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In order to investigate the hot deformation mechanism of a newly development Ni3Al‐based superalloy, hot compression tests at temperatures between 1100 °C–1250 °C and the strain rates of 0.001 s−1–1.0 s−1 were conducted. The results show that the curves of true stress‐strain indicate the thermal deformation is a typical dynamic recrystallization process, which the peak stresses and steady‐state stresses increase with decreasing temperatures and increasing strain rates. The softening mechanism is mainly dynamic recrystallization. The experimental data of peak stresses and steady‐state stresses is employed to calculate the constants in the Arrhenius equation. The steady‐state stresses are considered more reasonable for solving the parameters in the Arrhenius equation. Based on the constitutive equation obtained, the calculated values of steady‐state stresses match well with the experimental values at the strain rates of 0.001 s−1, 0.01 s−1 and 0.1 s−1, whereas there exists much deviation at 1.0 s−1. For the sake of accuracy of predicted results at 1.0 s−1 strain rate, a modified Zener‐Hollomon parameter Z' is introduced. The results show that the modified constitutive equations established in this study could well predict the value of steady‐state stress in hot deformation of the newly development Ni3Al‐based alloy. [ABSTRACT FROM AUTHOR]

Extrusion limit is an important evaluation criterion in extrusion process design as it determines the deformation degree in each operation. In this paper, a new method for establishment of extrusion limit diagram was proposed. To do so, the constitutive equation of Incoloy028 alloy (IN028) was established by hot compression test and the tube hot extrusion process was simulated by commercial Deform-2D software. In addition, the extrusion process is also analyzed by analytical method in which the billet heating temperature, extrusion speed and ratio were considered as influence factors. The analytical results of extrusion force and demoulding temperature were obtained. The maximum extrusion pressure of 60 MN and the eutectic melting temperature of IN028 (1,350 °C) was selected as the limit of extrusion force and the permissible maximum temperature. The limit diagram for IN028 tube in hot extrusion process were generated using the analytical and numerical methods simultaneously and the extrusion limit diagram of IN028 at different ratios is thus provided. [ABSTRACT FROM AUTHOR]

Nickel superalloys with cubic L1 2 structured γ′ (Ni 3 (Al, Ti)) precipitates exhibit high strength at high temperatures and excellent corrosion resistance when exposed to water. Unlike prior studies on irradiation damage of other Ni-based superalloys, our study on Rene N4 involves much larger γ′ precipitates, ∼450 nm in size, a size regime where the irradiation-induced disordering and dissolution kinetics and the corresponding mechanical property evolution are unknown. We report that under heavy ion irradiation at room temperature, the submicron-sized γ′ precipitates were fully disordered at ∼0.3 dpa and only later partially dissolved after 75 dpa irradiation. Nanoindentation experiments indicate that the mechanical properties of the alloy change significantly, with a dramatic decrease in hardness, with irradiation dose. Three contributions to the change in hardness were examined: defect clusters, disordering and dissolution. The generation of defect clusters in the matrix and precipitates slightly increased the indentation hardness, while disordering of the submicron-sized γ′ precipitates resulted in a dramatic decrease in the total hardness, which decreased further during the early stages of the intermixing between γ′ precipitates and matrix (<18 dpa). Controlling the long-range-ordering and chemical intermixing can be used to tailor the mechanical properties of Ni-based superalloys under irradiation. [ABSTRACT FROM AUTHOR]

NiCrAlY coatings with and without CrN or CrON interlayer as diffusion barrier were deposited on superalloy DSM11 by arc ion plating (AIP). The oxidation performance of the coating systems was evaluated by isothermal oxidation tests at 1100 °C for 100 h. The element interdiffusion and oxidation behavior of the coating systems were described. It was found that the NiCrAlY coatings provided protective effect for the DSM11 substrate. However, serious interdiffusion between the coatings and substrate resulted in rapid degradation of the coatings. The addition of CrN or CrON interlayer between the coatings and substrate markedly decreased the interdiffusion. CrON interlayer performed better than CrN interlayer, which was attributed to the excellent diffusion barrier ability of Al2O3 layer formed in the interlayer at high temperature. Also, the NiCrAlY/CrON coating system exhibited more effective protection for DSM11 than the NiCrAlY/CrN coating system. [ABSTRACT FROM AUTHOR]

