Characterizing the NRC Blackbody Sources for Radiation Thermometry from 150 °C to 962 °C

Validation of the various NRC blackbody sources below 962 °C has been hampered by the lack of a radiation thermometer with sufficient sensitivity and adequately small target size. Recently, progress was made in this area by having access to a NIST RT1550, a radiation thermometer operating at 1.55 μm with a thermoelectrically cooled InGaAs detector, a 3 mm nominal target size, a measuring range of 150 °C to 1064 °C, and a noise-equivalent temperature of 0.5 mK at 420 °C. Having the RT1550 for several months allowed sufficient time to intercompare our various blackbodies, both fixed-point and variable-temperature. It is these intralaboratory comparison results that are reported here.     

Thermal Conductivity of Magnesium Alloys in the Temperature Range from −125 °C to 400 °C

Magnesium alloys have been widely used in recent years as lightweight structural materials in the manufacturing of automobiles, airplanes, and portable computers. Magnesium alloys have extremely low density (as low as 1738 kg · m^?3) and high rigidity, which makes them suitable for such applications. In this study, the thermal conductivity of two different magnesium alloys made by twin-roll casting was investigated using the laser-flash technique and differential scanning calorimetry for thermal diffusivity and specific heat capacity measurements, respectively. The thermal diffusivity of the magnesium alloys, AZ31 and AZ61, was measured over the temperature range from ?125 °C to 400 °C. The alloys AZ31 and AZ61 are composed of magnesium, aluminum, and zinc. The thermal conductivity gradually increased with temperature. The densities of AZ31 and AZ61 were 1754 kg · m^?3 and 1777 kg · m^?3, respectively. The thermal conductivity of AZ31 was about 25 % higher than that of AZ61, and this is attributed to the amount of precipitation.     

Investigating the Inconsistency of ITS-90 for SPRTs in the Subrange 0 °C to 419.527 °C

The subrange inconsistency is a significant factor to uncertainty in the standard platinum resistance thermometer (SPRT) subranges of the International Temperature Scale of 1990 (ITS-90). This paper investigated the subrange inconsistency between the water–zinc and water–aluminum subranges. The calibration data for 60 SPRTs from four manufacturers were analyzed, and the result confirms that the coefficient c in the interpolation of ITS-90 is available to determine the subrange inconsistency in this temperature range again. The inconsistency, Δt, can be simply equal to 59.83c.     

Infrared Filter Radiometers for Thermodynamic Temperature Determination below 660 °C

At the Physikalisch-Technische Bundesanstalt (PTB), absolutely-calibrated filter radiometers based on silicon photodiodes are routinely used for thermodynamic temperature determinations of blackbodies in the range from the zinc fixed point (FP) (419 °C) up to 3,000 °C. To extend the temperature range down to the tin FP (232 °C), we have designed two new filter radiometers based on indium gallium arsenide (InGaAs) photodiodes with center wavelengths at 1,300 nm and 1,550 nm. For the absolute calibration of the spectral irradiance responsivity of the new InGaAs filter radiometers, the spectral responsivity measurement in the near-infrared (NIR) spectral range has been significantly improved. With a newly developed tuneable laser and monochromator-based cryogenic radiometer facility, the relative standard uncertainty of the NIR spectral responsivity has been reduced from 0.17 % to about 0.03 %. By using the calibrated InGaAs filter radiometer in conjunction with the large-area double sodium heat pipe of the PTB, the first results for the difference between the thermodynamic temperature T and the ITS-90 temperature T ₉₀ in the temperature range from the zinc FP up to the aluminum FP (660 °C) are presented. The values for T – T ₉₀ determined with the new InGaAs filter radiometers are consistent within their relative standard uncertainty of about 30 mK at 419 °C to about 60 mK at 660 °C. References to commercial products are for identification purposes only and constitute neither endorsement nor representation that the item identified is the best available for the stated purpose.     

