Crack Paths 2012

failure occurring at H ~ 0.25 at the higher strain rate ( Hf= 0.3 at the lowest strain rate). At

300° and 400°C (Fig. 1b and 1c), a plateau in stress values is obtained. At constant

strain, the stress values decrease with strain rate and with increasing T. With regard to

ductility, it increases with decreasing strain rate and increases with T.

180

H

12468024680

0,0

250°C

0,2

0,4

0,6

0,8

1,0

0,0

0,2

0,4

0,6

0,8

1,0

300°C

1460

a

b

10-3s-1

10-3s-1

1020

10-4s-1

80

10-4s-1

60

10-5s-1

40

10-5s-1

20

H

180 400°C

160

c

140

120

100

4680

10-3s-1

10-4s-1

020

0,0

0,2

0,4

0,6

0,8

1,0

H

Figure 1. Tensile flow curves at 250°C (a), 300°C (b) and 400°C(c)

Fig. 2 shows the dependence of peak stress Vp and strain to failure Hf on T at constant

strain rate. The peak stress values rapidly decrease with increasing temperature from

250° to 400°C. In particular at 10-3 and 10-4s-1, stress values are very close to each other

and at 400°C, values are almost coincident. Strain to failure Hf increase with temperature

at constant strain rate from 0.25 to almost 1. Its trend is opposite to that exhibited by

stress: at low temperatures, failure strain values are almost coincident, while at 400°C a

difference of 20%in ductility can be observed.

The microstructural analysis of the polished longitudinal surface of all the deformed

samples shows that the alloy exhibits cavitation (Fig.3a-c). Cavities have been mainly

detected at grain boundaries and at particles interface (Fig. d,e). Inclusions, triple points

and precipitates are in fact region of stress concentrations that favor the onset of cracks

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