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A densified graphite foam is being explored for its applicability as plasma-facing material in fusion devices. Three different graphite foam monoblocks are constructed and tested in the Garching Large Divertor Sample Testing Facility. The monoblock samples consist of graphite foam press-fit to a single tube, graphite foam cubes brazed to a single, and graphite foam cubes press-fit to a single tube. The tube is composed of CuCrZr with a steel twisted tape. The monoblocks are exposed to the heat fluxes of 5, 6, and 8 MW/m 2 for 30 s to determine the maximum surface and body temperatures measured with thermocouple for each monoblock design. The press-fit monoblocks are exposed to 8 MW/m 2 for 15 s for 100 cycles to determine the effect of thermal cycling on the contact between the graphite foam and the tube. STAR-CCM+ is used to predict how much the contact between the foam and tubes varies as a result of thermal cycling. In addition, the 6 MW/m 2 loading is modeled in STAR-CCM+ to compare the transient cooldown curves of the computational results to the recorded temperatures at the surface and two different thermocouple locations. This comparison is used to validate the temperature-dependent thermal conductivity and specific heat capacity used in the models of the graphite foam. The computational modeling of the experiment has been used to hypothesize ways to use and improve upon the graphite foam as a suitable material for fusion applications.

Assessing the effect of neutron irradiation of plasma-facing materials has been challenging due to both the technical and radiological challenges involved. In an effort to address the radio...

Extrusion based high-throughput Additive Manufacturing (AM) provides a rapid and versatile approach for producing complex structures by using a variety of polymer materials. An underexplored aspect of this technique is concerned with the formation of interfaces between successively deposited layers. This is particularly important for large-scale additive manufacturing of semi-crystalline polymers because of the highly non-isothermal conditions involved, which influence both nucleation and crystal growth. The objective of this work is to investigate the microstructure and the corresponding viscoelastic properties of carbon fiber (CF) reinforced polyphenylene sulfide (PPS) resulting from extrusion-based high-throughput AM process. Questions on development of morphology focus on polymer crystal structure and carbon fiber orientation in the vicinity of the interface between successive layers. This study attempts to establish a fundamental understanding of the role of the AM has in transferring a set of intrinsic material properties to the macroscopic properties of the final AM structure.

Components made by laser powder bed fusion (L-PBF) additive processes require extensive trial and error optimization to minimize defects and arrive at targeted microstructure and properties. In this work, in situ infrared thermography and ex situ surface roughness measurements were explored as methodologies to ensure Inconel® 718-part quality. For a given laser energy of 200 Watts, prismatic samples were produced with different exposure times (80 to 110 µs) and point spacings (80 to 110 µm). The infrared intensities from laser–material interaction zones were measured spatially and temporally. The conditions leading to higher IR intensity and lowest surface roughness values correlated well with less porosity and coarse solidification grain structure. The transition from highly columnar to misoriented growth is attributed to changes in thermal gradients and liquid–solid interface velocities. Hardness measurements and electron microscopy of the as-processed and post-processed heat-treated samples show complex transitions in microstructural states including the heavily dislocated FCC matrix, reduction of dislocation density, and copious precipitation, respectively. These results show that the geometry-process-structure-property correlations are dynamic, and they cascade depending on the transitions of phase states from powder to liquid to solid, as well as phase decompositions and deformations within the solid FCC phase. Validity of using analytical weld process models to describe the above phenomena is also highlighted.

Surface reliefs due to phase transformations in a 56.8Ni-5.6Pt-37.6Al at. pct alloy were characterized in situ using digital holographic imaging during thermal cycling from room temperature up to 405 K (132 °C). The 3D images of the surface revealed that the austenite plates formed during heating are exactly the same for each cycle, which is not the case for the martensite plates formed during cooling. The martensite start temperature was found to vary by up to ~ 20 K from one grain to another within the same specimen. The absence of Ni3Al γ′ precipitates, due to the relatively high Al content, results in the propagation of the martensitic transformation over grains up to a millimeter in size. Bright-field optical imaging showed the formation of large martensite plates in some grains, with cracks perpendicular to these plates, upon cycling. Cracks were also observed at grain boundaries and could be related to the height variations across the grain boundaries.

Local microstructure control in electron beam powder bed fusion (EB-PBF) is of great interest to the additive manufacturing community to realize complex part geometry with targeted performance. The local microstructure control relies on having a detailed understanding of local melt pool physics (e.g., 3-D melt pool shape as well as spatial and temporal variations of thermal gradient (G) and solidification rate (R)). In this research, a new scan strategy referred to as ghost beam is numerically evaluated as a candidate to achieve the targeted G and R of IN718 alloy. The boundary conditions for simulations, including the speed (490 mm/s) and spatial locations of the beam within a given layer, are obtained by using series of snapshot images, recorded at 12,000 frames per second, using a high-speed camera. The heat transfer simulations were performed using TRUCHAS an open-source software deployed within a high-performance computational infrastructure. The simulation results showed that reheating at short beam on-time and time delay decreases both G and R. Local variation of R at the center of the melt pool trailing edge showed periodic temporal fluctuations. Finally, the ghost beam scan strategy was compared to other existing raster and spot scan strategies.

