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New algorithm to determine the yield stress from FIMEC test
No full textThe indentation test is one of the most common techniques for the mechanical characterization of materials. Different tests have been standardized, depending on punch geometry and indentation parameters, and different models have also been set up to predict indentation hardness and to estimate uni-axial mechanical properties for all the geometries (cone, wedge, pyramid, sphere, etc.). A flat-ended cylindrical indentation technique (FIMEC) has been developed by one of the present authors. FIMEC employs a cylindrical punch with diameter ranging from 3.0 to 0.5 mm and gives pressure-penetration curves from which yield stress and elasticity modulus can be determined. The specific characteristics of FIMEC are: 1- the high simplicity of the apparatus; 2- the possibility to get information about the local material properties on a scale large enough to include many grains (data represent bulk characteristics and are not influenced by those factors which dramatically affect micro- and nano-indentation tests); 3- the large versatility in industrial applications such as the control of welding quality, 4- the on-line monitoring of forging or extrusion processes etc. This paper describes a new algorithm developed to calculate the yield stress from FIMEC curves. To assess the reliability of the method, it has been tested on several metals of known characteristics and the scattering of data with respect those from tensile tests resulted to be within ±7%. © (2014) Trans Tech Publications, Switzerland
Effects of heat treatments on tungsten for armours in NFR
No full textTungsten is a promising armour material for plasma facing components of nuclear fusion reactors (NFR) because of its low sputtering rate and favourable thermo-mechanical properties (high melting point and good thermal conductivity). This paper reports some results of an experimental campaign carried out for investigating the microstructural characteristics and the mechanical properties of tungsten (99.97% purity; 5% porosity) for fusion applications. Tungsten has been heat treated at 500 °C and 800 °C with increasing soaking time. The samples in as-supplied condition and after each step of the heat treatments have been examined by optical microscopy and TEM observations, X-ray diffraction (XRD) and micro-hardness tests. The original material has a dislocation density of 1.5 × 1010 cm-2 and a mean grain size of 65 μm. Grain size is not affected by the heat treatment at 500 °C which induces only a weak decrease of dislocation density leading to a little smaller hardness. The microstructure can be considered substantially stable even if a weak recovery of dislocations takes place. On the contrary, grain growth is observed after heating at 800 °C: 10 hours of treatment nearly doubles the average grain size. © (2014) Trans Tech Publications, Switzerland
Stress residui in W depositato mediante Plasma Spray: effetto del substrato e delle modalità di processo
Full text linkIl tungsteno è un ottimo materiale per ricoprire componenti di prima parete e proteggerli dai danni derivantidall’ esposizione al plasma nei futuri reattori a fusione nucleare. Mediante la tecnica del Plasma Spray sonostati realizzati rivestimenti spessi di tungsteno su diversi substrati tra cui l’acciaio austenitico AISI 316L,l’acciaio martensitico AISI 420 e la lega di rame CuCrZr. La tecnica del Plasma Spray è stata usata per lasemplicità, la possibilità di ricoprire superfi ci estese e di geometria complessa e i costi relativamente bassi.Questo lavoro descrive gli stress residui misurati con diffrazione dei raggi X nei diversi sistemi rivestimentosubstratoponendo particolare attenzione al ruolo dell’interfaccia. I risultati indicano chiaramente lafondamentale importanza di tale interfaccia e della sua ottimizzazione al fi ne della compatibilità termomeccanicatra tungsteno depositato e metallo del substrato
Implementazione di una rete neurale artificiale per la previsione delle curve di indentazione
No full textResidual stresses in tungsten deposited by plasma spraying: effect of substrate and processing methods
No full textOwing to its high melting point, favourable thermo-mechanical properties and good thermal conductivity tungsten is a candidate material for the divertor armour of the international thermonuclear experimental reactor (ITER) [1-6]. Wthin coatings on CFC and graphite substrates have been already used in JET [7] and ASDEX-U [8] tokamaks. However, its high elastic modulus, high brittleness and the high thermal expansion mismatch (e.g. aCu ≈ 4αw and αFe-α ≈3αw) make the joining of W with other metals really challenging. This paper reports results of an experimental campaign carried out for investigating W thick coatings on different metal substrates. For realizing the joints, plasma spray (PS) technique has been used for its simplicity, possibility to cover complex extended surfaces and relatively low cost. Particular attention was paid to study the effect of different substrates and a suitable interlayer on residual stresses in W. Residual stresses were measured by X-ray diffraction at room temperature and high temperature. Deposition of W coatings has been performed on 3 different substrates: CuCrZr alloy (with and without interlayer), austenitic steel AISI 316 L, and martensitic steel AISI 420. The CuCrZr alloy has been used in the past as structural material for actively cooled plasma facing components of ; nuclear reactors (Tore Supra and JET) and selected as heat sink material for divertor parts of ITER [5]. It was possible to manufacture mock-ups for ITER by depositing up to 5mm-thick W coatings on tubular substrates of CuCrZr, which iwere able to sustain a remarkable number of thermal fatigue cycles under high heat flux (up to 5 MW/m2) [1-2]. The ;microstructural and mechanical properties of this coating were extensively investigated and the results demonstrated jits good characteristics [9-11]. Similar promising results have been obtained also by Chong et al [12]. For reactors like DEMO, the cooling tubes made of copper based alloys could not be used because of the high neutron fluence, so it is necessary to realize W coatings on tubes made of steel [13-14], In order to determine residual stresses induced by PS process and the effect of increasing temperature, for each sample, XRD peak profiles have been recorded in the 20 angular range 16°- 21° The spacings dM measured from the most intense reflections have been compared to the values dCak calculated taking into account the values reported in < JCPDS-ICDD database and the thermal expansion: (1) a = a0( 1+α-δ7] The strain e was then obtained by the equation: ε = dSper-dCalc/dCalc The tests on the W-CuCrZr system with and without interlayer evidenced the fundamental importance of the interlayer. If there is the interlayer the residual stresses are present only in the interlayer. On the contrary, stresses are present in W and many defects like cracks and pores arise as a consequence of the different thermal expansion of the metals during cooling. The tests on W deposited on steels evidenced that metals forming the interlayer and layering must be chosen with care. In the case of the W-AISI 316 L system the strain of W coating is not negligible reaching a value of ∼ 3 x 103 after heating whereas the strain of Al interlayer is low. In W-AISI 420 system the strain value for W is very low also after heating up to 460 °C. The joining exhibits good adhesion and microstructural characteristics. From XRD tests performed on different W joints it is evident the importance of an appropriate interlayer for a good adhesion between W coatings and substrates. The quality of joints critically depends on the interlayer stratification in order to protect the W coating and concentrate residual stresses in the interlayer
Influence of welding parameters on microstructure of welded joints SMAW/GTAW steel X10 CrMoVNb 9-1 (P91)
No full textThis paper presents weldability results of P91 creep resistant steels performed through two different welding technologies: The " fully mechanized (GTAW)", and the "Shielding Metal Arc Welding (SMAW)" It was evaluated the influence of welding parameters on the microstructure of the joint and on the consequent mechanical characteristics (Strength, toughness and ductility) of the fused zone (ZF). With reference to the P91 creep resistant steel (Tab.1), the RCC-MRx code for the design and production of components for nuclear power plants, have data sheet about the chemical and mechanical features of "Base Material" (BM) but does not have data sheet about filler materials, as qualified for welding nuclear components class 1. Scope of this work is to evaluate possible candidate filler material (Tab.2) and to suggest welding technologies and related operative welding conditions to ensure that N1 class could be produced with the same requirements as the Base Material, in compliance to the design code. The main objective of this study is to evaluate the candidate filler materials and suggest welding conditions optimized for PWTH, Heat Input (HI), and Deposition Mode/Ratio(DM/DR), to obtain an elongation of more than 20 % and a toughness of more than 60 J to 0°C (as evaluated by Charpy KV test)in the fused zone (ZF). For both processes, according to the literature data, it was decided to analyze the influence of four parameters: Speed of deposition (deposition ratio DR ); mode of deposition (DM); Heat input (HI); duration of PWHT . To varying DR/ DM were chosen two different bevel angles (60 ° and 75 °), two modes of deposition (" String Beads"," Weave Beads "), obtained through different welding speed Ws. Two different holding times (2h , 4h ) for PWHT were investigate to evaluate the influence of Time on the feature of FZ. The test was carried out in compliance within the RCC- Mr and the correlate ISO Standard: ( UNI EN ISO 15614-1 ; Transversal tensile test: ISO 4136-2011 & ISO 6892-1 ; Longitudinal tensile test: IS05178 - 2011 and ISO 6892-2 , ISO 9015). The Data about the performed test are reported in Tab. 6. In general for both the welding technology evaluate, the Fused Zone as welded have a fully martensitic microstructu- res, this is demonstrated by the high value of hardness. After the PWHT the hardness in FZ decreases from more of 400 to 230-250 HV5, typical values of tempering martensite. The comparison between the hardness profiles measured at different conditions and PWHT show that the duration of the holding time influences the hardness (Fig.1). If the hoi-ding time increases the hardness in FZ decreases. About SMAW, the toughness improves with increasing the holding time of the PWHT. However only for the condition of welding "weave beads" the value is in compliance with the RCC- MR (Tab. 6). In general, a little reduction of tensile strength was observed after the PWHT, and the differences increase with the increase in holding time. At the same way, the test on GTAW coupons, confirming that longer PWHT holding time induces a reduction in the hardness of fused zone. The micro hardness test highlighted the well know problem of softening in the interface between of HAZ and BM, where the material was subjected to an unavoidable over-tempering (Fig.3). The V notch Charpy tests on GTAW weld shown very high values (higher than SMAW ) in all the case in compliance , with the requirement of RCC-MR. The longitudinal tensile test at room temperature for GTAW ZF specimens (Tab.10), shows very high values of Rm than SMAW. However, this high values are not in compliance with the requirements of the RCC-MR (Max 760 MPa). At the same time the values of elongation, both for GTAW and SMAW processes, is