Biomedical Engineering Reference
In-Depth Information
6.3
Physical and mechanical properties of metal matrix
nanocomposites (MMNCs)
6.3.1 Properties of MMNCs with different fabrication
methods
Adding microsize ceramic particles to a metal matrix has proven to
successfully improve strength, stiffness, and creep resistance. However, due
to the large size of the particles, the ductility of metal matrix is always
reduced. A uniform dispersion of nanoparticles provides a good balance
between the strengtheners and interparticle spacing effects and is predicted
to maximize the yield strength and still retain ductility. Therefore, MMNCs
with nanoparticles acting as strengtheners have been the most promising
approach to produce the desired mechanical properties in materials (i.e.
enhanced hardness, Young's modulus, 0.2% yield strength and ultimate
tensile strength (UTS)) (Tjong, 2007).
Ma et al. (1996), Cao et al. (2008a), Hassan et al. (2008) and Hassan
(2011) reported that all the mechanical properties, including ductility, were
improved by adding nanoparticles into the metal matrix. All the reported
experiments show adding ceramic nanoparticles will improve elastic
modulus, hardness, and UTS. However, the majority of the experiments
indicated that by adding nanoparticles, ductility is reduced, mostly due to
process defects.
Ma et al. (1996) compared the effect of nanosized and microsized
reinforcement in their research. In the experiment, the 1 vol% Si
3
N
4
(15 nm)/Al nanocomposite exhibited similar tensile strength but significantly
higher yield strength than the 15 vol% SiCp(3.5
m)/Al microcomposite.
The creep resistance of the 1 vol% Si
3
N
4
(15 nm)/Al nanocomposite was
about two orders of magnitude higher than that of the 15 vol% SiCp
(3.5
μ
m)/Al microcomposite. Cao et al. (2008a) reported that by adding SiC
nanoparticles in Mg-4Al-1Si melt, the yield strength of the matrix was
improved by 33%, UTS by 23%, and the ductility of the matrix was not
reduced. In Cao's experiment, microsized SiC clusters could still be observed
on the grain boundary without impairing the overall mechanical properties.
It was explained that the negative effect caused by some SiC microclusters
was compensated by the significantly positive effects of the grain refining
and strengthening of the well-dispersed SiC nanoparticles. The effects of
adding reinforcements to the mechanical properties of metal matrix are
listed in Table 6.3.
Even with a limited number of encouraging results, most of the research
shows that adding nanoparticles into the metal matrix could improve yield
strength and hardness, but also lead to a negative impact on ductility. The
results of different experiments are not constant and most tested properties
μ