We have investigated the relationship between structure and thermal conductivity in additively manufactured interpenetrating A356/316L composites. We used X-ray microcomputed tomography to characterize the pore structure in as-fabricated composites, finding microporosity in both constituents as well as a 50 μm thick layer of interfacial porosity separating the constituents. We measured the thermal conductivity of a 43 vol% 316L composite to be 53 Wm−1K−1, which is significantly less than that predicted by a simple rule-of-mixtures approximation, presumably because of the residual porosity. Motivated by these experimental results we used periodic homogenization theory to determine the combined effects of porosity and unit cell structure on the effective thermal conductivity. This analysis showed that in fully dense composites, the topology of the constituents has a weak effect on the thermal conductivity, whereas in composites with interfacial porosity, the size and structure of the unit cell strongly influence the thermal conductivity. We also found that an approximation formula of the strong contrast expansion method gives excellent estimates of the effective thermal conductivity of these composites, providing a powerful tool for designing functionally graded composites and for identifying mesostructures with optimal thermal conductivity values.

Innovative designs for turbines can be achieved by advances in nickel-based superalloys and manufacturing methods, including the adoption of additive manufacturing. In this regard, selective electron beam melting (SEBM) and selective laser melting (SLM) of nickel-based superalloys do provide distinct advantages. Furthermore, the direct energy deposition (DED) processes can be used for repair and reclamation of nickel alloy components. The current paper explores opportunities for innovation and qualification challenges with respect to deployment of AM as a disruptive manufacturing technology. In the first part of the paper, fundamental correlations of processing parameters to defect tendency and microstructure evolution will be explored using DED process. In the second part of the paper, opportunities for innovation in terms of site-specific control of microstructure during processing will be discussed. In the third part of the paper, challenges in qualification of AM parts for service will be discussed and potential methods to alleviate these issues through in situ process monitoring, and big data analytics are proposed.

A356/316L interpenetrating phase composites were fabricated by infiltrating additively manufactured 316L lattices with molten A356. Measurements of the thermal conductivity of the composites showed an inverse rule-of-mixtures dependence on the 316L volume fraction. Compression tests revealed that the stress-strain response of the composites can be tailored by adjusting both the volume fraction and the topology of the 316L reinforcement. Tension tests on composites with 39vol% 316L showed a strain to failure of 32%, representing an order of magnitude improvement over the strain to failure of monolithic A356. Inspection of the as-tested tensile specimens suggested that this exceptional damage tolerance is a result of the interpenetrating structure of the constituents. These results together demonstrate that this infiltration processing route avoids problems with intermetallic formation, cracking, and poor resolution that limit current fusion-based additive manufacturing techniques for printing metallic composites. Keywords: Additive manufacturing, Composites, Microstructure design, Infiltration, Damage-tolerance

The nucleation and growth of chimney pores during powder-bed electron-beam additive manufacturing is investigated using in situ infrared thermography and micro-computed tomography. The chimney pores are found to nucleate heterogeneously at dimples on the side surfaces of additively manufactured components, and to grow through a molten-film rupture process. Further, these nucleation and growth processes are found to be strongly influenced by the beam diameter. Several strategies for suppressing the formation of chimney pores are discussed in light of these results.

Additive Manufacturing provides the opportunity to fabricate components of nearly limitless complexity compared to that of traditional manufacturing techniques. However, thermal gyrations imparted into the material from the passing of the heat source cause challenges in fabricating complex structures with the proper process parameters. While the thermal history of the material can be simulated, validating the simulations requires access to thermal data generated through in-situ process monitoring. While generation of in-situ thermal data seems trivial, acquiring and developing reliable calibrations for metallic materials is difficult due to the physical state of the material transitioning from powder to liquid to a solid. To be discussed is the methodology taken to integrate IR in-situ process monitoring within the electron beam melting process and the approach developed to accurately correlate a materials emissivity to temperature during the build process. Further the wealth of information contained within the thermal data will be discussed in the context of understanding of microstructural evolutions within the material during the build process, identification of material defects, and ability to determining the similarity/repeatability of builds fabricated with identical processing parameters as based only on the thermal signature of the build.

To reduce the uncertainty of build performance in metal additive manufacturing, robust process monitoring systems that can detect imperfections and improve repeatability are desired. One of the most promising methods for in situ monitoring is thermographic imaging. However, there is a challenge in using this technology due to the difference in surface emittance between the metal powder and solidified part being observed that affects the accuracy of the temperature data collected. The purpose of the present study was to develop a method for properly calibrating temperature profiles from thermographic data to account for this emittance change and to determine important characteristics of the build through additional processing. The thermographic data was analyzed to identify the transition of material from metal powder to a solid as-printed part. A corrected temperature profile was then assembled for each point using calibrations for these surface conditions. Using this data, the thermal gradient and solid-liquid interface velocity were approximated and correlated to experimentally observed microstructural variation within the part. This work shows that by using a method of process monitoring, repeatability of a build could be monitored specifically in relation to microstructure control.

