Embrittlement of reduced-activation ferritic/martensitic steels irradiated in HFIR at 300°C and 400°C (original) (raw)
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Journal de Physique IV (Proceedings), 2002
Tensile tests and microstructural examinations were performed on 100 pm thick specimens of 9Cr-1Mo (EMlO) and modtfied 9Cr-1Mo (T91) martensmc steels homogeneously implanted wrth 23 MeV a particles to a concentration of 5000 appm. Two implantatron temperatures were selected, 250 and 550°C which correspond respectively to the lower (hrgher) bound of the operation temperature range foreseen for the window of Accelerator Driven Systems devoted to waste transmutation. 25O'C is also the maximum operatmg temperature of the ESS (European Spallation Source) window. The spectmens were tested at room and rmplantatron temperatures and the fracture surfaces were characterized using scanmng electron microscopy. It was found that Implantation at 250°C induces a very strong hardening of both materials together wtth a total loss of ductility. Embrtttlement was also observed for the specrmens implanted at 550°C however the ductibty loss was much less severe. Prelimmary Transmrssron Electron Mtcroscopy (TEM)-observations are presented. Hehum bubbles were observed in the specrmens Implanted at 550°C but none could be detected m the samples implanted at the lower temperature. However, based on results of Small Angle Neutron Scattermg experrments performed on samples implanted together w:th the tensile specimens, It IS proposed that the high degree of hardenmg followmg tmplantatron at 250°C is due to the formatton of a high density of tiny hehum bubbles. It IS furthermore suggested that the brittle, intergranular fracture mode dtsplayed by these specimens results from the combined effects of pronounced intragranular hardening and weakening of Prior Austenite Gram (PAG) boundarres due to helium. Pr8-104 JOURNAL DE PHYSIQUE IV caracttrisation des facets de rupture a ete effect&e par Microscopic Electronique a Balayage. 11 a Cte constate que l'implantation d'helium a 250°C mdmt un durcissement tres important associe a une perte totale de ducttlite. Une fragilrsation est egalement muse en evidence a 55O"C, mais les Cchantillons conservent neanmoms une certaine ductilite. Des resultats prelimmaires d'observations par Microscopic Electronique en Transmission (MET) sont present&. Des bulles d'helium sont observees dans les Cchantlllons implant& a 550°C mais la presence de bulles n'a pas pu Ctre detectee dans les echantillons implant& a plus basse temperature. Neanmoins, sur la base de resultats d'expenences de Diffusion de Neutrons aux Petits Angles effect&es recemment sur des Cchantillons implant& dans les memes conditions que les Cprouvettes de traction, nous pensons que le tres fort durcissement induit par l'implantation a 250°C est dQ a la formation d'une densite ClevCe de petltes bulles d'helium. Nous suggtrons par ailleurs que le mode de rupture fragile et mtergranulaire observe apres implantation a 250°C est le resultat des effets combmes du durcissement et d'une dimmution de l'energie de cohesion au niveau des joints de grain induite par la presence d'helmm.
