Biomedical Engineering Reference
In-Depth Information
Table 6.4
Characteristic mechanical properties of various metallic biomaterials
compiled from different sources. na = data is not available
Density
s
0.2
s
(MPa)
Young's
Fatigue
Toughness
(g cm
-3
)
(MPa)
modulus
limit
(MPa
√
m)
E
(GPa)
Ta
16.6
138-345
205-515
185-190
na
na
316 L
7.9
172-690
485-860
190-200
241-820 100
CoCrMo
8.4
450-648
655-860
210-230
207-310 100
CoNiCrMo
9.2
240-1585
793-1793
586-793
Ti
4.5
170-485
240-760
105
300-430 na
Ti-6Al-4V
4.4
760-895
900-970
110
500-689 80
b
Ti-alloys
530-1060
590-1310
55-100
na
na
NiTi austenitic
6.7
100-800
800-1500
70-110
350
na
NiTi martensitic
50-300
100-1100
21-69
na
Mg alloys
1.7-2
100-200
220-290
45
na
28
Al
2
O
3
-
280-550
380
na
4.2-5.9
Cortical bone
1.8-2.1
-
50-150
7-30
na
2-12
Cast Co-base alloys usually have large grain sizes (~ 4 mm) and undesirable
defects like inclusions and micropores that impair their mechanical properties.
Wrought
Co-base alloys are multiphasic and hardening derives from the
combination of cold working, grain size refinement (~ 8 mm), solid solution
hardening and carbide precipitation (up to 15%). The resulting mechanical
properties make the alloys among the strongest available for implant
applications.
Commercially pure titanium has a relative low strength and high ductility.
Cold working (around 30 %) is used to enhance mechanical properties.
Differences in yield strength between the different grades result from
variations in the interstitial and impurity level. similarly, for a given grain
size, fatigue strengths are also increased with higher levels of oxygen.
30
Mechanical properties of Ti-6al-4V are affected by the processing and
oxygen content. solution treatments and further ageing can increase the
strength of a+b alloys by 30-50% over the annealed condition. equiaxed
microstructures provide high strength and ductility and relatively low
fracture toughness, whereas a lamellar structure provides good fracture
toughness but with some compromise on strength and ductility.
31
With
regard to the high cycle fatigue, the bimodal microstructure provides the
highest value followed by the equiaxed structure, with the lamellar structure
having the lowest fatigue resistance. In addition, for a given microstructure,
finer microstructures result in higher cycle fatigue strength.
32
With regard
to their biofunctionality value, which is given by the ratio of the fatigue
strength over the Young's modulus, titanium and its alloys demonstrate their
superiority.
one of the major problems in orthopaedic surgery is the large mismatch of