A well-established method for determining the thermal diffusivity of materials is the laser flash method. The work presented here compares two analysis methods for flash heating tests on anisotropic carbon bonded carbon fiber. This material exhibits a higher conductivity in the direction in which the fibers are oriented than in the direction perpendicular to the fiber orientation. Of the two analysis methods used, one method uses the temperature data from the entire surface of the sample by examining 201 temperature histories simultaneously, with each temperature history originating from an individual pixel within a line across the middle of the sample. The other analysis method uses only the temperature history from a single pixel in the center of the sample, similar to the data that is traditionally generated using the classical flash diffusivity method. Both analysis methods include accommodations for modeling the penetration of the laser flash into the porous surface of the carbon bonded carbon fiber ...

Non-destructive, in-line quality control methods were adopted for evaluating the thickness and homogeneity of wet and dry lithium secondary battery electrodes. Laser caliper and infrared (IR) thermography methods were implemented in a systematic fashion for the first time to evaluate the quality of electrodes during the coating process on a slot-die coater. Laser caliper sensors were mounted, aligned, and subsequently calibrated at the oven inlet of the coating line in order to examine the thicknesses of different cathodes and anodes. The effect of various factors such as substrate vibration, temperature, surface reflectivity and laser positions on the thickness measurement during slot-die coating were evaluated. The setup was used to monitor the wet thickness of the cathode and anode, and the precision of the in-line laser thickness measurement was determined to be less than ±2%. Thickness deviation for cathodes was typically ±2.0–2.3%, and for anodes it was typically ±2.2–2.6%, which confirms excellent precision of the measurement. The homogeneity of the dried electrodes was also evaluated by IR thermography at the oven outlet of the coating line. Temperature profiles from thermography images of dry electrodes were carefully examined to detect any flaws and inhomogeneity present in the electrodes. An increase or decrease in the temperature profiles indicated defects/flaws in the electrodes that could not be observed in optical images. The techniques applied in this work will be helpful for detection of electrode flaws and contamination during large-scale manufacturing and to identify flawed product prior to lithium-ion cell assembly.

The thermal interface resistance at the macro scale is mainly described by the physical gap between two (inter) faces and constriction resistance due to this gap. The small gaps and surface geometry mismatch between the two material faces makes up the majority of thermal interface resistance ( R c ) at the macro scale. There are various models to predict R c at macro scale. Although R c represents thermal resistance accurately for macro size contacts between two metals, it is neither suitable nor accurate to describe interface resistance of a modern composite Thermal Interface Material (TIM) containing micron to nano-sized particles. The thermal discontinuity at a perfectly bonded interface of two dissimilar materials is termed as thermal boundary resistance ( R b ) or Kapitza resistance. It is necessary to understand feasibility of using nanoparticles in composite TIM by having better understanding of thermal boundary resistance at that scale. The phenomenon of thermal boundary resistance is an inherent material property and arises due to fundamental mechanisms of thermal transport. For metal–matrix particulate composites, R b plays a more important role than R c . The free flowing nature of the polymer would eliminate most of the gaps between the two materials at their interface. This means almost all of the thermal resistance at particle/matrix interface would occur due to R b . Here, the thermal boundary resistance for silica nanoparticles embedded inside epoxy resin is studied. The bulk conductivity of the sample is measured, and R b is back calculated using the Hasselman–Johnson’s (H–J) equation. The numerical validation of the equation is also presented, including extrapolation study to predict effective conductivity of the nanocomposite TIM.

High performance mid-wave infrared (IR) cameras are used for in-situ electron beam melt process monitoring and temperature measurements. Since standard factory calibrations are insufficient due to very low transmissions of the leaded glass window required for X-ray absorption, two techniques for temperature calibrations are compared. In-situ measurement of emittance will also be discussed. Ultimately, these imaging systems have the potential for routine use for online quality assurance and feedback control.

A method has been developed to utilize a high-intensity plasma arc lamp located at Oak Ridge National Laboratory for the measurement of thermal diffusivity of bulk refractory materials at elevated temperatures. The applicability of standardized test methods to determine the thermal diffusivity/conductivity of refractory materials at elevated temperatures is limited to small sample sizes (laser flash) or older test methods (hot wire, guarded hot plate), which have their own inherent problems. A new method, based on the principle of the laser flash method, but capable of evaluating test specimens on the order of 200 mm × 250 mm × 50 mm, has been developed. Tests have been performed to validate the method and preliminary results are presented in this paper.

