A Mechanism of Carbon-Cluster Strengthening through Atomic Simulations

Abstract

To investigate the reason why low-carbon steels with carbon-clusters shows the maximum strength during low-temperature aging, interactions between an edge dislocation and carbon clusters are performed through molecular dynamics (MD) simulations. Carbon clusters are modeled based on atom probe tomography (APT) observations. To express a transition process of carbon configurations from solid solution state to carbon cluster state to precipitation state during aging process, we reduce a carbon presence area with a fixed number of carbon atoms, i.e., the carbon concentration can be continuously increased. The MD simulations can represent the age hardening/softening tendency observed in the experiment and the carbon cluster state shows the maximum strength where the dislocation passes through the carbon cluster not by the Orowan but by the cutting mechanism. The MD analysis found that partial clusters in the carbon cluster act as the main resistance to dislocation passage; the biased distribution of carbon atoms is also confirmed in the actual observed carbon clusters by APT. A new interaction mechanism between dislocation and carbon clusters is developed based on the phenomena in the MD simulations and the availability is discussed.

Carbon Migration Behavior during Rolling Contact in Tempered Martensite and Retained Austenite of Carburized SAE4320 Steel

“…Dislocations that migrate within α-Fe shear carbon clusters via a cutting mechanism have been experimentally confirmed 39) and predicted via molecular dynamics simulations. 40) Carbon clusters are particles that interact weakly with dislocations, so the repeated passage of dislocations causes the clusters to decompose owing to shear, resulting in the re-dissolution of the carbon in the matrix. Not only the redissolved carbon but also carbon that was initially dissolved in the matrix are believed to migrate easily via dislocations that form the Cottrell atmosphere; therefore, as shown in Fig.…”

Best Papers Awarded in 2021 by <i>Materials Transactions</i>

“…11 (2020) pp. 21392148) 5,13) To investigate the reason why low-carbon steels with carbon-clusters shows the maximum strength during lowtemperature aging, 34) interactions between an edge dislocation and carbon clusters are performed through molecular dynamics (MD) simulations. 35,36) Carbon clusters are modeled based on atom probe tomography (APT) observations.…”

“…4 Prediction of critical shear stresses for dislocation to pass through carbon clusters with different diameters by three types of dislocationcarbon cluster interaction mechanisms. 5,13) Fig. 5 Overview of the prediction method for grain boundary segregation using the nano-polycrystalline grain boundary model.…”

“…(This is a national project started in 2018 for 5 years with the support by Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.) Besides the 4 awarded papers associated with the highentropy alloys, readers can find two papers are for shape memory alloys, 4,11) two for microstructural analyses by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), 4,10) two for simulations 5,6) and two for Mg alloys. 11,12) It should be noted that SEM and TEM are useful tools for microstructural analyses and often become important topics in advanced research areas.…”

“…It is commented that five out of the 11 papers were originally published in Japanese in Journal of the Japan Institute of Metals and Materials, 1317) and these five were translated to English following the rule of Materials Transactions. 5,6,1012) The 11 awarded papers 212) are introduced below with brief summaries provided by the corresponding authors. The development of high entropy alloys (HEAs) for metallic biomaterials (BioHEAs) in the equiatomic TiNb TaZrMo 18) system opened up a frontier in metallic biomaterials.…”