Biomedical Engineering Reference
In-Depth Information
Table 10.5
S
ome properties of NiTi SMA. Gathered from [336] and Johnson Matth
ey Medical
Property
Unit
Value
E (austenite)
GPa
90
YS (austenite)
MPa
195-690
YS (martensite)
MPa
70-140
UTS (martensite)
MPa
800-1,000
Fatigue strength (
N
D
10
6
)
MPa
350
Hysteresis
ı
C
5-50
Maximum one-way memory
%
8
Normal two-way memory
%
1.2
Normal working stress
MPa
100-130
Superelastic strain
%
6-8
J g
1
Superelastic energy storage
6.5
Maximum recovery stress
MPa
600-900
J g
1
Work output
4
Corrosion resistance
Excellent
Biological compatibility
Excellent
Table 10.6
Flexural and tensile properties of
ˇ
-Ti from 12 and SS archwires from 10 different
manufacturers; averaged and rounded values
Units
ˇ
-Ti
SS
Flexural
E
modulus
GPa
80
170
Tensile
E
modulus
GPa
70
170
YS
MPa
1,140
1,750
10
3
Spring back (YS/E)
13
10
UTS
MPa
1,150
2,060
Strain at fracture
%
3.5
2.0
(11.3%w/w), zirconium (6.6%), tin (4.3%) and titanium being the balance. Molyb-
denum stabilizes the
-phase, zirconium and tin increase strength and hardness
without, however, allowing the formation of the embrittling
ˇ
!
-phase. A true partic-
ularity of the
modulus centered around 65 MPa
and high YS of about 200 MPa. That compares in particular for endoprosthetic
use favorably with tempered stainless steel and CoCr with values centered around
200 GPa for
ˇ
-alloy is its unusual mix of a low
E
1,000 MPa for YS. Moreover, they are nickel-free, which is
another attractive aspect of these alloys. See also the discussion in Sect. 2.2.3 of
Chap. 2 on
E
and
>
-alloys and the formation of oxide layers [59]. In Table
10.6
,acom-
parison is made of the flexural and tensile properties of two groups of wires from
different manufacturers, 12 for
ˇ
-Ti and 10 for SS. The intragroup variability is nar-
row, so the values, calculated from data of a paper by Verstrynge, were averaged
and rounded [337].
The higher the ductility, the higher the allowed plastic deformation before frac-
ture. Rematitan, a nitinol, showed the highest ductility with a strain at fracture of
5.2%. The YS is below average (848 MPa). The highest ranked strain at fracture
ˇ
