Fine-tuning the ductile-brittle transition temperature of Mg_2Si intermetallic compound via Al doping

Brittleness is a dominant issue that restricts potential applications of Mg_2Si intermetallic compounds(IMC). In this paper, guided by first-principles calculations, we found that Al doping will enhance the ductility of Mg_2Si. The underlying mechanism is that Al doping could reduce the electronic exchange effect between Mg and Si atoms, and increase the volume module/shear modulus ratio, both of which are beneficial to the deformation capability of Mg_2Si. Experimental investigations were then carried out to verify the calculation results with Al doping contents ranging from Al-free to 10 wt%. Results showed that the obtained ductile-brittle transition temperature of the Mg_2Si–Al alloy decreased and the corresponding ductility increased. Specifically, the ductile-brittle transition temperature could be reduced by about 100℃. When the content of Al reached 6 wt%, α-Al phase started to precipitate, and the ductile-brittle transition temperature of the alloy no longer decreased.

Atomic modeling for the initial stage of chromium passivation

The well-known anti-corrosive property of stainless steels is largely attributed to the addition of Cr,which can assist in forming an inert film on the corroding surface.To maximize the corrosion-resistant ability of Cr,a thorough study dealing with the passivation behaviors of this metal,including the structure and composition of the passive film as well as related reaction mechanisms,is required.Here,continuous electrochemical adsorptions of OH-groups of water molecules onto Cr terraces in acid solutions are investigated using DFT methods.Different models with various surface conditions are applied.Passivation is found to begin in the active region,and a fully coated surface mainly with oxide is likely to be the starting point of the passive region.The calculated limiting potentials are in reasonable agreement with passivation potentials observed via experiment.

Finite element analysis of stress corrosion cracking for copper in an ammoniacal solution

Finite element analyses including a cohesive zone model （CZM） were conducted to investigate the role of corrosion product films （CPFs） in stress corrosion cracking （SCC） for copper in an ammoniacal solution. It is found that a tensile CPF-induced stress generates near the interface between the CPF and the copper substrate at the substrate side in front of the notch tip for a U-shaped edgenotched specimens. The CPF-induced stress is superimposed on the applied stress to enhance emission and motion of dislocations. The peak opening stress （S11） increases with an increase in CPF thickness and a decrease in CPF Young＇s modulus. Damage mechanics based on the CZM was applied to study the stress corrosion crack initiation and propagation by analyzing the stress redistributions and load-displacement curves. The results show that the crack initiates first in the CPF and then propagates to the copper substrate. The fracture strain of the specimen covered a CPF is lower than that without a CPF. Based on the simulation results, the mechanism of the CPF-induced SCC, which promoted the initiation and propagation of the stress corrosion cracks, was discussed.

First-principles calculation of Aun@(ZnS)(42)(n=6-16)hetero-nanostructure system

The structure stability and electronic and optical properties of a series of Au@ZnS core-shell nanocomposites with different sizes were investigated theoretically by first-principle calculation based on density functional theory(DFT).A series of Aun@(ZnS)(42)structures with different n values from 6 to 16 were optimized and obtained.Based on the core-shell interaction energy and second-order difference of total energy of these structures,it is found that Au(13)@(ZnS)(42)turns out to be the most stable structure.Based on the model of Au(13)@(ZnS)(42),the density of state and charge density difference were studied and provided a deeper understanding of the electronic structures of Au@ZnS.On the other hand,absorption coefficient and dielectric function were investigated to study the optical properties.It is found that an optical absorption peak appears in visible-light region,indicating that the photo-catalytic can be improved prominently due to the optical redshift to visible-light region when forming core-shell structure from ZnS bulk.And the redshift phenomenon accords well with experiment.Furthermore,the electronic structure further confirms the existence of redshift of optical absorption spectrum.

Relationship between Hydrogen Diffusion and Blistering Nucleation and Growth

The formation condition of hydrogen blister in 18Ni maraging steel without any inner or external stress was investigated. The results show that the critical diffusible hydrogen concentration of a blister forming is about 1.4×10^-5 , which is corresponding to the current density of 30 mA/cm^2 during cathodic charging in a sodium hydroxide solution. For a 0.1 cm thick sample, no matter the current density is equal to or much larger than the critical value, it spends at least about 132 h to form a hydrogen blister when hydrogen charging in single direction. It is approxi- mately equal to the time for hydrogen atom to diffuse throughout the sample, which exactly depends on the hydrogen diffusion coefficient and the penetration depth. The very first clear suggestion was reported that the incubation period for hydrogen blister nucleation was necessary. According to the Fick＇s laws, calculations show that the normalized hydrogen concentration in the escaping surface almost reaches 0.96 times of the charging surface, which means that the diffusion almost reaches a dynamic balance. A model was illustrated to describe the competitive relationship between hydrogen diffusion and blister formation.

Correction to:Influence of inclusions on hydrogen-induced delayed cracking in hot stamping steels

Correction to:J.Iron Steel Res.Int.(2019)26:1199-1208 https://d0i.0rg/l 0.1007/S42243-019-00312-z The original version of this article unfortunately contained a mistake.Table 6 was incorrect.The corrected table is given below.The line 11 of page 1205 is revised as“The diffusion coefficient of hydrogen in CSPS is 2.76×10^(-7)cm^(2)/s,which is lower than that of CRS”.