چكيده به لاتين
Superalloys, including Inconel 718 superalloys, undergo microstructural changes during working conditions and high temperatures. These changes include: stability or instability of precipitation phases (γ′, γ′′ and δ), formation of harmful phases, carbide reactions, change in morphology of phase γ′, formation of cracks and boundary cavities. Therefore, control of heat treatment conditions and production process parameters such as hot forging to achieve the desired microstructure is of great importance. Therefore, the aim of the present study in the first stage is to determine the appropriate conditions for hot deformation of Inconel 718 superalloy using process maps and in the second stage the effect of aging heat treatment on the superalloy microstructure after hot work. For this purpose, hot pressure test was performed at 1150, 1100, 1050 and 1000 °C and strain rates of 0.1, 0.01 and 0.001 s-1 were applied to this alloy. Then, process maps for this alloy were drawn using flow curves. The deformed samples were then subjected to aging heat treatment for 18 hours at 620 and 720 °C. Examination of process and microstructure maps obtained from hot pressure test shows that the most suitable temperature range for hot deformation for this superalloy is in the range of 1000 to 1050 °C and the strain rate 0.1 to 0.01 s-1. In these areas, maximum process efficiency and instability do not occur. Also at 1150 °C and strain rates of 0.1 and 0.01 s-1, instability was observed in the structure and process map, which indicates that the conditions are not suitable for deformation. Also, the results of aging heat treatment show that the size and volume fraction of phase γ' and γ'' have increased and this has caused a significant increase in hardness (about 200 Vickers) in the samples.
