Biomedical Engineering Reference
In-Depth Information
volume fraction in the structure of the UFG alloy at 500
С can be higher
than before annealing, as has been shown in [199], using quenching from
the annealing temperature. h ough there are no visible particles of any
second phase, aging processes could lead to the formation of grain bound-
ary segregations that could additionally contribute to the enhancement of
properties of the UFG alloy subjected to annealing [201, 202].
Investigations of fatigue properties of the UFG Ti-6Al-4V ELI alloy
revealed that high strength and enhanced ductility at er SPD processing
and additional annealing at 500
°
С (1370 МPа and 12%) resulted in fatigue
limit enhancement on the basis of 10
7
cycles up to 740 МPа in comparison
with 600 МPа in the initial coarse-grained (CG) state (Figure 1.8).
h e fatigue limit for the UFG Ti-6Al-4V alloy, observed in [196] under
the conditions of rotating bending, slightly exceeded the value reported
previously, [197, 203], which testii es to the fact that the level of fatigue
properties depends on the measurement technique.
h us, the results show that high strength can be achieved in UFG
Ti-6Al-4V ELI alloy through ECAP and additional mechanical and ther-
mal treatment. Herewith, varying the SPD parameters, in particular tem-
perature, strain rate, strain, provides the opportunity to control grain
boundary structure in UFG materials, and consequently produce the best
combinations of strength and ductility, as well as increasing the fatigue
endurance limit of up to 740 MPa, well beyond the 600 MPa level mea-
sured in the coarse-grained alloy.
°
850
800
750
700
650
Ti-6AI-4V Hot rolling
Ti-6AI-4V
600
UFG + annealing
500°C, 1 h
10
5
10
6
10
7
Number of cycles to failure
N
Figure 1.8
Fatigue test results of the smooth samples out of CG and UFG alloy at er
annealing at 500 °С, 1 hour.