Transient strain of self-compacting concrete loaded in compression heated to 700 °C

Self-compacting concrete (SCC) tends to spall when subject to high temperature in case of an accidental fire. Proper understanding its deformation properties at elevated temperatures is necessary in avoiding detrimental effects. This paper presents the experimental results carried out on SCC specimens subjected to high temperatures when they are loaded. The transient strain and load induced thermal strain of SCC are measured under the variation of temperature level, heating rate, stress level, strength grade of SCC, and content of polypropylene fibres. Furthermore, measurements with differential thermal analysis, SEM and mercury intrusion porosimetry had been conducted on samples taken from thermal-loading tests to investigate the mechanism that induces transient strain.     

Plasma nitriding response at 400 °C of the single crystalline Ni-based superalloy MC2

Plasma nitriding of MC2, a single crystalline (γ/γ′) Ni-based superalloy, was performed at 400 °C for 1 and 4 h. Owing to its monomodal γ′ particle size distribution, MC2 was used as a model material in an attempt to investigate the behavior of precipitates during the nitriding of a γ matrix. The nitrogen profiles, the morphology, and the nature of the phases in the nitrided layer were characterized by glow discharge optical emission spectroscopy, scanning electron microscopy, and X-ray diffraction. The γ matrix appeared to be nitrided similarly to the γ solid solution in austenitic stainless steels with the development of an expanded γ_N phase. The amount of nitrogen in the γ matrix varies from ~30 at.% at the surface till ~20 at.% at the interface with the non nitrided matrix. On the contrary, the γ′ precipitates accommodate no more than few at.% of nitrogen. This disparity modifies the morphology and the average γ channel width increased by ~25 %.     

Numerical Modeling of Oxidized 2D C/SiC Composites in Air Environments Below 900 °C: Microstructure and Elastic Properties

A numerical model is presented for simulation of the oxidation-affected behaviors of two dimensional carbon fiber-reinforced silcon carbide matrix composite (2D C/SiC) exposed to air oxidizing environments below 900 °C, which incorporates the modeling of oxidized microstructure and computing of degraded elastic properties. This model is based upon the analysis of the representative volume cell (RVC) of the composite. The multi-scale model of 2D C/SiC composites is concerned in the present study. Analysis results of such a composite can provide a guideline for the real 2D C/SiC composite. The micro-structure during oxidation process is firstly modeled in the RVC. The elastic moduli of oxidized composite under non-stress oxidation environment is computed by finite element analysis. The elastic properties of 2D-C/SiC composites in air oxidizing environment are evaluated and validated in comparison to experimental data. The oxidation time, temperature and fiber volume fractions of C/SiC composite are investigated to show their influences upon the elastic properties of 2D C/SiC composites.     

Experimental study on impact behaviour of concrete-filled steel tubes at elevated temperatures up to 800 °C

The dynamic behaviour of normal strength concrete-filled steel tubes (CFT) at elevated temperatures up to 800 °C under axial impact loading was experimentally studied by using a newly developed spilt Hopkinson pressure bar (SHPB) together with an electrical furnace. The effects of high temperature, impact velocity, steel ratio and slenderness ratio on the impact behaviour of CFT at elevated temperatures were experimentally studied. The stress and strain time history curves of the tested specimens were recorded to analyze the impact behaviour of CFT at elevated temperatures. The failure modes and the effects of the experimental parameters on the impact resistance of CFT are discussed. The test results showed that normal strength concrete-filled steel tube at elevated temperatures had a more excellent impact resistance in the paper than that described in Huo et al. (2009). A simplified calculation method was updated by introducing the reasonable dynamic increase factor model of hot concrete to reasonably assess the impact resistance of CFT at elevated temperatures.     

