Microstructure Characteristics of the Second Phase in Heat Affected Zone of Pressure Resistance Welded Joints of Zircaloys

The Zr-4 alloy tube and Zr-Sn-Nb zircaloy tube were connected with Zr-4 alloy column by pressure resistance welding on a thermal simulator. The morphology, composition and crystal structure of the second phase in the heat affected zone of the joint were studied and compared with those of the base metal. The results show that the second phase particles in the heat affected zone near the fusion line of Zr-4 alloy joint were completely dissolved under the thermo-mechanical coupling effect of pressure resistance welding, and the number of the second phase particles of the hexagonal close-packed structure Zr (Fe, Cr)₂ Laves phase near the base metal was significantly reduced, and the average diameter increased. The number of the second phase particles in the heat affected zone near the fusion line of the Zr-Sn-Nb alloy joint was small, and mainly consisted of body-centered cubic structure β-Nb phase with a diameter less than 50 nm. The number of the second phase particles in the heat affected zone near the base metal was between that of the base metal and that in the heat affect zone near fusion line, and the second phase was composed of fine body-centered cubic structure β-Nb phase and coarse face-centered cubic structure (Zr, Nb) Fe₂ phase.