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Alloy 625 plays a crucial role in high-pressure hydrogen environments typical of hydrogen refuelling stations, where cyclic temperature and loading conditions prevail. In this study, we reveal that hydrogen-induced ductility loss of nickel-based alloy 625 significant difference which change from 11.9% at slow strain rate to 20.1% at conventional strain rate. The difference can be attributed to a change in deformation mode: from dislocation slipping under slow strain rate to twinning under conventional strain rate. Specifically, hydrogen-refined deformation twins and the promotion of twin bundles under conventional strain rates diminish the twin-induced plasticity effect of the alloy. This shift in deformation mode also alters the hydrogen embrittlement mechanism across the two strain rates. These findings provide valuable insights for hydrogen embrittlement-resistant designing and evaluating hydrogen compatibility for alloy 625. [Display omitted] • The nickel-based alloy 625 has more significant hydrogen-induced ductility loss at 5 × 10−3 s−1 than that at 5 × 10−6 s−1. • The deformation mode change from dislocation slipping at 5 × 10−6 s−1 to twinning at 5 × 10−3 s−1. • Hydrogen weakens the TWIP effect of the alloy because of hydrogen refining DTs. • Hydrogen will promote the formation of deformation twin bundles, resulting in cracking along DTs. • A new mechanism of hydrogen-induced cracking along DTs in nickel-based alloys was proposed. [ABSTRACT FROM AUTHOR]

The microstructure evolution of nickel based alloy used in advanced ultra-supercritical power plants was studied in the strain range of 0.22–0.91 at 1000–1100 °C/0.01 s−1 by using the electron backscattered diffraction technique. The interaction of the dislocation with the Σ3 twin boundary causes the Σ3 twin boundary to deviate from its specific misorientation. The Σ3 twin boundary is stripped of its signature by the interaction between the dislocation and the Σ3 within the deformed grain. In the process of recrystallization, the Σ3 twin boundaries are affected by both recrystallization fraction and the size of recrystallization grain. Three recrystallization mechanisms, including DDRX, CDRX and TDRX, play their role in the deformation of the alloy. Leading to the recrystallized grains with high misorientation, CDRX tends to grow and promote twin nucleation, and the mechanism of CDRX becomes less significant with the increase of deformation temperature. Due to deformation, the orientation of the grain shifts to <101> direction. At 1000 °C and 1050 °C, the recrystallization texture inherits the deformation texture due to the effect of CDRX and the slow diffusion of the recrystallization process, which causes the recrystallization texture to show a sharp <101> fiber texture. At 1100 °C, the enhancement of the DDRX mechanism and the high diffusivity of the recrystallization process lead to the randomization of the texture, and the oriented growth of recrystallized grains at 1100 °C/0.91 enhances the <001> texture. In addition, both recrystallization and twinning are contributory to the randomization of texture. • The accumulation of dislocations near the Σ3 twin boundary makes Σ3 transform into a random HAGBs. • CDRX tends to inherit the high misorientations in the parent grain. • The texture evolution of the alloy and its relationship with recrystallization and twin boundary were investigated. [ABSTRACT FROM AUTHOR]

Abstract The effects of ion irradiation on the atomic local structure of GH3535, a nickel based alloy and candidate of pressure vessel material for molten salt reactor, were investigated by X-ray absorption fine structure (XAFS). We investigated the local structure of the three major solid solution atoms: Mo, Cr, and Fe under the irradiation of two species of ions: He+ and Ni13+. The changes to the coordination number of these atoms after irradiation were determined from XAFS data. The results reveal that ion irradiation causes selective damage to the elements in alloy. No matter for He+ and Ni13+, Cr is the most vulnerable atom in the alloy to the irradiation with the most decrease in its local coordination number. Mo, on the contrary, changes little under either type of ion irradiation. The irradiation damage to Fe lies in between. The degree of ion damage, however, is closely related to the ion species and energy. XRD results show slight increase of lattice constant in the alloy after irradiation with Ni13+, while the lattice remains unchanged after irradiation with He+. The MD simulation in pure nickel system suggests the lattice expanse effect by the competition between interstitials and vacancies. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of He bubbles on the swelling and hardening of nickel based alloys, 1.2 MeV He ion irradiation was performed on UNS N10003 alloy at 650 °C. The number densities and sizes of He bubbles increase with increasing irradiation dose. Neither “black spots” nor dislocation loops were observed in TEM images of the as-irradiated samples. Irradiation dose up to 6.18 displacements per atom (dpa) causes a swelling of 2.67%, which is mainly ascribed to He bubbles. He bubbles induced hardening increases with increasing irradiation dose. The irradiation hardening behavior was compared with heavy ion irradiation. The result reveals that the obstacle strength of He bubbles is less than that of the saturated heavy ion induced irradiation defects. [ABSTRACT FROM AUTHOR]