NiCoCrAlYSiB coatings were deposited on the Co-based superalloy K40 by arc ion plating (AIP). The oxidation behavior of the bare alloy and of the coated specimens was tested in static air for 200 h at 1000 °C and 100 h at 1050 °C. The results showed that the oxidation rate of the system was greatly reduced by the addition of the NiCoCrAlYSiB coatings. Thin and adherent á-A12O3 scales that formed on the coated specimens protected the substrates from further oxidation attack while non-protective oxide scales, mainly of Cr2O3 and CoCr2O4, appeared on bare K40 alloy. Element profiles on metallographic cross sections indicated that apparent interdiffusion occurred between the coatings and the substrates. The interdiffusion behavior and the resulting microstructure were investigated. As compared to aluminide coatings, NiCoCrAiYSiB coatings have less influence on the substrate microstructure. [ABSTRACT FROM AUTHOR]

Abstract: Arc ion plating had been employed on a cobalt-base superalloy K40S to deposit a NiCrAlYSi coating to improve its oxidation resistance at 1323–1423K in air. The K40S superalloy had poor oxidation resistance because a non-protective and easy spalling surface oxides scale mixed of Cr2O3 and CoCr2O4 was formed on its surface. After coated with NiCrAlYSi coating, a dense and protective α-Al2O3 scale was formed on the coating and excellently improved its oxidation resistance. Inter-diffusion obviously occurred between the coating and the substrate K40S superalloy in oxidation process, which resulted from Co atoms in K40S outwards diffused. A richen Cr and W carbides inter-diffusion layer was formed, which could acted as a diffusion barrier that barred Al atoms in coating inwards diffusion. Though the NiCrAlYSi changed into NiCoCrAlYSi during oxidation process, it still possessed a good oxidation resistance and had a considerable long-term life. [Copyright &y& Elsevier]

• An method of electroplating, AIP and diffusion treatment was proposed to prepare ReCr co-doped β-NiAl coating. • ReCr co-doped β-NiAl coating was mainly consisted of β-NiAl, wherein plentiful ReCr-rich phases formed. • ReCr-rich precipitates were α-Cr phase, wherein some Re solubilized in α-Cr phase. To prepare ReCr co-doped β-NiAl coating, an innovative method that electroplating NiRe combined with arc ion plating (AIP) Cr, AIP Al and followed by diffusion treatment was proposed. ReCr co-doped β-NiAl coating contained an outer β-NiAl layer with fine dispersive ReCr-rich precipitates, an inner β-NiAl layer with fine dispersive W-rich precipitates and bottom interdiffusion zone (IDZ). And ReCr-rich phases were mainly distributed in the interior of coating grain. The TEM results proved that ReCr-rich precipitates were α-Cr phase as main phase, wherein some Re solubilized in α-Cr phase and it did not change the phase structure of α-Cr. [ABSTRACT FROM AUTHOR]

Highlights • The hot corrosion behaviour of Pt modified aluminized NiCrAlYSi coating was investigated. • The Pt modified aluminized NiCrAlYSi coating showed superior hot corrosion resistance. • The addition of Pt suppressed the internal oxidation and sulfidation during hot corrosion test. • The outward diffusion of Ti in Pt modified aluminized NiCrAlYSi coating was inhibited. Abstract The hot corrosion tests of Pt modified aluminized NiCrAlYSi coating coated with mixed salt films of Na 2 SO 4 + K 2 SO 4 and NaCl + Na 2 SO 4 were carried out at 900 ℃. Compared to the aluminized NiCrAlYSi coating, the Pt modified aluminized NiCrAlYSi coating exhibited an enhanced hot corrosion resistance in these two types of mixed salts. The existence of Pt in the aluminized coating restrained the outward diffusion of substrate elements and effectively suppressed internal sulfidation and oxidation during hot corrosion test. The degradation mechanism of the coating in the corrosion condition was also discussed. [ABSTRACT FROM AUTHOR]

