Effects of cold rolling on the mechanical properties and grain structure of Inconel 718 alloy
Master thesis
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https://hdl.handle.net/11250/3081791Utgivelsesdato
2023Metadata
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Sammendrag
This master thesis in material science aimed to investigate the influence of increaseddegree of cold rolling reduction of precipitation formation in commercially producedNickel-base superalloy Inconel 718, and evaluate the mechanical properties. Theresearch involved mechanical testing through tensile testing and Vickers microhardnesstesting, accompanied by microstructural investigation with optical and scanningelectron microscope.
The material was machined into thin strips and solution heat treated at 1100◦C for1 hour and water quenched to normalize the material. Subsequently, the samplesunderwent cold rolling with a constant reduction down to 20% and 50% of theiroriginal thickness, followed by a two-step precipitation hardening treatment at720◦C for 8 hours, furnace cooling to 650◦C for another 8 hours and air cooling toroom temperature.
The mechanical testing revealed a clear increase in hardness, yield strength andtensile strength with increased cold rolling reduction, while also decreasing theductility. The precipitation of secondary strengthening phases also contributed toincreased strength, albeit to a lesser extent as degree of deformation increased.
The microstructure revealed a transformation from an equiaxed, well defined grainstructure with a significant amount of deformation twins, to a visibly deformedgrain structure characterized by elongated grains and deformation bands. Further,the microstructure showed indication of texture formation with a preferred grainorientation and intergranular slight variations in orientation.