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The stress corrosion cracking (SCC) behaviors at slow strain rate tensile (SSRT) test of AISI301L stainless steel laser-MIG welded joints in 3.5 wt.% NaCl solution at 20C, 40C and 60C were investigated. The results showed that the weld metal composed of as-cast with -Fe and austenite. The base metal (BM) and heat affected zone (HAZ) contained strain-induced M phase. The stress and strain decreased with the increasing temperature. The SCC cracks are initiated by anodic dissolution at 20C. Besides the anodic dissolution mechanism, hydrogen-induced SCC mechanism had appeared in 3.5 wt.% NaCl solution at 40C and 60C. [ABSTRACT FROM AUTHOR]

The Al-Zn-Mg aluminum alloy A7N01S-T5 used in high speed trains was designed by orthogonal method. The effect of elemental composition on the tensile properties and fracture toughness has been investigated. The alloys with different compositions were tested by tensile and three point bending tests: the range analysis results showed that the compositions of Zn and Mg were the main factors that affect the strength and plasticity of the alloys. The tensile testing results showed that the #1 alloy Al-4.34Zn-1.43 Mg-0.27Mn-0.13Cr-0.12Zr-0.07Ti had the best combination of tensile strength, yield strength and elongation, which were 415 MPa, 378 MPa and 13.5%, respectively. Furthermore, this alloy showed the excellent ability to hinder the crack propagation with a value of J0.2BL(12) = 23.37 kJ·m-2. The microstructure, grain size, compositions and fracture characteristics of the alloy were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), backscattered electron diffraction (EBSD) and transmission electron microscopy (TEM). The results indicated that the strength is mainly determined by the volume fraction, size and distribution of precipitated n(MgZn2) phase. The discontinuous distribution of n(MgZn2) phase, narrow precipitated-free zones (PFZs) and fine grain size played important roles to obtain high fracture toughness. [ABSTRACT FROM AUTHOR]

Humidity is a key factor affecting the quality of welded joints for high-speed trains. Welded joints made of A7N01S-T5 aluminum alloy were fabricated under five relative environmental humidity conditions: 50%, 60%, 70%, 80%, and 90%. The microstructures of the welded jointswere examined using an optical microscope and porosity quantities were calculated from macrographs using image analysis software. The fatigue strength of the welded joints was measured with high-cycle fatigue testing. It was determined that the microstructures and grain sizes in the weld zone and heat-affected zone (HAZ) were similar under different humidity conditions; however, porosity distribution varied significantly. Porosity quantity increased as humidity increased. The weld joint made under the 90% humidity condition had the highest quantity of porosity, while the weld joint made under the 70% humidity condition had the maximum diameter and area of porosity. The weld joint made under the 70% humidity condition also had the lowest fatigue strength. Fracture morphology of fatigue samples showed that the weld joint made under the 70% humidity condition had brittle fracture, while others showed ductile fracture. Therefore, 70% humidity was determined to be the critical humidity level for welding joints in high humidity environment. [ABSTRACT FROM AUTHOR]

We use a combination of conventional density functional theory (DFT) and post-DFT methods, which include the local density approximation plus Hubbard U (LDA+U), PBE0, and self-consistent GW, to study the electronic properties of Ni-substituted PbTiO3 (Ni-PTO) solid solutions. We find that LDA calculations yield unreasonable band structures, especially for Ni-PTO solid solutions that contain an uninterrupted NiO2 layer. Accurate treatment of localized states in transition-metal oxides such as Ni-PTO requires post-DFT methods. B-site Ni/Ti cation ordering is also investigated. The B-site cation arrangement alters the bonding between Ni and O, and therefore strongly affects the band gap (Eg) of Ni-PTO. We predict that Ni-PTO solid solutions should have a direct band gap in the visible light energy range, with polarization similar to the parent PbTiO3. This combination of properties makes Ni-PTO solid solutions promising candidate materials for solar energy conversion devices. [ABSTRACT FROM AUTHOR]

Nanostructured and ultrafine WC–17Co coatings have been prepared by means of the high velocity oxyfuel (HVOF) technique. The structures of the two feedstock powders were analysed. The wear resistances at the elevated temperature (600°C) of the two coatings were compared using GCr15 steel as a counterpart in sliding wear tests. The results show that the WC particles are of nanosize, ranging from 50 to 500 nm. Finer subparticles of 2–5 nm are also found, composed of the nanosized WC particles. These subparticles can act as crystallising nuclei and make the grains much finer during the HVOF spraying process, which is beneficial to the formation of nanostructure in the coating. The wear resistance and fracture toughness of the nanostructured coatings at elevated temperatures are better than that of ultrafine coatings. [ABSTRACT FROM AUTHOR]

Composite structures made of 2 mm-thick titanium and 10 mm-thick carbon steel are widely used in infrastructures such as long-distance gas transportation. However, cracking, which is caused by intermetallic compounds (ICs), is a dominate failure mode in welds of this structure. Thus, a common way to improve the in-service life of is reduce the number of ICs. In this paper, we employ a novel hybrid welding method to fabricate composite structures of TA2 titanium and Q235 carbon steel. Specifically, Ti and carbon steel is welded by laser and double Cold Metal Transfer (CMT) welding, respectively. The microstructure near the interface of Ti and steel is then examined using SEM, EBSD, EDS, with emphasis on the ICs in terms of chemical elements and morphologies. Results show that FeTi and Fe2Ti are the main ICs near the interface, and responsible for the failure of the welds. The effect of welding heat input on the formation of ICs is investigated as well. Results show that ICs are smaller when the heat input is low. Under low heat input circumstance, the tensile strength of the weld can reach up to 420 MPa. [ABSTRACT FROM AUTHOR]

