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The fatigue crack growth (FCG) behavior and microstructure of Ni-based alloy welded joint, fabricated by narrow gap tungsten inert gas welding (NG-TIG), were systematically investigated in this paper. The microstructure of weld metal (WM) and base metal (BM) are columnar grains and equiaxed grains respectively, plentiful irregular carbides aggregate at grain boundaries and the number of twin crystals decreases distinctly in HAZ due to the thermal input. The FCG tests results indicated that a higher FCG rate (d a /d N ) as well as a lower FCG threshold (Δ K th ) for WM were obtained compared to BM and HAZ. It was found that crack deflection and branching in the whole welded joint occurred at FCG path in near-threshold regime. The misorientation of grain boundaries is considered as the main factor to account for the deceleration and retardation behavior revealed by electron back-scattered diffraction (EBSD) analysis. EBSD results also indicate that the misorientation of 20–30° is a critical value from a tortuous path to a relative straight path. A contrasting morphology of Paris regime and near-threshold regime showed the fracture mode transition from tensile mode to intense shear mode. [ABSTRACT FROM AUTHOR]

The iron content in Ni-Cr- x Fe ( x = 0–9 at.%) alloys strongly affected the properties of oxide films after 978 h of immersion in the simulated PWR primary water environment at 310 °C. Increasing the iron content in the alloys increased the amount of iron-bearing polyhedral spinel oxide particles in the outer oxide layer and increased the local oxidation penetrations into the alloy matrix from the chromium-rich inner oxide layer. The effects of iron content in the alloys on the oxide film properties after 500 h of immersion were less significant than those after 978 h. Iron content increased, and chromium content decreased, in the outer oxide layer with increasing iron content in the alloys. Increasing the immersion time facilitated the formation of the local oxidation penetrations along the matrix/film interface and the nickel-bearing spinel oxides in the outer oxide layer. [ABSTRACT FROM AUTHOR]

Amechanism of local formation of crystals of random orientation in growth of single-crystal billets of refractory nickel alloys for blades of gas turbine engines is suggested. Aturn of the lattice is initiated at the place of contact between the initial melt and the surface of hard particles of NbC carbide and/or TiN nitride. [ABSTRACT FROM AUTHOR]

Homoepitaxial growth film for (001), (110) and (111) Ni substrates is investigated by means of molecular dynamics (MD) simulation. Embedded atom method (EAM) is considered to represent the interaction potential between nickel atoms. The simulation is performed at 300K using an incident energy of 0.06eV. In this study, the deposition process is performed periodically and the period, , is relative to a perfect layer filling. The coverage rate of the actual expected level, , can be considered a determinant for thin-film growth of nickel. The level is the most filled level during the deposition on (001) substrate, while it is the less filled one in the case of (111) substrate. Moreover, the upper level is the one which is responsible for the surface roughness and the appearance time of an upper layer may also be a factor influencing the surface roughness. The deposition on (111) substrate induces the most rigorous surface with a rapid appearance time of the upper layers. The layers are almost completely filled for all substrates. The and lower layers are completely filled for (001) and (110) substrates while for (111) substrate the completely filled layers are and lower ones. [ABSTRACT FROM AUTHOR]

Nickel and antimony co-doped Ti/SnO 2 (Ti/Ni Sb SnO 2 ) anodes were prepared by spray pyrolysis. Effects of nickel concentration on the structure and onset potential for oxygen evolution of Ti/Ni Sb SnO 2 anodes have been systematically investigated. XRD analyses suggest that SnO 2 thin films grow in preferential orientation along (101) plane as the nickel concentration increases. The enhanced onset potential of oxygen is above 2.4 V vs NHE due to the introduction of nickel doping, and increases slightly with the nickel concentration. The calculated results show that work function of Ni/Sb co-doped SnO 2 also increases with the Ni doping level, which contributes to the enhancement of onset potential for oxygen evolution. [ABSTRACT FROM AUTHOR]

