000150258 001__ 150258
000150258 005__ 20180501105939.0
000150258 0247_ $$2doi$$a10.5075/epfl-thesis-4802
000150258 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis4802-5
000150258 02471 $$2nebis$$a6121832
000150258 037__ $$aTHESIS_LIB
000150258 041__ $$aeng
000150258 088__ $$a4802
000150258 245__ $$aMicrostructure and Mechanical Behaviour of Ordered Au-Cu-Pt Alloys
000150258 269__ $$a2010
000150258 260__ $$aLausanne$$bEPFL$$c2010
000150258 300__ $$a169
000150258 336__ $$aTheses
000150258 520__ $$aThis thesis investigates nine new compositions of the       ternary Au-Cu-Pt system, containing from 75 to 78 wt% Au with       0 to 15 wt% Pt, by means of in-situ synchrotron       radiation X-ray diffraction, differential scanning       calorimetry, transmission electron microscopy and mechanical       tests, including hardness, tensile and repeated       stress-relaxation testing. X-ray diffraction data show that the alloys can be       separated into three groups according to their stable       low-temperature ordered phase(s), namely L10,       L12, or the two combined. Platinum increases       transformation temperatures in comparison with binary AuCu,       two-phase ordered alloys showing the highest transformation       temperatures. Details of the evolution of the peak structures       upon heating and cooling point to significant differences       between mechanisms of disordering and ordering: whereas       ordering visibly proceeds at significant undercooling by       nucleation and growth, disordering appears, from the visible       shifts in peak position, to progress in more homogeneous       fashion within the alloy. Alloys containing 2.5 wt% Pt show different       microstructural evolutions when ordered at 250 or 400 °C       after annealing at 650 °C and a water quench. With 75 and       76.5 wt% Au, the microstructural evolution depends on the       ordering temperature. At 400 °C, a classical polytwin       structure with two L10 crystal orientation       variants is formed; this evolves into a two-phase,       L10 + A1, checkerboard-like microstructure after       106 s. At 250 °C, ordering develops a stable (up       to 105 s) structure containing all three       L10 crystal variants and a network of       perpendicular {110} twins roughly 30 nm wide. The 78 wt %Au       alloy develops at both ordering temperatures a similar       three-variant nanotwinned structure that also remains stable       up to 105 s. With all three alloys containing 2.5       wt% Pt, superior hardness and tensile strength, coupled with       lower ductility, are obtained with the three-variant       nanotwinned structure formed at 250 °C compared with the       more classical polytwin structure that develops at       400 °C. Activation volumes characteristic of room-temperature       compressive plastic deformation in Au- 21 wt% Cu- 2.5 at% Pt,       are measured using the repeated stress-relaxation method on       the classical polytwin and the three-variant structures. All       ordered nanotwinned microstructures obtained have an initial       effective activation volume Veff of 100 to       120 b3; this is values typical of       cross-slip or twin boundary bypass in FCC metals. The two       structures differ strongly as they work-harden: the       two-variant polytwin structure yields a straight line on a       Haasen plot, suggesting that work hardening is associated       with an increase in slip obstacle density, most likely       dislocation debris at intervariant boundaries. The       three-variant structure on the other hand shows a constant       activation volume. This suggests the presence of a mechanism       by which obstacles that accumulate during deformation of the       two-variant structure can be removed when three variants are       present; a possible mechanism is debris elimination by       intraboundary glide coupled with triple line leakage or loop       annihilation. Alloys containing 7.5 or 15 wt% Pt have microstructures in       which the L12 phase is found, either alone or in       combination with L10. Whereas fully L12       alloys (of higher Pt content) are relatively soft, two-phase       alloys are nearly as hard and ductile as fully L10       alloys, and feature relatively stable structures, which TEM       observation suggests consist in several variants of the       L10 phase embedded in a matrix of       L12.
000150258 6531_ $$aAuCu
000150258 6531_ $$aTEM
000150258 6531_ $$asynchrotron radiation
000150258 6531_ $$aordering
000150258 6531_ $$amechanical properties
000150258 6531_ $$aAuCu
000150258 6531_ $$aMET
000150258 6531_ $$asynchrotron
000150258 6531_ $$amise en ordre
000150258 6531_ $$apropriétés mécaniques
000150258 700__ $$0242398$$aKlay, Edwina$$g137114
000150258 720_2 $$0240159$$aMortensen, Andreas$$edir.$$g112836
000150258 720_2 $$0240145$$aDiologent, Frédéric$$edir.$$g168992
000150258 8564_ $$s22887451$$uhttps://infoscience.epfl.ch/record/150258/files/EPFL_TH4802.pdf$$yTexte intégral / Full text$$zTexte intégral / Full text
000150258 909C0 $$0252046$$pLMM$$xU10336
000150258 909CO $$ooai:infoscience.tind.io:150258$$pDOI$$pthesis$$pthesis-bn2018$$pDOI2$$pSTI
000150258 918__ $$aSTI$$cIMX$$dEDMX
000150258 919__ $$aLMM
000150258 920__ $$b2010
000150258 970__ $$a4802/THESES
000150258 973__ $$aEPFL$$sPUBLISHED
000150258 980__ $$aTHESIS