Flow behavior and microstructural investigation of GTD 111 cast nickel base superalloy during hot pressure test

To investigate the behavior of the superalloy deformation behavior of GTD 111 casting, the hot-pressure tests were carried out at a temperature range of 950 -1100 ° C and strain rates of 1- 0.001 s-1. All of the flow curves showed a relatively linear tension increase to one peak point and then its descent to a strain of 0.5, and the region of steady state deformation with constant stress was not observed. This process was attributed to the control of dislocations by the dendritic structure and their amplification at peak point. Microstructural investigations showed that the hot work would break the structure of the dendritic network and create separate cells. An increase in the temperature of the hot work, resulted an increase in the decomposition of the structure and the achievement of larger cells coused by dissolution of broken dendritic particles. Also, with the increase in the rate of deformation at a given temperature, the decomposition rate of the dendritic network decreased and its elongation increased in the direction of the deformation. Using the fundamental constants of material, n, b and a were determined at the peak point. Also, with the help of the fundamental relationship of sinuses hyperbolic, the amount of activation energy at the peak and the strain of 0.4 samples was 947 kJ / mol and 890 kJ / mol, respectively. These results showed that the deformation activation energy decreases with increasing strain and breaking the dendritic structure into distinct cells.