• NiPt-Hf layer provided Ni element required to form the coating. • There was no TCP phase precipitation in DAZ for PtHf co-doped γʹ coating. • The thickness of DAZ in PtHf co-doped γʹ+β coating was about 18 μm. • The proportion of β-NiAl in coating increased with the increase of Al layer thickness. Two PtHf co-doped Ni-Al coatings were fabricated by the following steps: first, NiHf layer and Pt layer were electroplated on the substrate, then vacuum annealed at 800 ℃ for 5 h; Second, Al layer was deposited via arc ion plating (AIP); Finally, vacuum annealing was proceeded at 1050 ℃ for 2 h. The Al contents in PtHf co-doped γʹ coating and PtHf co-doped γʹ+β coating were about 24 at.% and 42 at.%, respectively. In addition, no topologically close-packed (TCP) phases were precipitated in the diffusion affected zone (DAZ) in the PtHf co-doped γʹ coating, while many TCP phases were precipitated in the DAZ in the PtHf co-doped γʹ+β coating. The interdiffusion coefficient of Al gradually decreased with the reduction of Al content and the increase of Pt content in coating, consequently suppressing the precipitation of TCP phases. [ABSTRACT FROM AUTHOR]

Pt modified aluminide (Pt-Al) coatings were prepared on the third- and fourth-generation single crystal superalloys by electroplating Pt and successive aluminization. The isothermal oxidation behaviors of both coatings were investigated at 1100 ℃ for 350 h. The results showed the Pt-Al coating on the fourth-generation single crystal superalloy had superior oxidation resistance. Ru in the fourth-generation single crystal superalloy diffused into Pt-Al coating during isothermal oxidation and increased spallation resistance of oxide scale. The effects of Ru on the anti-spallation property of oxide scale and the interdiffusion between coating and substrate were discussed. The diffusion process of Ru was investigated. • Ru in the substrate diffused towards the coating. • The diffusion of Ru promoted the expansion of SRZ. • Ru aggregated in the β phase of the coating. • The presence of Ru inhibited the transition of β to L1 0 phase. [ABSTRACT FROM AUTHOR]

An aluminized NiCrAlYSi coating and Pt modified aluminized NiCrAlYSi coating were prepared on a Ni-based superalloy. Isothermal and cyclic oxidation behaviour of both coatings were investigated. The Pt modified aluminized NiCrAlYSi coating showed an enhanced oxidation resistance due to the presence of Pt decreasing the oxidation rate and improving the adherence of alumina scale. The addition of Pt in aluminized NiCrAlYSi coating inhibited the phase transformation from β to γ′. Besides, the surface rumpling of Pt modified aluminized NiCrAlYSi coating was suppressed as compared to the aluminized NiCrAlYSi coating. [ABSTRACT FROM AUTHOR]

A Pt modified AlSiY coating was prepared on a Ni-based superalloy DD5 by electroplating and arc ion plating (AIP). The outer layer of the coating was mainly composed of β-(Ni,Pt)Al with dispersed CoWSi. The hot corrosion behaviour of Pt modified AlSiY coating at 900 °C was investigated. Compared to AlSiY coating, the Pt modified AlSiY coating provided improved hot corrosion resistance. The addition of Pt in AlSiY coating accelerated the phase transformation from θ-Al 2 O 3 to α-Al 2 O 3 in the initial stage, improved the scale adhesion and effectively suppressed the formation of internal oxides and internal sulphides. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microstructures of two Co modified NiAl coatings have been studied. [•] The addition of Co improves the corrosion resistance in sulfate salts at 700°C. [•] For the sulfide and its eutectic of Co are more stable than those of Ni. [•] In chloride salts coating with medium Co content has best corrosion resistance. [ABSTRACT FROM AUTHOR]

The NiCrAlYSi coatings with or without Re-based diffusion barriers (DB) were prepared on K438 and K465 superalloys by electroplating Re-Ni layer, arc ion plating (AIP) NiCrAlYSi coating and following vacuum annealing. Isothermal oxidation behaviors of all coatings were investigated at 1100 ℃ in static air. The results showed that better oxidation resistance was achieved for NiCrAlYSi coatings with Re-based DB and for NiCrAlYSi coatings on K438 than that on K465. Re diffused into NiCrAlYSi coatings during isothermal oxidation and increased spallation resistance of oxide scale. The role of Re-based DB and the effects of substrate compositions were discussed. • The dual roles of Re-based DB were found for NiCrAlYSi coating with it. • NiCrAlYSi coatings with DB transformed to Re modified coatings during oxidation. • Re diffusing in NiCrAlYSi coatings increased spallation resistance of oxide scale. • Cr and W in substrate had an important impact on oxidation resistance of coating. • The outward diffusion of W from substrate to Re-based DB made it more stable. [ABSTRACT FROM AUTHOR]

