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91.
Ercan Balikci A. Raman R. A. Mirshams 《Metallurgical and Materials Transactions A》1997,28(10):1993-2003
IN738LC is a modern, nickel-based superalloy utilized at high temperatures in aggressive environments. Durability of this
superalloy is dependent on the strengthening of γ′ precipitates. This study focuses on the microstructural development of IN738LC during various heat treatments. The 1120
°C/2 h/accelerated air-cooled (AAC) solution treatment, given in the literature, already produces a bimodal precipitate microstructure,
which is, thus, not an adequate solutionizing procedure to yield a single-phase solid solution in the alloy at the outset.
However, the 1235 °C/4 h/water quenched (WQ) solution treatment does produce the single-phase condition. A microstructure
with fine precipitates develops if solutionizing is carried out under 1200 °C/4 h/AAC conditions. Agings at lower temperatures
after 1200 °C/4 h/AAC or 1250 °C/4 h/AAC or WQ conditions yield analogous microstructures. Agings below ∼950 °C for 24 hours
yield nearly spheroidal precipitates, and single aging for 24 hours at 1050 °C or 1120 °C produces cuboidal precipitates.
Two different γ′ precipitate growth processes are observed: merging of smaller precipitates to produce larger ones (in duplex precipitate-size
microstructures) and growth through solute absorption from the matrix. Average activation energies for the precipitate growth
processes are 191 and 350 kJ/mol in the ranges of 850 °C to 1050 °C and 1050 °C to 1120 °C, respectively, calculated using
the precipitate sizes from microstructures in the WQ condition, and 150 and 298 kJ/mol in the analogous temperature ranges,
calculated from precipitate sizes in the microstructures in the slow furnace-cooled condition. 相似文献
92.
Murali Raman 《Information Systems Management》2006,23(4):59-66
This article provides a brief tutorial of Wiki technology as a collaborative tool. A case example from a university administration context suggests that - like many other end-user technologies - training and support needs should be carefully considered before the potential value of using this “free” technology to support knowledge management efforts can be satisfactorily realized. 相似文献
93.
A uniplanar GaAs monolithic microwave integrated circuit /spl times/4 subharmonic mixer (SHM) has been fabricated for 60-GHz-band applications using an antiparallel diode pair in finite ground coplanar (FGC) waveguide technology. This mixer is designed to operate at an RF of 58.5-60.5 GHz, an IF of 1.5-2.5 GHz, and an LO frequency of 14-14.5 GHz. FGC transmission-line structures used in the mixer implementation were fully characterized using full-wave electromagnetic simulations and on-wafer measurements. Of several mixer configurations tested, the best results show a maximum conversion loss of 13.2 dB over the specified frequency range with a minimum local-oscillator power of 3 dBm. The minimum upper sideband conversion loss is 11.3 dB at an RF of 58.5 GHz and an IF of 2.5 GHz. This represents excellent performance for a 4/spl times/ SHM operating at 60 GHz. 相似文献
94.
Equilibrium phase fields of the ternary Pb-Bi-O system were established by long-term equilibration in the temperature range 660-840 K. Using these results, the partial phase diagram of the ternary system has been constructed. The standard molar Gibbs energy of formation of the ternary oxides, 〈Pb5Bi8O17〉 and 〈PbBi12O19〉, was determined by measuring the equilibrium oxygen partial pressures over the relevant phase fields by static manometry in conjunction with a solid oxide electrolyte-based emf cell. Further, the standard molar Gibbs energy of formation of 〈Pb3O4〉 was also measured by the manometric method. The oxide that coexists with the Pb-Bi eutectic alloy (LBE) has been experimentally confirmed as [β-PbO]ss. Using the thermochemical data measured, the compositions of Pb-Bi alloys that coexist with [β-PbO]ss and ternary oxides were derived and reported. 相似文献
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The cyclic deformation behavior of Pb-2 pct Sn solid solution alloy has been investigated. Results indicate that grain boundary
migration and sliding occur in a systematic manner, giving rise to a series of migration markings on the surface of deformed
specimens. Extensive cracking and cavitation takes place at migrating boundaries leaving an array of microcavities at high
strain amplitudes. This feature was not observed at the low strain amplitudes investigated. Dynamic recrystallization and
the evolution of a diamond grain configuration from an initial random distribution of grains were observed. These microstructural
observations are discussed in relation to their influence on high temperature fatigue fracture.
Formerly with IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598. 相似文献
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