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

Abstract

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.

Keywords:

• Single-crystal superalloy
• orientation
• slip bands (SBs)
• fracture
• in situ tension

Acknowledgements

The authors are grateful to Prof. Z.G. Wang and Prof. S.X. Li for their good suggestions and advices. Thanks are also due to H.H. Su, W. Gao, R.T. Qu and Q.K. Zhang.

Funding

This work is supported by the National Basic Research Program of China [grant number 2010CB631206]; the National Natural Science Foundation of China (NSFC) [grant number 51001104], [grant number 50931004], [grant number U1037601].