Effects of helium on irradiation-induced phase instability in a NiCrFeTiNbAl alloy

Abstract

The Ni–Fe–Cr based superalloy with percentage additions of Nb, Al and Ti, called "Inconel X750 superalloy", is studied with its importance in nuclear application. Under reactor neutron irradiation, the strengthening phase Ni3(Al, Ti) in the form of gamma prime precipitates were somehow disordered, and dissolved eventually, by which the mechanical properties of materials were degraded. It is of high interests to investigate the effects of transmutation production helium on radiation-induced instability of gamma prime in the materials. The transmission electron microscope in situ heavy ion irradiations with and without pre-injected helium are performed purposely. The precipitates were disordered by heavy ion irradiation after 0.06 displacement per atom (dpa). The presence of 2×10−4 atoms helium delayed the disordering of Ni3(Al, Ti) precipitates to 0.68 dpa. With 4×10−4 atoms helium, the precipitates required doses of > 2.7 dpa to become disordered. In addition, the precipitation of M23C6 particles were observed at 600 °C irradiation to 5.4 dpa with 4×10−4 atoms helium pre-injected.