Dina V. Dudina, Oleg I. Lomovsky
Institute of Solid State Chemistry and Mechanochemistry,
Siberian Branch of Russian Academy of Sciences, Kutateladze 18,
Novosibirsk 630128, Russia
E-mail: [email protected]
Mechanical milling greatly alters the state of a powder mixture
introducing plastic strain and defects into the components and
creating new interfaces and mutual configurations of nano-sized
grains. This opens up a possibility to design microstructures of the
composite to be synthesized by modifying the initial state of reacting
powder mixtures. In certain mechanically milled reactive systems,
one can observe microstructure refinement of the product [1-2], an
increase in the yield of the reaction [3], improved distribution of the
phases [3, 4] and lower reaction onset and developed temperatures
[1-2]. The presentation intends to demonstrate several successful
examples of this approach for synthesizing composites by selfpropagating high-temperature synthesis (SHS), shock compression
and electric-current assisted sintering.
SHS in the mechanically milled Ti-B-Cu powder mixtures was
successfully performed and resulted in a TiB2-Cu composite [1-2].
Compared to untreated powders, in the mechanically milled mixtures,
titanium and boron started reacting at a reduced ignition temperature,
while lower combustion temperatures developed in the combustion
wave favored formation of submicron grains of TiB2.
The powder particles brought to react with each other by shock
compression of the mixture may not fully transform into the products
if the loading is too short and the temperatures developed during the
pressure rise and the post-loading period are not high enough. In the
mechanically milled mixture, the yield of the reaction can be
increased as a result of the decreased grain size of the initial reactants
and shorter diffusion distances (example: Ti-Cu-B system, partial and
complete reaction of Ti and B [3]).
When the sintering process ensures temperatures and time
sufficient for the completion of the reaction, in the mechanically
milled mixture one can expect more uniform microstructure and finer
grains of the products (example: Ti-B-C system forming B4C-TiB2
phases during electric-current assisted sintering [4]).
Ball milling can refine the microstructure of the as-synthesized
composites and can be used to introduce additional quantities of the
constituents in the composite. This was applied in order to develop
highly conductive Cu-based composites. One of the possible reasons
for low conductivity of in-situ dispersion strengthened copper may be
the incompleteness of the reaction between the initial reactants,
which form solid solutions with the copper matrix. In this regard, we
conducted an in-situ synthesis of TiB2-Cu composites starting from
the powder mixtures with the limited content of copper ensuring a
high probability of contact between the particles of titanium and
boron and, as a result, their full conversion into the TiB2 phase. The
nanoparticles were formed in a self-propagating mode in the ball
milled Ti-B-Cu powder mixture corresponding to the 57 vol.%TiB2Cu composition. Afterwards, in order to adjust the composition, the
composite was “diluted” with the required amount of copper using
subsequent ball milling [5].
The consolidated nano- and microcomposite materials
developed on the basis of the described systems were tested for their
enhanced mechanical properties (fracture tough composites B4C-TiB2
[4]), electric erosion resistance [6] and electric conductivity [5]. In
this presentation, each property is discussed as resulting from the
phase and microstructure evolution during the synthesis of the
material by the selected processing method.
Parts of this work were carried out by DVD at the University
of California, Davis, USA during her postdoctoral appointment. The
authors greatly appreciate the collaboration with Dr.Korchagin
(ISSCM SB RAS), Dr. V.I.Mali and Dr. A.G.Anisimov (Institute of
Hydrodynamics, SB RAS, Novosibirsk, Russia) and Prof. J.S.Kim
(University of Ulsan, South Korea).
1. D.V.Dudina, O.I.Lomovsky, M.A.Korchagin, V.I.Mali. Chem.
Sust. Dev. 12 (2004) 319-325.
2. M.A.Korchagin, D.V.Dudina. Comb. Expl. Shock Waves, 43 (2)
3. D.V.Dudina, V.I.Mali, A.G.Anisimov, O.I.Lomovsky. Mater. Sci.
Eng. A 503 (2009) 41-44.
4. D.V.Dudina, D.M.Hulbert, D.Jiang, C.Unuvar, S.J.Cytron,
A.K.Mukherjee. J.Mater.Sci, 43 (2008) 3569-3576.
5. J.S.Kim, D.V.Dudina, J.C.Kim, Y.S.Kwon, J.J.Park, C.K.Rhee. J.
Nanosci. Nanotech. 10 (2010) 252-257.
6. J.-S.Kim, Y.-S.Kwon, D.V.Dudina, O.I.Lomovsky, M.A.Korchagin,
V.I.Mali. J.Mater.Sci., 40 ( 2005)3491 - 3495.