Experimental study on dynamic behaviours of concrete after exposure to high temperatures up to 700 °C

A Split Hopkinson pressure bar were used to experimentally study the dynamic behaviours of normal-strength concrete after exposure to elevated temperatures up to 700 °C. The dynamic strength and stress–strain relation curves of fire-damaged concrete were measured to unveil the effects of high temperature and strain rate on the dynamic behaviours of fire-damaged concrete. Test results showed that fire-damaged concrete still experienced remarkable strain rate effect and the dynamic stress versus strain relations of fire-damaged concrete were significantly different from those of concrete at room temperature. There was no obvious effect of temperature and strain rate on the shape of the ascending branches of normalized stress–strain relation curves of concrete after exposure to high temperatures. The tested results also showed that high temperature and strain rate had remarkable effect on the dynamic increase factor (DIF) for the fire-damaged concrete. The effect of high temperature on DIF of the fire-damaged concrete decreased as the temperature increased. The tested results can be a basis for assessing the impact resistance and anti-collapse resistance of fire-damaged concrete structures.     

Comparison of oxidation resistance of NiCoCrAlTaY-coated and -uncoated Mar-M247 superalloys in the air at 1150 °C

Oxidation resistance of NiCoCrAlTaY coated and uncoated Mar-M247 superalloys were compared experimentally in the air at 1150 °C. It was found that the oxidation behavior of the NiCoCrAlTaY coated and uncoated Mar-M247 superalloys generally followed the parabolic kinetics with the rate of 1.5 and 9.8 × 10⁻³ mg²/cm⁴ h for each one. Microstructural observation and elemental analysis indicated that after 200 h the uncoated alloy covered with an oxide scale of 6–10 times thicker than the coated one, beneath which a fairly continuous and relatively thin α-Al₂O₃ could be found along the interface close to the substrate. Comparatively, the NiCoCrAlTaY coated alloy uniformly produced the continuous, dense and thick α-Al₂O₃ layer adhesive to the coating to prevent the metal elements against excessive oxidation, and finally formed the steady oxide scales: outer (Ni, Co)(Al, Cr)₂O₄ spinels, NiO, (Al, Cr)₂Ni₃; inner protective α-Al₂O₃ with a little Cr₂O₃. On the surface of the uncoated alloy, however, it mainly formed the Ni-rich oxides in which a large quantity of cracks propagated to result in the more oxidation.     

Influence of precipitated phases on properties during prolonged aging in TP347H steel at 700 °C

The aging of austenitic stainless steel TP347H (18% Cr-12% Ni-1% Nb) was performed at 700 °C for 500, 800, 1500, 2500 and 3650 h. Microstructure, precipitates and mechanical properties were examined on aged materials to analyze the impact of microstructure on mechanical properties. These tests showed that the main precipitate of the TP347 specimen was Nb(C,N) while M₂₃C₆ carbides precipitated at the aging time of 500 h, with the coarsening of M₂₃C₆ and MX phases during prolonged aging. The fine and dispersive Nb(C,N) particle precipitation up to 1500 h aging is a benefit for hardness and creep resistance. After aging for 3650 h, σ phase precipitated. Meanwhile, coarsening of Cr₂₃C₆ and Nb(C,N) led to creep cavity and brittle intergranular fracture. No clear change in tensile properties at room temperature during aging were observed. A distinct decline in creep properties was caused by an average diameter increase and precipitation of σ phase and bulky Cr₂₃C₆.     

Strain rate and oxidation effects on crack initiation at 600 and 650 °C in a nickel-based superalloy

Nickel-based superalloys are sensitive to an oxidation-assisted intergranular crack (OAIC) growth mechanism. Crack initiation during slow strain rate tensile tests is investigated at 600 and 650 °C, at different strain rates, with or without oxidation on a direct-aged material. A V-shaped sample geometry is used to promote damage initiation for a specific stress triaxiality. The critical mechanical loading paths inducing intergranular crack initiation as well as the effect of oxidation are discussed.     

