Direct measurements of irradiation-induced creep in micropillars of amorphous Cu56Ti38Ag6, Zr52Ni48, Si, and SiO2

Abstract

We report in situ measurements of irradiation-induced creep on amorphous (a-) Cu56Ti38Ag6, Zr52Ni48, Si, and SiO2. Micropillars 1 μm in diameter and 2 μm in height were irradiated with ∼2 MeV heavy ions during uniaxial compression at room temperature. The creep measurements were performed using a custom mechanical testing apparatus utilizing a nanopositioner, a silicon beam transducer, and an interferometric laser displacement sensor. We observed Newtonian flow in all tested materials. For a-Cu56Ti38Ag6, a-Zr52Ni48, a-Si, and Kr+ irradiated a-SiO2 irradiation-induced fluidities were found to be nearly the same, ≈3 GPa−1 dpa−1, whereas for Ne+ irradiated a-SiO2 the fluidity was much higher, 83 GPa−1 dpa−1. A fluidity of 3 GPa−1 dpa−1 can be explained by point-defect mediated plastic flow induced by nuclear collisions. The fluidity of a-SiO2 can also be explained by this model when nuclear stopping dominates the energy loss, but when the electronic stopping exceeds 1 keV/nm, stress relaxation in thermal spikes also contributes to the fluidity.

In-situ TEM irradiation creep experiment revealing radiation induced dislocation glide in pure copper

“…• The underlying irradiation creep mechanism (with the ion beam switched on) is very sensitive to stress, and occurs for stresses just below the critical stress for dislocation motion (with the ion beam switched off). • The magnitude of the flux affects the dislocation activity, since for a flux of 1.2 × 10 10 ions/cm²/s very few motions were observed in comparison to higher fluxes (above 3 × 10 10 ions/cm²/s) • The mean pinning lifetime of dislocations was estimated to be around 40 seconds.…”

“…An alternative approach is to use heavy ions, which better simulate the neutron damage and do not activate the matter, but have an even more limited penetration than light ions. Despite the efforts of few research teams to use miniaturized specimen coupled with heavy ion beams [7,8,9,10,11,12,13,14,15], the access to the underlying irradiation creep mechanisms remains indirect. The in-situ imaging of crystal defects under both straining and heavy ion irradiation inside a TEM can allow for a direct access to the active mechanisms [16].…”

Irradiation-induced creep in metallic nanolaminates characterized by In situ TEM pillar nanocompression

“…MeasuringIIC presents substantial experimental challenges. [22,23] Experiments performed in reactors are enormously expensive, and they require excessively long experimental times to reach doses on the order of a DPA (displacement per atom). Moreover, in-reactor experimentstypically offer little opportunity to systematically vary the applied stresses and temperature.…”

“…In that work, creep was measured in metallic and oxide glasses for which the creep rates are quite high. [22,23]The lower creep rates associated with polycrystalline materials are far more challenging. In this work, we use high-energy, heavy-ion irradiation combined with insitu TEM nanocompression to study IIC.…”

In situ TEM Measurements of Ion Irradiation Induced Creep

“…High energy heavy ions simulate neutrons reasonably well and can achieve 10's to 100's of dpa on the order of 1 day, but their average penetration range is typically on the order of 100's of nanometers. As a result, there is potential for accelerated IIC experiments using high energy heavy ion irradiation, provided that the experiments are performed on nanoscale specimens [6][7][8][9]. Such small specimens present a variety of challenges when tested ex situ [6,7].…”