Microstructure and Properties of Corrosion-Resistant Zirconium-Tin-lron-Chromium-Nickel Alloys

Long-term autoclave tests in steam at 673 K and mechanical property (tensile and creep) tests have been conducted to evaluate the effects of chromium (0 to 0.3%) and nickel (0 to 0.08%) additions on the corrosion and mechanical properties of dilute zirconium-tin-iron alloys. The base alloys contain 0.4% iron and either 0.5% or 1.0% tin. Multiple regression analysis showed tin concentration to have a statistically significant effect on corrosion, hydrogen pickup, creep, and tensile strength. The corrosion resistance of the alloys increased significantly when the tin concentration decreased from 1.0 to 0.5%. An additional improvement in corrosion resistance was observed with increasing chromium content. Nickel additions had no apparent effect on corrosion for the alloy compositions examined. Lower hydrogen pickup fractions were measured for alloys containing 0.5% tin compared to alloys containing 1.0% tin. No significant effects of chromium or nickel additions to hydrogen pickup were observed. Creep rate decreased with increasing tin concentration and to a lesser extent with increasing chromium content. Nickel additions produced a large increase in creep rate for some alloys but not others. This suggests a possible interaction between nickel and the other alloy additions in determining creep strength. Intermetallic particle type and size distribution varied with alloy composition. Chromium additions tended to decrease the particle size distribution of Zr(Fe,Cr)2 intermetallic particles. Conversely, nickel additions produced large particles of the Zr2(Fe,Ni) type intermetallic. Changes in the intermetallic particle distributions and matrix compositions are discussed with regard to the observed changes in corrosion and mechanical properties of the alloys.