The laser flash method as a means of measuring thermal diffusivity is well established and several manufacturers produce equipment for performing these types of experiments. Most analysis methods for analyzing the data from these experiments assume one-dimensional transient conduction with insulated surfaces during the time subsequent to the flash. More recently, models of grater sophistication have been applied to flash diffusivity experiments using nonlinear regression. These models assume an instantaneous flash and are highly accurate for most samples of moderate diffusivity and sample thickness. As samples become thinner and more highly conductive, the duration of the experiments becomes very short. Since the duration of the flash is typically on the order of several milliseconds, the assumption that this period of time is instantaneous becomes less valid for very short experiments. A model accounting for the duration of the flash is applied to three samples of stainless steel of varying thicknesses in this research and analyzed with two different mathematical models. One model accounts for the duration of the flash and the other does not. The model accounting for the flash duration generates results that are much more consistent between samples than the model assuming an instantaneous flash. Moreover, the conformancemore » of the mathematical model accounting for flash duration is much closer to the measured data than the model which assumes an instantaneous flash. As part of the finite flash duration model, the length of the flash is estimated by non-linear regression, optimizing the conformance of the model to the measured data. Additionally, the starting time of the flash is treated as a parameter and is estimated simultaneously with flash duration, thermal diffusivity and flash intensity. Statistical methods are also used for showing the validity of the added level of sophistication of the more advanced mathematical model. Research sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract number DE-AC05-00OR22725.« less

Thermal diffusivities of air plasma sprayed (APS) thermal barrier coatings (TBCs) were measured by the laser flash method. The data were used to calculate thermal conductivity of TBCs when provided with density and specific heat data. Due to the complicated microstructure and other processing-related parameters, thermal diffusivity of TBCs can vary as much as three- to four-fold. Data collected from over 200 free-standing ZrO2-7-8wt.%Y2O3 TBCs are presented. The large database gives a clear picture of the expected “band” of thermal diffusivity values. When this band is used as a reference for thermal diffusivity of a specific TBC, the thermal transport property of the TBC can be more precisely described. This database is intended to serve researchers and manufacturers of TBCs as a valuable resource for the evaluation of TBCs.

Advanced Li-ion batteries with high energy and power density are fast approaching compatibility with automotive demands. While the mechanism of operation of these batteries is well understood, the aging mechanisms are still under investigation. Investigation of aging mechanisms in Li-ion batteries becomes very challenging, as aging does not occur due to a single process, but because of multiple physical processes occurring at the same time in a cascading manner. As the current characterization techniques such as Raman spectroscopy, X-ray diffraction, and atomic force microscopy are used independent of each other they do not provide a comprehensive understanding of material degradation at different length (nm2 to m2) scales. Thus to relate the damage mechanisms of the cathode at mm length scale to micro/nanoscale, data at an intermediate length scale is needed. As such, we demonstrate here the use of thermal diffusivity analysis by flash method to bridge the gap between different length scales. In this paper we present the thermal diffusivity analysis of an unaged and aged cell. Thermal diffusivity analysis maps the damage to the cathode samples at millimeter scale lengths. Based on these maps we also propose a mechanism leading to the increase of the thermal diffusivity as the cells are aged.

In this article, a method for measuring the thermal conductivity of paper using a hot disk system is introduced. To the best of our knowledge, few publications are found discussing the thermal conductivity of a coated paper, although it is important to various forms of today’s digital printing where heat is used for imaging, as well as for toner fusing. This motivated an investigation of the thermal conductivity of paper coating. This study demonstrates that the thermal conductivity is affected by the coating mass and the changes in the thermal conductivity affect toner gloss and density. As the coating mass increases, the thermal conductivity increases. Both the toner gloss and density decrease as the thermal conductivity increases. The toner gloss appears to be more sensitive to the changes in the thermal conductivity.

Thermophysical properties were investigated for zirconium diboride (ZrB2) and ZrB2–30 vol% silicon carbide (SiC) ceramics. Thermal conductivities were calculated from measured thermal diffusivities, heat capacities, and densities. The thermal conductivity of ZrB2 increased from 56 W (m K)−1 at room temperature to 67 W (m K)−1 at 1675 K, whereas the thermal conductivity of ZrB2–SiC decreased from 62 to 56 W (m K)−1 over the same temperature range. Electron and phonon contributions to thermal conductivity were determined using electrical resistivity measurements and were used, along with grain size models, to explain the observed trends. The results are compared with previously reported thermal conductivities for ZrB2 and ZrB2–SiC.

During the high pressure die casting process, lubricants are sprayed in order to cool the dies and facilitate the ejection of the casting. The cooling effects of the die lubricant were investigated using thermogravimetric analysis (TGA), heat flux sensors (HFS), and infrared imaging. The evolution of the heat flux and pictures taken using a high-speed infrared camera revealed that lubricant application was a transient process. The short time response of the HFS allows the monitoring and data acquisition of the surface temperature and heat flux without additional data processing. A similar set of experiments was performed with deionized water in order to assess the lubricant effect. The high heat flux obtained at 300 °C was attributed to the wetting and absorbent properties of the lubricant. Pictures of the spray cone and lubricant flow on the die were also used to explain the heat flux evolution.