Influence of helium on impact properties of reduced-activation ferritic/martensitic Cr-steels
Journal of Nuclear Materials, 1999
Instrumented Charpy impact tests of the reduced activation type 8Cr2WVTa steel F82H have been performed after homogeneous implantation of 300 appm helium at 250°C. The results are compared with investigations on mixed spectrum neutron irradiated (HFR Petten) specimens. After neutron irradiation at 250°C to the same low damage dose of 0.2 dpa, the ductile±brittle transition temperature shift (DDBTT) amounts to 18°C, whereas a much higher DDBTT of 42°C has been measured after helium implantation. These results are compared with other neutron irradiated ferritic/ martensitic steels having dierent boron levels and thus dierent helium contents. A model is proposed which describes the dynamic brittle fracture of martensitic/ferritic steels by a stress-induced propagation of micro-cracks, taking into account radiation induced hardening as well as helium bubble formation. Ó
Journal of Nuclear Materials, 1978
Samples of a heat-resistant austenitic steel (both boron free and with 0.005% by weight boron added) were irradiated in the active zone of Reactor WWR-M with a neutron flux of 4 X 1013 n/cm'. s (E 2 3 MeV) and 6 X 1013 n/cm2. s (E Q 0.03 eV) at fixed temperatures in the range of 600°C to 850°C. The neutron fluence was 6 to 8 X 1019 n/cm2. For the study of the helium release kinetics the samples were annealed with a constant heat-up rate. The experimental equipment and procedure were described previously. Most of the helium (70 to 90%) is released at temperatures of 1420 to 1490°C. This is connected with the melting of the samples. Helium release during the annealing in the range 20 to 1300°C is observed in the form of seven peaks on the curve of gas-release rate. Attempts to interpret the helium diffusion mechanism of each stage is given by determination of the activation energies and other data. Irradiation in a helium atmosphere leads to penetration of helium into the samples, which is proportional to the external gas density. A significant intensification of the generation of helium cavities occurs at irradiation temperatures of 750 to 850°C. Des kchantillons d'acier austenitique resistant i chaud (i la fois exempt de bore et contenant 0.005% en poids dc bore) ont et& irradies dans la zone active d'un reacteur WWR-M par un flux de neutrons de 4 X 10 l3 n/cm2. s (E > 3 MeV) et 6 X 1013 n/cm2. s (E Q 0.03 eV) i temperature constant dans l'intervalle 600-850°C. La fluence neutronique etait de 6 i 8 X 1019 n/cm2. Pour etudier la cinetique de degagement de l'helium, les echantillons etaient recuits avec une vitesse de montee en temperature constante. L'iquipement et le processus experimental ont CtC decrits anterieurement. La plus grande partie de l'hdlium (de 70 i 90%) est d&gag&e aux temperatures de 1420 a 1490°C. Ceci est relic i la fusion des echantillons. Le degagement de l'helium durant le recuit dans l'inteivalle 20-l 300°C est observe sous la forme de 7 pits sur la courbe de vitesse de digagement de gaz. Des essais d'interprgtation du mecanisme de diffusion de l'helium i chaquc stade sont bases sur la determination des energies d'activation et sur d'autres donnees. L'irradiation dans une atmosphere d'helium conduit a la penetration de l'helium dans les echantihons, penetration qui est proportionnelle i la densitd du gaz externe. Une intensification significative de la creation de cavites d'helium se produit aux temperatures d'irradiation de 750 a 850°C. Wlrmebestlndige austenitische Stahlproben (borfrei und mit einem Borzusatz von 0.005%) wurden in der aktiven Zone des Reaktors WWR-M in einem Neutronenfluss von 4 X 1013 n/cm2 s (E > 3 MeV) und 6 X 1013 n/cm2. s (E G 0.03 eV) bei bestimmten Temperaturen zwischen 600 und 850°C bestrahlt. Die Dosis betrug 6 bis 8 X 1019 n/cm2. Zur Untersuchung der Kinetik der Heliumfreisetzung wurden die Proben bei konstanter Aufheizgeschwindigkeit wlrmebehandelt. Apparatur und Methode wurden ktirzlich beschrieben. Der grijsste Teil des Heliums (70 bis 90%) wird zwischen 1420 und 1490°C freigcsetzt, was mit dem Schmelzen der Proben im Zusammenhang steht. Die Heliumfreisetzung wiihrend der WCrmebehandlung zwischen 20 und 1300°C wird in form von sieben Peaks in der Gasfreisetzungsgeschwindigkeitskurve beobachtet. Die Versuche zur Deutung des Heliumsdiffusionsmechanismus in jeder Stufe erfolgen durch Bestimmung der Aktivierungsenergien und anderer Daten. Die Bestrahlung in einer Heliumatmosphare fiihrt zu einem Eindringen des Heliums in die Proben, das der Dichte des Lusseren Gases proportional ist. Eine verstlrkte Heliumporenbildung tritt bei Bestrahlungstemperaturen zwischen 750 und 850°C auf.