In this study, the influences of uniaxial compressive load on martensitic transformation from austenite to 5M martensite were studied in a directionally solidified Ni–Mn-Ga polycrystalline alloy with coexisting <0 0 1> A and <1 1 0> A preferred orientations parallel to the solidification direction (SD). Based on the neutron diffraction, the direct evidence on the variant redistribution induced by the thermal-mechanical treatment was presented and the selection of preferential variants was found to be strongly dependent on the austenite orientation. For the austenite with a <0 0 1> A preferred orientation, the compressive loading direction (LD) along the SD can promote the formation of preferred variants with {0 2 0} 5M ⊥SD (LD). On the other hand, for the austenite with a <1 1 0> A preferred orientation, the variants with {1 2 5} 5M /{ 1 ¯ 2 5} 5M ⊥SD (LD) are more favorable after the thermal-mechanical treatment. Such variant selection is originated from the accommodation between the anisotropic lattice distortion in martensitic transformation and the external constraint. The present investigations may offer some fundamental information on variant selection subject to external stress field and the necessary guidelines for microstructure optimization of polycrystalline Ni–Mn-Ga alloys through external field training. [ABSTRACT FROM AUTHOR]

Tensile behavior of the nickel-base single-crystal superalloy DD6 was studied from room temperature to 1020 °C. The plate specimens were along [001] orientation parallel to the loading axis in tension. The microstructures on the surface and fracture morphology were investigated after tensile test to rupture by scanning electron microscopy (SEM). The results of the present investigation indicate that the yield strength at 650 °C is superior to that at room temperature, 850 °C and 1020 °C. Low ductility and serrated flow in stress–strain curves were also observed at 650 °C. The microstructures on the surface of the plate specimens and fracture morphology observation indicated that localized slip which resulted in glide plane decohesion caused the low ductility of DD6 alloy. [ABSTRACT FROM AUTHOR]

Grain contrasts produced during ion induced secondary electron imaging depend upon grain orientation and ability of Ga-ion beam to channel in it. The current study aims to investigate critical Ga-ion dose for Ni-alloy where a transition from grain surface imaging to sputtering dominated Ga-ion channeling occurs. It is observed that critical dose is in the vicinity of 10 15 ions/cm 2 . Strong orientation dependent Ga-ion channeling effects were observed at dose values higher than 10 17 ions/cm 2 . When a normalized orientation dependent grain transparency factor was estimated for each grain in a limited sampling volume, it was observed that despite low sampling volume for a random polycrystalline orientations and variation in Ga-ion dose, the range of sputter depth variation during Ga-ion channeling remains above 80% indicating dose or sampling volume (for randomly oriented poly-crystals) independency in the sputter dominated dose region. This study attempts to establish a correlation between high resolution imaging, applied Ga-ion dose and orientation dependent Ga-ion beam channeling effects. [ABSTRACT FROM AUTHOR]

Abstract: By means of the stress–strain finite element method (FEM) in elastic–plastic regime, the influences of the applied stress on the distribution of von Mises stress and evolution of shape regularity of γ′ phase in a [011] oriented single crystal nickel-based superalloy are investigated. Results show that, after full heat treatment, the microstructure of [011] oriented single crystal superalloy consists of the cuboidal γ′ phase embedded coherently in the γ matrix phase, and on (100) plane aligned regularly at angle of 45° relative to the [011] orientation. During compressive creep, the cuboidal γ′ phase is transformed into the mesh-like lamellar rafted structure on (100) plane. Therefore, the changes of the lattice strain, the strain energy density and interfacial energy are thought to be the driving forces of the element diffusion and γ′ phase directional growth. During compressive creep, the lattice contraction occurs on (100) plane of the cuboidal γ′ phase along [001] and [010] directions, whose extruding effect may repel Al, Ti atoms with bigger radius. Therefore, the expanding strain of lattices along [100] direction on (010) and (001) planes of the cuboidal γ′ phase may trap Al, Ti atoms to promote the directional growth of γ′ phase on (100) plane along [001] and [010] directions, which is thought to be the main reason for the γ′ phase growing directionally into the mesh-like lamellar structure. [Copyright &y& Elsevier]

