Rapid Thermal Cycling Research Articles

Multi-objective optimization of heating system for rapid thermal cycling molding mold with internal induction heating

A rapid thermal cycling molding (RTCM) with novel internal induction heating mode is proposed in this work. The induction coils are directly inserted in the corresponding mounting holes of mold with an annular gap in between. During mold heating, eddy current losses confined at the walls of the mounting holes act as thermal sources to rapidly heat the mold cavity surface. Water passed through the annular gaps can be utilized to cool the mold in the cooling stage. Moreover, a design framework of the internal induction heating system in the RTCM mold is also developed. Firstly, a unit cell model of the mold was established to evaluate mold thermal response via numerical simulations, in which the effect of frequency and magnitude of coil current, the layout of induction coils and the annular gap size were examined. Then, a hybrid multi-objective optimization method was applied to optimize the induction heating system for the unit cell model. Finally, based on the obtained optimal parameters, a novel design strategy was adopted to conformally arrange the induction coils for the industrial RTCM molds. The blow mold of automotive spoiler was taken as an example to validate the effectiveness of the proposed approach. The results show that the present approach cannot only improve the mold thermal response performance, but also facilitate the mold heating system design process. This work may provide an effective method to realize RTCM of industrial plastics parts with free-form shape.

The Dilution Effect in High-Power Disk Laser Welding the Steel Plate Using a Nickel-Based Filler Wire

High-power disk laser welding a steel plate using the Inconel 82 (IN82) filler wire with a 1.2 and 3.0 m/min feeding rate has been investigated in the experiment. The rapid thermal cycle combined with convection induced by the keyhole mechanism in laser welding results in the rapid solidification of the fusion zone (FZ). However, the microstructure of the FZ is not homogeneous at the macroscopic scale. The dilution of the FZ is important in determining the final microstructure of the weldment. For the specimen with a 1.2 m/min wire feeding rate, a lower amount of Ni-based IN82 filler is introduced into the weld pool, and the dilution of the FZ is between 65% and 100%. The BCC structure with high density boundaries dominates the entire FZ. For the specimen with a 3.0 m/min wire feeding rate, part of the filler melt is trapped on the top of the weld pool, and solidified into austenite alloyed with a Ni concentration above 15 at%. The range of dilution in the FZ with a 3.0 m/min wire feeding rate is decreased to 50–90%. There are hot cracks initiated/propagated along interdendritic austenite and in the austenite free of boundaries. Boundaries, especially for high-angle ones, in the BCC structure retard hot crack propagation in the FZ. The application of quantitative chemical analyses of Fe or Ni concentrations in the weldment provides a good approximation in evaluating the dilution of the FZ in laser welding. The methodology proposed in this study shows potential to obtain the dilution of any specific location in the FZ for industrial application in the future.

Effect of metal additive manufacturing residual stress on post-process machining-induced stress and distortion

This work represents the first investigation into the influence of residual stress (RS) from powder-based metal additive manufacturing (AM) on the post-process machining-induced stress and distortion for thin-walled components. Machined part distortion and surface residual stress pose major challenges in several industries, including for aerospace applications involving monolithic structures. However, the influence of initial RS in the bulk material on high-speed machining-induced stress and distortion is still not well understood. This is particularly true for more recent hybrid (additive and subtractive) manufactured components in which significant tensile and compressive RS develops from the rapid thermal cycles during the AM build. It is hypothesized in this work that, even for a simple thin-walled structure, the initial RS in the AM bulk material significantly influences the RS and distortion induced by high-speed machining. It is further hypothesized that the degree of influence of the initial RS on machining-induced RS and distortion varies significantly according to the specific tool path, even for the same net material removal. To test these hypotheses, a numerical modeling approach is presented considering a thin-walled directed energy deposition (DED) structure subjected to high-speed end-milling. A compatible RS field for the DED build is established using an iterative reconstruction algorithm based on limited neutron diffraction measurements, and the full reconstructed RS field is then imposed as an initial state in the end-milling simulation that follows. To assess the influence of the initial DED RS on the machining-induced stress and distortion, as well as to examine how this influence varies with machining strategy, two different tool paths are considered for the same net material removal, both with and without considering RS inherent to the DED build. The findings reveal significant influence of the DED RS on the high-speed machining-induced distortion and RS, and further, this influence is seen to vary greatly with the machining strategy. Normalized root-mean-square differences (NRMSD) of up to 25% and 29%, respectively, are observed in the machining-induced RS for the two different tool paths when DED inherent RS is considered. Likewise, maximum NRMSD of up to 44% and 40% are revealed in the post-machining distortion for the two respective machining strategies when DED RS is included. In addition, variations observed in the stress triaxiality computed during machining suggests that inclusion of the DED RS influences the localized response of the material near the tool-workpiece interface. The technical approach demonstrated can be extended beyond hybrid manufacturing to generate important scientific insights regarding distortion and machining-induced stress for conventionally manufactured monolithic components in the aerospace and other performance-critical industries.

Fast and Accurate Control Strategy for Portable Nucleic Acid Detection (PNAD) System Based on Magnetic Nanoparticles.

