Preparation of CuCr pseudo-alloys by deposition of copper from a solution onto chromium powders with simultaneous mechanical activation of the mixture

CuCr composite particles were obtained using the method of copper deposition from the solution of its sulfate onto chromium powder particles with the simultaneous mechanical activation (MA) of the mixture in an AGO-2 planetary ball mill for 5 minutes. CuSO₄·5H₂O concentration in the solution with complete copper reduction provided a molar ratio of Cu/Cr = 1. Since deposited fine crystalline copper is highly active and rapidly oxidizes to Cu2O oxide in air, the obtained composite powders were washed, dried, and stored in an argon atmosphere. After drying, the mixture was subjected to additional MA for 5 minutes. Composite particles with a laminate structure begin to form in the solution during MA. Tablets were pressed with a diameter of 3 mm, height of up to 1.5 mm, and density of 4.2–4.5 g/cm³ from the powders obtained. Samples were sintered in an argon atmosphere at 700– 1400 °С. For comparison of microstructures, samples were also sintered from mixtures of Cr and Cu metal powders with a volume ratio of chromium to copper of 50 : 50 obtained by simple mixing in a porcelain mortar for 20 minutes and MA for 10 minutes. Three areas of the alloy structure formation can be distinguished depending on the heating temperature. At heating temperatures below the eutectic melting point, composite particles are sintered at certain points. At heating temperatures above the liquidus temperature, the alloy melts with its phases separated; one part of the sample consists of copper enriched in chromium, and the other part consists of chromium enriched in copper. At intermediate heating temperatures, liquid phase sintering occurs accompanied by phase separation. Copper-enriched chromium particles become spherical and are located in a chromium-enriched copper matrix. Comparison of samples sintered under the same conditions from powder mixtures obtained by different methods showed that a more uniform and fine-grained structure is obtained in samples with deposited

pseudo-alloys, copper deposition, mechanical activation, sintering, phase separation

1. Kojima H., Nishimura R., Okudo H., Sato H., Saito H., Noda Y. Conditioning mechanism of Cu—Cr electrode based on electrode surface state under impulse voltage in vacuum. IEEE Trans. Dielectr. Electr. Insul. 2011. Vol. 18. No. 6. P. 2108—2114. DOI: 10.1109/TDEI.2011.6118651.

2. Zhang C., Yang Z., Wang Y., Ding B. Properties of nanocrystalline CuCr50 contact material. Adv. Eng. Mater. 2005. Vol. 7. No. 12. P. 1114—1117. DOI: 10.1002/adem.200500139.

3. Shkodich N.F., Rogachev A.S., Vadchenko S.G., Moskovskikh D.O., Sachkova N.V., Rouvimov S., Mukasyan A.S. Bulk Cu—Cr nanocomposites by high-energy ball milling and spark plasma sintering. J. Alloys Compd. 2014. Vol. 617. P. 39—46. http://dx.doi.org/10.1016/j.jallcom.2014.07.133.

4. Chang S.-H., Chen S.-H., Huang K.-T., Liang C. Improvement in sintering characteristics and electrical properties of Cr60Cu40 alloy targets by hot isostatic pressing treatment. Powder Metall. 2013. Vol. 56. No. 1. P. 77—82. DOI: 10.1179/1743290112Y.0000000038.

5. Dobatkin S.V., Gubicza J., Shangina D.V., Bochvar N.R., Tabachkova N.Y. High strength and good electrical conductivity in Cu—Cr alloys processed by severe plastic deformation. Mater. Lett. 2015 Vol. 153. P. 5—9. http://dx.doi.org/10.1016/j.matlet.2015.03.144.

6. Zhang C., Yang Z., Wang Y., Ding B., Guo Y. Preparation of CuCr25 contact materials by vacuum induction melting. J. Mater. Process. Technol. 2006. Vol. 178. P. 283—286. https://doi.org/10.1016/j.jmatprotec.2006.04.010.

7. Dirks A.G., Van den Broek J.J. Metastable solid solutions in vapor deposited Cu—Cr, Cu—Mo, and Cu—W thin films. J. Vac. Sci. Technol. 1985. Vol. A3. P. 2618—2622. https://doi.org/10.1116/1.572799.

8. Cherdyntsev V.V., Kaloshkin S.D., Serdyukov V.N., Tomilin N.A., Shelekhov E.V. Kinetics of mechanical alloying in the immiscible system Cu50Cr50. Fizika metallov i metallovedenie. 2004. Vol. 97. No. 4. P. 71—78 (In Russ.).

9. Rogachev A.S., Kuskov K.V., Moskovskikh D.O., Usenko A.A., Orlov A.O., Shkodich N.F., Alymov M.I., Mukasyan A.S. Effect of mechanical activation on thermal and electrical conductivity of sintered Cu, Cr, and Cu/Cr composite powders. Dokl. Phys. 2016. Vol. 61. P. 257—260. DOI: 10.1134/S1028335816060082.

10. Fang Q., Kang Z., Gan Y., Long Y. Microstructures and mechanical properties of spark plasma sintered Cu— Cr composites prepared by mechanical milling and alloying. Mater. Des. 2015. Vol. 88. P. 8—15. https://doi.org/10.1016/j.matdes.2015.08.127.

11. Fang Q., Kang Z. An investigation on morphology and structure of Cu—Cr alloy powders prepared by mechanical milling and alloying. Powder Technol. Ser. A. 2015. Vol. 270. P. 104—111. DOI: 10.1016/j.powtec.2014.10.010.

