A helium-induced shift in the temperature dependence of swelling

Abstract

In an annealed austeniiic alloy undergoing bombardment with k MeV Ni ions to doses between I and 70 dpa at 840, 900, 950, 1025 and 1100 K, the introduction of simultaneously-implanted helium at a rate of 20 appm He/dpa moves the swelling versus temperature curve up the temperature scale by ItO to 70 K. Co-implantation of hydrogen (deuterium) at a rate of 50 appm D/dpa simultaneously with the helium causes little or no additional syste ,atic effects. The major change in microstructure caused by the gases is an enhancement of cavity nucleation by factors of 2 to 5 at 8'iO to 950 K, increasing to factors of thousands at 1)00 K. Concurrently there is a reduction in the size of cavities and in swelling at all temperatures below 1025 K, and an increase in cavity size and in swelling at 1100 K, where the cavities are gas stabilized. At 1025 K the increase in nucleation of cavities outpaces the reduction in size and causes increased swelling. The primary effects of the gases are decided at low doses below 1 dpa where cavity nucleation is completed and where the conditions governing cavity growth are established; at higher doses swelling is determined by cavity growth, which is dependent on dose only. The gases cause copious formation of cavities on grain boundaries, boding ill for mechanical properties.

Effect of pre-implanted helium on void swelling evolution in self-ion irradiated HT9

“…12 shows the expected bell-shaped swelling curve as a function of temperature. This agrees with expected results from both void swelling theory [10] and the literature [8,9]. Void diameter and number density also follow the same behavior with temperature.…”

“…However, these results differ in that the swelling peak is narrower than that seen in the literature. [8,9] The full width at tenth maximum (FWTM) for alloy HT9 in Smidt's experiment was approximately 100°C. Toloczko [24] recently reported the temperature dependence on swelling of MA957, in which the FWHM was $90°C.…”

“…In a study performed by Farrell and Packan [8], Fe-17Cr-16.7Ni-2.5Mo-0.005C was irradiated with either 4 MeV Ni ++ or 4 MeV Ni ++ and 0.2-0.4 MeV He + ions. At a dose of 70 dpa, they found that the addition of helium shifted the peak swelling rate location by $40-70°C higher from 680°C with no helium additions.…”

Helium trapping in carbide precipitates in a tempered F82H ferritic–martensitic steel

“…This was attributed to tungsten vacancies having no thermal mobility at the low temperature resulting in the bubbles growing through interstitial emission, whereas at the higher irradiation temperatures, He bubble growth resulted from the capture of the thermally mobile, radiation-induced vacancies. Similar effects are also observed when irradiating steels such as HT-9 and EM-12 with He ions [30,31].…”

Phase field modelling voids nucleation and growth in binary systems

“…This phenomenon was discovered by Evans [8]. Partially ordered void super-lattices have been reported for irradiated pure materials, for example, Mo [8], Al [9], Nb [10], Ni [11], and alloys: Ni-Al [12], Cu-10%Ni [13], Nb-Zr [14], Mo-0.5Ti [15], stainless steel [16,17] irradiated to damage levels of 10−80 dpa (displacements per atom) [18]. It was found that typical void size is 2−7 nm in pure materials with void super-lattice parameter 20−30 nm, whereas for steels, the void size is around 30−100 nm, depending on irradiation conditions (dose rate and temperature).…”