Optical fiber sensor and assembly method for measuring the tensile strain of a nickel-based directionally solidified superalloy in a high-temperature environment.

Nickel-based superalloys are widely used in key hot-end components such as aero engines and industrial gas turbines due to their excellent comprehensive properties. Real-time monitoring of engine blades and other structures in high-temperature environments can promptly discover possible internal damage to the structure. Optical fiber sensing technology has unique advantages that traditional electrical sensors do not have, such as anti-electromagnetic interference, small size, light weight, and corrosion resistance. The technology is gradually replacing traditional methods and becoming an important means of structural health monitoring. We propose an optical fiber sensor and assembly method that can be used to measure the strain of a nickel-based directionally solidified superalloy in a high-temperature environment more accurately. The proposed technology is simple to manufacture and also has low cost and a high survival rate, which is of great significance for high-temperature strain measurements in aerospace and other fields.

First-principles thermodynamics and experimental study of interface oxidation in Ni/Ni3Al structures.

Anti-oxidation is one of the significant properties of nickel-based superalloys useful for their potential applications in industry. However, previous research mainly focused on single-phase compounds of NiAl or Ni3Al. In the present study, first-principles density functional theory coupled with thermodynamics analysis are employed to investigate the atomistic oxidation behaviours of the Ni/Ni3Al composites systematically. An oxidation experiment with a DD6 alloy is conducted as well to further confirm the theoretical prediction. Initial surface formation energy analysis shows that the systems composed of Ni(111) and Ni3Al(100)/(111) surfaces are more stable and therefore are selected for further investigation. Thermodynamics calculations indicate that the Ni3Al phase is oxidized first, accompanied by Al-segregation on the top surfaces. This is followed by subsequent oxidation of the Ni phase. Surface oxidation diagrams with respect to the surface formation energies show that oxygen adsorption could enhance Al-segregation to the surface and Ni3Al(111) surfaces tend to be oxidized completely with slightly lower oxygen coverage. Oxidation at the interface is also investigated and the results show that oxygen atoms bind with the upper layers of the Ni3Al phase from the point of view of binding energy. The experimental results provide a reasonable explanation for the selective oxidation of Al atoms at the atomic-scale so as to form a dense anti-oxidation membrane. The present work could serve as a beneficial reference for subsequent investigations of oxidation or adsorption processes of two-phase composites.

Tensile Deformation Behavior of Typical Porous Laminate Structure at Different Temperatures.

In this study, the Ni-Cr-W superalloy GH3230 is used as the test material. According to the actual structure of the flame tube, a porous laminate structure specimen is designed. The structure consists of impact holes, overflow holes and pin fins. High-temperature tensile tests at 650 °C, 750 °C and 850 °C were carried out to study the high-temperature mechanical properties and fracture mechanism of the specimens of porous laminate structure, and the strain nephogram of the specimens were obtained by digital image correlation (DIC) technique. Due to the large number and dense arrangement of overflow holes, an obvious hole interference effect can be found from the strain nephogram. The stress concentration around the pore and the interference between the pores provide priority places and paths for the initiation and propagation of microcracks. The test found that the microcracks of the porous laminate structure first occurred around the hole, the overflow surface fractured first, after which the impact surface fractured. The strength of the alloy exhibits a significant temperature sensitivity to temperature. From 650 °C to 750 °C, the ultimate strength (σb) and yield strength (σ0.2) decrease slightly, but they decrease significantly at 850 °C. The microstructure of the fracture surface shows that all microcracks occur at the interface between the matrix and the carbides but that the fracture mode of the specimens gradually changes from intergranular fracture to transgranular fracture as the temperature increases. Due to the pinning effect of the intracrystalline diffusive solute atoms on the dislocations, the stress-strain curves of the high-temperature tensile tests at 650 °C and 750 °C showed zigzag characteristic fluctuations during the strengthening stage.

The Effect of the Cooling Rates on the Microstructure and High-Temperature Mechanical Properties of a Nickel-Based Single Crystal Superalloy.

The as-cast alloy of nickel-based single-crystal superalloy was used as the research object. After four hours of solution treatment at 1315 °C, four cooling rates (water cooling (WC), air cooling (AC) and furnace cooling (FC1/FC2)) were used to reduce the alloy to room temperature. Four different microstructures of nickel-based superalloy material were prepared. A high-temperature tensile test at 980 °C was carried out to study the influence of various rates on the formation of the material's microstructure and to further obtain the influence of different microstructures on the high-temperature mechanical properties of the materials. The results show that an increase of cooling rate resulted in a larger γ' phase nucleation rate, formation of a smaller γ' phase and a greater number. When air cooling was used, the uniformity of the γ' phase and the coherence relationship between the γ' phase and the γ phase were the best. At the same time, the test alloy had the best high-temperature tensile properties, and the material showed a certain degree of plasticity. TEM test results showed that the test alloy mainly blocked dislocations from traveling in the material through the strengthening effect of γ', and that AC had the strongest hindering effect on γ' dislocation movement.