Y.Z. Zhou

Effect of orientations on in situ tensile deformation and fracture behaviours of nickel-base single-crystal superalloys

After systematically investigating in situ tensile deformation and fracture behaviours of nickel-base single-crystal superalloys with four different orientations, their slip and fracture modes in relation to the orientations are obtained and shown as follows. In [0 0 1] oriented specimen, four slip systems were activated and the crack initiated along the interactive location between the third slip bands (SBs) and deformation bands in priority. The crack propagation involves all three crack opening types of I, II and III. [0 1 1] oriented specimens exhibited obvious low strain hardening rate and high ductility, which can be attributed to the balance between the softening caused by the propagation of SBs and the latent hardening caused by the propagation of deformation bands. Except for case, the critical resolved shear stress (CRSS) of the other oriented superalloys at room temperature is approximate, which is due to non-Schmid behaviour in superalloys. Lall–Chin–Pope model is used to explain the orientation dependence of CRSS. Furthermore, the fracture modes of different oriented specimens depend on the intensity of intrusion and extrusion and the degree of match between normal stress and shear stress. The shear stress is beneficial to the crack initiation and the normal stress contributes to the crack propagation.

Differences in the micromechanical properties of dendrites and interdendritic regions in superalloys

Abstract Statistical analysis of white-light interferometry (WLI) experiments performed on Ni-based single-crystal superalloys (SX) have revealed a different height distribution between the dendritic cores (DCs) and the interdendritic regions (IRs) of the polished samples. The micromechanical property difference is largely ascribed to the uneven distribution of the alloying elements. In this context, possible reasons for this difference are discussed by comparing with different experiment results obtained by previous researchers, and a proposal forecasting the hardness ratio of IRs/DCs is put forward.