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

Rosalia Rementeria,Ricardo Domínguez-Reyes,Francisca G Caballero,Carlos Garcia-Mateo,Carlos Capdevila

doi:10.1038/s41598-020-57469-x

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.

Highlights

Since the quantification of solid solutions in APT datasets is not trivial[11,12], the APT analyses approach was recently reconsidered[13] finding that the amount of carbon that remains in solid solution in bainitic ferrite is significantly smaller than that derived from the c/a ratio of bct bainitic ferrite as determined by diffraction studies
Each sample was austenitized at 900 °C, for 15 min and subsequently cooled at 50 °C/s to the bainite reaction temperature, between 220 and 300 °C, held for enough time to ensure the completion of the transformation, and subsequently quenched to room temperature
Bainitic structures are encoded as Bx, where x is the bainite transformation temperature, while the pearlite and martensite structures are encoded as pearlitic structure (PER) and MAR, respectively (See Table 1)

Summary

Introduction

Since the quantification of solid solutions in APT datasets is not trivial[11,12], the APT analyses approach was recently reconsidered[13] finding that the amount of carbon that remains in solid solution in bainitic ferrite is significantly smaller than that derived from the c/a ratio of bct bainitic ferrite as determined by diffraction studies. For each of the structures, more than 106 single annihilation events were recorded in order to obtain the complete positron lifetime spectrum N(t), N(t) www.nature.com/scientificreports where the k different components contributing to the positron trapping with 2 source corrections components in the spectra with the individual lifetimes τi, and intensities Ii. Results in Table 1 were obtained from data fitting to Eq (1) by minimizing the Chi-square function defined as: Χ2

Results

Conclusion