Oxidation behavior of a new Fe–Ni–Cr-based alloy in pure steam at 750 °C

The isothermal oxidation of a new Fe–Ni–Cr-based alloy has been investigated in pure steam at 750 °C for exposure time up to 500 h using secondary electron microscope (SEM)/ X-ray energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Results showed that the alloy was oxidized approximately following a parabolic law with a parabolic rate constant k_p of 2.36 × 10^?13 g²/m⁴/s. As revealed by SEM/EDS and XRD results, a duplex-layered external oxide scale was formed, consisting of a thin outer layer of Ni(Fe, Al)₂O₄ and a thicker inner layer of (Cr, Mn)₂O₃. Underneath the external oxide scale, the internal oxidation of Ti to be TiO₂ occurred particularly along the grain boundaries of the matrix alloy. Internal oxide of Al₂O₃ was also observed but at a deeper depth. Based on the detailed compositional and microstructural characterization of the oxidized zone, the mechanism of the external and internal oxidation in steam is presented.     

Effects of environment on creep behavior of two oxide/oxide ceramic–matrix composites at 1200 °C

The tensile creep behavior of two oxide/oxide ceramic–matrix composites (CMCs) was investigated at 1200 °C in laboratory air, in steam, and in argon. The composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, have no interface between the fiber and matrix, and rely on the porous matrix for flaw tolerance. The matrix materials were alumina and aluminosilicate. The tensile stress–strain behavior was investigated and the tensile properties were measured at 1200 °C. Tensile creep behavior of both CMCs was examined for creep stresses in the 80–150 MPa range. Creep run-out defined as 100 h at creep stress was achieved in air and in argon for stress levels ≤100 MPa for both composites. The retained strength and modulus of all specimens that achieved run-out were evaluated. The presence of steam accelerated creep rates and reduced creep life of both CMCs. In the case of the composite with the aluminosilicate matrix, no-load exposure in steam at 1200 °C caused severe degradation of tensile strength. Composite microstructure, as well as damage and failure mechanisms were investigated. Poor creep performance of both composites in steam is attributed to the degradation of the fibers and densification of the matrix. Results indicate that the aluminosilicate matrix is considerably more susceptible to densification and coarsening of the porosity than the alumina matrix. The views expressed are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense or the U.S. Government.     

Analysis of interactions between damage and basic creep of HPC and HPFRC heated between 20 and 80 °C

The present study concerns the uniaxial compressive creep of High Performance Concrete (HPC) at moderate temperatures, 20–80 °C. The study was conducted on four formulations of HPC including two fibrous concretes envisioned for future storage structures of Intermediate Level Long-Life Nuclear Wastes. These wastes are exothermic and lead to maximal temperatures in the field ranging from 50 to 70 °C (Andra, Référentiel des matériaux de stockage de déchets à haute activité et à vie longue, 2005). Here, we investigate the basic creep under uniaxial compression at 50 and 80 °C and compare it to that obtained on the same HPC at 20 °C. The objective of this research is to contribute to a better understanding of the phenomenon of interaction between damage and basic creep of HPC at moderate temperature, especially with a view to its integration in Thermo-Hydro-Mechanical models dealing with the design of special structures (massive structures, specific serviceability conditions in nuclear or hydroelectric power plants, etc.). This test campaign allowed us to assess the effect of temperature on the magnitude of basic creep of HPC, and also the impact of various temperature and mechanical loading conditions on the Young’s modulus of HPC. Heating to 80 °C damages HPC (instantaneous Young’s modulus decrease) and thereby increases the creep capacity, showing a relation between damage and creep amplitude. Moreover, this study gives global activation energy of basic creep of HPC that should be useful for practitioners dealing with concrete structures sensitive to delayed strains and subjected to moderate temperature.     

Tension-Compression Fatigue of a Nextel™720/alumina Composite at 1200 °C in Air and in Steam

Tension-compression fatigue behavior of an oxide-oxide ceramic-matrix composite was investigated at 1200 °C in air and in steam. The composite is comprised of an alumina matrix reinforced with Nextel?720 alumina-mullite fibers woven in an eight harness satin weave (8HSW). The composite has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension-compression fatigue behavior was studied for cyclical stresses ranging from 60 to 120 MPa at a frequency of 1.0 Hz. The R ratio (minimum stress to maximum stress) was ?1.0. Fatigue run-out was defined as 10⁵ cycles and was achieved at 80 MPa in air and at 70 MPa in steam. Steam reduced cyclic lives by an order of magnitude. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. Specimens subjected to prior cyclic loading in air retained 100 % of their tensile strength. The steam environment severely degraded tensile properties. Tension-compression cyclic loading was considerably more damaging than tension-tension cyclic loading. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Mixed Convection of Water at 4 °C Along a Wedge with Variable Surface Temperature in a Porous Medium

