Biomedical Engineering Reference
In-Depth Information
medical applications) processed by SPD were conducted. h e processing
was performed using rods 40 mm in diameter made from the Ti-6Al-4V
ELI alloy (Intrinsic Devices Company USA) of the following composition:
Ti - base, Al - 6.0%; V - 4.2%; Fe - 0.2%; С - 0.001%; О
2
- 0.11%; N
2
-
0.0025%; Н
2
- 0.002% (wt.%). h e temperature of polymorphic transfor-
mation (T
PT
) in the alloy is 960
С. h e microstructure of the alloy in the
as-received state was a granular type with a grain size of 8 μm in a cross-
section, 20 μm in a longitudinal section. According to the X-ray analysis,
the corresponding volume fractions of α and β phases was about 85% and
15%, respectively. h e rods, 250 mm in length, were subjected to process-
ing in 2 stages: ECAP in a die-set with channel intersection angle Θ = 120
о
at a temperature of 600
°
С via route B
c
and multicycle extrusion with total
elongation ratio of 4.2 [198]. As a result of this processing, rods 18 mm in
diameter and up to 300 mm in length were produced. h e extrusion was
carried out at 300
°
С, and the last pass was conducted at room tempera-
ture in order to impart a high density of the crystal defects in the lattice
structure. Subsequent annealing was implemented within the temperature
range of 200
°
С for 1 hour, followed by air cooling.
Microhardness of the samples was measured using a Buehler Omnimet
machine with a load of P = 100 g for 10 seconds. h e microstructures of
these samples were studied by means of optical microscopy (OM) and TEM.
Figure 1.5 illustrates the dependence of microhardness of the alloy sub-
jected to combined SPD-processing on annealing temperature. Changes
°
С to 800
°
5400
5200
5000
4800
4600
4400
4200
4000
3800
3600
3400
3200
3000
2800
2600
-100
0
100
200
300 400 500
Temperature (°C)
600
700
800
900
Figure 1.5
Temperature dependence of microhardness of the UFG Ti-6Al-4V ELI alloy
samples at er heating for 1h.
