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S.K. Balijepalli, G. Barbieri, M. Cesaroni, G. Costanza, L. Ciambella, S. Kaciulis, G. Maddaluno, A. Mezzi, R. Montanari, A. Varone

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S.K. Balijepalli, L. Ciambella, S. Kaciulis, G. Maddaluno, A. Mezzi, R. Montanari

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Owing to its low physical sputtering rate, high melting point and high thermal conductivity, W is a candidate material for the divertor armour of the international thermonuclear experimental reactor (ITER). It is expected to resist to the steady state heat flux of 10 MW/m 2, and transient high energy events, like disruption, edge local modes and vertical displacement events. Application of W as armour material in ITER 1- Central solenoid 2- Shield/blanket 3- Active coil 4- Plasma 5- Vacuum vessel shield 6- Plasma exhaust 7- Cryostat 8- Poloidal field coils 9- Toroidal field coils 10- First wall 11- Divertor plates

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Study on bulk material The bulk material has a purity of 99.97% and porosity of 5%. Table - Young’s modulus E and yield stress σ Y up to 500 °C. W has been heat treated at 500 °C and 800 °C with increasing soaking time up to 10 hours. Examined by: 1.TEM 2.Light microscopy 3. X-ray diffraction (XRD) 4. Micro-hardness tests

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Microstructure is characterized by well defined grains containing many dislocations. The porosity is very low but in some zones pores of small size (~ 30 nm) can be observed. As-received W TEM

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Heat treatments at 500 ° C do not induce remarkable changes of grain size, only a weak decrease of dislocation density has been observed. No porosity was detected. 500 °C, 4 hours

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1 h 800°C 2 h 800°C 5 h 800°C10 h 800°C Light microscopy

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Heat treatments at 500 °C do not induce remarkable changes of grain size. On the contrary, grain growth is observed after heating at 800 °C. Micro-hardness test Grain size

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After the heat treatment at increasing soaking time the peak profile becomes progressively narrower and the centre shifts towards lower angles. X-Ray Diffraction

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Dislocation density evolution The dislocation density calculated by the Williamson-Smallman relationship : = ε 2 / k 0 b 2 where = 16 is a constant, b = nm the modulus of Burgers vector and k 0 1 a factor depending on dislocation interaction. The total line broadening T is due to two contributions, the size of coherently diffracting domains ( D ), i.e. the grains, and the micro-strains ( ): D = domain size, = average micro-strain, = Bragg angle, = wavelength, K = constant (= 0.89). Being D very large, i.e. of the order of some tens of microns, D can be considered negligible thus T .

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W deposited by Plasma Spraying W + Al-12%SiAISI 316L W W su AISI 420 Deformazioni dovute a tensioni residue W Lega CuCrZr Interlayer

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W deposited on CuCrZr Without interlayer With interlayer

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W deposited on AISI 316L

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W deposited on AISI 420

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L. Ciambella, R. Montanari

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ENEA is the coordinator of an European project called “MATTER” (MATerial Testing & Rules) based on the characterization of new materials able to work under extreme conditions for the development of new generation nuclear systems (Generation IV, ADS etc.). The aim of this research is the characterization of T91 steel with FIMEC indentation test in order to determine the principal mechanical properties of this steel like yield stress. Before the characterization is necessary to optimize and standardize the indentation test in order to draft a pre-normative for mechanical properties determination.

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The indentation test is one of the most common techniques for the mechanical characterization of materials. FIMEC is a flat-ended cylindrical indentation technique which employs a cylindrical punch made of sintered tungsten carbide. Unlike other indentation tests employing punches of different shape (pyramid, sphere, cone etc.), the contact area between punch and material is constant during the test. yield stress; elastic modulus E; ductile to brittle transition temperature (DBTT); surface creep; stress relaxation. Introduction to FIMEC (Flat-top cylinder Indenter for MEchanical Characterization)

