Investigating Texture Dependant Deformation Mechanisms in Waspaloy Using in-situ Tensile Testing, EBSD and Digital Imaging Correlation (DIC) Microanalytical Tools
Authors:   , Parkin James 
Published: March 2022

Strain accumulation from either monotonic or cyclic loadings can be heterogeneous in aerospace materials where deformation can become localised depending on microstructural features and processing parameters. The damage mechanisms are further reliant on deformation rates and temperature. Thus, the characterisation and dynamic observation of strain localisation during deformation at both macro and micro scales are vital for understanding the failure mechanisms of the alloy. In the current study, sections from the bore of a turbine disc were mechanically tensile tested to characterise the deformation mechanisms at ambient and elevated temperature. Two major microanalytical tools were utilised to investigate the deformation mechanisms in the nickel-based superalloy, Waspaloy;(1)in-situ mechanical tensile testing in an SEM to obtain EBSD crystallographic orientation information at the micro-scale to reveal the changes in grain morphology, texture and misorientation during interrupted tensile deformation. The aims of this were to obtain crystallographic orientation data at progressively increasing stages of deformation. This helped to quantify the orientation differences within the microstructure to asses which orientations were dominating and diminishing in the deformed microstructures as well as asses the geometrically necessary dislocation (GND) densities within certain grain textures.(2)Digital imaging correlation (DIC) during variant mechanical testing to provide a holistic visualisation of the deformation on a macro-scale. The aims of this were to reveal areas of localised plastic strain heterogeneities as the test pieces approach failure with the objective to characterise the deformation behaviour of grain textures within the localised areas of strain revealed through DIC tensile testing. For such, a speckle pattern was developed for the visualisation of macro-deformation via optical microscopy methods. Moreover, post-deformation grain textures were compared to pre-deformed, original microstructure textures to characterise which textures are dominating and diminishing in the deformed microstructure at varying test temperatures. It was observed that the Copper (112)<111> grain texture dominated and that the Rotated Cube (001)<110> texture component diminished as the tensile load was increasingly applied to failure. DIC tensile testing revealed localised strain approaching the failure strain of Waspaloy. From which, those localised areas were characterised to be dominated by the Copper type texture component with a reduction of the Rotated Cube component being observed with the localised, high strain areas. Furthermore, in a study of the deformation mechanisms of Cube (001)<100> and Brass (011)<211> texture components, it was concluded that the geometrically necessary dislocation (GND) density was highest near the grain boundaries in Cube textured grains and that in Brass texture grains the GND density was highest within the centre of the grains.