Depth Profile of Nitrogen and Oxygen absorbed in HAZ of ZrTN802D Alloy Tube by TIG Welding in Various Atmospheres (Report 1)

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Investigations were made on the depth profiles of nitrogen (N) and oxygen (O) absorbed in HAZ of ZrTN802D alloy (Zircaloy-2) tubes relative to the microstructure changes by TIG welding in the atmospheres with extremely low level of N₂ and O₂ partial pressures in total pressures of 0.10 and 0.32 MPa.
The original fine microstructures of cold worked and heat treated ZrTN802D alloy tubes were changed by transformation in the HAZ heated to α+β and β phase temperature ranges (1, 090-2, 113 K), and the regions microstructurally changed by welding at 0.32 MPa were narrower than those welded at 0.10 MPa.
By the measuring of secondary ion intensities of ⁹⁰Zr¹⁴N- and ¹⁸O- using SIMS continuously from surface into deeper portion in HAZ, it was made clear that N was absorbed and diffused at the portion heated to α+β and β phase temperature ranges therein and the content of N decreased exponentially toward inside. O was absorbed more at the portion heated within a phase temperature range (<1, 090 K) in HAZ rather than that of β phase range in HAZ and O was diffused thereinto within only a few μm in depth.