This study explores the corrosion response of irradiated nickel-based GH3535 alloy in impurity-enriched molten FLiNaK salt at 650 °C. Displacement damage resulting from Au ion irradiation formats dislocation loops, whose distribution is influenced by subsequent He ion irradiation and He bubble formation. Samples irradiated with Au ions exhibit a shallow corrosion layer with big-size and dense distributed Cr 2 O 3 particles, while a contrasting trend is observed in samples irradiated with He ions. Displacement damage decelerates Cr outward diffusion by promoting protective Cr 2 O 3 formation with SO 4 2- impurities, thereby inhibiting impurity-accelerated corrosion. However, the accelerating effect of He bubbles subsequently counteracts this inhibitory impact on corrosion. • Synergistic effect of ion irradiation and molten salt corrosion with impurity in GH3535 alloy was investigated. • Corrosion behavior was revealed by fine element distribution and microstructure characterization. • The inhibition mechanism of displacement damage on the accelerated corrosion by impurities was revealed. [ABSTRACT FROM AUTHOR]

The thermally activated dislocation motion due to plastic deformation in Inconel 690 has been carried out by performing tensile tests in air and in environmental hydrogen using the strain relaxation technique. The results show that the variation of - δ (Δ A/b 2 ) or ln( V H / V Air ) with ε p depends on the nickel content in the alloy and the microstructure, and generally increases with increasing Ni% for low value of ε p (tensile test). The maximum increase in the rate change was observed for the austenized and aged microstructure. On the other hand, fatigue crack propagation rate ( da / dN ) has been measured in the same environments. An attempt has been carried out to correlate the rate change - δ (Δ A/b 2 ) or ln( V H / V Air ) with the variation of ( da / dN ) H against ( da / dN ) Air (the variation of Ω ) and has shown that for the austenized and aged microstructure, Ω is higher than those for stress relieved or only aged at 700 °C. These results are similar to those obtained by the thermal activation parameter – δ (∆ A / b 2 ) or the ratio ln( V H / V Air ). The maximum values of – δ (∆ A / b 2 ) and Ω are obtained when the density of precipitates on the grain boundaries is higher than that in the matrix. In this case, intergranular fractures with fin slip lines features on the grain surfaces were observed. Finally, in the presence of environmental hydrogen, about the fatigue crack propagation rate, two relationships were established and expressed as: 1) in stages I and II: ( Δε p /2) = Θ Δ K + Γ and 2) only in stage II: ( da / dN ) II = c II ( Δε p / 2) λ , where λ ≈ m = 2, the power factor in Paris' law. [ABSTRACT FROM AUTHOR]

The subsurface damage mechanisms of Inconel 690 induced by fretting wear in pure water were investigated. The results showed that the major damage mechanism were oxidation, deformation, fatigue and delamination cracks in worn subsurface. Due to the low oxygen concentration in pure water, preferential oxidation of Cr occurred and plugged into tribologically transformed structure (TTS) at the interface of wear debris layer (WDL)/TTS, which produced complex structures of Cr-rich oxide zone surrounded by Ni-rich zone in TTS. Continued oxidation led to spread of Cr-rich oxide zone, accompanying with formation of WDL consisting of nano-sized oxides and Ni-based grains, however such a spread was limited by the TTS/general deformed layer (GDL) interface, and did not extend to GDL. [ABSTRACT FROM AUTHOR]

