Frequency and wave-form effects on the fatigue crack growth behavior of alloy 718 at 298 K and 823 K

摘要: The fatigue crack growth rate (FCGR) of Alloy 718 was measured on CT type specimens at 298 and 823 K. At K, the influence frequency studied in range between 5 – 10-3 Hz 20 Hz, using a sinusoidal wave form signal. A substantial increase FCGR occurred, particularly low stress intensity levels, as temperature increased from to K decreased elevated temperature, effect cyclic equally investigated, triangular square signals producing same 5.10-2 Hz. load led higher than form. In addition hold time 10 s both maximum minimum associated with had no significant FCGR. Electron microscopy used observe substructures that developed ahead cracks. These observations showed certain circumstances plastic deformation proceeded by propagation planar bands which were identified twins. room twinning found be abundant only threshold regime. observed domain FCGR, frequencies. Fractography carried out study micromechanisms propagation. intergranular cracking occurred decreased. comparison formed cycle those zones propagating cracks is made. importance acceleration when loading discussed.