In this study, the mixed convection of water at 4 °C along a wedge in a porous medium is investigated numerically using a finite difference method. To explore the effect of mixed convection, both forced and free convection-dominated regimes are considered. Non-similarity solutions are obtained for the variable walltemperature boundary condition. Velocity and temperature profiles as well as local dimensionless skin friction and the Nusselt number are obtained and compared with available numerical results for various values of different parameters. The wedge angle geometry parameter m and mixed convection parameter ξ ranged from 0 to 1 in both regimes, whereas different values of λ are considered for the purpose of comparison of heat transfer results.     

Further insight into interfacial interactions in nickel/liquid Sn–Ag solder system at 230–350 °C

Interfacial reactions are investigated between electrochemical deposited Sn-2 wt%Ag alloy and Ni for isothermal heating at various temperature (230–350 °C) and for various time to study initial stages (1–4 min) and latter stages of reaction (15 min–4 h). During the isothermal heating a continuous compound layer of Ni₃Sn₄ is formed at the interface between liquid Sn–Ag and solid Ni. In this study scallop like morphology with round and smooth surfaces of Ni₃Sn₄ intermetallic (IMC) layer is observed for shorter time of isothermal holding, which is in fact contradictory to the observations reported by recent studies which describe the morphology of IMC as elongated and faceted needles. For longer reaction times (>1 h) the scallop-like morphology is transformed gradually to a facetted abnormal growth morphology but not elongated structure. The average thickness of the reaction layer is proportional to a power function of the annealing time with an exponent n varying from 0.35 to 0.40 and the apparent activation energy for liquid–solid Ni₃Sn₄ formation was evaluated to be of about 21 kJ mol^?1. The role of deposition method of Ni and Sn layers on the morphology and the growth kinetics of the reaction layer is discussed. A theoretical analysis of the initial formation and growth of Ni₃Sn₄ phase at the Ni/Sn interface is also presented.     

Evaluation of corrosion performance of Superni 600 hung in secondary chamber of medical waste incinerator operating at 1050 °C

Incineration technique is widely used to dispose of contaminated waste, municipal waste or medical waste. Burning medical waste causes formation of highly corrosive environment inside the chambers. Present study deals with the performance of Ni based Superalloy Superni 600 hanged inside the secondary chamber of medical waste incinerator for 1000 h under cyclic condition. Superni 600 showed good corrosion resistance under this environment. Formation of dense and compact layer of Cr₂O₃ was observed at substrate oxide interface which acts as a diffusion barrier for corrosive species.     

Oxidation behavior of Cr<Subscript>2</Subscript>AlC ceramics at 1,100 and 1,250 °C

The isothermal oxidation behavior of Cr₂AlC ceramics oxidized in air at 1,100 and 1,250 °C for 20 h was studied. The phase compositions and microstructure of the oxidized surface were identified and observed by XRD and electron probe microanalysis (EMPA), respectively, while the cross sections of oxidized samples were also examined by EMPA equipped with energy dispersive spectrum capabilities. The results indicated that the oxidation of Cr₂AlC samples was carried out by the outward diffusion of Al, together with small amounts of Cr, and the inward diffusion of O to form a surface layer of α-Al₂O₃, while carbides (Cr₇C₃ and Cr₃C₂), rather than oxides (Cr₂O₃), were formed in a layer under the surface. The mass gain per unit surface area of oxidized Cr₂AlC followed a parabolic relation with oxidation time, and the parabolic rates, k _p, for oxidation at 1,100 and 1,250 °C were 1.1 × 10⁻¹² and 7.1 × 10⁻¹⁰ kg² m⁴ s⁻¹, respectively.