| New zirconium alloys of Zr-0.8Sn-xNb(x=0.2, 0.4, 0.8, 1.2) were manufactured into sheet by the qualified procedure; arc melting, beta-quenching, hot rolling, cold rolling, and annealing. Corrosion and mechanical properties with variation of Nb-content were investigated to find the optimal niobium content for new Zr alloy. Corrosion test was carried out in autoclave under 420℃ steam. Corrosion rate and hydrogen pickup decreased with increasing the Nb-content. The observation of oxide structure by using low angle diffraction method of X-ray showed that the amount of tetra-ZrO₂ in oxide increased with increasing the Nb-content. It is considered that Nb has an effect retarding the transition of oxide from tetra-ZrO₂ to mono-ZrO₂ which is porous and nonprotective oxide. Mechanical strength increased for the high Nb-containing alloy showing the solution hardening of Nb. Two type of precipitate. Zr-Nb-Fe and β-Zr, were found in Zr-0.8Sn-xNb alloys and corrosion resistance improved in the precipitate size above 0.1 ㎛. |
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