Nickel based alloys are very difficult to machine under dry environment due to its low thermal conductivity and high chemical affinity. Generation of high temperature and friction during machining of nickel alloys results in extremely high tool wear. In order to improve the effectiveness of the cutting inserts under dry environment, deep cryogenic treatment of coated and uncoated carbide has been carried out. Comparison of the performance of the cryogenically treated and non-treated inserts has been conducted during the turning of Nimonic 90 alloy. The results demonstrated that the cryogenic treatment has improved scratch resistance of the cutting inserts. Appreciable reductions in flank wear over tool nose, cutting forces and chip tool contact length have also been noticed for the treated inserts. [ABSTRACT FROM AUTHOR]

Reports about dissimilar joining of aluminum alloy and nickel base alloy are rare. The friction stir welding (FSW) technique reveals advantages over fusion welding in terms of dissimilar jointing. In the present research, FSW was employed to produce lap joints of aluminum alloy (2A70) and nickel-base alloy (Inconel 600) with various plunge depths (0–0.5 mm) under a given welding and rotation speed (1200 rpm, 40 mm/min). Macrographs were taken and the microstructure of the cross-section of the lap joints was investigated by optical microscopy and scanning electron microscopy. A fine-grained zone was discovered on both sides of the interface. A thin Al 3 Ni interlayer was generated at the interface. The plunge depth has a vital influence on the joint strength. The lap joint failed at a very low load when the pin did not reach the nickel alloy surface, while the maximum shear strength of the lap joint was obtained under a plunge depth of 0.3 mm and reached 7.9 KN. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical performance of the welded joints of UNS N10003 alloy have been investigated in this work. Primary precipitates in base metal and eutectic precipitates in Heat Affected Zone (HAZ) and weld metal have been characterized and identified as M 6 C type. The hardness value of HAZ (Eutectic zone) is significantly higher than the rest of joint, including weld and base metal. Tensile tests suggested the welded joints possess a very stable mechanical performance at elevated temperature from 650 °C to 725 °C. Moreover all the tensile samples were fractured in base metal, indicating that the eutectic carbides have no adverse effects on the short-time mechanical performance of joint. The fine carbides, acting as dispersion strengthening in weld metal, are main contribution to enhance the hardness and strength of weld. The good mechanical performance of HAZ is ascribed to the presence of eutectic carbides and twins. [ABSTRACT FROM AUTHOR]

This study investigated the creep deformation properties of GH3535, a Ni–Mo–Cr corrosion resistant structural alloy being considered for use in future Gen IV molten salt nuclear reactors (MSR) operating at around 700 °C. Creep testing of the alloy was conducted at 650–750 °C under applied stresses between 85–380 MPa. From the creep rupture results the long term creep strain and rupture life of the alloy were estimated by applying the Dorn Shepard and Larson Miller time-temperature parameters and the alloy's allowable ASME design stresses at the MSR's operating temperature were evaluated. The material's microstructural degradation at creep rupture was characterised using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural study revealed that the material failure was due to wedge cracking at triple grain boundary points and cavitation at coarse secondary grain boundary precipitates, nucleated and grown during high temperature exposure, leading to intergranular crack propagation. EBSD local misorientation maps clearly show that the root cause of cavitation and crack propagation was due to large strain localisation at the grain boundaries and triple points instigated by grain boundary sliding during creep deformation. This caused the grain boundary decohesion and subsequent material failure. [ABSTRACT FROM AUTHOR]

Microstructural and microchemical characterization of Ni-Ta-Al-Cr-C coating layer, deposited by Gas Tungsten Arc Welding (GTAW) method on AISI 310 is presented. The layer was characterized by X-ray diffraction (XRD), light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and hardness measurements. Results obtained by XRD and TEM show that the coating layer consists of a γ-nickel matrix strengthened by the γ′-Ni 3 (Al,Ta) phase, MC and M 7 C 3 carbides (of tantalum-and chromium-rich type, respectively). Growth mechanism, which depends on the cooling rate determines morphology of eutectic carbides. For slow growth rate MC carbides tend to be blocky, while for greater growth rate they exhibit a tendency to form more developed shapes. M 7 C 3 carbides have a polygonal and reticulated plate morphology with different sizes. The γ′-Ni 3 (Al,Ta) phase has a spherical shape with few nanometers in diameter. The average hardness of the AISI 310 substrate is 174 ± 5 HV1, while the hardness of Ni-Ta-Al-Cr-C coating layer is 359 ± 31 HV1. [ABSTRACT FROM AUTHOR]

