Ultrasonic vibration assisted gas tungsten arc welding of Inconel 690 alloy: Ultrasonic effect to refine grains and improve mechanical properties.

The Inconel 690 alloy is widely used in the manufacturing of nuclear equipment, such as pipe welding for steam generators (SG) and pressure vessels, due to its excellent high-temperature strength, corrosion resistance, and thermal stability. However, coarse grains have been observed in the welded joint of Inconel 690. Considering its crucial role as a structural material under high pressure, temperature, and corrosive conditions, improvements should be made to the microstructure of the welded joint. The ultrasonic-assisted gas tungsten arc welding (UA-GTAW) was used in Inconel 690 welding. The influence of ultrasonic vibration on the microstructure and mechanical properties of welded joints was studied. The results show that the ultrasonic refined the microstructure further to improve the mechanical properties. The UA-GTAW sample performed superiorities over regular GTAW joint in multi perspective including refined solidification grains, less element segregation, higher tensile strength and hardness. The Yield strength, ultimate tensile strength, and elongation increased from 320 MPa, 591 MPa, and 25.1 % to 387 MPa, 672 MPa, and 31.6 %, respectively.

Ag2Mo2O7: an oxide solid-state Ag+ electrolyte.

Ag2Mo2O7 powders and micro-crystals were prepared at 400 °C for 24 h and 500 °C for 6 h using solid-state reactions. The Ag2Mo2O7 samples crystalized in a triclinic P1̄ space group with the cell parameters a = 6.0972(1) Å, b = 7.5073(1) Å, c = 7.6779(2) Å, α = 110.43(1)°, ß = 93.17(1)°, γ = 113.51(1)°, and V = 294.17(1) Å3 from Rietveld refinements. Ag2Mo2O7 powder is homogeneous with size of 2-8 µm and the ceramic pellets are in good sintering conditions with a relative density ∼93%. The indirect band gaps E g(i) of Ag2Mo2O7 from reflectance measurements and DFT calculations are 2.63(1) and 1.80 eV. The vibrational modes of Ag2Mo2O7 were investigated by first-principles (DFT) calculations and Raman spectrum measurements with 24 of 33 predicted Raman modes recorded. According to DOS analyses, the valence bands (VB) of Ag2Mo2O7 are mainly constituted of O-2p and Ag-4d orbitals, while the conduction bands (CB) are mainly composed of Mo-4d and the O-2p orbitals. Regarding the impedance analysis, Ag2Mo2O7 is a silver oxide ion electrolyte with a conductivity of ∼5 × 10-4 S cm-1 at 450 °C. The carrier activation energy of Ag2Mo2O7 is 0.88(3) eV from the temperature dependent conductivity measurements.