On the Structural Features of Mechanically Alloyed Cu ... - Science Direct

Available online at www.sciencedirect.com

ScienceDirect Physics Procedia 84 (2016) 349 – 354

International Conference "Synchrotron and Free electron laser Radiation: generation and application", SFR-2016, 4-8 July 2016, Novosibirsk, Russia

On the structural features of mechanically alloyed Cu-Ag and AuCo by severe cold and cryogenic plastic deformation T. Tolmacheva*, V. Pilyugina,b, A. Ancharovc,d, A. Patselova, E. Chernysheva, K. Zolotareve a

c

M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences, st. S. Kovalevskoy, 18, Yekaterinburg, Russian Federation, 620990 b Ural Federal University, 19 Mira Street, Yekaterinburg, 620002, Russia Institute of Solid State Chemistry and Mechanochemistry, Russian Academy of Sciences, 18, Kutateladze str., Novosibirsk, 630128, Russia d Novosibirsk State University, 2 Pirogova Str., Novosibirsk-90, 630090, Russia e Budker Institute of Nuclear Physics SB RAS, Acad. Lavrentiev ave., 11, 630090, Novosibirsk, Russia

Abstract The effect of cryogenic temperature on the formation of solid solutions by mechanical alloying (MA) was studied using synchrotron diffraction and some additional methods. Two systems with different positive enthalpy of mixing (Cu-Ag и Au-Co) were involved. MA by severe plastic deformation at 293 K and 80 K leads to the formation of fcc substitutional solid solutions, with the excess of the equilibrium concentration for both systems. The effect of cryogenic deformation consists in smaller dissolution of the original basic element of the charge (Cu) for Cu-Ag solid solution and in increasing of solute (Co) for Au-Co one. Diffraction experiments were performed at the SR beamline №4 of the VEPP-3 storage ring. © Published by Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license 2016The TheAuthors. Authors. Published by Elsevier ©2016 (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility ofthe organizing committee of SFR-2016. Peer-review under responsibility of the organizing committee of SFR-2016.

Keywords: mechanical alloying, severe plastic deformation, synchrotron diffraction, positive enthalpy of mixing

* Corresponding author. Tel.: +7-343-378-3805; fax: +7-343-374-52-44. E-mail address:[email protected]

1875-3892 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SFR-2016. doi:10.1016/j.phpro.2016.11.059