Pulse thermal processing (PTP) of FePt nanoparticle films was studied using a high density infrared (HDI) plasma arc lamp. FePt nanoparticle films on silicon substrates were processed using 0.25- second infrared (IR) pulses. The processing was aimed at reaching a peak target temperature for multiple pulses of 550 C. Numerical simulations of the heat transfer for the PTP were performed to determine the operating power levels for the plasma arc lamp. Infrared measurements were conducted to obtain experimental data for the surface temperature of the FePt nanofilm. Parameters needed for the heat-transfer model were identified based on the experimental temperature results. Following the model validation, several numerical simulations were performed to estimate the power levels. It was shown that the FePt nanoparticle films were successfully processed using the power levels provided by the heat-transfer analysis.

The lost foam casting (LFC) process is emerging as a reliable casting method. The metal-fill profile in LFC plays an important role among several factors that affect casting quality. The metal-fill profile is in turn affected by several factors. Several casting defects may result due to an improper metal-fill process. Hence, it becomes essential to characterize and control, if possible, the metal-fill process in LFC. This research presents instrumentation and a technique to monitor and characterize the metal-fill process. The characterization included the determination of the position of the metal front and the profile in which the metal fills up the foam pattern. The instrumentation included capacitive sensors. Each sensor is comprised of two electrodes whose capacitive coupling changes as the metal fills the foam pattern. Foundry tests were conducted to obtain the sensors' responses to the metal fill. Two such sensors were used in the foundry tests. Data representing the responses of these sensors during the metal-fill process were collected using a data acquisition system. A number of finite element electrostatic simulations were carried out to study the metal-fill process under conditions similar to those experienced in foundry tests. An artificial neural network was trained using the simulation data as inputs and the corresponding metal-fill profiles as outputs. The neural network was then used to infer the profile of the metal-fill during foundry tests. The results were verified by comparing the metal-fill profile inferred from the neural network to the actual metal-fill profile captured by an infrared camera used during the foundry tests. The match up between the inferred profiles and the infrared camera measurements was satisfactory, indicating that the developed technique provides a reliable and cost effective method to monitor the metal-fill profile in LFC.

The thermal conductivity of thin, high-conducting ceramic bars—commonly used in mechanical tensile testing—is measured using a variant of the short transient hot-strip technique. As with similar contact transient methods, the influence from the thermal contact resistance between the sensor and the sample is accurately recorded and filtered out from the analysis—a specific advantage that enables sensitive measurements of the bulk properties of the sample material. The present concept requires sensors that are square in shape with one side having the same width as the bar to be studied. As long as this requirement is fulfilled, the particular size of the thin bar can be selected at will. This paper presents an application where the present technique is applied to study structural changes or degradation in reinforced carbon–carbon (RCC) bars exposed to thermal cycling. Simultaneously, tensile testing and monitoring of mass loss are conducted. The results indicate that the present approach may be utilized as a non-destructive quality control instrument to monitor local structural changes in RCC panels.

This papers deals with the high-density plasma-arc processing of FePt nanoparticle films. For short processing times, different materials, and multiple length scales of the system considered, the estimation of the optimum combination of process parameters is a difficult task. The process parameters can be obtained efficiently from a combined experimental and computational process analysis. The development of a computational methodology for plasma-arc processing is presented. Data on material properties are used to simplify the analytical model. An effective extinction coefficient was used to describe the absorption, of the radiation into the nanofilm. Experimental data for the surface temperature of the FePt nanofilm were obtained by infrared measurements. Parameters needed for the energy transport model were identified based on measured temperature data. The model presented can be used to for mulate process schedules for given time-temperature constraints.

State-of-the-art infrared (IR) thermal imaging was used to monitor the heating of ZnO varistors by electrical transients. On a macroscopic scale (e.g., 10 mm), heating in large varistor blocks (i.e., diameter of 42 mm) was found to be the greatest near the block edges and to be approximately radially symmetric in blocks fabricated at a low aspect ratio. In blocks fabricated at a higher aspect ratio, the heating was less symmetric, presumably because uniform properties are more difficult to achieve. Nonuniform heating in large blocks can be attributed to processing-induced variations in the electrical properties of the blocks. On an intermediate size scale (e.g., 1 mm), the heating in small varistor disks (e.g., diameter of 10 mm) was observed to be most intense along localized electrical paths. The high electrical conductivity of these paths originates from the statistical fluctuations in properties that inevitably occur in polycrystalline materials. On a microscopic scale (e.g., 10 μm), the heating in thin varistor slices (e.g., thickness of 100 μm) was observed to be localized in strings of tiny hot spots. The hot spots occur at the grain boundaries in a conducting path, where the potential is decreased across Schottky-type barriers and the heat is generated. The experimentally observed heating is interpreted by applying transport theory and using computer simulations. It is shown that, on the scale of the grain size, the heat transfer is too fast to permit temperature differences that could cause a varistor failure. Current localization and nonuniform heating on an intermediate size scale can have a microstructural origin (e.g., statistical fluctuations of grain sizes and grain-boundary properties). However, these are shown to be significant only in small varistors, whereas destructive failures (puncture and cracking) of large varistor blocks can be caused only by nonuniform heating on a macroscopic scale.

