Crack Paths 2012

Electrical conductivity 24500°C

H R F250°C

H R F400°C

167890050505050

20 390

tivit y [ M S / m ]

2678

o n d u c

H R F

2425123

E le c t r ic a l c

0,1

1

10

100 1000

Log Time [min]

Figure 5. hardness and electrical conductivity curves Vs time for as-cast samples aged

at 250°C and 400°C

a

b

Figure 6. optical micrographs of polished longitudinal surface of deformed samples at

250°C 10-3s-1 (a) and 400°C 10-3s-1(b) after solution heat treatment showing that

cavitation is reduced by solutioning.

Analysis of cavity distribution (Fig. 4a-f) shows that the highest value of cavitation is

close to the fracture surface, except at 400°C where cavitation is more uniformly

distributed along the sample (it is not always at maximumon the longitudinal axis of the

samples). If the cavitation was maximumon the longitudinal axis and close to the

survaceof fracture, then the crack growth would have been controlled by dislocations

motion and, consequently a transgranular ductile fracture would be obtained. Both these

aspects (growth phase and type of fracture) have been further verified by the use of both

theoretical models and Asbhy map. Theoretical modelling on cavitation in general takes

into account the three distinct stages of damage generation, i.e. nucleation, growth and

coalescence [24], but, among these, the growth appears the critical phase [25]. When

cavity growth is controlled by plastic deformation, the simplest model for cavity growth

assumes the following form [12]:

1127