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1HXWURQ'LIIUDFWLRQ0HDVXUHPHQWVRI'HIRUPDWLRQDQG5HFU\VWDOOL]DWLRQ 7H[WXUHVLQ&ROG:LUH'UDZQ&RSSHU Ph. Gerber1,a, S. Jakani1,b, M.H. Mathon1,c and T. Baudin2,d 1
Laboratoire Léon Brillouin, CEA(DSM-DRECAM)-CNRS, CEA Saclay, 91191 Gif sur Yvette, France 2 Laboratoire de Physico-Chimie de l’Etat Solide – CNRS-UMR 8648, ICMMO, Université Paris-Sud, 91405 Orsay, France a
[email protected],
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[email protected], d
[email protected] .H\ZRUGV copper, wire-drawing, recrystallization, activation energy, neutron diffraction.
$EVWUDFW The crystallographic texture of electrolytic tough pitch copper has been investigated by neutron diffraction after deformation by cold wire-drawing (reduction of area between 51 and 94 %) and after static recrystallization. The deformation texture characterized by a strong fiber is reinforced with increasing strain, while the volume fraction of fiber is reduced. In turn, we show that the fiber is strongly reinforced after recrystallization when intensity of the maxima increases with the level of deformation. Since the fiber disappears first during annealing, the static recrystallization has been followed “in situ” by measurements of the diffracted intensity evolution in the center of the {111} pole figure. From these experimental data and taking into account the Arrhenius equation, the activation energy of the recrystallization process has been determined for each deformation rate. ,QWURGXFWLRQ
The large industrial applications have shown that the recrystallization is the fundamental process used to recover the final properties of deformed materials. Indeed, in some cases, this procedure may help to reduce the anisotropy of forming metals and alloys. But, the static recrystallization of metallic materials represents, still at this time, an important area of research, relied to the level of complexity of the involved mechanisms. The two main hypotheses, called respectively “oriented nucleation” [1] and “oriented growth” [2], evoked long time ago in order to explain the texture and microstructure evolution during recrystallization, are still now a fundamental subject of polemic. The first hypothesis deals with the preferential development in the deformed matrix of grains with specific orientations. The second one supposes that nuclei in particular crystallographic relation with the neighboring grains grow preferentially. In the particular cases of fcc metals, many parameters have been considered as determinant ones for nucleation and growth of new grains, such as mainly the deformation texture and microstructure [3-5], the temperature and the deformation mode [6], the intra and intergranular heterogeneities developed during deformation [7]. Nevertheless, the deformed state influence on the recrystallization is far to be understood completely. New experimental investigations are therefore required in order to determine the relevant factors for recrystallization. Recently, a large number of experimental studies combine local orientation determination (within the Scanning Electron Microscope through Electron Back Scattered Diffraction or within the Transmission Electron Microscope) and macroscopic texture analysis [8-10]. The second type of measurements is still useful in order to go further into the understanding of recrystallization mechanisms. In particular, the neutron diffraction has been used since long time to follow the evolution of deformation and recrystallization processes. As this technique provides good statistics due to the large volume of investigated matter, it has been largely applied to the investigations of texture evolution during recrystallization [11-13]. This paper presents the first part of a combined
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macroscopic-mesoscopic (local orientations measurements with Electron Back-Scattered Diffraction technique) study of deformation and recrystallization textures in wire-drawn copper. We present here some quantitative measurements from neutron diffraction (texture evolution analysis and activation energy of recrystallization process estimation) performed in copper wires after deformation at high level of strain and after recrystallization. ([SHULPHQWDOGHWDLOV The material classified as Electrolytic Tough Pitch (ETP) contains a minimum copper rate of 99.99 %, LH the impurities level is less than 100 ppm (the impurity content of this material is given in table 1). The copper has been first industrially hot rolled and cold wire-drawn between ∆=51 and 94 % (reduction in the surface, diameter after reduction G=5.54 to 1.93 mm, true strain ε=0.73 to 2.84). The copper wires have been annealed in the laboratory in oil bath for a given temperature of 260°C. The measurements of the deformation and recrystallization textures have been performed by neutron diffraction using the four-circles diffractometer 6T1 localized at the Laboratoire Léon Brillouin in CEA/Saclay, France. From the {111}, {200}, {220} and {311} pole figures using a 5×5 (°) grid, the Inverse Pole Figures (IPF) were calculated using the LaboTex software from the LaboSoft company. 7DEOH Chemical composition of copper given in ppm (in weight).
In order to perform “ in situ” neutron diffraction measurements, a special furnace has been recently installed on the 6T1 diffractometer. Under a vacuum environment of 10-3 Torr, the temperature of 1000°C can be reached with the heating rate of 300°C/min. A more precise technical description of the device is given elsewhere [14]. The copper wires have been “ in situ” annealed in the temperature range 160-300°C. 5HVXOWVDQGGLVFXVVLRQ
'HIRUPDWLRQWH[WXUHV The production of the deformation texture in wire-drawn material has been reviewed since long time. From the early 1950’s, Hibbard [15] has described - in copper and some alloys - the wire-drawn texture as a combination of the two fibers and . The IPF related to the deformation textures of copper wires are presented Fig. 1. These materials present a deformation texture composed of unbalanced and fibers. It is clearly shown that the intensity of the fiber increases with increasing strain (from I(J)=9.6 for 51 % reduction to 26.9 for 94 %). In the deformed state, the fiber is less intense than the fiber, but the intensity related to the ideal position tends to increase with increasing strain (from I(J)=3.3 for 51 % reduction to 7.3 for 94 %). The same phenomenon is observed for both fibers, LH increase of the intensity at the ideal position and decrease of scattering around this same position. In this way, we show that the deformation texture becomes sharper with increasing strain, because more and more grains stabilize around these both orientations during deformation. The same observation has been made in cold rolled copper by Hirsch and Lücke [16]. These authors have established that the deformation texture of cold rolled copper is stabilized at very high strain around the main orientations.
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