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The influence of artificial ageing on the corrosion behaviour of Cu-4 wt.% Ti alloys in 3.5 wt.% NaCl solution was studied. Corrosion tests showed that ageing treatment changed the corrosion morphology of the alloys. All specimens were susceptible to both intergranular and pitting corrosion. The pitting corrosion susceptibility decreased with increasing ageing time. In particular, the presence of abundant cellular β-Cu 4 Ti precipitates refined microstructures in specimen aged at 773 K for 24 h, providing “enveloping effect” that dramatically improved the corrosion resistance. The corrosion resistance of the aged Cu-4 wt.% Ti alloys followed the order: over-aged > peak-aged > early-aged > solution treated. [ABSTRACT FROM AUTHOR]

Fe and Fe-Cr (Cr = 10–16 at.%) specimens were neutron-irradiated at 300 °C to 0.01, 0.1 and 1 dpa. The TEM observations indicated that the Cr significantly reduced the mobility of dislocation loops and suppressed vacancy clustering, leading to distinct damage microstructures between Fe and Fe-Cr. Irradiation-induced dislocation loops in Fe were heterogeneously observed in the vicinity of grown-in dislocations, whereas the loop distribution observed in Fe-Cr is much more uniform. Voids were observed in the irradiated Fe samples, but not in irradiated Fe-Cr samples. Increasing Cr content in Fe-Cr results in a higher density, and a smaller size of irradiation-induced dislocation loops. Orowan mechanism was used to correlate the observed microstructure and hardening, which showed that the hardening in Fe-Cr can be attributed to the formation of dislocation loops and α′ precipitates. [ABSTRACT FROM AUTHOR]

The microstructural evolution in ferrite and austenitic in cast austenitic stainless steel (CASS) CF8, as received or thermally aged at 400 °C for 10,000 h, was followed under TEM with in situ irradiation of 1 MeV Kr ions at 300 and 350 °C to a fluence of 1.9 × 10 15 ions/cm 2 (∼3 dpa) at the IVEM-Tandem Facility. For the unaged CF8, the irradiation-induced dislocation loops appeared at a much lower dose in the austenite than in the ferrite. At the end dose, the austenite formed a well-developed dislocation network microstructure, while the ferrite exhibited an extended dislocation structure as line segments. Compared to the unaged CF8, the aged specimen appeared to have lower rate of damage accumulation. The rate of microstructural evolution under irradiation in the ferrite was significantly lower in the aged specimen than in the unaged. This difference is attributed to the different initial microstructures in the unaged and aged specimens, which implies that thermal aging and irradiation are not independent but interconnected damage processes. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the atmospheric corrosion behaviour of ingot and as-extruded AM60 Mg alloys in a polluted city. The corrosion rate of the ingot samples was higher than that of the extruded samples. The size of dust particle conglomerates adsorbed on the sample surfaces was related to the pit sizes. The main corrosion products of both alloys included MgSO4·6H2O and MgSO3·6H2O. The extruded samples had more homogeneous structures and less second-phase contents compared with the ingot samples. As a result, the corrosion films formed on the extruded samples had better protective effects than those formed on the ingot samples. [Copyright &y& Elsevier]

Abstract: A gradient structure was produced in a pure copper plate by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer was reduced to nanoscale and the grain size increased gradually along the depth of the treated sample. In situ transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) observation was performed on the nanocrystalline copper after implantation of carbon. Carbon atoms first precipitated along the edges of the copper substrate or at the surface, then formed amorphous carbon layers. Subsequently, onion-like fullerenes were formed under electron-beam irradiation. The effects of ion implantation, electron beam irradiation, nanostructure of the substrate and interaction of C and Cu atoms on the formation of the onion-like fullerenes are discussed. [Copyright &y& Elsevier]

Abstract: In this paper, microstructures and properties of die casting components with various thicknesses made of AZ91D alloy have been investigated by means of scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM), etc. It is concluded that mechanical properties of the die casting components mainly depend on grain size of α-Mg phase. At the same time, however, the voids formed by entrapping air during die casting process have a remarkable detrimental effect on the mechanical properties. To what extent the effect is caused is determined by quantity, size and shape of the voids, which are related to the thicknesses and position of the component in die. Nanometer particles found on the wall of the voids are magnesium oxide compounds, which are formed when oxygen from the entrapped air reacts with magnesium during die casting process. The compounds have no obvious effect on the mechanical properties even though there is possibly volume change present to form other compounds in the course of the components’ being used. [Copyright &y& Elsevier]