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FIMEC apparatus Linear actuator: electro-mechanical drive equipped with a stepping motor. The motor rotation is transmitted to a ball screw by a precision reduction gear; the ballscrew converts the rotation at the gear output to translation. Linear Voltage Displacement Transducer (LVDT): measures the displacement between the sample holder and the indenter. Load cell: located under the sample holder measures the applied load. Cylindrical punch: made of tungsten carbide (WC), providing high rigidity and strength. Heating system: Tubular furnace, which guarantees a constant temperature (±2 °C) in a vertical zone of about 10 cm, where punch, sample holder and sample are located. FIMEC PARAMETERS Advancement speed (mm/s) 1 · · LVDT resolution (mm)1 Load cell resolution (N)1 Cylindrical punch diameters (mm) 0,5 ÷ 1 Range Temperature (°C)- 196 ÷ 600

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During a FIMEC test the applied load and the penetration depth are measured; it is possible to determine pressure (p) vs. penetration depth (h) curves by dividing loads by the punch- surface contact area A. Elastic stage up to a pressure load p L. Below p L the curve is fully reversible and no permanent deformation occurs on the sample. The first plastic stage is almost linear and end at a pressure p y : the imprint shows permanent sharp edges. The second plastic stage occurs for p > p y and is characterized by a sudden slope decrease. During this stage the materials start to protrude around the imprint. The third plastic stage shows a trend with an almost constant slope. The pressure-penetration curves

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Under standardised conditions (penetration rate 0.1 mm/min and deformation rate in tensile test s -1 ), it is possible to determine the value of the yield stress Y from the p Y value, according to the equation below: p Y 3 Y This equation has been verified to be valid for several metals (steels, Cu alloys, Ti alloys, Al alloys, metal matrix composites, superalloys etc.).

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The Method description: Analysis of LP curves Owing to the inhomogeneous plastic behaviour in the initial part of punch penetration (1st plastic stage) is quite difficult to find a relationship suitable to describe this stage and useful for directly identifying the pressure p Y for all the metals. On the contrary, the 2nd and 3rd stages, where the plastic deformation occurs in a large volume under the punch, can be described by the equation: p = K (h 0 + h) n The method can be divided in 3 steps. 1- First of all the experimental pressure-penetration curve is filtered to remove possible noise. 2- The values of K, h 0 and n are determined which give the best fit of the 2nd and 3rd stages of the curve. 3- The pressure p Y is calculated at a fixed depth h Y = h 0 + h = mm by substituting into this equation the values of K and n determined by the best fitting.

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Fitting of T91 For T91 steel the values K and n are: K = 4347 N·mm -(n+2) n = h 0 + h = mm Replacing these values in the previously described equation: It is possible to obtain the pressure p Y : p Y = 1752 MPa FIMEC = p Y /3 = 584 MPa Since the yield stress provided by standard tensile stress is: Y =580 MPa p = K (h 0 + h) n

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To assess the general validity of the algorithm some materials relevant for nuclear applications have been tested at increasing temperatures and the results compared with those obtained by tensile tests with standard probes. MaterialT [°C]Kh 0 [mm]n FIMEC [MPa] Y [MPa] = ( Y – FIMEC ) / Y Manet-II ,052110, , ,033970, , ,045870, , ,041140, , ,037430, ,05 F82H mod ,033540, , ,039770, , ,039530, , ,037280, , ,033710, , ,040290, ,03 Eurofer ,031130, , ,033450, , ,033630, , ,031960, , ,031870, , ,025150, ,01 EM ,051550, , ,037550, , ,025960, ,05 The Table reports for each material the parameters K, h 0 and n giving the best fit, the value FIMEC determined through the algorithm, the yield stress Y from standard tensile test and the relative difference . The Y values of tensile tests have been taken from the literature.