12. Patra S., Mondal K. Densification behavior of mechanically milled Cu—8 at % Cr alloy and its mechanical and electrical properties. Prog. Nat. Sci. Mater. Int. 2014. Vol. 24. P. 608—622. https://doi.org/10.1016/j.pnsc.2014.10.006.

13. Song-Hua Si, Hui Zhang, Yi-Zhu He, Ming-Xi Li, Sheng Guo. Liquid phase separation and the aging effect on mechanical and electrical properties of laser rapidly solidified Cu100–xCrx alloys. Metals. 2015. No. 5. P. 2119— 2127. DOI: 10.3390/met5042119.

14. Chai Lin Jiang, Zhou Zhi Ming, Xiao Zhi Pei, Tu Jian, Wang Ya Ping, Huang WeiJiu. Evolution of surface microstructure of Cu—50Cr alloy treated by high current pulsed electron beam. Sci. China. Tech. Sci. 2015. Vol. 58. P. 462—469. DOI: 10.1007/s11431-015-5774-7.

15. Rogachev A.S., Kuskov K.V., Shkodich N.F., Moskovskikh D.O., Orlov A.O., Usenko A.A., Karpov A.V., Kovalev I.D., Mukasyan A.S. Influence of high-energy ball milling on electrical resistance of Cu and Cu/Cr nanocomposite materials produced by Spark Plasma Sintering. J. Alloys Compd. 2016. Vol. 688. P. 468—474. http://dx.doi.org/10.1016/j.jallcom.2016.07.061.

16. Kuskov K.V., Sedegov A.S., Novitskii A.P., Nepapushev A.A., Moskovskikh D.O., Shkodich N.F., Rogachev A.S., Mukasyan A.S. Influence of chromium in nanocrystalline copper—chromium pseudoalloy on its structure and properties. Nanotechnologies in Russia. 2017. Vol. 12. Iss. 1—2. P. 40—48. DOI: 10.1134/S1995078017010074.

17. Weichan C., Shuhua L., Xiao Z., Xianhui W., Xiaohong Y. Effect of Mo addition on microstructure and vacuum arc characteristics of CuCr50 alloy. Vacuum. 2011. Vol. 85. P. 943—948. DOI: 10.1016/j.vacuum.2011.02.001.

18. Sheibani S., Heshmati-Manesh S., Ataie A. Influence of Al2O3 nanoparticles on solubility extension of Cr in Cu by mechanical alloying. Acta Mater. 2010. Vol. 58. P. 6828—6834. https://doi.org/10.1016/j.actamat.2010.09.012.

19. Yang Z., Zhang Q., Zhang Ch., Sun Y., Ding B. Influence of microstructure of CuCr25 cathode on the motion of vacuum arc spots. Phys. Lett. 2006. Vol. A 353. P. 98—100. DOI: 10.1016/j.physleta.2005.12.023.

20. Vadchenko S.G., Boyarchenko O.D., Shkodich N.F., Rogachev A.S. Thermal explosion in various Ni—Al systems: Effect of mechanical activation. Int. J. SHS. 2013. Vol. 22. No. 1. P. 60—64. DOI: 10.3103/S1061386213010123.

21. Hiroaki Okamoto. Desk handbook — Phase diagrams for binary alloys. 2-nd ed. Ed. ASM Int. Mater. Park. Ohio. USA. 2010. P. 276. 44073-0002. www.asminternational.org.

22. Aleksandrov V.D., Aleksandrova V.N., Barannikov A.A., Dobritsa N.V., Malinovskaya N.E., Frolova S.A. Melting and crystallization of copper, silver, and gold droplets. Tech. Phys. Lett. 2001. Vol. 27. Iss. 3. P. 258—259. https://doi.org/10.1134/1.1359845.

23. Gao J., Wang Y.P., Zhou Z.M., Kolbe M. Phase separation in undercooled Cu—Cr melts. Mater. Sci. Eng. 2007. Vol. A. No. 449—451. P. 654—657. DOI: 10.1016/j.msea2006.02.379.

24. Zhiming Zhou, Tao Zhou, Linjiang Chai, Jian Tu. Microstructure and liquid phase separation of CuCr alloys treated by high current pulsed electron beam. Mater. Res. 2015. Vol. 18. Suppl. 1. São Carlos Nov. Epub. Oct. 23. 2015. http://dx.doi.org/10.1590/1516-1439.323714.

25. Wang Y., Song X., Sun Z., Zhou X., Guo J. The solidification of CuCr alloys under various cooling rates. Mater. Sci. Poland. 2007. Vol. 25. No. 1. P. 199—207. https://doi.org/10.1016/S1003-6326(06)60367-1.

26. Hauf U., Kauffmann A., Kauffmann-Weiss S., Feilbach A., Boening M., Mueller F.E.H., Hinrichsen V., Heilmaier M. Microstructure formation and resistivity change in CuCr during rapid solidification. Metals. 2017. Vol. 7. Iss. 11. P. 478. DOI:10.3390/met7110478.

27. Sheibani S., Heshmati-Manesh S., Ataie A. Synthesis of nano-crystalline Cu—Cr alloy by mechanical alloying. Int. J. Modern Phys. Conf. Ser. 2012. Vol. 5. P. 496—501. DOI: 10.1142/S2010194512002395.