LONG TERM COARSENING IN RENÉ 80 Ni-BASE SUPERALLOY

The influence of temperature and time on the microstructure of Rene 80 after long term aging was examined. The alloy was subjected to aging heat treatments at five different temperatures ranging from 850°C to 1,050°C for five different times 1000h, 2000h, 5000h, 10000h and 20000h. The microstructural evolution was characterized with scanning electron microscopy. The average particle radius of �’ precipitates was calculated and the growth of the precipitates was compared to both the cube and square rate laws in an attempt to identify the dominant mechanism. Assuming diffusion controlled growth, the coarsening activation energy was calculated to be 127 kJ/mol. The particle size distributions (PSD) for the populations of �' precipitates were compared with theoretical models. There was generally a poor fit between the experimentally measured values and the theoretical distribution but the LSEM model, which accounts for encounters between particles, resulted in the best fit.