Effect of Microstructural Evolution on Flow behavior of Al0.2CoCrFeNi HEA

Dudala, Srinivas and Korla, Rajesh (2018) Effect of Microstructural Evolution on Flow behavior of Al0.2CoCrFeNi HEA. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

Recently the research interest towards High Entropy Alloys(HEAs) is increasing because of their different alloy design concept and improved properties over conventional alloys. HEA composed of 5 or more elements in 5 at% to 35 at% and configurational entropy >1.5R. Limited studies on grain growth in high entropy alloys showed sluggish grain growth kinetics even at significantly high homologous temperatures (T/Tm where Tm is the melting point of the alloy) and it was attributed to the sluggish diffusion in these alloys. But, there is no systematic study to support this statement. One of the main objectives of the present study was to understand the microstructural evolution and grain growth behavior and calculate the activation energy for grain growth. A High Entropy, Al0.2CoCrFeNi, single phase Face Centered Cubic (FCC) alloy was produced through induction melting and processed using hot forging followed by 80% cold rolling. Systematic studies were performed to understand the grain growth behavior at different temperatures for different time periods. Both Optical and EBSD studies showed significant amount of annealing twin fractions. Grain growth kinetics could be described by a power law of 3 and the activation energy for growth was calculated as 200 kJ mole-1. Significant grain growth resistance was observed at 1100°C. To further understand this behavior TEM studies were performed and observed no second phases or precipitation along the grain boundaries. Influence of the grain size on the plastic flow behavior was studied using tensile experiments. The yield stress of the material measured as a function of grain size, and the result was found to follow the classical Hall–Petch strengthening. Strain to fracture was reduced after particular grain size was observed. Dimple type fracture surface along with high fracture strains suggest the ductile behavior of the alloy.

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