Identifying microstructural changes responsible for retarded grain growth during tungsten recrystallization after helium plasma exposure

Thompson, Matt; Song, Kay; Temmerman, G. De; Chen, H.; Kirby, Nigel; Bradby, Jodie; Bhattacharyya, Dhriti; Hoang, Calvin; Corr, Cormac

doi:10.1016/j.jnucmat.2021.153448

Cited by 8 publications

(8 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is the reason for the lower measured hardness in this case, since the greater load in the present case resulted in a larger indentation depth, hence a smaller indentation size effect [41]. However, the results show the same general trend as in that work, except for the fact that the drop in hardness after annealing at 1200 • C is much greater for the unexposed sample than the plasma-exposed sample in this case, in contrast to the previous work [29]. Thus, the present work demonstrates more clearly the effect of plasma exposure on retarding recrystallization than before.…”

Section: Nanoindentationsupporting

confidence: 52%

“…of observations. The hardness values here are measured with a much higher load than in the previous paper, where the maximum load was 10,000 µN or ~1 gf [29]. This is the reason for the lower measured hardness in this case, since the greater load in the present case resulted in a larger indentation depth, hence a smaller indentation size effect [41].…”

Section: Nanoindentationmentioning

confidence: 52%

“…Surface cracks in the plasma-exposed samples are thought to be formed by the accumulation of He bubbles at the grain boundaries, followed by their aggregation, which causes the physical separation of grains, as reported in an earlier paper by Thompson et al [29]. It is thought that, at low plasma exposure temperatures, the He trapped at grain boundaries (GBs) near the surface does not diffuse out and this exacerbates the agglomeration of bubbles and consequent cracking.…”

Section: Sem Characterizationmentioning

confidence: 88%

“…The pinning of grain boundaries by He bubbles is thought to be a manifestation of Zener drag [26,27], where the total drag force is inversely proportional to the size of the bubbles, assuming the volume fraction of bubbles is constant [24,28]. In a previous paper by the current authors, it was shown that exposure to He at sample temperatures of 300 • C, 500 • C and 800 • C for 1 h caused a suppression of recrystallization, and that this effect was the maximum in the sample exposed at 300 • C [29]. This suggests significant memory effects where prior operating conditions not only affect material properties at the time of plasma exposure but can lead to synergistic effects with future operating conditions to influence material behaviour in a non-trivial manner.…”

Section: Introductionmentioning

confidence: 94%

“…The heating and cooling of the samples were performed at rates of 2 • C/min. For details about the He plasma irradiation process, please refer to reference [29].…”

Section: Plasma Exposure and Annealingmentioning

confidence: 99%

See 4 more Smart Citations

Effect of He Plasma Exposure on Recrystallization Behaviour and Mechanical Properties of Exposed W Surfaces—An EBSD and Nanoindentation Study

Bhattacharyya,

Thompson,

Hoang

et al. 2023

Metals

Self Cite

View full text Add to dashboard Cite

Fusion reactors are designed to operate at extremely high temperatures, which causes the plasma-facing materials to be heated to 500 °C to 1000 °C. Tungsten is one of the target design materials for the plasma-facing diverter components in Tokamak designs, such as ITER, because of its excellent high-temperature strength and creep properties. However, recrystallization due to high temperatures may be detrimental to these superior mechanical properties, while exposure to He plasma has been reported to influence the recrystallization behaviour. This influence is most likely due to the Zener effect caused by He bubbles formed near the surface, which retard the migration of grain boundaries, while at the same time modifying the surface microstructure. This paper reports a study of the effect of plasma exposure at different sample temperatures on the recrystallization behaviour of W at different annealing temperatures. The characterization after plasma exposure and annealing is pursued through a series of post-exposure annealing, followed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) characterization and nanoindentation to determine the mechanical properties. Here, it is shown that the hardness is closely related to the recrystallization fraction, and that the plasma exposure at a sample temperature of 300 °C slows down the recrystallization more than at higher sample temperatures of 500 °C and 800 °C. Atomic force microscopy (AFM) was subsequently used to determine any changes in pile-up height around the nanoindents, to probe any indication of changes in hardenability. However, these measurements failed to provide any clear evidence regarding this aspect of mechanical behaviour.

show abstract

Section: Nanoindentationsupporting

confidence: 52%

Section: Nanoindentationmentioning

confidence: 52%

Section: Sem Characterizationmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 94%

“…The heating and cooling of the samples were performed at rates of 2 • C/min. For details about the He plasma irradiation process, please refer to reference [29].…”

Section: Plasma Exposure and Annealingmentioning

confidence: 99%

See 3 more Smart Citations