350

T. Tolmachev et al. / Physics Procedia 84 (2016) 349 – 354

1. Introduction The components of Au-Co are characterized by a significant difference in physical, mechanical and service properties instead of Cu-Ag case. Both systems have positive mixing enthalpy: +5 kJ/mol for Cu-Ag and +34 kJ/mol for Au-Co (Miedema et. al. 1980) and very restricted solubility (Okamoto et. al. 1985, Subramanian et. al. 1993). At 293 K and below the elements of the systems are almost insoluble. There is almost no information about obtaining Au-Co solid solutions by mechanical alloying. The Cu-Ag has been widely studied for a long time involving the mechanical alloying related researches (Kormout et. al. 2015), that’s why it is a model system. Severe plastic deformation by high pressure torsion (SPD HPT) allows to realize the greatest strain in material which often leads to ultrafine grained structure (Estrin et. al. 2013, Langdon 2013) and dissolution of insoluble elements as a mechanical alloying method (Teplov et. al. 1993, Dobromyslov et. al. 2010). Cryogenic SPD HPT allowed to obtain an even smaller grain size than by cold deformation for a number of metals (Pilyugin et. al. 2008, 2012) which can be perspective in a case of mechanical alloying of immicible elements. The HPT has a specific feature which can be occurred not only after cold- but in a cryo-deformation. One is that the strain distributes non-uniformly along the thickness of a sample. That’s why there is a necessity in a high beam permeability to get a complete data not only from the surface but from the volume of the sample. Synchrotron radiation due to its sufficient intensity allows in a very short time (several seconds) to obtain structural data for the entire sample thickness (Ancharov et al. 2001, Levichev 2016). So, the aim of this work is to study the structural transformations of cold- and cryogenically produced alloys by high pressure torsion of systems with different value of positive enthalpy of mixing, Cu-Ag and Au-Co, using synchrotron radiation and additional required methods. 2. Experiment To produce the alloys the SPD HPT at room (293 K) and at liquid nitrogen (80 K) temperatures in Bridgman anvils was used. The hydrostatic pressure was about 6 GPa for Cu-Ag and 8, 11 GPa for Au-Co The rotation speed of the anvil was 1 turn per minute and number of turns was 40 or 3-stage reprocessing (10 turns at one reprocessing, after each one the sample in a disk shape is cut into sectors, then this parts are put back into a processing cell and the procedure repeats). The alloying systems were in a condition of powder mixtures and following compositions Cu80Ag20, Au80Co20, Au50Co50, at.% were used. The structure of the samples was examined by transmission synchrotron radiation (SR) in a beam with the cross section of 0.3x0.3 mm2 at the wavelength of 0.03685 nm (Ancharov et al. 2001) useing the SR beamline №4 of the VEPP-3 storage ring. Marr-345 detector was used to record an SR diffraction pattern. For convenience, SR diffraction patterns were transformed into traditional plots of intensity-diffraction angle dependences. Also, we used X-ray diffraction technique (reflection geometry) at the laboratory DRON-3 diffractometer with Cu-Ka – radiation. To see an internal structure of the sample in a section scanning electron microscopy (SEM) of the fracture surface was performed using Quanta-200 Pegasus SEM. 3. Results The gross deformation of Cu-Ag mixture at both cold- and cryogenic temperatures leads to presence of the fcc solid solution peaks on the diffractograms (Fig.1a,b). Despite such strain there is some amount of noncompletely dissolved copper phase which peaks are not fully separated from solid solution peaks but nevertheless visible in XRD. This is more highlighted in the case of XRD of the sample after cryo-deformation. The intensity of the solid solution phase prevails along its relative amount in the alloy. The lattice parameter value of the sample after cold deformation is lower than after cryo-deformation and correlation of the values with the Vegard law (see inset in Fig.1) shows a less amount of Cu dissolved in the solution after cryo-deformation (see the values in Table 1). The large deformation also results in a presence of the fcc solid solution peaks in the XRDs for Au 80Co20, at.% composition of the mixture. An effect of cryogenic deformation is the inverse one to the case of Cu-Ag: the lattice parameter of cryogenically deformed sample showed a lower value and correlation with the generalized dependence


351

‘the lattice parameter vs. composition’ of the literature data by Xinming et.al 1984, Korn et. al. 1979, Kataoka et.al. 1995, gave the same composition as for the initial mixture of Au and Co powders. XRD of the sample after cold deformation also includes peaks which are responsible for a second phase of noncompletely dissolved cobalt, which peaks of weak-intensity in the diffractogram are discernible. A similar situation occurs if the cobalt content is increased in the initial mixture to 50 at.%: respectively this leads to increasing of the cobalt content in the Au-based solid solution. Cryogenic deformation leads one to more content comparing to the cold deformation. Additionally, increasing the pressure to the same value as for composition Au80Co20 leads to an increase of cobalt content in the solid solution.

Fig. 1. SR XRDs of mechanically alloyed by HPT powder mixtures Cu80Ag20, at.% at cold (a) and cryogenic (b) deformations; (c) XRD in CuKα: inserts – value of lattice parameter vs. content of Cu, at.% combined with SR data of alloyed samples after foolowing alloying temperatures: ႒ ದ 293 K (a = 0.373 nm; content of Cu 75.0 at.%); Ⴜ ದ 80 K (a = 0.376 nm; content of Cu 69.5 at.%); (b) Δ – as cast sample 293 K (a = 0.371 nm; content of Cu 80.0 at.%); (d) microscopic image of surface of fracture at the center of the disk.

Summarizing diffraction data in a Table 1 shows how changes of the lattice parameter depend on the deformation temperature. Also, possibility of solubility enhancing of the second component are shown, at least for the Au-Co system.