Abstract: In this paper, the microstructures of a thin-wall die-cast commercial magnesium (Mg) alloy, aged at 200°C for various times, were investigated using transmission electron microscopy. A martensite-like phase was observed. The crystal lattice parameters of this phase are a =0.30948nm, c =0.50498nm, and axial ratio c/a =1.6314. Orientation relationship of the martensite-like phase and the parent has been determined as , and or . The driving force of the possible martensitic transformation (MT) might came from the residual microstructure stresses left during die-cast process. [Copyright &y& Elsevier]

This study aimed to develop a microstructure-based mechanistic approach to address the long-term thermal aging effect on yield stress and ultimate tensile strength and to provide a physical basis for developing thermal aging factors for G91 for a design life of 60 years. Several heats of G91 steel were examined. Controlled aging experiments were conducted on two heats at temperatures of 550, 600, and 650 °C for times up to ~64,000 h. Specimens were also taken from archived creep-tested specimens of G91 and from a tube removed from the Kingston coal-fired power plant to obtain data that cover a wide range of temperatures and for aging times up to 155,000 h. Thermal aging caused significant subgrain recovery, coarsening of M 23 C 6 carbides at subgrain boundaries and MX carbonitrides within subgrains. The intermetallic Laves phase forms during aging and grows rapidly. The growth rate of the subgrain width and MX mean size during thermal aging were described by kinetic models. Thermal aging results in the reductions in the yield stress and the ultimate tensile strength of G91. The effects of thermal aging on the reductions in yield stress and ultimate tensile strength were well described by the microstructure-strength model that considers three superimposed strengthening mechanisms, namely, sub-boundary strengthening, MX precipitation hardening, and Mo solid solution strengthening. The model was independently validated by the ASME Code values and is being used by the ASME to develop the aging-induced strength reduction factors for G91 steel for a design life of 60 years. [ABSTRACT FROM AUTHOR]

Surface-porous Mg–Al alloys with different microstructures were fabricated via a new method of electrochemical dealloying in a neutral 0.6M NaCl solution. A bimodal porous structure with 47.57 ± 11.43 μm large pores and 265.60 ± 78.68nm honeycomb-like fine pores was obtained by direct electrochemical dealloying of as-cast Mg 80 Al 20 alloy. Following annealing, the eutectic structure disappeared and a bicontinuous, single-sized, porous structure with 7.10 ± 1.96 μm ligaments was created by an annealing-electrochemical dealloying approach. The porous formation mechanism is governed by selective dissolution of the α-Mg phase, which leaves the Mg 17 Al 12 phase as the porous layer framework. [ABSTRACT FROM AUTHOR]

This paper presents a study of carbon transfer and its effect on microstructure and tensile properties of Grade 91 (G91) ferritic-martensitic steel exposed to sodium at 550–650 °C. Sodium exposure tests were conducted in Argonne's forced convection sodium loops up to exposure times of ∼40,000 h. Thermal aging study of G91 steel was conducted in parallel to isolate the thermal aging effect from the sodium effect. It was found that sodium exposures at 650 °C dissolved M 23 C 6 carbides, eliminated the martensite subgrain structure resulting in excessive grain growth and reduced the tensile strength by >50%, while sodium exposures at 550 and 600 °C had an insignificant effect on its microstructure and tensile properties. These effects were attributed to the carburization/decarburization process of G91 steel in sodium environments. Carbon concentrations in sodium were determined by a foil equilibration method. The estimated carbon concentration was in the range of 0.8–1.2 ppm in the SMT-1 loop and 0.3–0.7 ppm in the SMT-2 loop. Thermodynamic analysis of the carburization – decarburization process was conducted for G91 steels exposed in sodium environments. The carbon activity-concentration relationship for G91 was evaluated by considering four phases in G91, i.e. bcc ferrite, M 23 C 6 , NbC and VC carbides. It was found that the carburization-decarburization process in G91 steel was dictated by M 23 C 6 carbides at high carbon activities, while NbC and VC carbides dominated the process at low carbon activities. The calculated carburization-decarburization boundary showed that G91 would undergo decarburization at 650 °C and carburization at 550 °C in the sodium loop environments, which was consistent with our experimental observations. This experimental and theoretical analysis provided a basis for predicting the effect of carbon transfer on the integrity of reactor components in sodium environments and for the design of new alloys used in sodium-cooled fast reactors. [ABSTRACT FROM AUTHOR]

A surface-porous Mg-Al eutectic alloy was fabricated at room temperature via electrochemical dealloying in a neutral, aqueous 0.6 M NaCl solution by controlling the applied potential and processing duration. Selective dissolution occurred on the alloy surface. The surface-porous formation mechanism is governed by the selective dissolution of the α-Mg phase, which leaves the Mg 17 Al 12 phase as the porous layer framework. The pore characteristics (morphology, size, and distribution) of the dealloyed samples are inherited from the α-Mg phases of the precursor Mg 70.5 Al 29.5 (at.%) alloy. Size control in the porous layer can be achieved by regulating the synthesis parameters. [ABSTRACT FROM AUTHOR]