Zirconia doped with 3.2-4.2 mol% (6-8 wt%) yttria (3-4YSZ) is currently the material of choice for thermal barrier coating topcoats. The present study examines the ZrO 2 -Y 2 O 3 -Ta 2 O 5 /Nb 2 O 5 systems for potential alternative chemistries that would overcome the limitations of the 3-4YSZ. A rationale for choosing specific compositions based on the effect of defect chemistry on the thermal conductivity and phase stability in zirconia-based systems is presented. The results show that it is possible to produce stable (for up to 200 h at 1000°-1500°C), single (tetragonal) or dual (tetragonal + cubic) phase chemistries that have thermal conductivity that is as low (1.8-2.8W/m K) as the 3-4YSZ, a wide range of elastic moduli (150-232 GPa), and a similar mean coefficient of thermal expansion at 1000°C. The chemistries can be plasma sprayed without change in composition or deleterious effects to phase stability. Preliminary burner rig testing results on one of the compositions are also presented.

The effect of thermal shock and oxidation-induced damage on the thermal diffusivity of unidirectional Nicalon-LAS glass–ceramic composites is presented in this study. The data presented show that thermal diffusivity measurements provide a sensitive nondestructive method whereby damage progression may be assessed. Samples were exposed to isothermal oxidation and thermal shock environments. In addition, combined cycles of oxidation and thermal shock were also evaluated. The thermal diffusivity transverse to the fibers was measured to detect changes in material integrity. Significant decreases up to 23% were observed in the thermal diffusivity of the material.

A new set of heat spreader coatings consisting of multilayers of diamond/AlN/diamond were deposited on high heat capacity substrates of molybdenum and silicon nitride. Bonding of the heat spreaders to the device wafers using gold-tin eutectic solder was carried out after metallization layers of titanium, gold and copper were deposited on diamond. Prior to bonding, backside of the silicon wafers was also metallized with titanium, gold and copper and the gallium arsenide wafers with titanium, copper-germanium alloy and gold. Characterization of the multilayer diamond films was carried out by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The bonded wafers were tested for adhesion strength, resistance against peeling due to thermal cycling and failure under stress. Further, the bonded regions were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray mapping of different elements. The heat spreader characteristics of the single layer diamond and the multilayer diamond substrates were tested by infrared imaging. The results illustrate that the multilayer diamond heat spreader coatings provide better heat dissipation and also possess better adhesion strength and resistance against peeling under thermal cycling. These novel multilayer diamond/AlN/diamond heat spreaders are expected to considerably improve the life of high frequency power devices.

We report the laser-induced pressure-wave and the barocaloric effect captured by an infrared detector during thermal diffusivity measurements. Very fast (

Both mid-wave and long-wave IR cameras are used to measure various temperature profiles in thermoplastic parts as they are printed. Two significantly different 3D-printers are used in this study. The first is a small scale commercially available Solidoodle 3 printer, which prints parts with layer thicknesses on the order of 125μm. The second printer used is a “Big Area Additive Manufacturing” (BAAM) 3D-printer developed at Oak Ridge National Laboratory. The BAAM prints parts with a layer thicknesses of 4.06 mm. Of particular interest is the temperature of the previously deposited layer as the new hot layer is about to be extruded onto it. The two layers are expected have a stronger bond if the temperature of the substrate layer is above the glass transition temperature. This paper describes the measurement technique and results for a study of temperature decay and substrate layer temperature for ABS thermoplastic with and without the addition of chopped carbon fibers.

Interfacial temperatures have been measured using fibre optic inserts in the stationary brake ring during ring-on-ring, subscale dynamometer aircraft brake testing. The brake materials are carbon fibre-reinforced, carbon-matrix (carbon-carbon) composites. The temperature distribution varies with dynamometer test conditions and demonstrates the non-uniformity of contact pressure within the interface. A two-dimensional, axis-symmetric finite element model (FEM) is presented that is used to estimate temperature profiles during braking using either a constant pressure or constant energy flux assumption. The model incorporates the measured temperature-dependence of the thermal diffusivity and specific heat capacity for the composite materials. The surface temperatures obtained from the FEM are compared with the measured surface temperatures. Substantial differences between the two results are observed and discussed.