Damage behavior in helium-irradiated reduced-activation martensitic steels at elevated temperatures
Journal of Nuclear Materials, 2014
Dislocation loops induced by helium irradiation at elevated temperatures in reduced-activation martensitic steels were investigated using transmission electron microscopy. Steels were irradiated with 100 keV helium ions to 0.8 dpa between 300 K and 723 K. At irradiation temperatures T irr 6 573 K, small defects with both Burger vectors b = 1/2h1 1 1i and b = h1 0 0i were observed, while at T irr P 623 K, the microstructure was dominated by large convoluted interstitial dislocation loops with b = h1 0 0i. Only small cavities were found in the steels irradiated at 723 K.
Helium ion irradiation induced swelling and hardening in commercial and experimental ODS steels
2014
The radiation resistance of two promising ferritic ODS steels, PM2000 and 15CRA-3, is studied. More specifically, the effect of helium on these materials is studied by examining the swelling and hardening after He + implantation to 1dpaat4000appm/dpa.Whitelightinterferometryisusedtomeasurethepost−irradiationsurfacedisplacementwhereasmirco−hardnessmeasurementsarecarriedouttodeterminetheradiationhardening.Thesemethodsprovetobeveryefficientandfastworking,thusmakinggoodstatisticsobtainableinareasonabletime.Lowswellingisfoundinbothalloys,althoughthePM2000showsalowerresistance,withanincreasedswellingof1 dpa at 4000 appm/dpa. White light interferometry is used to measure the post-irradiation surface displacement whereas mirco-hardness measurements are carried out to determine the radiation hardening. These methods prove to be very efficient and fast working, thus making good statistics obtainable in a reasonable time. Low swelling is found in both alloys, although the PM2000 shows a lower resistance, with an increased swelling of 1dpaat4000appm/dpa.Whitelightinterferometryisusedtomeasurethepost−irradiationsurfacedisplacementwhereasmirco−hardnessmeasurementsarecarriedouttodeterminetheradiationhardening.Thesemethodsprovetobeveryefficientandfastworking,thusmakinggoodstatisticsobtainableinareasonabletime.Lowswellingisfoundinbothalloys,althoughthePM2000showsalowerresistance,withanincreasedswellingof0.8% dpa À1 at 600°C, while the 15CRA-3 presents an almost constant swelling of around 0.4% dpa À1 throughout the complete temperature range. Radiation hardening follows a similar trend, whereby hinting towards an annealing mechanism taking place at the interfaces between the very fine distribution of Y 2 O 3 nanoparticles and the matrix, interfaces which act as sites of enhanced point defect recombination as well as traps for the implanted helium.
Experimental determination of the effect of helium on the fracture toughness of steel
Journal of Nuclear Materials, 2002
A fundamental issue with the use of structural steels for fusion applications is the effect of helium on mechanical properties. This concern has been difficult to address due to the limited neutron energies, hence limited helium production, of the fission reactor facilities used to simulate the effects of irradiation on properties such as fracture toughness. This paper compares results from identical pre-cracked DCT fracture toughness samples irradiated using spallation and fission neutrons at ~60-90°C. Materials studied were 304L and 316L stainless steel. The spallation neutron irradiated specimens were irradiated over a dose range up to ~ 10 dpa with a helium and hydrogen-to-dpa ratio of approximately 60 and 400 appm/dpa, respectively. Fracture toughness was seen to rapidly decreased from a value of ~250 MPa-m 1/2 to ~ 200 MPa-m 1/2 by the 1 dpa level. Following fission irradiation in the 1-1.5 dpa range, fracture toughness results were indistinguishable from those irradiated in the spallation neutron. The calculated helium and hydrogen concentration for the fission neutron irradiated materials was ~ 1 appm and ~30 appm, respectively.
