Microstructure response of ferritic/martensitic steel HT9 after neutron irradiation: effect of dose

Helium bubble nucleation and growth in alloy HT9 through the use of in situ TEM: Sequential he-implantation and heavy-ion irradiation versus dual-beam irradiation

“…The dose rate may also affect the size distribution shape but there is lack of studies on the matter. In our studies [10,12,13], the bimodal void size distribution was observed in HT9 at 690K (~ 417 °C) at ~18 dpa under neutron irradiation [12] but irradiating the same alloy with dual ion beam in bulk at a similar temperature and dose (432 °C to 16.6 dpa) resulted in a unimodal distribution [10] and in the current study, irradiating the same alloy with dual beam in a thin foil at the same temperature and similar dose (430 °C and 15 dpa) also gives a unimodal distribution; from that perspective the current study (in the thin foil geometry) shows the same effect of higher dose rate of the size distribution shape i.e. an apparent "suppression" or delaying of the occurrence of the bimodal size distribution aspect.…”

“…In this study done in situ in the TEM at 430°C, all bubble size distributions were monomodal with sizes less than 5 nm, which suggests that the bubbles were not able to reach the critical radius or the critical number of helium atoms within the bubble to allow for larger bubbles to grow to form the bimodal distribution. Based on the literature, for a given He appm/dpa ratio the formation of a bimodal distribution depends on the temperature [31,32], which was also observed in the BOR60 irradiations of the same HT9 alloy [12] and possibly on dose [13]. The dose rate may also affect the size distribution shape but there is lack of studies on the matter.…”

“…The nominal chemical composition for this steel is given in table 1. Details about the heat used in this study and detailed characterization of the as received state can be found elsewhere [10][11][12][13][14][15]. It is basically composed of sub-micron laths with M23C6 carbides decorating prior-austenite grain boundaries and lath boundaries, as well as intragranular MX precipitates such as Vanadium rich nitrides.…”

Nanocluster evolution and mechanical properties of ion irradiated T91 ferritic-martensitic steel

“…Gómez-Ferrer et al [30] observed Ni clustering in their APT data after heavy ion irradiation to 0.5 dpa at 300 o C, but did not see any clustering below this dose value. Most Fe-Cr-based commercial alloys, such as T91, have been known to form MNSP under both neutron [3,4,8,28,[33][34][35][36][37][38] and proton irradiation [3,26,27,29,39,40]. Furthermore, [33] have shown that parallels can be drawn between the understanding of precipitation in reactor pressure vessel (RPV) steels (low alloy ferriticbainitic steels [41][42][43][44][45][46][47][48][49]) and Fe-Cr based alloys (T91, HT9 etc) [1,2,27,50].…”

Effects of Silicon Content and Tempering Temperature on the Microstructural Evolution and Mechanical Properties of HT-9 Steels

“…Advanced 9%-12%Cr ferritic/martensitic (F/M) steels including HT-9 (12Cr-1MoVW) have been considered as one of the most promising candidate reactor fuel cladding and structural materials in Generation IV advanced nuclear reactors, owing to their superior thermomechanical properties, irradiation resistance (void swelling and embrittlement) and corrosion resistance at elevated temperatures [1][2][3][4][5][6][7][8][9][10]. In the past few decades, a large amount of HT-9 steels have been widely studied all over the world.…”