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The early corrosion development of ultra-low carbon bainitic (ULCB) low alloy steel in NaCl solution was studied by ex situ imaging of corrosion morphology and in situ monitoring of microarea current density and potential, and the corrosion mechanism from initial localized corrosion to uniform corrosion was interpreted. The results indicate that the corrosion development of ULCB steel from initial localized corrosion around inclusions to the uniform corrosion on the whole steel surface is controlled by the galvanic couple effect between different phases resulting from their electrode potential difference in electrolyte solution. The early localized corrosion of steel matrix is initiated and accelerated by the galvanic couple effect between MnS inclusions and steel matrix to form the initial corrosion gaps and the circular corrosion spots around inclusions. The ohmic drop caused by solution resistance influences the acceleration effect of the galvanic couple. With the separation of inclusion from steel matrix, this galvanic couple effect becomes invalid, which results in the expansion from localized corrosion to uniform corrosion. The microgalvanic couple between martensite/residual austenite (M/A) islands and bainite ferrite also accelerates the anodic dissolution of bainite ferrite phase; however, its acceleration corrosion effect is much weaker than that caused by MnS inclusion. [ABSTRACT FROM AUTHOR]

Microstructure and texture evolution of an Mg-7Gd-5Y-1Nd-0·5Zr (EW75) extruded alloy after normal rolling (NR) or cross-rolling (CR) up to three passes with 20% reduction per pass were investigated. The results showed that microstructures with finer grains and weaker textures were developed due to the strain state change during cross-rolling between passes in comparison with the conventional normal rolling. It is suggested that, fewer twins and more secondary particles benefit the dynamic recrystallisation and weaken the texture. Tensile tests conducted at room temperature showed that the material subjected to cross-rolling (CR) after three passes resulted in an enhanced ductility and almost isotropic strength, which mainly attributed to the finer grain structure and texture modification with the (0002) poles distributing more homogeneously. [ABSTRACT FROM AUTHOR]

The tensile testing bars of the Mg–2.7Nd–0.6Zn–0.5Zr (wt.%) alloy were prepared by sand casting. The effect of solution temperature and aging time on the microstructures and mechanical properties were investigated. The as-cast alloy was composed of α magnesium matrix and Mg12Nd eutectic compounds. After solution treatment at 500 °C for 18 h, the volume fraction of eutectic compounds decreased from ∼7.8% to ∼2.3%, and some small Zr-containing particles were observed to precipitate at grain interiors. As the solution temperature increased to 525 °C for 14 h, most of the eutectic compounds dissolved into the matrix. Peak-aged at 200 °C for 12 h, fine β″ particles was the dominant strengthening phase. The yield strength, ultimate tensile strength and elongation in the peak-aged condition were 191 MPa, 258 MPa and 4.2%, respectively. Moreover, the Mg–2.7Nd–0.6Zn–0.5Zr alloys under different heat treatment conditions exhibited different tensile fracture modes. [ABSTRACT FROM AUTHOR]

A FeCrMoMnWBCSi amorphous metallic coating was prepared by using high-velocity oxy-fuel spray. The influence of processing parameters on microstructure, porosity level, amorphous phase fraction and corrosion behaviour of the coatings was characterised by scanning electron microscopy, X-ray diffraction, differential scanning calorimeter and electrochemical methods. The results indicated that the microstructures of the coatings were sensitive to the spray parameters considerably. Porosity and unmelted particle proportion decreased with the oxygen/fuel (O/F) ratio and increased with the powder feed rate. The trend of oxides content was opposite to the porosity and unmelted particle proportion. The coatings obtained with higher O/F ratio and lower powder feed rate exhibited higher hardness. The low coating hardness was mainly due to the high porosity especially when the porosity was higher than 1.21%. The spraying parameters strongly affected the amorphous phase fraction. There was a critical passive current density for balancing the porosity and the amorphous phase fraction. Corrosion resistance is dominant by the amorphous phase fraction when the porosity is less than 1.21%, while by porosity when it is higher than that. Open-circuit potential, potentiodynamic polarisation and electrochemical impedance spectroscopy results showed that the coatings obtained with the O/F ratio of 4.2 and the powder feed rate of 40 g/min exhibiting the best corrosion resistance in 1 wt% sodium chloride solution. [ABSTRACT FROM AUTHOR]

