Anisotropic thermomechanical fatigue of a nickel-base single-crystal superalloy Part I: Effects of crystal orientations and damage mechanisms

Thermomechanical fatigue in distinct crystal orientations of nickel-base single-crystal superalloy was studied. Crack initiation modes and damage mechanisms were characterized on fracture surfaces and longitudinal sections by scanning electron microscope and optical microscope. Creep damage nucleated from casting pores in IP-TMF and propagated under mode I. The creep facets were controlled by the activated slip systems, whereas fatigue damage was orientation-dependent and developed by slipping along different crystallographic planes. Oxidation-assisted cracking in OP-TMF tests was non-crystallographic for all crystal orientations. Multi -layer structures near the crack tip revealed successive growth of oxide and the crack grew within the oxidized material.

Automated summary

This study investigated the thermomechanical fatigue behavior of nickel-base single-crystal superalloy with different crystal orientations. The crack initiation modes and damage mechanisms were characterized using SEM and optical microscopy. In IP-TMF, creep damage originated from casting pores and propagated under mode I. The creep facets were influenced by activated slip systems, while fatigue damage depended on crystal orientation and developed by slipping along different crystallographic planes. In OP-TMF tests, oxidation-assisted cracking was non-crystallographic for all crystal orientations, with the crack growing within the oxidized material.