HightemperaturemechanicalbehaviorofZr–2.5%NballoyOriginalResearchArticle

Zr–2.5%Nballoyiswidelyusedasstructuralmaterialforpressuretubesofchannelnuclearpowerreactorscooledbyheavypressuredwater(CANDU-PHW)andboilerwater(RBMK,Fugen).TensileandcreepbehaviorofZr–2.5%Nballoysignificantlydependonheattreatment.Zr–2.5%Nballoyisusedafterdifferentheattreatmentstosatisfydesignrequirementstoreactorpressuretubes:α-annealing(reactorRBMK-1000),waterorgasquenchingandaging(reactorRBMK-1500andFugen),cold-workandstress-relief(reactorCANDU).AnexperimentalprogramhasbeenelaboratedtoresearchresistancetoplasticflowandruptureofZr–2.5%Nballoyatthetemperatures20–1200°C.Tensiletestswerecarriedoutataconstantcross-headspeedintherange10−2to10−4s−1andcreeptestsunderuniaxialload.Temperaturedependenceofflowandrupturestressweredistinguishindifferenttemperatureranges.Threerangesoftemperaturewereobservedwheretherateofthestrengthreductionwassignificantlydifferent.Extremelylargeelongationwasobservedinthe600–800°Crangethatismanifestationofsuperplasticity.Thetemperaturecorrespondingtomaximumelongationwasequal∼700°C.Increaseofstrainratefrom∼10−4to10−2s−1didnotchangedthetemperaturerangesofsuperplasticityobservationbutresultedindecreaseofelongationvalues.