TGA). 1.3-2.5 μm thick uniform coatings were obtained after curing at 500 Â°C for 1 h. The coatings adhered well to the steel substrates. It was determined by salt spray tests that the coatings enhance corrosion resistance. The aim of hydrophobic fluorosilane modification of hBN nanoparticles was to enrich hBN quantity on the top surface of the coatings. Coatings containing fluorosilane modified hBN nanoparticles presented slightly lower friction coefficient values than the other coatings.
Open Access
Nonlinear laser lithography to control surface properties of stainless steel
(Elsevier BV, 2015) Orazi, L.; Gnilitskyi, I.; Pavlov, I.; Serro, A. P.; Ilday, S.; Ilday, F. O.
In the present work a novel method to improve the surface properties of stainless steel is presented and discussed. The method, based on the use of a high repetition rate femtosecond Yb fibre laser, permits generation of highly reproducible, robust, uniform and periodic nanoscale structures over a large surface area. The technique is characterized by high productivity, which, in its most simple form, does not require special environmental conditioning. Surface morphology is scrutinized through SEM and AFM analyses and wettability behaviour is investigated by means of the sessile drop method using distilled-deionized water. It is shown that optimization of process parameters promotes anisotropic wetting behaviour of the material surface.