CC BY
44ÏSHS2019
Moscow, Russia
HIGH ENERGY BALL MILLING OF SHS MIXTURES: MECHANISMS AND OPPORTUNITIES
A. S. Rogachev*", S. G. Vadchenko", N. A. Nepapushevfi, and D. O. Moskovskikh
aMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of
Sciences, Chernogolovka, Moscow, 142432 Russia bNational University of Science and Technology MISiS, Moscow, 119049 Russia
*e-mail: rogachev@ism.ac.ru
DOI: 10.24411/9999-0014A-2019-10137
Experimental, theoretical, and applied results in the field of mechanical activation of reactive powder mixtures by means of arrested high-energy ball milling (HEBM) and materials synthesis using activated mixtures are considered in the overview. Influence of regimes of activation on combustion temperature and velocity, self-ignition temperature, reaction energy of activation, as well as microstructure and atomic structure of the reactive compositions are discussed. Special attention is paid to revealing structural transformations that result in increasing chemical activity of the powder mixtures. Some examples of practical application of the reviewed processes are presented.
It is known that HEBM allows expanding limits of combustion synthesis in low-exothermal systems, e.g., Si-C, B-C, etc. The HEBM process can be used also for mechanical alloying of high entropy alloys (HEA), such as CoCrFeNiMn, AlCoCrFeNi, etc., and ceramic-metal composites [1]. However, processes inside the milling vials and structural transformations that result in increasing chemical activity of the powder mixtures and alloying of multicomponent materials, have not been adequately studied up to now. Thus, three general aspects of the problem should be outlined: (i) kinematics and dynamics of milling bodies inside the mill jar; (ii) structural transformations in reactive mixtures caused by HEBM and resulting to increase reactivity, and (iii) application of HEBM for materials synthesis.
Using specially designed technique of high-speed video recording and images treatment, we studied in-situ dynamics of the balls motion during high energy ball milling, including balls trajectories and velocities (Fig. 1).
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Fig. 1. High-speed video frame of the movement of balls during HEBM.
The results proved that multiple shear deformations due to friction play a major role in the mechanical activation, as compared to impacts of the balls.
Another important aspect concerns the transformations induced by HEBM in reactive powder mixtures to produce new phase (i.e. mechanical alloying) or to enhance their reactivity.
XV International Symposium on Self-Propagating High-Temperature Synthesis
SEM and TEM study of micro- and nano-structural transformations proved leading role of shear deformations and sliding friction in the activation effect (Fig. 2). Influence of regimes of activation on combustion temperature and velocity, self-ignition temperature, reaction energy of activation, as well as microstructure and atomic structure of the reactive compositions are discussed (Fig. 3).
Fig. 2. Microstructure of the Ni + Al reactive Fig. 3. Dependence of self-ignition mixture after 5 min of HEBM: the layer temperature on duration of HEBM [3].
stuck on the surface of milling ball [2].
Finally, examples of application of HEBM conjugated with SHS, hot pressing and spark plasma sintering for obtaining consolidated ceramics, ceramic-metal composites and multicomponent alloys are presented. It is shown that HEBM + SHS + SPS technique provides exciting opportunities for production of advanced materials.
This work is supported by Ministry of Science and Higher Education of the Russian Federation in the framework of the Federal Target Program "Research and Development on Priority Directions of the Scientific and Production Complex of Russia for 2014-2020", agreement no. 14.587.21.0051, project RFMEFI58718X0051, in the frames of International Russian-French PHC Kolmogorov "RECIPES" (no. 41144SG).
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2. A.S. Rogachev, N.F. Shkodich, S.G. Vadchenko, F. Baras, R. Chassagnon, N.V. Sachkova, O.D. Boyarchenko, Reactivity of mechanically activated powder blends: Role of micro and nano structures, Int. J. Self-Propag. High-Temp. Synth., 2013, vol. 22, pp. 210-216.
3. A.S. Rogachev, N.F. Shkodich, S.G. Vadchenko, F. Baras, D.Yu. Kovalev, S. Rouvimov, A.A. Nepapushev, A.S. Mukasyan, Influence of the high energy ball milling on structure and reactivity of the Ni + Al powder mixture, J. Alloys Compd., 2013, vol. 577, pp.600-605.
