Hatem Akbulut

Dry wear and friction properties of δ-Al2O3 short fiber reinforced AlSi (LM 13) alloy metal matrix composites

Abstract Planar-randomly oriented alumina short fiber (Saffil) reinforced Al Si (LM 13) alloy metal matrix composites (MMCs) were produced by a modified liquid infiltration technique. The wear and friction behavior of LM 13 alloys containing up to 30 vol % Al2O3 fiber were investigated in sliding against a hard steel counterface (63 HRC) by continuous loading experiments carried out in a pin-on-disk machine under dry conditions at room temperature in the transverse section of the composites. Sliding tests were conducted at five loads (5 N, 10 N, 20 N, 40 N and 60 N) and under a constant sliding speed of 1 m/s. The wear and coefficient of friction against sliding distance initially showed a short transient period and then reached a steady state behavior. The wear behavior of the composites was dependent on fiber volume and applied load. The wear rate decreased with increased volume fraction of fiber and increased with increasing load. The wear resistance of the composites over the range of loads and volume fraction of fibers studied was found to range from almost 1.2 to about 4.0 times that of unreinforced alloy. Coefficient of friction decreased with increased fiber volume percent and applied normal load. To analyze wear mechanisms, wear surfaces were examined by scanning electron microscopy and it was found that the wear of the unreinforced alloy and composites occurred by groove formation and its subsequent growth, the magnitude of which increased with increasing fiber volume and applied normal load.

The characterization of borided 99.5% purity nickel

Abstract A series of experiments were performed to evaluate some properties of borided 99.5% purity nickel. Boronizing was carried out in a solid media consisting of Ekabor powders at 950°C for 2, 4, and 8 h, respectively. Data on intermetallic silicides and borides (Ni 5 Si 2 , Ni 2 B) that formed on the surface of nickel substrate during boronizing were confirmed by a classical metallographic technique and X-ray diffraction (XRD) analysis. It was observed that the predominant phase in the coating layer was a silicide. It is probable that the formation of the nickel silicide layer was due to silicon in the boronizing powder. The hardness of silicides was measured by using a Vickers indenter with a load of 0.5 N. The microhardness of silicides formed on the surface of the nickel substrate reached up to 805 HV. Metallographic studies revealed that the silicide layer has an equiaxed granular morphology, whereas the boride layer formed had a needle-shaped structure. Depending on process temperature and boronizing time the thickness of coating layers ranged from 123 to 281 μm. The thickness of silicide and boride layers depended strongly on the processing time at 950°C. The longer boronizing time resulted in the thicker surface layer. The distribution of alloying elements from the surface to the interior was determined using energy dispersive X-ray spectroscopy (EDS).

Wear Behavior of AISI 8620 Steel Modified by a Pulse-Plasma Technique

In this study, the micro-hardness, wear behavior, and microstructure of AISI 8620 steel, which was initially annealed at 700°C and carburized for 2 h at 900°C, were studied before and after pulse-plasma treatment. The surfaces of the samples were modified by a mixture of nitrogen, C3H8, and oxygen gases by using a pulse-plasma technique. Two different battery capacities of 800 and 1000 μ F and two different sample plasma gun nozzle distances of 60 and 80 mm were chosen for surface modification. Microhardness measurements were carried out on the sections perpendicular to the surfaces treated and hardness profiles from the outer surface to the inner sections of the samples modified by pulse-plasma were determined. The measurements showed that pulse-plasma treatment resulted in a remarkable increase in surface hardness of an AISI 8620 steel after the conventional carburizing process and the maximum hardness value measured was as high as HV910. Ball-on-disc wear tests according to ASTM G99 were also conducted on the treated samples of AISI 8620 steels in order to investigate their wear and friction performance in dry sliding conditions. Worn surfaces were analyzed and dominant wear mechanisms were identified using the SEM and EDS techniques. It was found that the pulse-plasma treatment considerably improved the wear resistance of all treated materials. However, it was shown that the process parameters as well as the initial heat treatment had a profound effect on the wear rate and the maximum wear resistance was obtained from those initially subjected to heat treatment and then treated by pulse-plasma at the battery capacity of 800 μ F and nozzle distance of 80 mm.

Pulse electrocodeposition of Ni/MWCNT nanocomposite coatings

Abstract Nickel/multiwalled carbon nanotube (MWCNT) metal matrix composite coatings were deposited by pulse electrocodeposition method from a Watts type electrolyte. The influence of peak current density on the particle codeposition and distribution, the surface morphology, microstructure, microhardness and wear resistance of nanocomposite coatings were studied. Copper substrates were used for electrocodeposition and MWCNTs with the diameter of 50–60 nm and length of 10 μm used as reinforcements. The electrodeposited Ni matrix coatings were characterised by scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis.

