Influence of Zirconium Alloy Chemical Composition on Microstructure Formation and Irradiation Induced Growth

Abstract

The studies of the dislocation structure, phase, and microchemical compositions of alloy Zr-1Nb-1.2Sn-0.35Fe (E635) and its modifications containing Fe from 0.15 to 0.65% were carried out before and after research reactor irradiation at ∼350°C to maximal fluence of ∼1027 m-2 (E > 0.1 MeV) and at ∼60°C. The size and concentration of the <a>-type loops depend on the alloy composition and fluence and saturate even at low doses (<1 dpa). The evolution of the <c>-component dislocation structure in recrystallized alloys of E365 type is determined by the chemical and phase compositions of alloys specifically, by the Fe/Nb ratio and the threshold dose, and is consistent with the irradiation growth strain acceleration. In E635 alloy containing 0.15%Fe the accelerated growth is observed after the dose of 15 dpa and is attended with the evolution of the <c> dislocation structure which is similar to Zr-1Nb (E110) alloy behavior. The irradiation induced growth of E635 type alloy containing 0.65% Fe is similar to that of E635 having the normal composition; no <c> dislocations are observed up to the dose of 20 dpa. E635 alloy contains precipitates Zr(Nb1-xFex)2 (HCP) as the basic excess phase and individual (Zr,Nb)2Fe (FCC) precipitates; in 0.15%Fe alloy aside from Zr(Nb,Fe)2 also β-Nb (BCC) particles precipitate, while 0.65%Fe alloy contains Zr(Nb,Fe)2 and (Zr,Nb)2Fe particles. Irradiation at 330 –350 °C does not effect an amorphization of β-Nb or Zr(Nb,Fe)2 precipitates; however, at higher fluences the β-Nb phase becomes depleted in Nb and Zr(Nb,Fe)2 in Fe. Irradiation at 60°C leads to the amorphization of Zr(Nb,Fe)2 in E635. The analysis revealed that the key factors promoting a delay in the accelerated irradiation growth in Zr-Nb-Fe-Sn alloys are the composition of (Nb,Fe,Sn) solid solution and the Fe/Nb ratio in alloys.

The Effect of Iron on Dislocation Evolution in Model and Commercial Zirconium Alloys

“…These samples had been irradiated to a fluence of between 8.7 and 14.7 x 10 25 n m -2 for E > 1MeV. Using a conversion of 6.0 x 10 24 n m -2 dpa -1 [23], these damage levels correspond to between 14.5 and 24.5 dpa. [26].…”

“…In Zr-Sn, Zr-Nb and Zr-Sn-Nb alloys the addition of more Fe led to a decrease in growth strain [22]. Shishov et al also showed data from the BOR-60 test reactor, which indicated that increased Fe leads to a lower IIG strain in variants of the E635 Nb containing alloy [23].…”

The characterisation of second phases in the Zr-Nb and Zr-Nb-Sn-Fe alloys: A critical review

“…Interestingly, the authors observed no β-Nb phases within α-Zr when the alloy Nb content is 0.29 wt.% and did observe β-Nb when the Nb content was 0.49 wt.%. This leads to the conclusion that Nb TSS in α-Zr is in the range 0.29-0.49 wt.% at temperatures below the Zr-Nb monotectoid temperature (<600 °C), a value much greater than that suggested by Canay et al Figure 1 Ternary Zr-Nb-Fe diagram generated from data after [3,[20][21][22][23][24][25][26][27]29,[41][42][43][44]46,[62][63][64]. All compositions are given in at.%.…”

“…This designation of β-Nb should be distinguished from the β-Nb that exists after heattreatments below the Zr-Nb monotectoid. The Fe content in β-Nb below the Zr-Nb monotectoid is reported in commercial alloys but only convincingly in phases that were ZrNbFe ternary phases prior to irradiation that had undergone irradiation-induced Fe depletion resulting in a composition such as Zr42Nb50Fe8, at.% [27]. Again, the description of the phase as β-Nb is somewhat ambiguous given that β-Nb has a Nb composition ~85%-90% according to the binary Zr-Nb phase diagram [28].…”

Effects of ion irradiation on microstructure and properties of zirconium alloys—A review

“…The uniform corrosion is enhanced while the nodular corrosion resistance of neutron irradiated Zr-2 is improved due to the neutron irradiation [22]. Considering the mechanical effects, the zirconium alloys exhibit irradiation hardening [23,24], irradiation growth [2, 25,26], and reduction of plastic anisotropy [27,28].…”