•γ′ at both the grain interior and boundary coarsen obviously during long-term aging.•Coalesce of γ′ permits the dislocation easily moves across the grain interior.•The grain strength significantly decreases as the γ′ particle space keeps increases.•Grain boundary shear the large γ′ particle during the alloy deformation.•Large γ′ improves the boundary ductility by retarding the stress concentration.GH2984 alloy is a Ni3Al (γ′) particle strengthened by Fe-Ni-base alloy with a promise to be used in boiler tubes in the next generation power plants. A primary concern over this material is its alloy property degradation during long-term service in the designed environment. This work investigates the microstructural evolution of the alloy during aging and the impact of the evolution on deformation behavior of the alloy. The results show that the γ′ uniform precipitation during short-term aging (8 h) at 750 °C provides a superior alloy strength. Nevertheless, the γ′ coarsens obviously during long-term aging (5400 h), and the Orowan strengthening effect decreases significantly as the particles spacing increases. On the other hand, large γ′ particles increase the ductility of the grain boundary, and thus inhibits the crack nucleation during alloy deformation. However, the effect of large γ′ particles on the strength of grain boundary is relatively small.

•Effect of Al content on the corrosion of Ni alloys in molten glass was evaluated.•The corrosion mechanism is strongly dependent on the Al content in the alloy.•A small amount of Al content (2–5 wt.%) is beneficial to inhibit the corrosion.•High Al content (>8 wt.%) accelerates the corrosion process by surface spalling.Ni-base alloys with different Al contents of 0–10 wt.% were designed and the corrosion behaviour was evaluated by static immersion in molten glass at 1050 °C. Results indicate that a small amount of Al (2–5 wt.%) is advantageous to mitigate the corrosion of the commercial Ni-base alloy, whereas further increase of Al content (8–10 wt.%) accelerates the corrosion process. In Al-added alloys, the corrosion of Cr element is suppressed by the Al dissolution, and the formation of inner alumina in high Al alloys leads to the surface exfoliation. The corrosion mechanism strongly depends on the Al content in alloys.

•Molten glass mainly attacks Cr carbide along grain boundaries in Ni-Cr alloy.•Adding 5 wt.% Al changes the corrosion mode of Ni-Cr alloy.•The alloy with 5 wt.% Al and Nb addition has the highest corrosion resistance.•Excessive Al content deteriorates the corrosion resistance.The corrosion behaviour of commercial Ni-Cr alloys added with Fe, Ti, Nb and Al was evaluated in molten glass at 1050 °C. The static-immersion results reveal that the corrosion depth after testing for 100 h roughly remains at the same level for the alloys added with 5 wt.% Al or added with Fe, Ti and Nb (FeTiNb) separately, but decreases greatly by co-adding 5 wt.% Al with FeTiNb. However, a further increase of Al content to 15 wt.% in the co-added alloy degrades the corrosion resistance. The corrosion mechanism was discussed based on the analysis of the corrosion layer.

•A high strength, low cost Ni–Fe-based superalloy was developed.•Careful identification of dislocation-based deformation mechanisms was performed.•The transition from Orowan looping to precipitates shearing occurs at around 700 °C.A low cost Ni–Fe-based superalloy due to its good mechanical properties and good workability has been evaluated as a promising candidate boiler material for advanced ultra-supercritical coal-fired power plants with temperature up to 700 °C. The major concerns with Ni–Fe-based alloys are the fundamental deformation mechanisms at intermediate temperatures. In this paper, great emphasis is placed on the dislocation configurations induced by tensile deformation in this low cost Ni–Fe-based superalloy. Two typical deformation-induced microstructure features, Orowan looping and precipitates shearing, are present during tensile deformation. Careful identification of dislocation-based deformation mechanisms by transmission electron microscopy was performed in tensile strained specimens at 20 °C, 500 °C, 650 °C, 700 °C and 750 °C in order to correlate the macroscopic behavior with the tension controlling mechanisms.

•A high strength, low cost NiFe-based superalloy was developed.•Careful identification of dislocation-based deformation mechanisms was performed.•An interesting crack initiation and propagation mechanism was presented.The 700 °C class Advanced Ultra-Super-Critical (A-USC) technology with higher thermal efficiency is being developed for next-generation coal-fired power plant in recent years to reduce environmental impacts of energy consumption. A new wrought NiFe-based superalloy with excellent high creep strength and low cost has been developed recently and evaluated as a candidate material for the 700 °C class A-USC steam turbine rotor application. Creep tests were conducted on the new NiFe-based alloy at 700 °C/200 MPa, 700 °C/250 MPa and 725 °C/150 MPa using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The creep-rupture testing results show the new NiFe-based alloy has better creep-rupture strength than the existing commercially available NiFe-based and even some Ni-based alloys. The focus of this study is on understanding the relative important causes of better creep resistance and reduced rupture life in grain interiors and grain boundaries. Detailed creep deformation behaviors and related creep-rupture mechanisms were analyzed and discussed to explore the potential approaches for performance improvements. The results presented are helpful in providing a new approach to design and develop novel high performance alloys for A-USC steam turbine rotor application.

This work investigated the effect of long-term service on the evolution of microstructure and properties of HR3C alloy. Its results show that large amount of discontinuous chromium carbide is accompanied by a chromium depletion area that is formed along the grain boundary. This depletion area promotes the crack nucleation and propagation at the carbide-matrix interface at the grain boundary, leading to a decrease in the alloy ductility at room temperature. However, this deteriorative effect is not obvious at high temperatures primarily because the fast drop of the grain strength. Therefore, the crack propagates easily across the grain during the alloy deformation at high temperatures.