The coupling model of temperature-phase transformation-mechanics is constructed in this paper. The effect of solid state phase transformation and different hardening models on the residual stress distribution of S355J2W welded joints have been studied with finite element method (FEM) simulation. The microstructure, micro hardness and residual stress of welded joints are also studied. It has been shown that the microstructure of weld seam is composed of bainite structure with little martensite, while the base metal is ferrites and pearlites. The simulation results by FEM were in good accordance with the X-ray results. The maximum tensile residual stress is 463 MPa in the weld. The tensile residual stress was decreased with the larger distance to the weld. [ABSTRACT FROM AUTHOR]

This study has analyzed the welding joint of carbon fiber reinforced plastics (CFRP) and aluminum alloys. The surface of CFRP and 5083 Al alloy was modified by electroplating with nickel at first. Then the effect of electroplating parameters on coating was explored. SEM images revealed that the coating gradually became well but then began to fall off with the current density and the plating time increased. CFRP and aluminum alloys were brazed at 285 ∘ C and held for 20 s. Shear test was used to evaluate the strength of the joint and the strength was probably 7.56 MPa. SEM and EDS tests showed that there existed diffusion of the elements in the welding process and the joint reached the bonding of atomic or molecular sizes. Thus, this experiment achieved the tight brazing joining between thermoset CFRP and aluminum alloys providing the joining method of the application for CFRP. [ABSTRACT FROM AUTHOR]

In this paper, we study the droplet transition behavior of narrow gap laser wire filling welding under the condition of changing welding speed and wire feeding speed, and it was observed by high-speed photography. It was found that with the increase of welding speed, the frequency of droplet transfer was reduced and the transition period was prolonged. With the increase of wire feeding speed, the wire was not fully melted and finally inserted into the molten pool. [ABSTRACT FROM AUTHOR]

Abstract: A 9‐week feeding experiment was conducted to investigate the effects of dietary bile acids (BAs) on juvenile genetically improved farmed tilapia (GIFT) (Oreochromis niloticus) based on the evaluations of growth performance and parameters relevant to lipid metabolism. Each of five vegetable protein‐based diets containing BAs at a level of 0, 0.05, 0.15, 0.45 or 1.35 g/kg diet was fed to three replicates with 40 fish (8.2 g per fish). The results showed that weight gain (WG) increased significantly with the increase in BAs from 0 to 0.15 g/kg diet and then decreased significantly at a higher BA supplementation. Dietary BAs significantly reduced the crude lipid content in the whole body, muscle and liver tissue of GIFT. Fish fed diet with 1.35 g BAs/kg diet developed serious nuclear migration and vacuolization in hepatocytes. Gall bladder appeared to contain white solid and has fragile capsules. Dietary BA supplementation had significant effects on serum biochemical indices and activities of lipid metabolism enzymes in liver and intestine. In conclusion, dietary bile acid supplementation (0.15 g/kg) can facilitate the lipid metabolism and therefore promote the growth of tilapia. However, overdosed dietary BAs induced gallstone development, disrupted lipid metabolism and depressed the growth performances of GIFT. [ABSTRACT FROM AUTHOR]

Through investigating the corrosion fatigue crack initiation behavior of A7N01P-T4 aluminum alloy welded joints in 3.5 wt.% NaCl solution, corrosion fatigue crack initiation life is formulated as and the mechanism of corrosion fatigue crack initiation is proposed. SEM and TEM tests revealed that several corrosion fatigue cracks formed asynchronously and the first crack does not necessarily develop into the leading crack. The uneven reticular dislocations produced by fatigue loading are prone to piling up and tangling near the grain boundaries or the second phases and form the 'high dislocation-density region' (HDDR), which acts as an anode in microbatteries and dissolved to form small crack. Thus the etching pits, HDDR near the grain boundaries and second phases are confirmed as the main causes inducing the initiation of fatigue crack. [ABSTRACT FROM AUTHOR]

The hydrogen-induced stress corrosion cracking (HISCC) behavior of SUS301L-MT stainless steel laser-arc hybrid welding (LAHW) joints was investigated using slow strain rate tensile (SSRT) method in 3.5 wt.% NaCl solution under different cathodic potentials. With the negative shift of applied potentials from open circle potential (OCP) to −1400 mV SCE , the HISCC susceptibility index ( I SSRT ) decreased from 0.15 (OCP) to 0.06 (−400 mV SCE ), then increased to 0.28 (−1400 mV SCE ). The specimens tested in air and under OCP to −800 mV ruptured in weld metal zone with ductile features of dimples. While with the potential turned more negative, the specimens ruptured in base metal zone with brittle features of transgranular cleave in martensite, intergranular failure and secondary cracks [Chen et al., Int. J. Adv. Manuf. Technol.73, 1695 (2014)]. [ABSTRACT FROM AUTHOR]