EFFECT OF SHEAR STRAIN ON MICROSTRUCTURE EVOLUTION OF DEFORMED INCONEL 718 ALLOY

Abstract

Inconel 718 is a nickel super alloy with face-centered cubic structure. It has high strength, ductility, excellent corrosion resistance and high creep resistance. These desirable attributes make it one of the highest manufactured superalloys and is profusely used in aerospace industries. The main applications of Inconel 718 are gas turbine discs, combustion casings of engines and shafts. The deformation behaviour of Inconel 718 at higher temperatures and higher strain rates has been very well documented over the years, whereas the studies based on shear deformation in ambient temperature are limited. Understanding the deformation behaviour, microstructure and deformation mechanism caused due to shear deformation is eminent for manufacturing the components using processes such as shear spinning or flow forming. Therefore, the present study aims to understand the effect of shear strain on the deformation behaviour and microstructure of compressed Inconel 718 samples with and without prior shear deformation. The solution treated Inconel 718 alloy was deformed by compression and shear-compression in room temperature at strain rates ranging from 0.001s-1 to 3s-1. The deformed samples were also annealed at 1010°C for 1min. All the samples were characterized in X-ray diffractometer and FESEM to observe the microstructure. Microstructures of the samples are characterized with the presence of severe deformation bands. Distance between the deformation bands reduced first and then increased as the strain rate increased. Electron Back Scattered Diffraction was used to study the microstructure development. Non-uniform strain localisation was observed in the deformed samples and this further resulted in heterogenous grain growth behaviour leading to either bimodal or multimodal grain size distribution. The compressed samples had stronger texture compared to shear-compression deformed samples. Annealed samples were noticed to have weaker texture due to annealing twins. The local mechanical properties were characterized using nano-indentation measurements.