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Positron Annihilation Spectroscopy Study of Carbon-Vacancy Interaction in Low-Temperature Bainite.

ABSTRACT: Nano-scale investigations of bainitic structures formed at temperatures below 350?°C have shown that the bainitic ferrite lattice is super-saturated in carbon. A high density of intrinsic defects would be playing a part in the carbon-supersaturation levels detected. In this work, the role of C-vacancy complexes on carbon-supersaturation in low temperature bainite is investigated by means of Positron Annihilation Spectroscopy. Results reveal the presence of a significant amount of monovacancies in the structures that plays an important role on the formation of carbon clusters in the ferrite lattice of nano-scale bainitic structures.

SUBMITTER: Rementeria R

PROVIDER: S-EPMC6965194 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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Positron Annihilation Spectroscopy Study of Carbon-Vacancy Interaction in Low-Temperature Bainite.

Rementeria Rosalia R Domínguez-Reyes Ricardo R Capdevila Carlos C Garcia-Mateo Carlos C Caballero Francisca G FG

Scientific reports 20200116 1

Nano-scale investigations of bainitic structures formed at temperatures below 350 °C have shown that the bainitic ferrite lattice is super-saturated in carbon. A high density of intrinsic defects would be playing a part in the carbon-supersaturation levels detected. In this work, the role of C-vacancy complexes on carbon-supersaturation in low temperature bainite is investigated by means of Positron Annihilation Spectroscopy. Results reveal the presence of a significant amount of monovacancies i ...[more]

PMID: 31949280

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Project description:Plastic deformation of low/high density polyethylene (LDPE/HDPE) was analyzed in this work using positron annihilation lifetime spectroscopy (PALS). It was shown that in undeformed LDPE, both the mean ortho-positronium lifetime (τ3) and its dispersion (σ3), corresponding to the average size and size distribution of the free-volume pores of the amorphous component, respectively, were clearly higher than in HDPE. This effect was induced by a lower and less uniform molecular packing of the amorphous regions in LDPE. During the deformation of LDPE, an increase in the τ3 value was observed within the local strains of 0-0.25. This effect was mainly stimulated by a positive relative increase in interlamellar distances due to the deformation of lamellar crystals oriented perpendicular (increased by 31.8%) and parallel (decreased by 10.1%) to the deformation directions. At the same time, the dimension of free-volume pores became more uniform, which was manifested by a decrease in the σ3 value. No significant effect of temperature or strain rate on the τ3 and σ3 values was observed during LDPE deformation. In turn, in the case of HDPE, with an increase in the strain rate/or a decrease in temperature, an intensification of the cavitation phenomenon could be observed with a simultaneous decrease in the τ3 value. This effect was caused by the lack of annihilation of ortho-positonium (o-Ps) along the longer axis of the highly anisotropic/ellipsoidal cavities. Therefore, this dimension was not detectable by the PALS technique. At the same time, the increase in the dimension of the shorter axis of the cavities was effectively limited by the thickness of amorphous layers. As the strain rate increased or the temperature decreased, the σ3 value during HDPE deformation increased. This change was correlated with the initiation and intensification of the cavitation phenomenon. Based on the mechanical response of samples with a similar yield stress, it was also proven that the susceptibility of the amorphous regions of LDPE to the formation of cavities is lower than in the case of amorphous component of HDPE.

Dataset Information

Positron Annihilation Spectroscopy Study of Carbon-Vacancy Interaction in Low-Temperature Bainite.

Publications

Positron Annihilation Spectroscopy Study of Carbon-Vacancy Interaction in Low-Temperature Bainite.

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