N. Parkansky
L. Glikman
I. I. Beilis
B. Alterkop
R. L. Boxman and D. Gindin
Electrode erosion was studied in pulsed arcs ignited between two electrodes comprised of 99.99%C (graphite) and 99.5%W submerged in deionized water or analytical (99.8%) ethanol. In the both cases the erosion rate increased proportionally to the pulse energy, and the total electrode erosion per unit energy was inversely proportional to the discharge pulse duration. Fifteen and sixty-μF discharge capacitors were used for formation of the pulses in water. It was obtained that, respectively (a) erosion of the tungsten anode (Wa) was by factors of 5–6 and ∼10 greater than that of the carbon (Cc) cathode; (b) erosion of the carbon anode (Ca) was by a factor of 1.34 greater and by a factor of 2.65 less than that of the tungsten cathode (Wc); (c) the total erosion rate of both electrodes (anode and cathode) per unit pulse energy for the Wa–Cc pair was greater by factors of 11 and 12.5 than that for the Wc–Ca pair.
Ribeiro, J.
dos Anjos, D. M.
Leger, J. -M.
Hahn, F.
Olivi, P.
de Andrade, A. R.
Tremiliosi-Filho, G.
Kokoh, K. B.
Binary and ternary Pt-based catalysts were prepared by the Pechini-Adams modified method on carbon Vulcan XC-72, and different nominal compositions were characterized by TEM and XRD. XRD showed that the electrocatalysts consisted of the Pt displaced phase, suggesting the formation of a solid solution between the metals Pt/W and Pt/Sn. Electrochemical investigations on these different electrode materials were carried out as a function of the electrocatalyst composition, in acid medium (0.5 mol dm(-3) H2SO4) and in the presence of ethanol. The results obtained at room temperature showed that the PtSnW/C catalyst display better catalytic activity for ethanol oxidation compared to PtW/C catalyst. The reaction products (acetaldehyde, acetic acid and carbon dioxide) were analyzed by HPLC and identified by in situ infrared reflectance spectroscopy. The latter technique also allowed identification of the intermediate and adsorbed species. The presence of linearly adsorbed CO and CO2 indicated that the cleavage of the C-C bond in the ethanol substrate occurred during the oxidation process. At 90 degrees C, the Pt85Sn8W7/C catalyst gave higher current and power performances as anode material in a direct ethanol fuel cell (DEFC).
(Ti, W)C-Ni cermets with different contents of Mo2C were produced by the spark plasma sintering (SPS) method. The grain size (GS), composition of ceramic phases, and mechanical properties of the sintered cermets were investigated. The amount of Mo2C had a significant influence on the microstructure and mechanical properties of as-prepared cermets. GS and fracture toughness (K-Ic) were decreased as a result of increasing the amount of Mo2C. By increasing the amount of Mo2C, the transverse rupture strength (TRS) and hardness (HRA) were enhanced. However, above 10 wt.%, the TRS was reduced. The conventional black cores observed by field-emission scanning electron microscopy (FE-SEM) in backscattered electron imaging (BSE) in (Ti, W)C-Ni cermets will be partially turned into some white cores which contain higher Mo, except for Ti and W elements, when content of Mo2C reaches similar to 15 wt.%. Batch mechanical tests indicate that cermets with some white cores have refined microstructure and higher hardness, but relatively lower transverse rupture strength (TRS) and fracture toughness (K-Ic) at room temperature.
It has been shown that W–Co–C phases could dissolve a substantial amount of metals such as V, Cr and Ta, which are known to positively influence the microstructure of hardmetals with respect to uniform grain size distribution and fine grain size. This offers a tool to circumvent the conventional doping of hardmetals with individual carbides. In the present study we used double- and triple-alloyed κ-W9Co3C4 (i.e. κ-(W,V,Cr)9Co3C4 and κ-(W,V,Cr,Ta)9Co3C4) and applied a variety of sintering experiments to obtain WC–Co, WC–(Ti,Ta,Nb)C–Co and WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. We also prepared κ-W9Fe3C4, alloyed κ-W9Ni3C4, and κ-W9(Fe/Ni)3C4, and used the latter for sintering.Sintering was studied in situ by mass spectrometric outgassing experiments (MS-EGA) and dilatometry (DIL). The reactively-sintered hardmetals can be obtained with a very low amount of platelets and show the same properties as hardmetals with platelets. The latter are obviously not responsible for the high KIc values in these hardmetals. The alloy status of the starting alloyed κ-W9Co3C4, especially a certain amount of Ta, plays a role in WC grain growth for avoiding platelets. The good KIc is most probably due to a uniform Co distribution (the binder phase and WC form simultaneously by reaction of κ phase with C. Upon this formation, V, Cr and Ta are directly involved, because they are dissolved in the κ phase). The influence of the starting grain size of alloyed κ-W9Co3C4 on the grain size of reactively sintered hardmetal is crucial. This is probably due to the short diffusion distance of C, which causes the formation of very fine WC particles upon reaction with C. Together with alloyed κ-W9Co3C4, oxides were used to form fcc carbides by in situ carburisation. The microstructure of such prepared WC–(Ti,Ta,Nb)C–Co hardmetals is finer and the interpenetration of the WC and fcc particles is better than by use of fcc carbides in the starting mixture. The same is true if nitrogen atmosphere is used (and C level in the starting formulation is reduced) to form WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. With respect to the fracture toughness/hardness relationship, some of the prepared hardmetal grades show better properties than industrial grades and could thus possibly outperform the latter in cutting applications.
Adharapurapu, Raghavendra R.
Kumar, Deepak
Zhu, Jun
Pollock, Tresa M.
The surface and microstructure stability of experimental W- and Re-rich Ni-based alloys in an impure-helium environment containing only CO and CO2 as impurities (ppm level) have been investigated at 1000 degrees C All the alloys carburized during 50 h of exposure and depending on the alloy composition different carbides of the type M6C M7C3 and M23C6 formed on the alloy surface in grain interiors and at grain boundaries Microprobe analysis and Calphad-based calculations indicated that the chromium carbides (particularly Cr23C6) were enriched by rhenium Extended exposure (225 h) led to the disappearance of surface transient carbides and the growth of surface oxide Cr2O3 occurred (C) 2010 Elsevier Ltd All rights reserved
A titanium based carbonitride alloy containing Ti, Nb, W, C, N and Co. The alloy also contains, in addition to Ti, 9-14 at % Co with only impurity levels of Ni and Fe, 1-<3 at % Nb, 3-8 at % W and has a C/(C+N) ratio of 0.50-0.75. The amount of undissolved Ti(C,N) cores should be kept between 26 and 37 vol % of the hard constituents, the balance being one or more complex carbonitrides containing Ti, Nb and W. The alloy is particularly useful for milling of steel.