Abstract: The high temperature oxidation and hot corrosion behaviour of a NiCoCrAlYSi coating and a gradient coating were investigated. The gradient coating showed better performance of re-healing alumina scale due to its possession of more β phase as Al reservoir. The degradation process of the gradient coating was favorably retarded by the formation of Cr(W)-rich σ precipitates in the interdiffusion zone. The corrosion results also confirmed an improved corrosion resistance of the gradient coating. The improved high temperature performance of the gradient coating owes to the Al enrichment of Al in the outer layer. [Copyright &y& Elsevier]

Abstract: A gradient NiCoCrAlYSi coating was prepared by a combined method of arc ion plating and subsequent diffusion treatment. The microstructure of the gradient coating was investigated in the as-annealed condition and after oxidation at 1000°C. During the oxidation, an in situ diffusion barrier composed of Cr(W)-rich σ phases was formed in the interdiffusion zone, resulting in an effective inhibition of inward diffusion of Al. The formation of the in situ diffusion barrier layer is also discussed. [Copyright &y& Elsevier]

Abstract: The coating systems of a NiCrAlYSi overlayer with or without a diffusion barrier (DB) were deposited by one-step arc ion plating (AIP). Isothermal and cyclic oxidations were performed at 1050°C for 100h and 100 cycles, respectively. The results indicate that the duplex coating system exhibits a more effective protection for the substrate, where thin and continuous scales are adhered to the overlayer surface, and very limited oxidation and interdiffusion attacks are detected. After exposure for 100h or 100 cycles, the DB is stable and efficient. The oxidation resistance mechanism for the two coating systems is discussed. [Copyright &y& Elsevier]

Abstract: An AlSiY diffusion coating was developed by a combined approach of arc ion plating and subsequent diffusion treatment. Cyclic and isothermal oxidation behaviour of the coating specimens was tested in a muffle furnace at 1000°C and 1100°C. The results confirmed an enhanced performance of the diffusion coating due to the presence of β-NiAl enriched outer layer. The microstructure change and the oxidation behaviour of the diffusion coating are discussed. [Copyright &y& Elsevier]

Abstract: A gradient NiCoCrAlSiY coating consisting of Al-enriched outer zone and Cr-enriched internal zone was prepared using arc ion plating method and subsequent annealing treatment. Isothermal oxidations were performed at 1000°C and 1100°C in static air. The results confirmed an enhanced performance for the gradient NiCoCrAlSiY coating in contrast to the conventional NiCoCrAlSiY, due to the high-Al content and the in-situ Cr(Re,W)-rich diffusion barrier which exists in the gradient coating. The degradation mechanisms for the two coatings and the formation mechanism for the diffusion barrier are discussed. [Copyright &y& Elsevier]

Abstract: A gradient NiCoCrAlYSiB coating was prepared on a Ni-base superalloy using arc ion plating (AIP) and subsequent gaseous phase aluminisation techniques. Hot corrosion of normal NiCoCrAlYSiB and the gradient coating in pure Na2SO4 and Na2SO4/NaCl (75:25, wt./wt.) salts was performed at 900°C in static air. The corrosion results indicated an enhanced corrosion resistance to both salts for the gradient NiCoCrAlYSiB coating, which the improved performance of it should be attributed to the β aluminide ‘‘pool” at the surface layer. By partially sacrificing Al2O3 (i.e. Al), the gradient NiCoCrAlYSiB coating specimen behaved excellently in the two kinds of salts. The grain growth during the gaseous phase aluminisation and the corrosion mechanism, including the role NaCl played in the mixture salt corrosion, are discussed. [Copyright &y& Elsevier]