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Why PbBi? Low melting temperature (~125°C) high boiling point (~1670°C) excellent chemical stability It is also possible to eliminate secondary heat transport loops and associated intermediate heat exchangers because LBE does not exothermically react with water and air. The ADS technology however requires special operating conditions: the materials need to resist temperatures ranging between °C under a high energy neutron flux and in contact with the LBE: the limitation of ADS life is due to the relatively low corrosion resistance of structural materials in the LBE environment The compatibility of structural materials with liquid LBE at high temperature is one of the key issues for the commercialization of such fast reactors. Liquid Pb–Bi eutectic (LBE) alloy has been selected as a coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system (ADS).

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The structural evolution of LBE has been investigated by : Internal friction Dynamic modulus measurements High-temperature X-ray diffraction Material and experimental After quenching the samples have been investigated by: Standard XPS Scanning photoemission microscopy (SPEM)

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IF and dynamic modulus measurements Experiments were carried out by employing the mechanical analyser VRA NEW METHOD : Metal is cast inside hollow reed (stainless steel AISI 316), closed to one end. After filling the reed is sealed. Experimental data must be corrected from the contribution of the container measured in the same conditions using not filled reeds. R. Montanari, A. Varone

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IF and dynamic modulus measurements After melting the modulus of eutectic alloy decreases with nearly constant slope up to 350 °C where drops and finally, above 520 °C, continues to decrease with a slope very close to the initial one. In correspondence of the modulus drop two IF maxima are observed. R. Montanari, A. Varone

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HT-XRD measurements The analyses of XRD patterns show that positions and shapes of RDF peaks progressively change as temperature increases: in particular r 1 slowly decreases whereas r 2 increases. R. Montanari, A. Varone

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T(°C)P 1 (Ǻ)P 2 (Ǻ)P 2 /P For describing the liquid structure the ratio between average distance r between the 1st (central position of the 1st RDF peak) and 2 nd (central position of the 2nd RDF peak) nearest neighbour atoms is of particular relevance and. HT-XRD measurements P 2 /P R. Montanari, A. Varone

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Icosahedron and cuboctahedron are related polyhedra that can be built up from the octahedron that has 12 edges. If atoms occupy the central position of each edge they form the vertexes of a cuboctahedron, if atoms occupy the positions dividing the edge in the golden ratio, i.e. (1/1.618)a = 0.61a, they form the vertexes of an icosahedron. Therefore, if they are arranged in intermediate positions between 0.5a e (1/1.618)a a intermediate configuration is obtained. Model R. Montanari, A. Varone

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XPS and SPEM measurements The SPEM experiments were financially supported by ELETTRA synchrotron project n and n The SPEM technique was employed because of its high lateral resolution (below 50 nm) S. K. Balijepalli, S. Kaciulis, A. Mezzi, R. Montanari, A. Varone, M. Amati Study if the transformations occurring in the liquid state involve the clustering of alloying elements. Surface Analysis : ELETTRA synchrotron (Trieste)

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Surface Analysis : SPEM measurements Maps (13 × 13 μm2) of Pb/Bi intensity ratio for the alloy quenched at 401 °C. Pb and Bi are strongly clustered after melting, and the size and composition of the clusters evolve as temperature increases. The cluster evolution could be due to diffusion processes between clusters and matrix, leading to the progressive disgregation of clusters and to the homogenization of the liquid alloy S. K. Balijepalli, S. Kaciulis, A. Mezzi, R. Montanari, A. Varone, M. Amati

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G. Barbieri, M. Cesaroni

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Summary Main proprieties of 9 Cr 1 Mo V, Nb modified steel (P91) Greater strength, that permits increased safety margins in existing units Significant longer component life under given creep and fatigue loads Reduced wall thickness for components for the same condition that permit to reduce thermal stress. Welding aspects 2/ 3 different chemical compositions of material: Base Material, filler material, Fused zone in function of the dilution ratio. Correct time and Temperature for PWHT, pre heating and interpass Temperature Comparison with Standard Manual practices GTAW+SMAW Main welding aspects investigated Influence of low and high speed of welding; Influence of ratio and mode of deposition; Influence of PWHT in terms of holding Time and tempering Temperature; Target Review of the RCC-MR specifications for welding consumables, welding processes and related base metal.