•A new low cost Ni-Fe-base alloy is a promising advanced ultra-supercritical material.•Dislocation configurations during creep rupture are carefully identified.•Creep rupture deformation mechanisms are presented.A Ni–Fe based superalloys with excellent high temperature mechanical properties and low cost have been evaluated as the promising candidate materials for advanced ultra-supercritical coal-fired power plants. The major concerns with the Ni-Fe-based alloys are the insufficient fundamental deformation mechanisms at intermediate temperatures. In this study, dislocation-based deformation mechanisms were identified carefully in creep ruptured specimens beyond 700 °C. The motion of dislocations allows plastic deformation to occur. Two types of dislocation configurations mainly occurred during the creep rupture tests beyond 700 °C. Below 750 °C, Orowan looping are more likely occur and considered as the predominant deformation mechanism. Above 750 °C, the predominant model of deformation mechanism becomes γ′ precipitates shearing. Detailed identification of dislocation configurations were performed in the creep rupture specimens in order to correlate the macroscopic behavior with the creep controlling mechanisms.

Creep–rupture behavior of a Fe–Ni-base alloy crept under various conditions has been studied using Electron Backscatter Diffraction (EBSD) and Transmission electron microscopy (TEM). The results indicate that grain orientation did not change after the alloy crept at 700 °C/300 MPa and changed greatly crept at 700 °C/200 MPa. The recrystallization texture near rupture–fracture surface was observed after the alloy crept at 750 °C/150 MPa. A better creep performance was found in the samples with the occurrence of grain rotation dependence of the microstructure and the grain store energy.

•A new low-cost Ni–Fe-base alloy with high creep strength has been developed.•This alloy possesses good workability, excellent microstructural stability, and good oxidation resistance.•This alloy is a promising candidate for A-USC power plant applications beyond 700 °C.Ni-base superalloys are the best candidate alloys for advanced ultra-supercricial (A-USC) plant applications in terms of creep strength but they are prohibitively expensive. Here we developed a new low-cost, high creep strength Ni–Fe-base alloy. It also has excellent workability, good microstructural stability and oxidation resistance, and high yield strength. The creep rupture resistance of this new alloy was comparable to the levels exhibited by Ni-base candidate alloys CCA617 and Nimonic 263 and was much better than the state-of-the-art Ni–Fe-base alloys HR6W and GH984. The results suggest that this alloy is a promising candidate for A-USC power plant applications beyond 700 °C.

Fatigue crack growth (FCG) rates of a new superalloy TMW-2 in air was studied by a fracture mechanics test method. Compact tension specimens were tested under load control with a triangular wave form to investigate the effects of temperature (400, 650, and 725 °C) and load ratio (0.05 and 0.5) on FCG rates. The results showed that the FCG rates increased significantly with increasing the temperature. Compared with the creep effects, the results showed that the degradation of mechanical properties and the oxidation assisted crack growth may dominate the FCG rates of TMW-2 at elevated temperatures. Load ratio had a little (at 400 °C) or moderate (at 650 and 725 °C) influence on the FCG rates, which increased as the load ratio increased. The load ratio effects were successfully accounted for by applying the Walker model. The fractographic observations showed that the fracture mode was transgranular at 400 °C and was mixed transgranular and intergranular at 650 and 725 °C.Highlights► The fatigue crack growth rates increased significantly with increasing the temperature. ► Load ratio had a little (at 400 °C) or moderate (at 650 and 725 °C) influence on the fatigue crack growth rates. ► The load ratio effects were successfully accounted for by applying the Walker model. ► The fracture mode was transgranular at 400 °C and was mixed transgranular and intergranular at 650 and 725 °C.

Low cycle fatigue behavior was studied at 400, 650 and 725 °C in the total strain ranges of 0.79–1.22% for a recently developed Ni-base superalloy containing high Co and Ti contents. Detailed examinations were conducted on cyclic hardening/softening behavior, deformation substructure, fatigue life, as well as crack initiation and subsequent propagation. Continuous cyclic hardening at 400 °C was observed whereas cyclic softening at 650 and 725 °C was examined, except at 650 °C and low strain range (0.8%) where alloy exhibited relative stable stress response until crack initiation. Transmission electron microscopy analysis suggests that cyclic hardening is caused by the inhomogeneous dislocation activity and interactions of dislocations, and cyclic softening is related to shearing of gamma prime precipitates by stacking faults and coupled dislocation pairs combining with thermal activation process. The relation between fatigue life and plastic strain followed the Coffin–Manson law. Fatigue cracks often initiated on or near the surfaces of specimen during cycling, while subsurface carbide clusters initiation was also observed. Oxidation accelerated crack propagation at 650 and 725 °C.Highlights► Cyclic hardening at 400 °C is mainly due to the interaction of dislocations. ► Cyclic softening at 650 and 725 °C is related to shearing of γ′ precipitates. ► The relation between fatigue life and plastic strain followed the Coffin–Manson law. ► Cracks often initiated on or near the surfaces of specimen.

A new kind of Ni–Co-base superalloys with a γ/γ′ two-phase structure has been proposed recently for turbine disk applications. Some of these Ni–Co-base superalloys are assessed by tensile tests. The results show that the Ni–Co-base alloys can be processed by cheap cast and wrought route and show superior tensile strength at temperatures up to 750 °C and higher creep resistances up to 725 °C than those of the UDIMET 720 LI alloy.

To provide information relevant to Ir-based two-phase alloys for future ultra-high-temperature applications, the compression creep properties for the Ni-added Ir85Nb15 alloys were investigated at 1800 °C under 137 MPa. The results show that Ni addition has a significant effect on the creep resistance of the Ir85Nb15 two-phase refractory superalloy.