Biomedical Engineering Reference
In-Depth Information
monocrystalline ones for materials with the same chemical composition
(e.g. Ferna´ ndez-Bertran, 1999; Ivanov and Suryanarayana, 2000; Suryan-
arayana, 2001a; S
ˇ
epelak, 2002; Kelsall et al., 2005; Bala´ zˇ , 2008). From a
practical point of view, the desired features of nanocrystalline powders can
be intensified by creating multiphase composites from them. Therefore, bulk
composites are engineering materials made from two or more components
with significantly different physical and/or chemical properties that remain
separate and distinct on the macroscopic level within the finished structures.
One of the components is a matrix and the other provides structural
support. Three types of composite categories can be defined based on the
characteristics of the matrix:
.
metallic matrix composites (MMCs)
.
ceramic matrix composites (CMCs)
.
polymer matrix composites (PMCs).
Application of the relevant composite powders to produce the final bulk
product or any other composite product is one of the most attractive
features in their fabrication. These composite powders need to be
consolidated at elevated temperatures by thermomechanical processing
and then their microstructure stability and microhardness should be
determined in order to estimate the optimal parameters for the consolida-
tion process. Actual metal-ceramic composite powders usually incorporate
light alloys such as Al, Mg and Ti. Other metals commonly used are Cu, Ni,
Fe, Co, Zn and Mo. Metals, ceramics or polymers can be used to support
MMC powders.
Metal matrix reinforced phases can exist as dispersed particles of
(Kaczmar, 2000; Koch, 2001; Agrawal and Sun, 2004):
.
metal oxides (ZrO
2
,Al
2
O
3
, ThO
2
,Cr
2
O
3
)
.
carbides (SiC, TaC, WC, B
4
C)
.
nitrides (Si
3
N
4
, TaN, ZrN, TiN)
.
borides (TaB
2
, ZrB
2
, TiB
2
, WB).
Cermetals are composed of metallic and ceramic components, which
combine the physical properties of metals and ceramics. The properties of
metals include:
.
ductility
.
tensile strength
.
thermal and electrical conductivity.
Ceramics possess physical properties such as:
.
high melting point
.
chemical stability
