| Nowadays,accident tolerant fuel(ATF)claddings are extremely urgent to increase the safety margin of light water reactors(LWRs),especially after the Fukushima accident in 2011.Zirconium alloys have served as commercial LWRs fuel cladding materials well more than half a century.However,zirconium alloy reacts easily with high-temperature steam when loss of coolant accidents occurs,which can release dangerous levels of hydrogen gas as well as lots of heat,giving rise to a hydrogen explosion.So that,it is indispensable to develop ATF claddings to completely eliminate or effectively prevent the oxidation reaction of zirconium alloy with high-temperature steam,and this study has important scientific significance and important practical application significance of engineering.The motivation of this work is preparing a protective coating on Zr to improve the high-temperature steam oxidation resistance of Zr.It can be found that the previous studies have mainly focused on the pure Cr metallic coatings or the Cr-based binary crystal coatings,but less attention has been paid on the application of multiple alloy crystal and amorphous coatings to increase the high-temperature steam oxidation resistance of Zr-based alloys.From an alloy-design viewpoint,ternary and higher alloying additions can decrease the solubility of the oxygen in the alloy,and therefore favor protective scale formation.(1)Cr-Al-Si-(N)protective coatings,with various N contents(0-38.3 at.%),were deposited on Zr substrates by magnetron sputtering.The thickness of the coatings varied from ~4 ?m or 11.5 ?m.Subsequently,microstructure,mechanical properites,and behavior of high-temerature steam oxidation of the coatings,were investigated.(2)With the increase of the N content,the growth structure of the coating evolves from dense columnar,through dense featureless,to loose columnar.The coatings exhibite better mechanical properties than the uncoated Zr coupon.The hardness of the coatings is in the range from 10.2 GPa to 14.6 GPa,and the elastic modulus of the coatings is in the range from 184 GPa to 228 GPa.(3)The high-temperature steam oxidation tests were performed at 1000 °C for 15 min,and at 1200 °C for 30 min,respectively.It was observed that the Cr-Al-Si coating(0 at.% N)and the CrAlSiN coating(28.6 at.% N)could greatly enhance the oxidation resistance of the Zr substrate.After the 1200 °C-30 min test,the thickness of the oxided Zr in the uncoated Zr was 100 ?m.While the thickness of the oxided Zr was 42 ?m and 8 ?m beneath the Cr-Al-Si(4 ?m thickness)and Cr-Al-Si-N(28.6 at.% N,4 ?m thickness)coatings,respectively.The substrate Zr of the Cr-Al-Si-N(28.6 at.% N,11.5 ?m thickness)coating sample was not oxidized after the 1200 °C-30 min test,only 5 ?m-thick oxidation of the coating was observed.The results indicated that the coating with good high-temperature steam oxidation resistance needs not only dense structure,but also the compositions that favored to selective oxidation.(4)The four coatings of the deposition state are completely exposed at the load of 33-49 N,which showed that the four coatings have a good adhesion with Zr substrate.Moreover,the adhesion of three coatings and substrate is improved after the hightemperature oxidation,with the adhesion strength of the oxidized coating-Zr substrate more than ~50 N.The improved adhesion could be greatly attributed to the interdiffusion between the coating and the Zr substrate.Based on the evaluation in terms of mechanical properties and oxidation resistance.The dense amorphous Cr-Al-Si-N coating with 28.6 at.% N and dense columnar CrAlSi coating have the potential to be used as surface protection coatings for nuclear-use Zr claddings. |
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