Fig. 2. SR XRDs of mechanically alloyed by HPT powder mixtures Au 80Co20, at.% at cold (a) and cryogenic (b) deformations; Au80Co20, at.% at cold (c), cryogenic (d) and cryogenic at increased pressure (d); inserts – summarized from literature data (Xinming et.al 1984, Korn et. al. 1979, Kataoka et.al. 1995) curve of lattice parameter value vs. content of Co, at.% combined with SR data of alloyed samples after following alloying temperatures: □ – 80:20, 293 K (a = 0.404 nm; content of Co 12.1 at.%); ○ – 80:20, 80 K (a = 0.401 nm; content of Co 20.5 at.%); Δ - 50:50 293 K (a = 0.399 nm; content of Co 24.6 at.%); - 50:50, 80 K (a = 0.397 nm; content of Co 30.0 at.%); ◊ - 50:50, 80 K (a = 0.394 nm; content of Co 35.0 at.%).

352


Considering diffraction patterns of the alloyed samples it is observed that for the samples prepared at room temperature from the initial powder mixtures of Cu80Ag20 and Au50Co50 compositions there are more brightly highlighted nonuniformity of intensity distribution of the diffraction rings as compared to cryogenic (Fig.3 a, b, e, f). And this is most pronounced for Au50Co50 (Fig.3 e, f). This suggests a greater preferred grain orientation after cold deformation than at cryogenic one. Further, for the samples of the initial composition of Au 80Co20, at.% the picture is not so pronounced, but is reverse to previous (Fig3c,d). It is probably due to the fact that in the case of cryogenic deformation, we have got a solid solution, equal to the composition of the original mixture, and are dealing with a typical single-phase fcc diffraction pattern of the alloy after HPT. Table 1.Mechanical alloying results. Original composition of powder mixture

Deformation temperature, K

Deformation pressure, GPa

Number of anvil rotations

Lattice parameter a, nm

Content of solute in a solid solution (Cu, Co), at.%

Cu80Ag20

293

6

3x10

0.373

75.0

Cu80Ag20

80

6

3x10

0.376

69.5

Au80Co20

293

11

40, 3x10

0.404

12.1

Au80Co20

80

11

3x10

0.401

20.5

Au50Co50

293

8

3x10

0.399

24.6

Au50Co50

80

8

3x10

0.397

30.0

Au50Co50

80

11

40

0.394

35.0

Fig. 3. SR patterns of mechanically alloyed by HPT powder mixtures Cu 80Ag20, at.% at cold (a) and cryogenic (b) temperatures; Au80Co20, at.% at cold (c) and cryogenic (d) temperatures; Au50Co50, at.% cold (e) and cryogenic (f) temperatures

Changing the deformation temperature leads to changes in the structural characteristics. The prevailing deformation mode (dislocation movement by sliding, climbing, cross-slip) during cold one is dependent on the temperature and its change leads to a change in the results of mechanical alloying (through the emergence of


deformation twins, stackin faults, localization bands to fine-grained structure formation). Smaller grain size as a result of cryo-deformation implies higher activation ability, including diffusion mobility due to nonequilibrium density of point defects generated by strain. Quasi-hydrostatic conditions imposed on such temperature conditions, create a state of stress, which involves the action of mechanisms facilitating the dissolution, i.e. stress diffusion, of immiscible components with radically different properties. However, the system with a lower enthalpy of mixing and sufficiently similar properties, with many of executed Hume-Rothery rules demonstrates inverse structural characteristics (as compared to the Au-Co). There is a possibility that the Cu-Ag system has time to undergo a decay by the time of shooting, so there are mutual processes competing to dissolution during deformation. 4. Conclusions It was found that for a system with a large positive enthalpy of mixing, Au-Co, the cryogenic deformation contributed to higher content of dissolved Co compared to the cold deformation by using SR diffractometry. Then, for the original alloying composition of 50:50, at.% there is a less preferred grains orientation after cryogenic one. More than that, for 80:20 – composition, at.%, there have been a solid solution formation, correspondent to the composition of the respective original mixture. By the way, for a system with a low positive enthalpy of mixing, CuAg, of 80:20 – composition, at.%, there has been the opposite effect from cryogenic deformation which consisted in a less dissolution. However, in the near-surface zone a solid solution has been formed, and it is entirely consistent with the composition of the starting mixture. Acknowledgements X-ray synchrotron measurements were carried out at the experimental station Diffractometry in the “Hard” X-ray Range (Ancharov et. al 2001, Levichev 2016) at the Center of Collaborative Access of the Siberian Synchrotron and Terahertz Radiation Center, Budker Institute of Nuclear Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk. The electron microscopic studies were performed at the Center of the Collaborative Access Test Center of Nanotechnologies and Advanced Materials, Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, Yekaterinburg. The research was carried out within the state assignment of FASO of Russia (theme “Deformation” No. 01201463327), supported in part by RFBR (project No. 16-33-00750). Development of equipment for the experimental station was supported by the Russian Science Foundation (project N 14-50-00080).

