Microstructure Mechanical Property Relationship in Superalloys.

The primary objectives of this program were to investigate the conditions leading to the abnormal grain growth behavior in Rene 95 extrusions, and to study the microstructure of AF115 and the effect of hold time conditions on the low-cycle fatigue behavior of necklace Rene 95. In the study of grain growth behavior, it was found that the material when extruded below the gamma-prime solvus temperature did not undergo secondary recrystallization in a subsequent anneal with a fast heating rate at a higher temperature. However, when a slow heating rate was employed, the extrusions showed significant indications of secondary recrystallization. When the material was extruded above the gamma prime solvus temperature, the tendency for abnormal grain growth increased tremendously. This was evident even in fast annealed specimens. AF115, which is a disk alloy developed for 1400F service, was examined using optical, replica and transmission electron microscopy. The microstructural study is summarized in the report. The introduction of a hold time was found to have a drastic effect on the LCF life.