more than 17%, which is promising for a filler material but less than the 20%, threshold required for the BM and the target for the welds. The influence of holding time of PWHT on the mechanical features is the same for the two processes analyzed. The strength is reduced and the elongation increased with augment of holding time of the PWHT. ' The longitudinal tensile test at 550°C were performed only for the GTAW coupons and shown values of Rp 0,2 more than required (260 MPa) and an elongation more than 20 (Tab.11). The SMAW and GTAW shown that the "weave beads" Deposition Mode allowed obtaining the best results in terms of toughness and ductility. The holding time of PWHT influenced the toughness, hardness and strength of the welds. The holding time of 4 h appear to allow the best results. The elongation in all tests for processes at room temperature were less than 20 %. The fully mechanized GTAW showed values of strength very high in association with very good toughness. In all the processes two main problem remain: The softening zone between HAZ and BM (Type IV Cracking zone); The elongation less than 20% , which is requested for the Base Material. Values of elongation of 17-18% are commonly achievable from a wide range of processes and welding parameters. To increase this value, the augment of the PWHT holding time seems to improve the elongation but a long time of PWHT ; means a higher over-tempering of the Type IV Cracking zone. So, in conclusion, the filler material used in this work is a good candidate to weld Nuclear component made of P91,; however the target in terms of ductility and maximum strength, required as BM of RCC-Mr, needs to be reviewed
Stress residui in W depositato mediante plasma spray: effetto del substrato e delle modalità di processo = Residual stresses in tungsten deposited by plasma ; spraying: effect of substrate and processing methods
No full textOwing to its high melting point, favourable thermo-mechanical properties and good thermal conductivity tungsten is a candidate material for the divertor armour of the international thermonuclear experimental reactor (ITER) [1-6]. Wthin coatings on CFC and graphite substrates have been already used in JET [7] and ASDEX-U [8] tokamaks. However, its high elastic modulus, high brittleness and the high thermal expansion mismatch (e.g. aCu ≈ 4αw and αFe-α ≈3αw) make the joining of W with other metals really challenging. This paper reports results of an experimental campaign carried out for investigating W thick coatings on different metal substrates. For realizing the joints, plasma spray (PS) technique has been used for its simplicity, possibility to cover complex extended surfaces and relatively low cost. Particular attention was paid to study the effect of different substrates and a suitable interlayer on residual stresses in W. Residual stresses were measured by X-ray diffraction at room temperature and high temperature. Deposition of W coatings has been performed on 3 different substrates: CuCrZr alloy (with and without interlayer), austenitic steel AISI 316 L, and martensitic steel AISI 420. The CuCrZr alloy has been used in the past as structural material for actively cooled plasma facing components of ; nuclear reactors (Tore Supra and JET) and selected as heat sink material for divertor parts of ITER [5]. It was possible to manufacture mock-ups for ITER by depositing up to 5mm-thick W coatings on tubular substrates of CuCrZr, which iwere able to sustain a remarkable number of thermal fatigue cycles under high heat flux (up to 5 MW/m2) [1-2]. The ;microstructural and mechanical properties of this coating were extensively investigated and the results demonstrated jits good characteristics [9-11]. Similar promising results have been obtained also by Chong et al [12]. For reactors like DEMO, the cooling tubes made of copper based alloys could not be used because of the high neutron fluence, so it is necessary to realize W coatings on tubes made of steel [13-14], In order to determine residual stresses induced by PS process and the effect of increasing temperature, for each sample, XRD peak profiles have been recorded in the 20 angular range 16°- 21° The spacings dM measured from the most intense reflections have been compared to the values dCak calculated taking into account the values reported in < JCPDS-ICDD database and the thermal expansion: (1) a = a0( 1+α-δ7] The strain e was then obtained by the equation: ε = dSper-dCalc/dCalc The tests on the W-CuCrZr system with and without interlayer evidenced the fundamental importance of the interlayer. If there is the interlayer the residual stresses are present only in the interlayer. On the contrary, stresses are present in W and many defects like cracks and pores arise as a consequence of the different thermal expansion of the metals during cooling. The tests on W deposited on steels evidenced that metals forming the interlayer and layering must be chosen with care. In the case of the W-AISI 316 L system the strain of W coating is not negligible reaching a value of ∼ 3 x 103 after heating whereas the strain of Al interlayer is low. In W-AISI 420 system the strain value for W is very low also after heating up to 460 °C. The joining exhibits good adhesion and microstructural characteristics. From XRD tests performed on different W joints it is evident the importance of an appropriate interlayer for a good adhesion between W coatings and substrates. The quality of joints critically depends on the interlayer stratification in order to protect the W coating and concentrate residual stresses in the interlayer
Influenza dei parametri di saldatura sulla microstruttura di giunti saldati SMAW/TIG di acciaio X10 CRMOVNB9-1 (P91)
No full textFIMEC indentation test for the mechanical characterization of steels and other alloys of MATTER interest
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