Hold-Time Fatigue Crack Growth of Allvac 718Plus®

Abstract

The hold-time fatigue behaviour of Allvac 718Plus was investigated both in the as-heat treated condition and after long-time exposure at temperature close to the maximum operating limit. At temperatures above 450°C the introduction of 90 s hold-time at maximum load significantly increased the fatigue crack growth rate. Both conditions showed purely cycle dependent behavior at 450°C and close to purely time dependent behavior at 700°C. At 600°C intermediate behavior was observed. The long-time exposure had little effect on the cyclic (0.5 Hz) crack growth rates, but the resistance to crack growth with 90 s hold-time decreased. No microstructural effects of long-time exposure (700°C/140 h + 675°C/460 h) could be observed by SEM, but there were indications that the hardness of the material increases somewhat after exposure.

High-temperature crack growth in a Ni-base superalloy during sustained load

“…Ni-base superalloys are well documented to exhibit time-dependent intergranular crack growth when subjected to sustained mechanical load at high temperatures in oxygen rich environments [1][2][3][4][5][6][7][8].…”