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Base & Filler Materials BASE MATERIAL Samples to weld come from INDUSTEEL plate (140 mm thickness) Austenitizing (1071°C / 4h08), water cooling, tempered (757°C / 5h31) Hardness measurement (207 HV1) The thinner 9Cr1MoVNb plate was not originally design for nuclear and its then not fully compliant with RCC- MR(x) recommendation (Ni content). FILLER MATERIAL Böhler welding,Thermanit MTS3,Stick Electrode, filler wire ( 1,2 mm) CSiMnPSCrMoNiAlNbVN Cu BM Industeel RCC-MR 2007 (RM ) Max Max Max 0.20 Max Max 0.10 FMBöhler

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Welding of P91 Were made test provided on the site about manual practices and mechanized TIG with 60 ° and 75 ° V angle to face Butt Join 12 mm (horizontal position) ; Standard Manual procedure (1 st pas TIG + filling SMAW); Welding of 4 coupons (2 with 60 ° chamfer and 2 with 75° chamfer) Influence of 2 PWHT Qualification specimens GTAW process: It has been defined the first test matrix for optimizing the welding speed and wire speed for string or weave beads for automated TIG Welding of 4 coupons (4 with 60 ° chamfer and 4 with 75° chamfer an different Deposition Ratio) Influence of 2 PWHT Qualification specimens Qualification tests planned after PWHT: Transverse tensile tests at room temperature Longitudinal tensile tests at room temperature and 550°C. Charpy tests for DBTT on FZ; Metallurgical examination. Fimec

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PWHT time and temperature and deposition mode The weave deposition techniques seams to guaranty better toughness than stringer beads; Typical thermal cycle for welding P91 Courtesy of Bhöler

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SMAW Weave beads String beads Average SMAW Ws=165 cm/min DR1=1,27 g/cm HI=1,18 KJ/cm Average GTAW Ws= 75 cm/min DR= 1,15 g/min HI=1,66 KJ/cm Average SMAW Ws=137 cm/min DR2=1,83 g/cm HI=1,48 KJ/cm Average GTAW WS= 63 cm/min DR= 1,12 g/min HI=1,90 KJ/cm Welding SMAW parameter

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Mechanized GTAW ModeIV Ws [mm/min] Wfs [mm/min] HI [kJ/mm] DR [g/cm] LDR ,38 0, ,50 0,34 TDR 23011, ,300, , ,430, , ,41 0, ,35 0,84 HDR ,50 1, , ,56 1,01 V 75 gap 1 TDRV 60 gap 1 TDR The as-tempered microstructure consists of a fine prior austenite grains containing a lath-like tempered martensite structure with a high dislocation density that is stabilized by M23C6 carbides and MX(Nb,V) carbo- nitrides. Dimensions of the re-affected and not re-affected µ- sctruttures increase with the deposition rate The as-tempered microstructure consists of a fine prior austenite grains containing a lath-like tempered martensite structure with a high dislocation density that is stabilized by M23C6 carbides and MX(Nb,V) carbo- nitrides. Dimensions of the re-affected and not re-affected µ- sctruttures increase with the deposition rate Welding GTAW parameter

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SMAW The 4 h PWTH reduce RM in FZ DR2_FZ 275 > 60 J (RCC-MR) No sample meets the requirements (RCC-MR) Corrispondence beetween Fimec and Tensile Test RCC The 4 h PWTH reduce HV in FZ

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GTAW Problem of Cracking IV Coupling “Target”

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Influence of PWHT The hardness increase from the cap to the rood due to the different dilution ratio and filler material (Electrode /wire Thermanit MTS3); The hardness is reduced by increasing of the PWHT holding time ( 2h 4) The tensile strength in BM decrease with PWHT; The RP0,2 & RM on FZ decrease if the holding time of PWHT is increased; The A% on FZ is less of the 20 %, The V60 with low DR and Low HI allow to obtain the higher value THANK YOU The holding time of the PWHT influence the Hardness of the welds: Mechanical Features

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