Mechanism of subsurface microstructural fatigue crack initiation during high and very-high cycle fatigue of advanced bainitic steels

Advanced bainitic steels with the multiphase structure of bainitic ferrite, retained austenite and marten-site exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue (HCF/VHCF) regimes. The subsurface microstructural fatigue crack initiation, referred to as "non-inclusion induced crack initiation, NIICI", is a leading mode of failure of bainitic steels within the HCF/VHCF regimes. In this regard, there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during VHCF. To address this aspect, we have developed a novel approach that explicitly identi-fies the knowledge gap through an examination of subsurface crack initiation and interaction with the lo -cal microstructure. This was accomplished by uniquely combining electron microscopy, three-dimensional confocal microscopy, focused ion beam, and transmission Kikuchi diffraction. Interestingly, the study indi-cated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels, includ-ing two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI, which resulted in the different distribution of fine grains in the crack initiation area. The fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain boundaries. The formation of fine grains assisted the advancement of small cracks. An-other important aspect discussed is the role of retained austenite (RA) during cyclic loading, on crack ini-tiation and propagation in terms of the morphology, distribution and stability of RA, which determined the development of localized cyclic plastic deformation in multiphase structure. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology

Novel process of coating Al on graphene involving organic aluminum accompanying microstructure evolution

A novel chemical reduction of organic aluminum for coating Al on the graphene surface is proposed. During the process, Al powder reacted with the (C2H5)2Br solution to produce (C2H5)3Al solution, followed by gradual decomposition of (C2H5)3Al into Al atoms. Al atoms gradually deposited on the surface of graphene, nucleated, grew up, until Al coating was formed on the surface of graphene. With the increase of reaction temperature, the decomposition rate of (C2H5)3Al increased, which was beneficial to the formation of Al atoms and Al coating. The reducing agent, NaH, promoted the reaction and formation of Al coating. When the reaction temperature was optimized to 100 °C, and the reaction time was 1.5 h, with NaH added to the solution, high quality Al-coated graphene was obtained

Resistance variation of conductive ink applied by the screen printing technique on different substrates

This research study focuses on the application of conductive ink by the screen printing technique to evaluate the potential of creating printed electrodes and to investigate the effect of washing upon electrical resistance and flexibility. Two conductive inks were applied by a conventional screen printing method on four different textile substrates, 100% cotton, 50%/50% cotton/polyester, 100% polyester and 100% polyamide. The inks were also applied on a multifibre fabric. Atmospheric plasma treatment was applied to improve the adhesion to the samples, and the resistance values were compared with those of non-treated samples. The values were measured before and after cleaning and washing tests, which were performed to simulate domestic treatment for garments to predict the behaviour of the inks after normal usage of the fabrics. Comfort properties like stiffness of the fabrics were also evaluated after five and 10 washing cycles. It was observed that PE 825 ink forms a thicker film on the fabric surface, contributing to the loss of flexibility of the textile. However, PE 825 ink also produced the best results in terms of durability and lower values of resistance. Polyamide fabrics lost their conductive property after five washing cycles due to weak bonding between the ink and the fibres, whereas cotton fibres provided the best results.This work is financed by Project“Deus ex Machina”, NORTE-01-0145-FEDER-000026, funded by CCDRN, through Sistema de Apoio à Investigação Cientifica e Tecnológica (Projetos Estruturados I&D&I) of Programa Operacional Regional do Norte, from Portugal 2020 and by Project UID/CTM/00264/2019 of 2C2T –Centro de Ciência e Tecnologia Têxtil, funded by National Founds through FCT/MCTES.Derya Tama thanks FCT for fellowship 2C2T-BPD-08-2017