The objective of this study is to understand irradiation-induced and assisted defect evolution in binary body center cubic (bcc) Fe-based alloys. The broader class of bcc ferritic alloys are leading candidates for advanced nuclear fission and fusion applications, in part due to their exceptional void swelling resistance. However, their irradiated microstructure evolution is sensitive to solute species present, since these solutes can act as traps for irradiation-induced defects due to the surrounding tensile or compressive stress fields. Here, three alloys (Fe-9.5%Cr, Fe-4.5%P, and Fe-2.3%N) are selected for study because they systematically exhibit varying solute sizes and solute positions (i.e., substitutional or interstitial). Ex situ and in situ ion irradiations reveal that Fe-P has a considerably finer and denser population of irradiation-induced defects than Fe-Cr and Fe-N at the same irradiation conditions, which is attributed to strong defect trapping at undersized substitutional P, consequently hindering the development of extended defects. Meanwhile, oversized substitutional solutes (e.g., Cr) and interstitial solutes (e.g., N) may also suppress dislocation loop development due to weak solute-defect trapping. [ABSTRACT FROM AUTHOR]

The additive manufacturing (AM) shows a great market prospect in the closed-impeller for the centrifugal compressor. In the paper, the precipitation hardened martensitic stainless steel (PHMSS) deposition with different heat input parameters by the selective laser melting (SLM) and the micro-Vickers hardness, tensile strength and impact toughness were detected respectively. The evolution laws of microstructure were analyzed by the SEM, TEM, EDS and EBSD. The tensile strength of the deposition with heat input of the 4.21 J/cm were best and the strength along the build surface direction (X and Y) and the build height direction (Z) were 1193.3 MPa、1222.1 MPa、1159.8 MPa respectively. The impact toughness of the deposition were lower than that of base metas and the tonghness between the sureface direction and the bulid heght direction was anisotropy. The crystals showed a conlumanr pattern along the Z direction and with the increase the heat input, the preferred orientation along the Z changed from the preferred crystal plane and crystal orientation to the pure preferred crystal orientation. A large amount of Cr 3 C 2 phase is precipitated and its size increased with the increase of heat input. The above research results normalize the influence of each parameter during the AM on the microstructure and mechanical properties of the deposition to the heat input, which is helpful to simplify the optimization of the procedure specification and promote its industrial application. • The maximum tensile strength of the 17–4PH deposition is higher than that of base metal. • The maximum impact toughness with heat input 3.52 J/cm is the 22.38 J but lower than that of base metal. • Cr 3 C 2 were found in the fracture and cross-section and the its size increased as the heat input increased. • With the increase of heat input, the preferred orientation of grains in the deposition becomes weaker. [ABSTRACT FROM AUTHOR]

The effect of samarium (Sm) addition on the microstructure, mechanical performance and corrosion behavior of extruded AZ41- x Sm (x = 0%, 1%, 2% and 3%) alloys has been investigated by using optical microscope (OM), X-ray diffusion (XRD), scanning electronic microscope (SEM) equipped with energy dispersive spectroscope (EDS), tensile testing, hydrogen evolved and electrochemical tests. It is observed that Sm alloyed AZ41 alloys consist of α -Mg substrate, β -Mg 17 Al 12 and Al 2 Sm intermetallic. The β -phase is gradually inhibited with increasing Sm content. The tensile testing result shows that the appropriate amount of Sm addition slightly enhances the mechanical strength. 2Sm alloyed alloy (AZ41-2Sm) displays optimal tensile properties, with a yield tensile strength (YTS) of 216.4 MPa, ultimate tensile strength (UTS) of 295.9 MPa and elongation (EL) of 15.9%, which is the result of second phase strengthening. The addition of Sm significantly improved the corrosion resistance of AZ41 alloy. The AZ41-1Sm alloy exhibits the best corrosion resistance properties with a corrosion rate about one-half that of the AZ41 alloy based on the hydrogen evolved and electrochemical test. • Al 2 Sm is formed in the as-extruded AZ41 alloy with Sm addition. • The AZ41 alloy is coarsened by the addition of 1–2% Sm, but refined by 3% Sm. • The mechanical properties of AZ41 alloy are enhanced slightly by the addition of Sm. • The AZ41-1Sm alloy shows the optimal corrosion resistance of the AZ41-xSm alloys. [ABSTRACT FROM AUTHOR]