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Blobaum, K.J.M.; Krenn, C.R.; Wall, M.A.; Massalski, T.B.; Schwartz, A.J. |
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Publication |
Nucleation and growth of the [alpha]' martensitic phase in Pu-Ga alloys |
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Journal Article |
Pages |
2006 |
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Abstract |
Acta Materialia |
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Corporate Author |
Acta Mater. |
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Publisher |
54 |
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Editor |
15 |
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Summary Language |
4001-4011 |
Series Editor |
Phase transformations; Martensitic phase transformation; Nucleation of phase transformations |
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Abbreviated Series Title |
In a Pu-2.0 at.% Ga alloy, it is observed experimentally that the amount of the martensitic α' product formed upon cooling the metastable δ phase below the martensite burst temperature (Mb) is a function of the holding temperature and holding time of a prior conditioning (“annealing”) treatment. Before subjecting a sample to a cooling and heating cycle to form and revert the α' phase, it was first homogenized for 8 h at 375 [degree sign]C to remove any microstructural memory of prior transformations. Subsequently, conditioning was carried out in a differential scanning calorimeter apparatus at temperatures in the range between -50 and 370 [degree sign]C for periods of up to 70 h to determine the holding time and temperature that produced the largest volume fraction of α' upon subsequent cooling. Using transformation peak areas (i.e., the heats of transformation) as a measure of the amount of α' formed, the largest amount of α' was obtained following holding at 25 [degree sign]C for at least 6 h. Additional time at 25 [degree sign]C, up to 70 h, did not increase the amount of subsequent α' formation. At 25 [degree sign]C, the Pu-2.0 at.% Ga alloy is below the eutectoid transformation temperature in the phase diagram and the expected equilibrium phases are α and Pu3Ga, although a complete eutectoid decomposition of δ to these phases is expected to be extremely slow. It is proposed here that the influence of the conditioning treatment can be attributed to the activation of α-phase embryos in the matrix as a beginning step toward the eutectoid decomposition, and we discuss the effects of spontaneous self-irradiation accompanying the Pu radioactive decay on the activation process. Subsequently, upon cooling, certain embryos appear to be active as sites for the burst growth of martensitic α' particles, and their amount, distribution, and potency appear to contribute to the total amount of martensitic product formed. A modeling approach based on classic nucleation theory is presented to describe the formation of α-phase embryos during conditioning. The reasons why the holding times during conditioning become eventually ineffective in promoting more α' formation on cooling are discussed in terms of the differences in the potency of the embryos created in the δ matrix during conditioning and in terms of growth-impeding volume strains in the matrix resulting from an increasing number of martensite particles, thus opposing further growth. It is suggested that the disparate amounts of the α' formation reported in the literature following various studies may be in part a consequence of the fact that conditioning times at ambient temperatures are inevitably involved in any handling of radioactive samples prior to testing. |
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NU @ karnesky @ |
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1916 |
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Cerezo, A.; Gibuoin, D.; Kim, S.; Sijbrandij, S. J.; Venker, F. M.; Warren, P. J.; Wilde, J.; Smith, W., G D |
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Materials applications of an advanced 3-dimensional atom probe |
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Journal Article |
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1996 |
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Journal de Physique IV |
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J. de Phys. IV |
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6 |
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C5 |
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205-210 |
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3D Atom Probe, Technique/review |
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An advanced 3-dimensional atom probe system has been constructed, based on an optical position-sensitive atom probe (OPoSAP) detector with energy compensation using a reflectron lens. The multi-hit detection capability of the OPoSAP leads to significant improvements in the efficiency of the instrument over the earlier serial position-sensing system. Further gains in efficiency are obtained by using a biassed grid in front of the detector to collect secondary electrons generated when ions strike the interchannel area. The improvement in detection efficiency gives enhanced performance in the studies of ordered materials and the determination of site occupation. Energy compensation leads to a much improved mass resolution (m/Δm full width at half maximum) making it possible to map out the 3-dimensional spatial distributions of all the elements in complex engineering alloys, even when elements lie close together in the mass spectrum. For example, in the analysis of a maraging steel, this allows separation between the 61Ni2+ and 92Mo3+ peaks, which are only 1/6 of a mass unit apart. |
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1954 |
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Dadykin, A. A.; Naumovets, A. G.; Yatsenko, A. F.; Andreev, V. D.; Nachal'naya, T. A.; Semenovich, V. A.; Lavrentovich, Y. I. |
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Emission characteristics of diamond-like films |
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Journal Article |
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1996 |
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Sverkhtverd. Mater. |
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1 |
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25-29 |
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Field Emission |
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1968 |
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Choi, W. B.; Myers, A. F.; Wojak, G. J.; McClure, M. T.; Cuomo, J. J.; Hren, J. J. |
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The effects of the interface and surface treatment on the electron emission from diamond coated field emitters |
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Journal Article |
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1996 |
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Int. Vac. Microelectron. Conf., 9th (1996), 288-292 Publisher: Nevskii Kur'er, St. Petersburg, Russia. |
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288-292 |
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Field Emission |
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1986 |
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Choi, W. B.; Cuomo, J. J.; Zhirnov, V. V.; Myers, A. F.; Hren, J. J. |
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Field emission from silicon and molybdenum tips coated with diamond powder by dielectrophoresis |
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Journal Article |
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1996 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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68 |
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720-722 |
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Field Emission |
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no |
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2035 |
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Liu, J.; Zhirnov, V. V.; Choi, W. B.; Wojak, G. J.; Myers, A. F.; Cuomo, J. J.; Hren, J. J. |
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Electron emission from a hydrogenated diamond surface |
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Journal Article |
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1996 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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69 |
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4038-4040 |
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Field Emission |
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no |
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2037 |
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Zhirnov, V. V.; Choi, W. B.; Cuomo, J. J.; Hren, J. J. |
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Diamond coated Si and Mo field emitters: diamond thickness effect |
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Journal Article |
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1996 |
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Applied Surface Science |
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Appl. Surf. Sci. |
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94/95 |
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123-128 |
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Field Emission |
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no |
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2101 |
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Choi, W. B.; McClure, M. T.; Schlesser, R.; Sitar, Z.; Hren, J. J. |
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Enhanced field emission from diamond coated molybdenum emitters |
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Journal Article |
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1996 |
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Journal de Physique IV |
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J. de Phys. IV |
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6-C5 |
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97-102 |
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Field Emission |
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no |
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2118 |
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Choi, W. B.; Liu, J.; McClure, M. T.; Myers, A. F.; Zhirnov, V. V.; Cuomo, J. J.; Hren, J. J. |
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Field emission from diamond coated molybdenum field emitters |
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Journal Article |
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1996 |
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Journal of Vacuum Science & Technology A |
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J. Vac. Sci. Technol. A |
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14B |
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2050-2055 |
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Field Emission |
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no |
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2170 |
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Myers, A. F.; Camphausen, S. M.; Cuomo, J. J.; Hren, J. J.; Liu, J.; Bruley, J. |
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Characterization of amorphous carbon coated silicon field emitters |
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Journal Article |
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1996 |
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Journal of Vacuum Science & Technology A |
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J. Vac. Sci. Technol. A |
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14B |
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2024-2029 |
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Field Emission |
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no |
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2207 |
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