Microstructure and Performance of Zr-1.0Cr-0.4Fe-xMo Alloys

Abstract

For the possibility to develop Zr-based alloys with good corrosion resistance and relatively high strength as well at elevated temperature, Zr-1.0Cr-0.4Fe-xMo (x = 0, 0.2, 0.4, 0.6) alloys with different Mo addition were studied. These alloys were prepared by vacuum arc melting, the microstructure, phase transformation, tensile strength, corrosion resistance and hydrogen uptake during corrosion of these alloys was studied and the effect of Mo addition was discussed. Mo addition had a refinement effect on the microstructure, the α-laths size of the alloys in as-cast condition was decreased by Mo addition, and the recrystal grains of the alloy with 0.6% Mo addition were several times smaller than those of the alloy with no Mo addition in general. Mo addition also affected the characteristics of the second phase particles (SPPs), with the increase of Mo content, the population density of the SPPs increased significantly, whereas the average diameter of the SPPs decreased. Mo addition had a stabilization effect on β phase, the/ (α+β) phase transition temperature decreased with Mo content, especially when Mo was added to the Mo free alloy. The tensile strength of Zr-1.0Cr-0.4Fe-xMo alloys was higher than that of Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr alloy at 350°C and tended to increase with Mo content. Zr-1.0Cr-0.4Fe-xMo alloys had excellent corrosion resistance in 500°C 10.3MPa steam due to the large number of fine SPPs in the matrix. Addition of Mo promoted the change of the oxidation from cubic kinetics to liner kinetics and the formation of cracks in the oxide layers. It was thought that the solute Mo atoms in Zr matrix played an important role on the degradation of corrosion resistance. Hydrogen uptake fraction of Zr-1.0Cr-0.4Fe-xMo alloys was high initially during corrosion and decreased with the exposure time in the pre-transition region, however, when cracks were formed in the oxide layers in pos-transition region, hydrogen uptake fraction of the alloys would reached to a high level again.