Embrittlement of CrMo steels after low fluence irradiation in HFIR
Journal of Nuclear Materials, 1995
Subsize Charpy impact specimens of 9Cr-IMoVNb (modified 9Cr-lMo) and 12Cr-lMoVW (Sandvik HT9) steels and 12Cr-MoVW with 2% Ni (12Cr-IMoVW-2Ni) were irradiated in the High Flux Isotope Reactor (HFIR) at 300 and 400°C to damage levels up to 2.5 dpa. The objective was to study the effect of the simultaneous formation of displacement damage and transmutation helium on impact toughness. Displacement damage was produced by fast neutrons, and helium was formed by the reaction of 58Ni with thermal neutrons in the mixed-neutron spectrum of HFIR. Despite the low fluence relative to previous irradiations of these steels, significant increases in the ductile-brittle transition temperature (DBTT) occurred. The 12Cr-IMoVW-2Ni steel irradiated at 400°C had the largest increase in DBTF and displayed indications of intergranular fracture. A mechanism is proposed to explain how helium can affect the fracture behavior of this latter steel in the present tests, and how it affected all three steels in previous experiments, where the steels were irradiated to higher fluences.
Helium and radiation defect accumulation in metals under stress
Vacuum, 2008
The results of investigations of radiation-induced porosity in 18-10 austenitic steel after irradiation by 40-keV He + ions and thermomechanical treatment are presented. External tensile stress was shown to result in an increase in He bubble size. Helium bubble migration and accumulation on grain boundaries was observed. Bubble clusters on grain boundaries are origins of brittle failure of the material. Helium bubbles increase also during post-radiation annealing. Post-radiation deformation of the material results in a considerable increase in the release rate of implanted helium gas. r
SANS and TEM of ferritic–martensitic steel T91 irradiated in FFTF up to 184dpa at 413°C
Journal of Nuclear Materials, 2013
Ferritic-martensitic steel T91 was previously irradiated in the Materials Open Test Assembly (MOTA) program of the Fast Flux Test Reactor Facility (FFTF) at 413°C up to 184 dpa. The microstructure was analyzed by small angle neutron scattering (SANS) and transmission electron microscopy (TEM). Both SANS and TEM revealed a large fraction of voids with an average size of 29-32 nm leading to a calculated void swelling of 1.2-1.6% based on the volume fraction of the voids in the sample. SANS gave no indication of second phase particles having formed under irradiation in the material. Using TEM, one zone was found where a few G-phase particles were analyzed. Quantities were however too low to state reliable particle densities. No alpha prime (a 0 ) or Laves phase were observed in any of the investigated zones.
Journal of Nuclear Materials, 2006
Tensile and Charpy specimens of 9Cr-1MoVNb (modified 9Cr-1Mo) and 12Cr-1MoVW (Sandvik HT9) steels and these steels doped with 2% Ni were irradiated at 300 and 400°C in the High Flux Isotope Reactor (HFIR) up to %12 dpa and at 393°C in the Fast Flux Test Facility (FFTF) to %15 dpa. In HFIR, a mixed-spectrum reactor, (n, a) reactions of thermal neutrons with 58 Ni produce helium in the steels. Little helium is produced during irradiation in FFTF. After HFIR irradiation, the yield stress of all steels increased, with the largest increases occurring for nickel-doped steels. The ductile-brittle transition temperature (DBTT) increased up to two times and 1.7 times more in steels with 2% Ni than in those without the nickel addition after HFIR irradiation at 300 and 400°C, respectively. Much smaller differences occurred between these steels after irradiation in FFTF. The DBTT increases for steels with 2% Ni after HFIR irradiation were 2-4 times greater than after FFTF irradiation. Results indicated there was hardening due to helium in addition to hardening by displacement damage and irradiation-induced precipitation.