High temperature and high pressure immersion tests in an autoclave were employed to study the corrosion behaviour of X52 pipeline steel in aqueous solutions containing high concentrations of H2S. The corrosion products generated were characterised using scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. It was seen that at a constant H2S concentration of 22 g/l, the corrosion rate increased with increasing temperature up to 90°C, thereafter decreased at 120°C and slightly increased again at 140°C while the corrosion rate increased with H2S concentration at a temperature of 90°C. When the temperature and H2S concentration increased, the corrosion product converted from iron rich to sulphur rich products in the following sequence: mackinawite→troilite→pyrrhotite, where the microstructure and stability of the corrosion products had an important effect on the corrosion rate. The corrosion film was formed through the combination of the outward diffusion of Fe2+ ions and the inward diffusion of H2S and HS- species. [ABSTRACT FROM AUTHOR]

Characterizations of the microstructure and mechanical property of the fusion boundary region of an Alloy 182-A533B low alloy steel (LAS) dissimilar weld joint were conducted. The existence of type-II boundary that parallels to the fusion boundary in the dilution zone (DZ) of Alloy 182 within a distance of about 50 μm was observed. The chemical composition transition was found in the narrow zone between the type-II and the fusion boundaries. Highest hardness was also found in this narrow zone in the fusion boundary region, implying a high residual strain level in the narrow zone. Lath martensite was observed in both sides of the type-II boundary in DZ, suggesting the localized enrichment of Fe and C adjacent to the type-II boundary due to the diffusion from LAS to DZ. Massive precipitations of carbides were observed on the type-II boundary but not on the fusion boundary. In addition, the orientation relationship at the fusion boundary between the lath martensite in the heat-affected zone in LAS and the austenite in the DZ was found to be Bain, K–S and N–W relationships. [ABSTRACT FROM AUTHOR]

Abstract: Samples prepared from as-extruded AZ61 plates were utilized in an axial fatigue crack propagation test. An investigation on fatigue crack propagation (FCP) behavior of as-extruded magnesium alloy AZ61 was made. The influences of the artificial ageing heat treatment or microstructure and loading frequency on FCP rates were discussed. The results demonstrated that the FCP rates of the AZ61 alloys were significantly affected by the microstructure and loading frequencies as well. [Copyright &y& Elsevier]

Highlights: [•] Basal precipitates formed during in-air cooling process after solution treatment. [•] Basal precipitates led to weak ageing hardening response and low strength. [•] Fine grains and compressive stress in casting surface result in 30MPa higher YS. [•] As tensile tested at high temperature, the NZ31 alloy exhibits serrated flow. [Copyright &y& Elsevier]

Abstract: Pure magnesium, Mg–Y (1, 3, 5) and Mg–1Zn alloy (nominal composition, in wt%) were selected to examine the influence of alloying on the microstructure, texture and mechanical properties of Mg plates after hot-rolling and subsequent annealing. It was found that the maximum intensity of the rolled texture was markedly decreased with increasing Y additions but slightly increased by the Zn addition, in comparison with that of pure Mg. The texture weakening efficiency of Y addition declined with increasing Y concentration. The weakening of texture in Mg–Y alloys was attributed to the solute-driven effect, manifest as solute segregation at grain boundaries, which was evidenced by the TEM examination. Tensile testing revealed that the Mg–1Y alloy exhibited the highest elongation-to-failure of 30% at room temperature, and EBSD analysis suggested that the observed high room-temperature ductility was attributed to the weakened texture which favored the operation of the basal slip and tensile twinning. [Copyright &y& Elsevier]

Abstract: AZ80 cast magnesium alloy has been fabricated by a combination of ECAE (equal channel angular extrusion) and subsequent forging processing to investigate the effect of second forging processing on the evolution of microstructure, texture and tensile properties. The AZ80 alloy produced by this process exhibited the ultimate tensile strength (UTS) of 434MPa, yield strength (YS) of 347MPa, and elongation-to-failure of 6%. The observed high strength in this sample has been ascribed to the effect of grain refinement and the formation of sharp basal texture by the subsequent forging processing. The contribution of second-phase particles to the mechanical properties was also discussed in this paper. [Copyright &y& Elsevier]

