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The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy. [ABSTRACT FROM AUTHOR]

The effect of aging treatments at various temperatures on the mechanical properties and microstructure of 10B21 cold heading steel with a 20% reduction in area (ε = 0.1) was investigated. The mechanical properties were evaluated based on tensile tests and hardness tests, while the evolution of microstructure was observed by using an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results reveal that aging treatment enhance the strength and hardness of 10B21 cold heading steel after drawing, and the highest values of strength and hardness are attained at an aging temperature of 300 °C. Specifically, the yield and ultrahigh tensile strength after aging at 300 °C are measured at 620 MPa and 685 MPa, respectively, which are 30 MPa and 50 MPa higher than the cold-drawn sample. Moreover, the hardness after aging at 300 °C reaches 293 HV, which has an increase of 30 HV compared to the cold-drawn state. The improvement in mechanical properties may be related to the strain-aging mechanism and the increased density of dislocations. In addition, the analysis of the TEM results reveal that the presence of the second-phase Ti(C,N) contributes to pinning the dislocations, whereas the dislocations are pinned between the cementite (Fe3C) lamellar and stacked at the grain boundaries, leading to strain hardening of the material. [ABSTRACT FROM AUTHOR]

The present study investigates the creep behavior and deformation mechanism of a third-generation single-crystal Ni-based superalloy at 1170 °C under a range of stress levels. Scanning electron microscopes (SEM) and transmission electron microscopes (TEM) were employed to observe the formation of a rafted γ′ phase, which exhibits a topologically close-packed (TCP) structure. The orientation relationship and elemental composition of the TCP phase and matrix were analyzed to discern their impact on the creep properties of the alloy. The primary deformation mechanism of the examined alloy was identified as dislocation slipping within the γ matrix, accompanied by the climbing of dislocations over the rafted γ′ phase during the initial stage of creep. In the later stages of creep, super-dislocations with Burgers vectors of a<010> and a/2<110> were observed to shear into the γ′ phase, originating from interfacial dislocation networks. Up to the fracture, the sequential activation of dislocation shearing in the primary and secondary slipping systems of the γ′ phase occurs. As a consequence of this alternating dislocation shearing, a twist deformation of the rafted γ′ phase ensued, ultimately contributing to the fracture mechanism observed in the alloy during creep. [ABSTRACT FROM AUTHOR]