Fatigue Crack Paths 2003

strong embrittlement of grain boundaries by water vapor which is not observed in air

(i.e. in presence of oxygen).

(a)

(b)

(c)

-6

10

High

vacuum,5 7 MPa.m1/2

1/2

H u m .argon, 2 2 M P a . m

High vacuum,26 MPa.m1/2

10-7

10-8

10-9

-10

10

-11

10

1

10

1/2

ΔΔK ( M P am

)

air, 5 7 M P a . m 1/2

air, 2 6 - 5 2M P a . m 1/2

(d)

(e)

(f)

Figure 8. Influence of environment in the near threshold behavior at 500°C (35 Hz). a,b:

hum. argon at Kmax= 22 MPa m, c: high vacuum at Kmax= 52 M P a m, d,e: ambient air

at Kmax= 57 MPa m, f: ambient air at Kmax= 52 MPa m.

C O N C L U S I O N

The near threshold crack path in titanium alloys at moderate and high temperature is

very sensitive to environment, microstructure and their coupled effect. Three main