Abstract: The grain boundary misorientation and dislocation structure for Alloy 690TT under mono-tension and biaxial tension at room temperature was investigated by using electron backscatter diffraction technique (EBSD) and transmission electron microscopy (TEM). The strain amplitudes for mono-axial tension were X3%, X5%, X7% and X9% respectively, and biaxial tension followed X3%, X5%, Y3%, X7%, Y7%, X9%, and Y9% tensile strains. The results showed that the mono-tension could decrease the amount of Σ3 twin boundaries, increased the amount of the low angle boundary and random grain boundary. The biaxial tension recovered some random boundaries partially back to Σ3 boundaries. Tension strains in Y direction restricted the decease of Σ3 boundaries. For the mono-tension specimen the dislocation had high energy pile-ups structure and for the biaxial tension specimen had low energy tangle structure. According to mechanochemical effect theory, the biaxial tension could retard stress corrosion cracking of Alloy 690TT. [Copyright &y& Elsevier]

The low chromium ferritic stainless steel, 410S, as a candidate control rod drive mechanism (CRDM) material used in nuclear power plants, was subjected to accelerated thermal aging at 400 °C in air up to an exposure period of 10,000 h (∼417 days). A series of analytical techniques including optical microscope (OM), electron back scatter diffraction (EBSD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and 3D atom probe tomography (3D-APT) were used to characterize the evolution of the microstructure with thermal aging time, whilst a couple of tests (i.e., hardness, Charpy impact and tensile tests) were employed to link the changes of mechanical properties at different thermal aging times with the microstructure. After ≤3000 h thermal aging treatment, Cr-rich α′ phase formed near the ferritic grain boundaries, leading to minor change in the hardness and strength of 410S but sharp decrease in impact energy. When the thermal aging time increased to 10,000 h, the formation of Cr-rich α′ phase spread from near the ferritic grain boundary to the inside of ferritic grain and the growth of carbides precipitated led to the slight increase in the hardness and strength but the decrease in the impact energy and plasticity. Under these circumstances, the decrease of free substitutional atoms (i.e., Cr) caused by the formation of Cr-rich α′ phase and the growth of carbides changed the dynamic strain aging type from type B to type A. [ABSTRACT FROM AUTHOR]

Unlike the recrystallization-induced shear band mechanism which has been well accepted for the RE-free Mg alloys during rolling, an understanding of deformed microstructure evolution (twin mode/variant selection and dislocations) at different strains is crucial for interpreting the shear band mechanism in the RE-containing Mg alloys upon hot rolling. In this study, a Mg-1.1Zn-0.76Y-0.56Zr alloy ingot was subjected to hot rolling at 440 °C with single-pass reductions of 10–50%, and the microstructure evolution and texture development of this hot-rolled plates at different reductions were investigated, with aim to disclose the roles of different types of twins/variants and dislocation mechanisms in the shear band (SB) formation and their correlation with the macro-texture characteristics. As the dominate twinning mode for most parent grains at lower reductions, and the primary {10−12} extension twins/variants together with basal slip activated in twins contribute to formation of basal texture in the twinned grains, thus subsequently facilitating the operation of secondary {10−11} and {10−13} compression twins and following {10–12} twins. Afterwards cross-grain boundary (GB) paired twins for compression twin and their double twins were frequently observed at the nearby basal-oriented parent grains with low misorientation (≤34.5°), which should correspond to the predecessor of SBs. Further EBSD observation at higher reductions (R0.4 and R0.5) reveals that most of the banding structures are distributed homogenously and are likely transformed from the {10–11}-{10–12} twins, which are the predominant twin types under such state. The 'RD-split' textures start to be formed at lower reductions (R0.3) and keeps stable at higher reductions (R0.4-R0.5), which were explained by the correlations with some variant pairs of {10–12} twins and/or {10–11}-{10–12} twins predicted by Schimid factor analysis as well as shear bands. Nevertheless, the contributions of slip to the 'RD-split' texture could be ignored on basis of corresponding EBSD analysis and reappearance of such texture after rolling at a low temperature (170 °C). • Primary {10-12} twins/variates and basal slip activated in twins contribute to basal texture formation in twinned grains. • Secondary compression twins and ternary {10-12} twins were mainly activated after basal orientation formation. • Paired twins for double twins at the nearby basal-oriented grains are likely the predecessor of shear bands. • The 'RD-split' texture was mainly correlated with {10-12} twins, double twins and shear bands with different activity. [ABSTRACT FROM AUTHOR]