Nickel based alloys of the type Hastelloy-N™ are ideal candidate materials for molten salt reactors, as well as for applications such as pressure vessels, due to their excellent resistance to creep, oxidation and corrosion. In this work, the authors have attempted to understand the effects of welding on the morphology, chemistry and crystal structure of the precipitates in the heat affected zone (HAZ) and the weld zone of a Ni–Cr–Mo–Fe–Si alloy similar to Hastelloy-N™ in composition, by using characterization techniques such as scanning and transmission electron microscopy. Two plates of a Ni–Cr–Mo–Fe–Si alloy GH-3535 were welded together using a TiG welding process without filler material to achieve a joint with a curved molten zone with dendritic structure. It is evident that the primary precipitates have melted in the HAZ and re-solidified in a eutectic-like morphology, with a chemistry and crystal structure only slightly different from the pre-existing precipitates, while the surrounding matrix grains remained unmelted, except for the zones immediately adjacent to the precipitates. In the molten zone, the primary precipitates were fully melted and dissolved in the matrix, and there was enrichment of Mo and Si in the dendrite boundaries after solidification, and re-precipitation of the complex carbides/silicides at some grain boundaries and triple points. The nature of the precipitates in the molten zone varied according to the local chemical composition. [ABSTRACT FROM AUTHOR]

Nickel based alloys, especially nickel based superalloys have gained the advantage over other alloys in the field of high temperature applications, and thus become irreplaceable at high temperature creep and aggressive corrosion environments, such as jet engines and steam turbines. However, the wear resistance of these alloys is insufficient at high temperatures. This work describes a microstructure of a new cast alloy. The microstructure consists of γ matrix strengthened by γ' fine precipitates (dendrites) improving the high temperature strength and of Chromium Cr7C3 primary carbides (in interdendritic eutectics) which are designed to improve wear resistance as well as the high temperature strength. [ABSTRACT FROM AUTHOR]

Ni-based alloy Haynes 230 is of interest for high temperature applications (e.g. Intermediate Heat eXchanger (IHX)) because of its high temperature strength and oxidation resistance. In this work, the temperature dependence of the tensile behavior of the alloy and the strain rate effect was studied by tensile tests in the temperature range of 25–950°C, at strain rates of 10−3 s−1, 10−4 s−1, and 10−5 s−1. The tensile strength decreased with increasing temperature regardless of the strain rate. The total elongation at rupture fluctuated more with temperature. The alloy showed an abnormal variation of the yield stress with increasing temperature i.e. the yield strength decreased slightly with temperature up to about 600°C and then increased between 600 and 850°C followed by a rapid decrease. This Yield Stress Anomaly (YSA) was however absent at the slowest strain rate of 10−5 s−1. SEM and TEM characterization was performed on fractured specimens to determine the predominant deformation mechanisms accounting for the observed Yield Stress Anomaly. Also, serrations were observed in the stress–strain curves at temperatures above 300°C, the shape and amplitude of which depended on temperature and strain rate. The analysis of the stress–strain curves coupled with the microstructure investigation of the fractured samples showed that two different deformation mechanisms occur depending on the temperature and strain rate. The saw-tooth type serrations at intermediate temperatures and higher strain rates were associated with dynamic strain aging whereas the oscillations with a sinusoidal shape were associated with dynamic recrystallization at temperatures higher than 800°C and slower strain rates. [ABSTRACT FROM AUTHOR]