Experimental thermophysical property data for composites of electrode and electrolyte materials are needed in order to provide better bases to model and/or design high thermal conductivity Li-ion cells. In this study, we have determined thermal conductivity ( k ) values for negative electrode (NE) materials made of synthetic graphite of various particle sizes, with varying polyvinylidene difluoride (PVDF) binder and carbon-black (C-Black) contents, using various levels of compression pressure. Experiments were conducted at room temperature (RT), 150 and 200°C. Requirements for designing a high thermal conductivity NE-material are suggested. Detailed statistical data analysis shows that the thermal conductivity of the NE-material most strongly depends on compression pressure, followed by graphite particle size, C-Black content and finally PVDF content. The maximum k -value was achieved for the samples made of the largest graphite particles (75 μm), the smallest C-Black content (5 wt.%) and the highest compression pressure (566 kg cm −2 ). Increasing the PVDF content from 10 to 15 wt.% increased the k -values by 11–13% only. The k -values of all samples decreased with increasing temperature; at 200°C, the k -values were close to each other irrespective of preparation procedure and/or raw material contents. This most likely is due to the relaxation of contact pressure among the graphite particles because of PVDF melting at 155–160°C.

Zirconia doped with 6-8 wt% (3.2-4.2 mol%) yttria (6-8YSZ), the most common thermal barrier coating material, relies mostly on oxygen vacancies to provide the phonon scattering necessary for low thermal conductivity. The present study examines whether specific substitutional defects—in addition to, or instead of, oxygen vacancies—can provide similar or greater reductions in conductivity. To this end a series of zirconia samples co-doped with varying levels of yttrium (trivalent) and tantalum/niobium (pentavalent) oxides were synthesized, thereby allowing oxygen vacancy and substitutional atom concentration to be varied independently. The results show that Nb-Y and Ta-Y co-doped zirconia samples containing only substi- tutional defects produce stable single-phase tetragonal materials with thermal conductivities very close to that of the conventional 6-8YSZ. In these samples, Nb 51 and Td 51 are similarly effective in lowering thermal conductivity, in contradiction to phonon scattering theories that consider primarily mass effects and thereby predict significantly greater conductivity reduction due to Ta 51 doping than Nb 51 doping. Finally, Nb 51 /Ta 51 - Y 31 doped samples, which contain both oxygen vacancies and substitutional defects, are found not to be stable in single-phase form; however, the thermal conductivities of the two-phase tetragonal 1 cubic mixtures are again as low as that of the conventional 6-8YSZ. © 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

The thermal diffusivity of free standing thermal barrier coatings (TBCs) was measured by the laser flash technique. The combination of low thermal conductivity (1 to 2 W/m K) and small TBC thickness (300 to 600 µm thick) can cause errors in the measurements. Back surface (opposite the laser) temperatures of free standing plasma-sprayed TBCs were measured as a function of time and laser power. The front surface temperatures were calculated using thermal transport equations. In the high power region, thermal diffusivity decreased significantly with increasing laser power. In the moderate power region, thermal diffusivity remained constant. In the low power region, measurement became unreliable because of noise. The detector nonlinearity was believed to be a possible cause of deviation in the high power region. Measurements at different laser power levels should be conducted in order to obtain reliable thermal diffusivity values for TBCs.

Experimental thermal property data of the Sony US-18650 lithium-ion battery and components are presented, as well as thermal property measuring techniques. The properties in question are specific heat capacity (C{sub p}), thermal diffusivity ({alpha}), and thermal conductivity ({kappa}), in the presence and absence of electrolyte [1 M LiPF{sub 6} in ethylene carbonate-dimethyl carbonate (EC:DMC, 1:1 wt %)]. The heat capacity of the battery, C{sub p}, is 0.96 {+-} 0.02 J/g K at an open-circuit voltage (OCV) of 2.75 V, and 1.04 {+-} 0.02 J/g K at 3.75 V. The thermal conductivity, {kappa}, was calculated from {kappa} {identical_to} {alpha}{rho}C{sub p} where {alpha} was measured by a xenon-flash technique. In the absence of electrolyte, {kappa} increases with OCV, for both the negative electrode (NE) and the positive electrode (PE). For the NE, the increase is 26% as the OCV increases from 2.75 to 3.75 V, whereas for the PE the increase is only 5 to 6%. The dependence of both C{sub p} and {kappa} on OCV is explained qualitatively by considering the effect of lithiation and delithiation on the electron carrier density, which leads to n-type semiconduction in the graphitic NE material, but a change from semiconducting to metallic character in Li{submore » x}CoO{sub 2} PE material. The overall effect is an increase of C{sub p} and {kappa} with OCV. For {kappa} this dependence is eliminated by electrolyte addition, which, however, greatly increases the effective {kappa} of the layered battery components by lowering the thermal contact resistance. For both NE and PE, the in-plane {kappa} value (measured along layers) is nearly one order of magnitude higher than the cross-plane {kappa}. This is ascribed mostly to the high thermal conductivity of the current collectors and to a lesser extent to the orientation of particles in the layers of electrodes.« less

Thermal diffusivity of automotive grade SAE G3000 (d) gray cast iron has been measured as a function of graphite flake morphology, chemical composition and temperature. Cast iron samples used for this investigation were cut from “step block” castings designed to produce iron with different graphite flake morphologies resulting from different cooling rates. Samples were also machined from prototype and commercial brake rotors, as well as from a series of cast iron slugs with slightly varying compositions. Thermal diffusivity was measured at room and elevated temperatures via the flash technique. Graphite flake morphology of the various cast iron samples was quantified stereologically with image analysis techniques. Several geometric features of the graphite flake morphology were quantified. It was found that the thermal diffusivity of these gray cast irons increases with carbon equivalent and has a strong linear correlation to graphite flake length. For gray iron with the same chemical composition, a four fold increase in the graphite flake size results in a 50% increase in thermal diffusivity. Amongst the commercial rotors, room temperature thermal diffusivity varied from 0.156 to 0.200 cm2/s.