Ni/MWCNT Coatings Produced by Pulse Electrocodeposition Technique

Nickel/multiwalled carbon nanotube (MWCNT) metal matrix composite coatings were deposited by pulse electrocodeposition method from a Watts-type electrolyte. The influence of the MWCNT content in the electrolyte on the particle codeposition and distribution, the surface morphology, microstructure, microhardness of nanocomposite coatings were studied. Copper substrates were used for electrocodeposition of Ni matrix/MWCNTs with the diameter of 50–60 nm and length of 10-µm carbon nanotube reinforcements. The electrodeposited Ni matrix coatings were characterized by scanning electron microscopy and X-ray diffraction analysis.

Wear Behavior of Bronze Hybrid MMCs Coatings Produced by Current Sintering on Steel Substrates

In this work, a bronze matrix (90 wt% Cu + 10 wt% Sn) was reinforced with SiC and graphite particulates using mechanical alloying and a subsequent current sintering technique. The mechanically ball-milled bronze hybrid matrix composite powders reinforced with 5.0 wt% SiC and 5.0 wt% graphite were cold-compacted on a 1040 steel substrate under a pressure of 300 MPa. The compacted structure was sintered at atmospheric conditions to nearly a full density within 10 min using current sintering, in which the powders were heated by a low voltage and high current and compressed simultaneously. The samples were sintered at three different applied currents (1,500, 1,700, and 1,900 A) to provide dense and well-bonded coatings on steel substrates. Microhardness testing and optical and scanning electron microscopes (SEM) were used for microstructural characterization of the hybrid composites. The tribological characterization of the resulting composites was tested by a block-on-disk method for determination of the wear loss and friction coefficient behaviors against a steel disk. It was pointed out that increasing applied current during the sintering/coating process resulted in obtaining high-hardness and wear-resistant hybrid composite coatings.

Sn/SnO2/Mwcnt composite anode and electrochemical impedance spectroscopy studies for Li-ion batteries

ABSTRACT Tin/tinoxide/multi-walled carbon nanotube (Sn/SnO2/MWCNT) core-shell structure nanocomposite anode is produced by thermal evaporation and subsequent plasma oxidation with using MWCNT buckypaper. Metallic tin is evaporated onto free-standing and flexible MWCNT buckypaper having controlled porosity and subsequent RF plasma oxidized in Ar:O2(1:1) gas mixture. X-ray diffraction and scanning electron microscopy are used to determine the structure and morphology of the obtained nanocomposite. The electrochemical characteristics of the nanocomposite anode are examined by using electrochemical impedance spectroscopy and galvanostatic charge–discharge experiments. Family of Nyquist plots during first discharge process are obtained and studied at different voltage values.

Cr- and V-Substituted LiMn2O4 Cathode Electrode Materials for High-Rate Battery Applications

Spinel Cr- and V-substituted LiMn2O4 cathode materials were prepared by facile sol–gel process, which used lithium carbonate and manganese carbonate as starting materials and citric acid as a chelating agent. In order to increase electronic conductivity and prevent the Mn ion dissolution into the electrolyte, surfaces of the as-synthesized powders were coated with Cu via electroless deposition technique. The structure and physicochemical properties of the obtained Cr- and V-substituted LiMn2O4 powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge discharge tests, and electrochemical impedance spectroscopy (EIS). The results have shown that the successful formation of Cr- and V-substituted LiMn2O4 product was highly dependent on its second-stage calcination temperature.

Li-O2 Piller için α-MnO2/Grafen/KNT Nanokompozit Elektrotlarının Üretimi ve Karakterizasyonu

Bu calismada Li-O 2 pilleri icin elektrot malzemesi α - MnO 2 /Grafen/KNT nanokompozitleri uretilmis ve karakterize edilmistir. Grafen Hummer metodu ile uretilmis ve tabakalar arasi bosluk yapici olarak karbon nano tup ilavesi yapilmistir. α - MnO 2 nano cubuklar sentezlenerek α - MnO 2 /Grafen/KNT nanokompozitleri vakum filtrasyon yontemi ile kagit halinde elektrot olarak uretilmistir. Uc farkli oranda ilave edilen α - MnO 2 nano cubuklari ile elektrotlarin yapisal karakterizasyonu FESEM, XRD kullanilarak ve elektrokimyasal karakterizasyonu da ECC-hava test hucreleri ile yapilmistir.

Freestanding graphene/MnO2 cathodes for Li-ion batteries

Different polymorphs of MnO2 (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers’ method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge–discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm−2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg−1, 198 mAhg−1, and 251 mAhg−1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg−1 after 200 cycles with 72% capacity retention.