Abstract: The high-cycle fatigue behavior of Ti46Al8Nb cast alloy with fully lamellar microstructure has been studied at room temperature, 400°C, 600°C and 750°C. The result shows that temperature has great influence on the fatigue strength of Ti46Al8Nb alloy. Compared with that at room temperature, fatigue strength is significantly reduced at 400°C. However, at 600°C the fatigue strength is slightly improved. A further increasing of temperature up to 750°C gives rise to larger scatter of fatigue life and produces a more flat S-N (stress amplitude versus number of cycles to failure) curve. Fractographic observations indicate that fatigue cracks initiate at the interior casting defects and the lamellar colonies near the surface. Mixed modes of delamination, translamellar fracture and stepwise fracture are observed on the fracture surfaces at all temperatures. [Copyright &y& Elsevier]

Abstract: High-velocity oxy-fuel-sprayed FeCrMoMnWBCSi amorphous metallic coatings were sealed with sodium orthosilicate (Na3SiO4), aluminium phosphate (AlPO4), and cerium salt sealants. The microstructure of the sealed coatings was characterised by scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction. Corrosion behaviour was examined using electrochemical methods of potentiodynamic polarisation, cyclic polarisation, electrochemical impedance spectroscopy, and Mott–Schottky tests. The results indicated that the uniform corrosion resistance of the three sealed coatings was enhanced greatly, and the passive current densities were decreased by one order of magnitude after the sealing treatments. The AlPO4 sealant can penetrate the coatings by no less than 50μm and enhance their hardness, which exhibited a more uniform corrosion resistance, fairly good pitting corrosion resistance, and can be applied in long-term corrosive and/or abrasive environments. The cerium salt-sealed coating showed better pitting corrosion resistance but inferior corrosion resistance in the local regions of micro-cracks, which was practically used for temporary corrosion protection. The Na3SiO4-sealed coating showed better uniform corrosion resistance and inferior pitting corrosion resistance, which can be applied in short-term corrosion environments. The stability of the passive film affected the corrosion behaviour of the sealed coatings. The AlPO4-sealed coating performed better as a protective passive film during the long-term immersion test for a lower defect concentration and a more protective passive film. [Copyright &y& Elsevier]

Abstract: The distributions of residual strains and grain boundary microstructures were investigated in the heat-affected zone (HAZ) of a weld joint between Alloy 690TT (thermally treated) and Alloy 52 using electron backscatter diffraction (EBSD) and transmission electron microscopy. The distributions of residual strains were examined at the top, middle, and root of the HAZ using EBSD to obtain the grain average misorientation. The weld residual strain increased from the top of the weld to the root while the peak of strain approached the fusion boundary (FB) in the HAZ. The maximum strains and their distances to the FB in the top, middle, and root was 15% and 800μm, 17% and 600μm, 20% and 200μm, respectively. The fraction of Σ3 special boundaries was about 40% in the HAZ but with obvious deviations from the structure of ideal boundaries. The HAZ region is considered to sustain the highest susceptibility to SCC at the root of the weld. [Copyright &y& Elsevier]

Abstract: The deformation and dislocation microstructure of a [013] double-slip-oriented copper single crystal under a symmetric tension–compression cyclic load were characterized at room temperature in open-air and a neutral 0.5M NaCl aqueous solution, respectively. The surface morphology of deformed specimens and the dislocation structures at saturation stage of cyclic deformation were observed using scanning electron microscopy (SEM) by the electron channeling contrast (ECC) technique and transmission electron microscopy (TEM). The results show that the saturation dislocation structures during the corrosion fatigue in the 0.5M NaCl aqueous solution mainly consist of labyrinth, wall and vein dislocation microstructures, as well as deformation twins, which differ from the wall and vein dislocation structures in open-air environment. More importantly, here we report TEM observations that provide evidence of deformation twinning in the [013] double-slip-oriented copper single crystal during corrosion fatigue at room temperature and a very slow strain rate, which was generally only observed at sub-ambient temperature and/or high strain rate conditions. [Copyright &y& Elsevier]