Biomedical Engineering Reference
In-Depth Information
suitable for dental precision casting of titanium alloys comparing
with alumina based mold materials [68]. Calcia based mold material
is also reported to be suitable for dental precision casting [88, 89].
It is important to note that between Ti-based alloys, only TiNi has
been put into wide practical use as super elastic and shape memory
alloy. Formerly, TiNi shape memory alloy was tried to apply to
implants [15, 16, 45]. However, since TiNi contains a large amount of
Ni, which causes allergy at high rate, the usage of TiNi shape memory
alloys is restricted. Therefore, the research and development of Ni-
free super elastic and shape memory titanium alloys composed of
non-toxic elements for biomedical applications are increasing.
Recently, the super multifunctional titanium alloy “GUM METAL”
has been developed. Gum metal is a multi-functional
β
-type titanium
alloy that has a body centered cubic structure with an ultra-low
elastic modulus (40 GPa), high strength (more than 1.100 MPa),
high elastic deformability (2.5%), high plastic deformability at room
temperature without work hardening, non-linear elasticity without
any hysteresis (the difference in stress-strain curve in uploading and
down-loading passes causing energy loss in elastic deformation)
as well as Invar and Elinvar properties. Gum metal has been put
into practical use for glass frames. The chemical composition of
gum metal is very similar to that of Ti-Nb-Ta-Zr system alloy for
biomedical applications [45, 104].
The super elastic behavior has been observed in Ti-29Nb-
13Ta-4.6Zr for biomedical applications [45, 104]. Ti-29Nb-13Ta-
4.6Zr has been also put into practical use for glass frames as a
brand name of bio-titan. Ti-Nb-Sn system alloy is developing as
Ni-free shape memory titanium alloy for biomedical applications.
Its martensite transformation temperature (M
s
point) decreases
with an increasingly amount of Nb or Sn, and the shape memory
effect is recognized when the alloy is deformed below austenite
transformation temperature (A
f
point) which is similar to the case
of Ti-Ni shape memory alloy. It has been reported that an elastic
strain of 3.5% is obtained at the composition of Ti-18 at.% Nb-4
at.% Sn [100]. The research and development of Ti-Mo-Ga system
alloy, Ti-Mo-Ge system alloy,
or Ti-Mo-Al system alloy, Ti-Ta system
alloy, Ti-Ta-Zr system alloy, Ti-Sc-Mo system alloy as shape memory
titanium alloys for biomedical applications are also noticeable
[95, 97]. They are all
β
type titanium alloys.
