Dissolution Mechanism And Numerical Simulation Of δ Phase In Inconel 718 Alloy

The dissolution behavior of 8 phase in the delta-processed (DP) Inconel 718 alloy was studied in different heat treatment conditions. The thermal evolution process of the microstructure of alloys under different time and temperature were studied by optical microscope and other analytical methods. Through the analysis of hardness measurement, the influence of the relative performance of the 8 phase on the Inconel 718 alloy was discussed. The change of the alloy grain size was predicted by using Deform-3D software during the dissolved process and comparing with the experiment results. These could provide theoretical basis for the establishment of delta-processed (DP) of Inconel 718 alloy.The results showed that the morphology changes of needle shaped 8 phase during dissolution process can be divided into two stages:at the early stage, it changes from a long needle shape into a short needle and globular ones. Then the short needle 8 phase dissolved into spherical at the later stage. The dissolution amount of 8 phase increased at the temperature of 950℃,980℃ and 1000℃. But it also could not dissolve completely. Finally, the dissolved quantity reached a stable value with the time increasing. The δ phase continuous dissolves and nearly complete when the temperature rises from 1020℃ to 1060℃.The hardness test results of Inconel 718 alloy during the dissolved process of 5 phase showed that at the same temperature as the extension of heat preservation time, the hardness values are continuously reduce. Under the same soaking time, the higher the heat treatment temperature, the lower the hardness of alloy. At the beginning of the dissolved, the alloy hardness value falling faster, then dissolved metal hardness gradually tends to a stable value. Comparing the delta-processed (DP) and the solution treatment process, the former could improve the hardness of alloy through increase of δ phase content in the alloy.The grain size and numerical simulation of Delta-processed (DP) Inconel 718 alloy during the dissolved process of 8 phase showed that when a certain time of heat preservation, obviously grain size grew up with the increase of heat treatment temperature. When the temperature of the heat preservation is constant, the grains grew up quickly with the extension of heat preservation time, the average grain size increased significantly with the grain growth into a parabolic rule changes. The grain growth speed slowed down with the heat preservation time continues to grow. The grain size growth model of 8 phase processing Inconel 718 alloy was established during heat treatment process. The maximum error of grain size was 4.2% between the prediction results and experimental results. It showed that the established model can be well used to describe the average grain size of Inconel 718 alloy during the dissolved process of δ phase.