Ni superalloys are engineered material systems, where each microstructural feature conveys specific strengthening mechanisms. This project establishes experimental techniques which focus on understanding deformation in Ni superalloys; building upwards from single crystal CMSX-4, to polycrystalline FGH96, to carburised CMSX-4 & 10. The project combines micromechanical testing and material characterisation with the aim of extracting engineering properties, to help further advance the micromechanics field and aid in the development of new alloys.
Micropillar compression experiments were used in this study and enable the analysis of deformation at characteristic strain(s) on the same length scale as the deformation processes.
The critical resolved shear stress of pillars fabricated in {001} {011} {111} on single crystal CMSX-4 varied by 380 ± 10 MPa, 420 ± 15 MPa, 460 ± 16 MPa respectively, the resolved shear stress of pillars fabricated on individual grains on a polycrystal0
line sample, with nearly identical areas in the same orientation varies by less than 5% and these results were found to be consistent with literature.
The critical resolved shear stress of pillars fabricated on single crystal CMSX-4, with carbide type phases captured on the top surface of the pillars varied by 400 ± 3.4 MPa, 420 ± 6 MPa 450 ± 23 MPa respectively, despite being the same crystal orientation and in similar locations ± 20 µm. The area fraction of the pillars mentioned above were; 5% 17% and 27% respectively. The variation in τcrss was found to be a consequence of the leeching of alloying elements, via the formation of carbide type phases which disrupted the ϒ/ϒ’ microstructure and disrupted the propagation of dislocations. The carbide size, area fraction, number density and shape abnormality were theorised to be proportional to the extent of ϒ/ϒ’ disruption. Transmission electron microscope (TEM), based analysis shows that the carbide type phases orientate themselves at junctions and dislocations tend to agglomerate around the phases at these points.