Complex thermally grown oxides (TGOs) are formed on a single-crystal Ni-based superalloy due to a large fraction of alloying elements. Combining atom-probe tomography and transmission electron microscopy analyses, the three-dimensional elemental distributions of metal oxides of the spinel and refractory metal-oxide regions are presented. A spinel-type oxide, Ni(Cr,Al)2O4, is formed with a crystallographic orientation relationship with the alloy substrate, which decomposes into other oxides. The sequence of oxides observed in the TGO are NiO→Cr2O3 →Ta2O5 →NiTaO4, NiTa2O6 →Ni(Cr,Al)2O4 →Al2O3. [Copyright &y& Elsevier]

Abstract: Morphology, orientation and diffraction patterns of δ-Ni2Si precipitates in a Cu–Ni–Si alloy are investigated by TEM and HREM. Many disk-shaped nanosized δ-Ni2Si precipitates are uniformly distributed in Cu–1.5wt%Ni–0.34wt%Si alloy in an over-aging condition. The δ-Ni2Si precipitates preserve an orthogonal structure with a =0.708±0.005nm, b =0.504±0.005nm, and c =0.364±0.005nm. The orientation relationships of six variants of δ-Ni2Si precipitates with Cu-matrix can be determined as (100)p||{001}Cu, [100]p||〈110〉Cu and [010]p||〈110〉Cu. Two typical diffraction pattern models under [001]Cu and [111]Cu zone axis are simulated according to diffraction effects of multiple variants, secondary diffraction and the size of particles, which coincide with the experimental results perfectly. [Copyright &y& Elsevier]

Abstract: The correlation between the grain boundary misorientation and the precipitation behaviors of intergranular M23C6 carbides in a wrought Ni–Cr–W superalloy was investigated by using the electron backscattered diffraction (EBSD) technique. It was observed that the grain boundaries with a misorientation angle less than 20°, as well as all coincidence site lattice (CSL) boundaries, are immune to precipitation of the M23C6 carbides; in contrast, the random high-angle grain boundaries with a misorientation angle of 20°–40° provide preferential precipitation sites of the M23C6 carbides at the random high-angle grain boundaries with a higher misorientation angle of 55°–60°/[2 2 3] turn to retard precipitation of M23C6 carbides owing to their nature like the Σ3 grain boundaries and retard the precipitation of M23C6 carbides. The low-angle and certain random grain boundary segments induced by twins were found to interrupt the precipitation of the M23C6 carbides along the high-angle grain boundaries. [Copyright &y& Elsevier]

Abstract: The rotary bending high cycle fatigue properties of a single crystal superalloy in three orientations were tested at 700°C in ambient atmosphere. The [011] orientation shows the highest fatigue strength. Moreover, the fatigue strength with 〈111〉 orientation is obviously higher than that with 〈001〉 orientation. There are two types of fracture modes, one is cleavage fracture for the [001] orientation, the other is the mixed fracture of cleavage and tearing for the [011] orientation. The 〈011〉 orientation shows more pronounced crystal lattice rotation than the 〈111〉 orientation. Nevertheless, lattice rotation does not occur in the crystals with [001] orientation. Fatigue steps of the [001] and [111] orientated crystals propagate along different {111} glide planes, which means that the slip in 〈111〉 orientation moves more easily than in 〈011〉 orientation. The typical deformation mode of [001], [011] or [111] orientation is respectively slip bands running through γ and γ′ phases, dislocation pairs shearing γ′ particles, or superlattice stacking faults besides high-density dislocation shearing γ′ particles. [Copyright &y& Elsevier]

In the original article author name Qiangqiang Zhang was misspelled. It is correct here. [ABSTRACT FROM AUTHOR]