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The oxidation behavior of GH2984 alloy in pure steam at 750℃ and 850℃ was investigated by using X-ray diffractometer (XRD) and scanning electron microscope equipped with energy dispersive spectra (SEM/EDS). Results show that GH2984 alloy is oxidized parabolically with time. The temperature rising greatly promotes the external and internal oxidation and also the evaporation of Cr. The composition and microstructure of the oxide films change obviously. At 750℃, a compact and single-layered (Cr,Mn)2O3 film is formed on alloy surface; the number of voids in oxide scale increases at 850℃, whereas a three-layered oxide scale consisting of thin Fe2TiO5 outer layer and much thicker (Cr,Mn)2O3 middle layer and thinner (Nb,Mo)2O5 inner layer is formed at the elevated temperature. Ti and Al are internally oxidized preferentially along grain boundaries to be TiO2 and Al2O3, respectively; both the number and the size of the two internal oxides increase with the temperature rising.

Unstressed exposure tests of Inconel 740H alloy tube were carried out at 750℃ for 500-3000h. The microstructure evolution and microhardness were studied by means of thermodynamic simulation, OM, FEG-SEM and microhardness testing. The results show that the tube is qualified if both chemical composition and tensile properties of the as-received alloy meet the corresponding requirements of ASME. After long term exposure, the main precipitates are γ' and M23C6, and no η and σ phase. With the prolonging of exposure time, the coarsening of γ' becomes faster and the law of relationship between the radius of γ' and time accords with LSW Ostwald ripening law; meanwhile, the change in size of M23C6 is not so obvious. During the whole process, microhardness increases firstly and then decreases, but the fluctuation is slight. The changes of microstructure and hardness indicate that, after long time exposure, the domestic Inconel 740H has good stability and can be used for further carrying out the investigation on the mechanical property of creep-rupture.

Refractory high‐entropy alloys (HEAs) have shown promising high temperature strengths, while their mechanical behaviors at room temperature are rarely reported. In this work, the room‐temperature mechanical properties of V20Nb20Mo20Ta20W20 refractory HEA under various different loading modes including tension, compression, bending, shear loading, and microhardness are investigated. The results show that this alloy exhibits very high compressive strength but quite low strengths under tension, bending, and shear loading, similar to the conventional brittle materials. However, pronounced plasticity and slip bands are observed in compression samples, and no indentation cracking is observed in low‐load microhardness tests, which indicate the potential ability of plastic deformation in this refractory HEA. The present work suggests that the microstructure or composition of this HEA should be carefully tailored before its practical usage to suppress its large tendency for cracking and eventually improve its ductility and strength under tension. [ABSTRACT FROM AUTHOR]

The oxidation behavior of a Ni-30Fe-20Cr base alloy with/without yttrium was studied in pure steam at 750 °C. Results showed that the oxide scale formed was equiaxed Cr 2 O 3 and grew parabolically with time. Underneath the scale, Si, Ti and Al was internally oxidized into SiO 2 , TiO 2 and Al 2 O 3 , respectively. Alloying 0.05–0.10 wt.% yttrium reduced the oxidation rate of the alloy by about 2 factors and improved the oxide adherence and also suppressed the internal oxidation. The reason for it probably lies in the decrease of the outward diffusion of chroumium along grain boundaries. [ABSTRACT FROM AUTHOR]