Abstract: Nickel based alloy coating has been successfully deposited onto pure copper surface by laser cladding with coaxial powder feeding. Coating with thickness in the region of 1.5 mm can be obtained by depositing two layers of overlapping laser clad tracks. The microstructure observation from optical microscopy and scanning electron microscopy indicated that the coating was free of cracks and pores, and soundly bonded with the substrate. The X-ray diffraction analysis results showed that the coating was mainly composed of γ-(Ni, Cr, Mo, W) solid solution, some carbides and silicides. The average hardness of the coating was about HV0.1 360, which was about 5 times that of the pure copper. The dry sliding wear tests showed the wear resistance of copper was significantly improved after laser clad nickel based alloy coating. [Copyright &y& Elsevier]

Nickel based hardfacing alloys Colmonoy-5 and Colmonoy-6 deposited on type 316L austenitic stainless steel substrate using the gas tungsten arc welding process, were characterised for their microstructure and hardness variations across the deposit/substrate interface, and for identification of the principal precipitates present in these hardface deposits. Hardness measurements and electron probe microanalysis (EPMA) across the interface revealed the presence of a dilution zone 2·5 mm wide in the Colmonoy-6 deposit and 1·5 mm wide in the Colmonoy-5 deposit. EPMA and X-ray diffraction studies of the precipitates showed that he blocky type precipitates were chromium borides and the needle-like precipitates were chromium carbides. Also, stress relief heat treatment at 1123 K for 4 h was found to have no significant effect on the hardness of these hard face deposits. [ABSTRACT FROM AUTHOR]

A composite coating with TiC particles of various shapes and sizes embedded in nickel based alloy has been in situ synthesized by laser melting a precursor mixture of nickel based alloy powder, graphite and titanium powders. The experiment result showed that the coating epitaxially grew from the substrate with excellent bonding between the coating and the carbon steel substrate. The coating is uniform, continuous and free of pores and cracks, and about 0.6 mm thick. The microstructure of the coating is mainly composed of γ-Ni dendrite, a small amount of interdendritic (γ-Ni+M23C6) eutectic, and dispersed TiC particles. The volume fraction of TiC particles and the microhardness gradually increased from the bottom to the top of the coating layer. [Copyright &y& Elsevier]

• High temperature corrosion of austenitic steel and nickel based alloy in HCl and H 2 S atmosphere. • Layered structure of the corrosion products was observed. • Corrosion behavior of materials changed when going to lower temperatures. • Supporting effect of nickel on corrosion resistance could not be observed at lower temperatures. In this paper the corrosion behavior of high temperature corrosion resistant alloys is investigated in a gas atmosphere containing HCl and H 2 S at 480 °C and 680 °C. By considering the vapor pressures of the metal chlorides and the water gas shift reaction, as well as the influence of H 2 S, the different corrosion behavior at 480 °C compared to 680 °C can be explained and a model of the course of corrosion is proposed. Corrosion tests were performed for 240 h with the austenitic stainless steels S31400 (20 wt% Ni) and N08811 (30.4 wt% Ni) and with the Ni-based alloy N06600 (72.5 wt% Ni). It could be shown that with increasing Ni-content in the alloy, the corrosion rate at high temperatures decreased, but this effect could no longer be observed at lower temperatures. While for N08811 and N06600 the mass loss was lower at 680 °C, it increased at temperatures of 480 °C. In the case of S31400 the mass loss increased with rising temperature. [ABSTRACT FROM AUTHOR]

• Ni-17Mo-7Cr superalloy was fabricated by Wire-arc additive manufacturing technique for the first time. • A significant decrease of hardness and tensile properties was observed in the superficial layers. • Performance degradation in the superficial layers was ascribed to the less carbides and lower strain. Ni-17Mo-7Cr superalloy was successfully fabricated by Wire-arc additive manufacturing (WAAM) for the first time. Mechanical properties and microstructures were analyzed along the deposition direction of the WAAM alloy layer by layer. Both the hardness and tensile properties are stable, whereas a sharp decrease was observed in the superficial layers. The performance degradation can be ascribed to the less carbides and lower strain in the superficial layer. It is novel to find that the residual strain in superficial layer is the smallest and resulted in the non-uniform mechanical properties. Therefore, removing the superficial layer metal or heat treatment is suggested after WAAM processing. [ABSTRACT FROM AUTHOR]