A generalization of the radial flash technique is presented whereby the thermal diffusivity of an orthotropic solid is measured in directions parallel and perpendicular to the flash source. The theoretical formulation is based on a Green's function approach which assumes a general orthotropic solid with three mutually orthogonal thermal diffusivities (or conductivities). Using this approach, a solution to this problem is presented which can be used to develop solutions for arbitrary pulse waveforms and incident geometries. Analytical and numerical results are presented for two-dimensional and three-dimensional cases of finite and semiinfinite solids. Characteristic equations which describe the ratio of the temperatures at two points along a principal axis are given. The equations show excellent agreement with numerical predictions as well as experimental results. A parameter estimation approach is given which improves on the accuracy of the radial flash technique in the determination of thermal diffusivity from experimental data.

In order to accommodate the ever increasing inlet temperatures of gas turbines, air plasma sprayed (APS) or electron beam physically vapor deposited (EB-PVD) yttria stabilized zirconia thermal barrier coatings (TBC`s) are used to insulate the metallic surfaces. Because of its historic use as a TBC, the thermal diffusivity and conductivity of single crystal and polycrystalline stabilized zirconia have been the subject of numerous experimental investigations. However, to the knowledge of the authors, the thermal conductivity of nanocrystalline (gain size < 100 nm) zirconia has not yet been determined. To ascertain whether or when grain boundary effects begin to dominate thermal conductivity, k, values for a variety of nanocrystalline zirconias of different densities (60--100%), grain sizes (30--400 nm), and purities (0--15wt.% yttria) are compared in this work. Finally the measured values are compared with the thermal conductivities of commercially available air plasma sprayed (APS) and electron beam physical vapor deposited (EB-PVD) coatings.

Oak Ridge National Laboratory (ORNL) has been utilizing the ARCAM electron beam melting technology to additively manufacture complex geometric structures directly from powder. Although the technology has demonstrated the ability to decrease costs, decrease manufacturing lead-time and fabricate complex structures that are impossible to fabricate through conventional processing techniques, certification of the component quality can be challenging. Because the process involves the continuous deposition of successive layers of material, each layer can be examined without destructively testing the component. However, in-situ process monitoring is difficult due to metallization on inside surfaces caused by evaporation and condensation of metal from the melt pool. This work describes a solution to one of the challenges to continuously imaging inside of the chamber during the EBM process. Here, the utilization of a continuously moving Mylar film canister is described. Results will be presented related to in-situ process monitoring and how this technique results in improved mechanical properties and reliability of the process.

An extended-range IR camera was used to make temperature measurements of samples as they are being manufactured. The objective is to quantify the temperature variation of the parts as they are being fabricated. The IR camera was also used to map the temperature within the build volume of the oven. The development of the temperature map of the oven provides insight into the global temperature variation within the oven that may lead to understanding variations in the properties of parts as a function of build location within the oven. The observation of the temperature variation of a part during construction provides insight into how the deposition process itself creates temperature distributions, which can lead to failure.

A well-established method for determining the thermal diffusivity of materials is the laser flash method. The work presented here compares two analysis methods for flash heating tests on anisotropic carbon bonded carbon fiber (CBCF). This material exhibits a higher conductivity in the direction in which the fibers are oriented than in the direction perpendicular to the fiber orientation. The two analysis methods being compared in this experiment use different portions of the data in obtaining results. One method utilizes the temperature data from the entire surface of the sample by examining 201 temperature histories simultaneously, with each temperature history originating from an individual pixel within a line across the middle of the sample. The other analysis method utilizes only the temperature history from a single pixel in the center of the sample, similar to the data which is traditionally generated using the classical flash diffusivity method. Both analysis methods include accommodations for modeling the penetration of the laser flash into the porous surface of the CBCF material. Additionally, both models include a parameter which accounts for the non-uniform heating of the sample surface from the flash. Although the sample surface is ostensibly heated uniformly in flash diffusivity experiments, the heating has been found to be somewhat non-uniform, with more energy deposited more heavily in the center of the sample. This affects the analysis results, particularly in tests on anisotropic materials. The results in this work show very little difference between the thermal parameters arising from the two methods. The robustness of the method using the single-pixel temperature history shows that anisotropic thermal diffusivity can be measured using standard flash diffusivity instruments, avoiding the additional complexity associated with a thermal imaging camera.