Fatigue behaviour in a PM Ni-base superalloy Udimet 720

摘要

S-N curve behaviour and fatigue growth of naturally-nucleated surface cracks were investigated in air under four point bending condition for a PM Ni-base superalloy Udimet 720. Cracks were found to nucleate from the surface pores and the S-N behaviour is independent of the defect content. The nucleation, nucleation life and growth resistance of fatigue cracks were investigated in terms of probabilistic modelling. The scatter of small crack growth rate is considered by treating C and m of Paris-Erdogan law as random variables. It is deduced that C and m have a log-normal and a normal distribution respectively.