• The EBSD and TEM were used to study the microstructures of Re-doped β-NiAl coating. • Outer layer of Re-doped β-NiAl coating was composed of coarser β-NiAl grains and nanometer sized γ-Re precipitates. • Inner layer of Re-doped β-NiAl coating was consisted of tiny β-NiAl grains and submicron sized α-W phases. • γ-Re and α-W phases were distributed in both β-NiAl grain boundaries and different zones within the grains. To figure out the microstructure and precipitation phases of a Re doped β-NiAl coating, the electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were both used. Re-doped β-NiAl coating was composed of outer coarser β-NiAl grains with nanometer sized γ-Re precipitates, inner tiny β-NiAl grains with submicron sized α-W phases and bottom interdiffusion zone (IDZ, consisted of strip TCP and β-NiAl phases). Moreover, these γ-Re and α-W nanoparticle phases were not only aggregated at β-NiAl grain boundary but also appeared within the grains. [ABSTRACT FROM AUTHOR]

Abstract: A MCrAlY+AlSiY composite coating was prepared by arc ion plating. Hot corrosion behaviours of the composite coating and the reference NiCoCrAlYSiB coating were investigated. The results indicate that the composite coating consisted of β-(Ni,Co)Al with dispersed σ-NiCoCr and Cr3Si in outer layer and Cr-rich phases in inner layer after annealing. As being corroded for 200h, the composite coating proved better corrosion resistance than that of reference NiCoCrAlYSiB coating. The enhanced corrosion resistance of the composite coating was due to the gradient distribution of Al-enriched outer layer and Cr-enriched inner layer. [Copyright &y& Elsevier]

NiCoCrAlY(SiB) coatings were deposited on the nickel base superalloys DZ125 and DSM11 by arc ion plating (AIP). The corrosion behavior of the bare alloys and the protective coatings in molten 75 wt.% Na2SO4+25 wt.% K2SO4 at 900 °C in air was tested for 90 h. The results indicated that DZ125 superalloy suffered catastrophic corrosion after 5 h exposure and a thick porous oxide scale (500–600 μm) interspersed with Ni3S2 and alloy particles formed on the alloy. For the Cr-rich DSM11 alloy, a mild corrosion attack happened, but severe internal Al-rich oxidation occurred inside the alloy. With NiCoCrAlY and NiCoCrAlYSiB coatings, the hot corrosion resistance of the systems was improved due to the formation of an α-Al2O3 scale. The hot corrosion resistance of the coatings with additions of Si and B can be improved by promoting the growth of a dense and continuous α-Al2O3 layer in the initial stage and improving the adherence of the oxide scale to the coating in the subsequent hot corrosion process. The hot corrosion degradation mechanism of the NiCoCrAlYSiB coatings and the influence of the substrate materials on the behavior of the whole system were also investigated. [Copyright &y& Elsevier]

• The NiCoCrAlY coating and NiCoCrAlYHfZr coating were prepared on a fourth generation single crystal superalloy by arc ion plating. • The NiCoCrAlYHfZr coating shows enhanced oxidation resistance and improved scale adhesion. • The addition of Hf and Zr in the coating inhibited the the formation of large voids. • The NiCoCrAlYHfZr coating has less effect on the substrate and less TCP phases can be found in the SRZ. The NiCoCrAlY coating and NiCoCrAlYHfZr coating were prepared on a fourth generation single crystal superalloy by arc ion plating. The cyclic and isothermal oxidation behaviours of the two coatings were both investigated in static laboratory air. Numerous large voids were formed in the oxide scale of NiCoCrAlY coating and they were responsible for the scale spallation. While the NiCoCrAlYHfZr coating showed better oxidation performance due to the enhanced scale adhesion. The advantage of Hf and Zr addition in the coating were discussed as well as the mutual diffusion behaviour between the coating and the substrate. [ABSTRACT FROM AUTHOR]

• • Ni 2 Al 3 coating was transformed to β-NiAl coating after vacuum heat treatment. • • Re-doped β-NiAl coating was consisted of four layers. • • Re-doped β-NiAl coating was basically formed by outward diffusion of Ni. To figure out the microstructure evolution of a Re doped Ni 2 Al 3 coating during vacuum heat treatment, the sample was heated to 1050 ℃ for 2 h and then transformed to Re doped β-NiAl coating. Re-doped β-NiAl coating was consisted of four layers including a layer with holes, β-NiAl and fine dispersed Re, a layer with β-NiAl and fine dispersed Re, a layer with β-NiAl and fine dispersed W-rich precipitates and a bottom layer of interdiffusion zone (IDZ). The β-NiAl type coating was primarily formed by outward diffusion of Ni from the substrate to react with Al of Re doped Ni 2 Al 3 coating. Moreover, the inward diffusion of Al also occurred, thus the formation of holes was attributed to the counter diffusion of vacancies in outer coating. [ABSTRACT FROM AUTHOR]