References Miedema, A. R., de Chatel, P. F., de Boer, F. R. 1980. Cohesion in alloys—Fundamentals of a semi-empirical model. Physica B+C 100, 1–28. Okamoto, H., Massalski, T. B., Nishizawa, T., Hasebe, M. 1985. The Au–Co (Gold–Cobalt) system. Bulletin of alloy phase diagrams 6, 449–454. Subramanian, P.R., Perepezko, J.H. 1993. The Ag-Cu (Silver-Copper) System. Journal of Phase Equilibria 14,62-75. Kormout, K.S., Yang, B., Pippan, R. 2015. Deformation behavior and microstructural evolution of Cu–Ag alloys processed by high-pressure torsion. Advanced Engineering Materials 17, 1828-1834. Estrin, Y., Vinogradov, A. 2013. Extreme grain refinement by severe plastic deformation: A wealth of challenging science. Acta Materialia 61, 782–817. Langdon, T.G. 2013. Twenty-five years of ultrafine-grained materials: Achieving exceptional properties through grain refinement. Acta Materialia 61, 7035–7059. Teplov, V.A., Pilugin, V.P., Gaviko, V.S., Chernyshev, E.G. 1993. Non-equilibrium solid solution and nanocrystal structure of Fe–Cu alloy after plastic deformation under pressure. Philosophical Magazine 68, 877–881. Dobromyslov, A.V., Churbaev, R.V. 2010. Synthesis of nanocrystalline and amorphous alloys from elementary powders by intensive plastic deformation under high pressure. International Journal of Modern Physics 6, 722–729. Pilyugin, V.P., Gapontseva, T.M., Chashchukhina, T.I., Voronova, L.M., Shchinova, L.I., Degtyarev, M.V. 2008. Evolution of the structure and hardness of nickel upon cold and low-temperature deformation under pressure. The Physics of Metals and Metallography 105, 409–418. Pilyugin, V.P., Voronova, L.M., Degtyarev, M.V., Chashchukhina, T.I. 2012. Structure refinement of pure iron during low-temperature highpressure deformation. Russian Metallurgy (Metally) 4, 297-302.

353

354


Ancharov, A.I., Manakov, A.Yu, Mezentsev, N.A., Tolochko, B.P., Sheromov, M.A., Tsukanov, V.M. 2001. New station at the 4th beamline of the VEPP-3 storage ring. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 470, 80–83. Levichev, E.B. 2016. Status and perspetives of VEPP-4 complex (in Russian). Particles and Nuclei, Letters. XIII, 7. Xinming, Zh., Khan, H. R., Raub, Ch. J. 1984. Study of metallurgical and electrodeposited Au–Co metastable solid solutions. Journal of lesscommon metals 96, 249–256. Korn, D., Schilling, D., Zibold, G. 1979. Magnetic properties of AuCo solid solutions and frequency dependent susceptibility maximum. Journal of Physics F: Metal Physics 9, 1111–1127. Kataoka, N., Takeda, H., Echigoya, J., Fukamichi, K., Aoyagi, E., Shimada, Y., Okuda, H., Osamura, K., Furusaka, M., Goto, T. 1995. GMR and microstructure in bulk Au–Co nanogranular alloys. Journal of Magnetism and Magnetic Materials 140–144, 621–622.