SHORT FATIGUE CRACK GROWTH IN A NICKEL-BASE SUPERALLOY AT ROOM AND ELEVATED TEMPERATURE

摘要

The fatigue behavior of Waspaloy was studied using an optical system developed to monitor short crack growth at elevated temperatures. Tests conducted at 19 and 500 C revealed the dominant mechanism of crack formation was slip band cracking. Crack formation was also associated with coarse carbide particles within the matrix. The dominant failure mechanism at 19 and 500 C was one of mixed mode 1 and 2 fractures, with mode 2 shear displacements giving rise to surface roughness induced non-closure. Oxide and plasticity induced non-closure processes made only a minor contribution to the overall growth process. Short fatigue crack growth measured at R 0.1 was faster at 500 C than at 19 C at an equivalent value of Delta-K(sub 1). This was attributed to a change in slip character from highly planar to one involving increasing amounts of cross slip at 19 and 500 C respectively.