• An effective and low-cost Re-doped Ni 2 Al 3 coating was firstly fabricated by electroplating and pack cementation. • Re were all dispersed in the outer layer of Re-doped Ni 2 Al 3 coating. • Re-doped Ni 2 Al 3 coating was basically formed by inward diffusion of Al. In order to prepare Re doped aluminide coating, an effective and low-cost method of electroplating Ni-Re layer and subsequent low temperature high activity pack cementation method was used. Re-doped Ni 2 Al 3 coating was consisted of an outer Ni 2 Al 3 layer with dispersed Re-rich precipitates, a middle Ni 2 Al 3 layer with dispersed W-rich precipitates and a bottom layer of interdiffusion zone (IDZ). Interestingly, Re existed in the outer coating in form of fine Re-rich precipitates because of low solid solubility of Re in Ni 2 Al 3. [Al] was produced and absorbed on the surface of Ni-Re layer, and the activity of Al was far higher than that of Ni during pack cementation at 800 °C. Thus, Re-doped Ni 2 Al 3 coating was mainly formed by virtually singular inward diffusion of [Al] through the Ni 2 Al 3 layer. [ABSTRACT FROM AUTHOR]

• 1Re-(Ni,Pt)Al coating was prepared by electroplating and arc ion plating. • Adding Re reduced the oxidation rate and extent of β to γ′ phase degeneration. • Doping Re in the coating had advantageous effects on the morphologies of TGO. • The spallation and rumpling behavior of TGO could be relieved by Re doping. • Formation of NiAl 2 O 4 spinel was avoided due to the existence of pure Ni layer. Two β-(Ni,Pt)Al coatings with or without Re doping and a PtAl diffusion coating were prepared on a single crystal Ni-based superalloy. Isothermal oxidation behavior of all the coatings was investigated at 1100 ℃ for 300 h. The Re doped β-(Ni,Pt)Al coating possessed the best isothermal oxidation resistance because Re reduced the oxidation rate and extent of β to γ′ phase degeneration. The oxidation mechanism of the PtAl diffusion coating and advantageous roles of Re on the effect of the morphologies, anti-spallation and rumpling behavior of thermally grown oxide (TGO) were discussed as well. [ABSTRACT FROM AUTHOR]

• NiCrAlYSc coatings were prepared by arc ion plating. • Minor addition of Sc in the coating shortened the transient oxidation stage. • Minor addition of Sc in the coating promoted the transformation from θ-Al 2 O 3 to α-Al 2 O 3. • Minor addition of Sc in the coating significantly improved the scale adhesion. The NiCrAlYSc coatings with different Sc content were prepared on the Ni-based superalloy by arc ion plating. Cyclic and isothermal oxidation behaviours of all the coatings were investigated. The results show that an appropriate addition of Sc in the coating can significantly improve the scale adhesion, shorten the transient oxidation stage and promote the transformation from θ-Al 2 O 3 to α-Al 2 O 3. The effects of Sc addition on the oxidation performance of the coating as well as the mechanism of oxide adherence were discussed. [ABSTRACT FROM AUTHOR]

• Re doped aluminide coatings were prepared by electroplating and arc ion plating. • Adding appropriate amount of Re decreased the oxidation rate of the coating. • The phase transition of θ to α-Al 2 O 3 could be accelerated by Re doping. • Re-contained IDZ had the effect of diffusion barrier. • Electroplating Ni improved the oxidation resistance of the coating. Three Re doped aluminide coatings with different Re content were prepared by electroplating and subsequent arc ion plating (AIP) method. Cyclic oxidation behaviour of all coatings was carried out at 1100 ℃. The results indicated that the oxidation resistance was significantly improved with an appropriate amount of Re addition and electroplating Ni. Besides, Re accelerated the θ-to-α Al 2 O 3 phase transformation. The oxidation mechanisms of aluminide coatings with Re doped and Ni electroplated were discussed as well. [ABSTRACT FROM AUTHOR]