Study on the Role of Second Phase Particles in Hydrogen Uptake Behavior of Zirconium Alloys

In an effort to better understand the role of second phase particles (SPPs) in the hydrogen uptake of zirconium alloys, four alloys and four heat treatments for each alloy were chosen to prepare specimens with different SPPs size distributions and area fractions. The hydrogen uptake performance of these specimens was investigated after autoclave testing in 400C/10.3 MPa steam. Results show that the hydrogen uptake is not always in a strict corresponding relationship with the corrosion resistance among the specimens, but it is closely related to the size, area fraction, and compositions of the SPPs. In the case of Zry-2 and Zry-4, the hydrogen uptake fraction (HUF) increased with increasing size and area fraction of the SPPs. The dependence was more notable for the Zry-2 than the Zry-4. In the case of N36 and N18, the HUF had only a slight variation with the size and area fraction of the SPPs. No matter which heat treatment was employed, the corrosion resistance of the N18 specimens was superior to the N36 specimens, but the HUF of the former was larger than that of the latter. These results clearly demonstrate that the effect of the size and area fraction of SPPs on the hydrogen uptake depends on the SPP compositions. Pressure-composition-temperature and kinetics of absorbing and desorbing hydrogen tests were conducted on Zr(Fe,Cr)₂, Zr₂(Fe,Ni), Zr(Nb,Fe)₂, and β-Nb alloys (which may be found as SPPs in the four zirconium alloys tested) as well as on pure zirconium. Results show that Zr(Nb,Fe)₂, Zr₂(Fe,Ni), and Zr(Fe,Cr)₂ alloys have a stronger reversible ability for hydrogen absorption and desorption than β-Nb alloy and pure zirconium. Based on the testing results, a model correlating the hydrogen uptake performance to the reversible ability of the SPPs to absorb and desorb hydrogen is proposed. The model can successfully explain the results.