Portable nucleic acid detection (PNAD) systems are performed for sample processing, amplification and detection automatically in an individual device realizing "sample in, answer out." For this goal, numerous function modules should be integrated in a diminutive device, in which temperature controller is one of the most important modules. In a nucleic acid detection process, both sample processing and polymerase chain reaction (PCR) require fast and accurate temperature control to increase concentration and purity of the extraction product and to improve amplification efficiency. In this paper, a dual-channel temperature controller for PNAD systems is developed, which contains a printed circuit board (PCB) and an integrated control program with a fast and accurate control strategy. According to the principle of nucleic acid detection based on magnetic nanoparticles, the controller can work in different modes such as high-precision heating control for nucleic acid extraction, rapid thermal cycle control for PCR, and rate adjustable constant heating/cooling control for melting curve. Evaluatively, the average heating/cooling rate of the module can exceed about 6 C/s, while the temperature fluctuation was less than ± 0.1°C, which can meet the demands of PNAD systems very well.

Investigation of Rapid, Moderate Temperature Change Thermal Cycles of a Micro-Tubular Flame-Assisted Fuel Cell

Abstract Despite many efforts and improvements over the last few decades, two of the major challenges facing solid oxide fuel cells (SOFCs) are slow heating rates to operating temperature (typically < 5 °C · min−1) and a limited ability to thermal cycle (<200 cycles). Recently, a novel hybrid setup that combines a fuel-rich combustion reformer with a SOFC was developed and utilized to investigate rapid heating, cooling, and thermal cycling of a micro-tubular SOFC. In this work, 3000 moderate thermal cycles are conducted at a heating rate exceeding 140 °C · min−1 and a cooling rate that exceeded 100 °C · min−1. The open-circuit voltage (OCV) was analyzed over the 150 h test, and a low degradation rate of ∼0.0008 V per 100 cycles per fuel cell was observed in the absence of the current collector degradation. Unlike a previous test, which was conducted at lower temperatures, significant degradation of the current collector was observed during this test. Electrochemical impedance spectroscopy shows that degradation in the SOFC was due to increases in ohmic losses, activation losses at the cathode, and increased concentration losses.

Thermal shock resistance of Ti3SiC2 ceramic under extremely rapid thermal cycling

A rapid throughput thermal shock resistance evaluation method was developed and tested on Ti3SiC2 ceramic traditionally known for its excellent thermal shock resistance. The sample was rapidly heated by the induction heating and dropped into the cooling water within 0.35 s. The three-point bending test of Ti3SiC2 after quenching at 1300 °C dropped from initial 332 MPa down to 35 MPa. The testing bars fractured after quenching at 1450 °C without any abnormal strength recovery that was instead reported in previous investigations. The degradation of residual strength might be ascribed to three factors: (i) the oxide layer on the sample surface contains a lot of pores and microcracks; (ii) large thermal tensile stresses impact on the substrate during quenching; (iii) weak grain boundaries are caused by water infiltration.

Phase field model for multiphase alloys under arbitrary thermal history: An application to IN718 super-alloy

Currently, it is still a significant challenge to predict the microstructural evolution of multiphase alloys in complex manufacturing processes such as joining, welding and additive manufacturing due to their complex thermodynamics and thermal history. In this work, we present a phase-field framework, aiming to predict the evolution of precipitate microstructure under arbitrary thermal history. Our model incorporates nucleation, growth and transformation by taking into account interfacial, chemical and elastic energies. In order to quantitatively describe the nucleation of phases, we leverage on experimental time-temperature-transformation data to parameterize the classical nucleation model. For demonstration, we employ super-alloy IN718, where thermodynamic and kinetic data is obtained using CALPHAD method and major precipitate phases, i.e. γ′,γ″ and δ and their variants are considered. The predicted continuous-cooling-transformation diagram is consistent with data existing in literature, thus validating the approach. We further predict the precipitate evolution under rapid thermal cycling to mimic a typical additive manufacturing process.

Theoretical prediction of high melting temperature for a Mo\u2013Ru\u2013Ta\u2013W HCP multiprincipal element alloy

While rhenium is an ideal material for rapid thermal cycling applications under high temperatures, such as rocket engine nozzles, its high cost limits its widespread use and prompts an exploration of viable cost-effective substitutes. In prior work, we identified a promising pool of candidate substitute alloys consisting of Mo, Ru, Ta, and W. In this work we demonstrate, based on density functional theory melting temperature calculations, that one of the candidates, Mo0.292Ru0.555Ta0.031W0.122, exhibits a high melting temperature (around 2626 K), thus supporting its use in high-temperature applications.

Exploring Coupled Extreme Environments via In-situ Transmission Electron Microscopy

Abstract

Fibrous nano composite reinforced surface on WC-Co cemented carbide achieved by pulsed electron beam irradiation and subsequent tempering

Exotic microstructures can be tailored by extreme conditions with combined material processing techniques for desirable properties. In this work, an innovative 2-staged process was explored for WC-10Co cemented carbide surface modification. Firstly, rapid thermal cycles were induced by high current pulsed electron beam (HCPEB) irradiation at energy density of 6 J/cm2, during which the micro-WC/Co was melted and re-solidified into a nano-scaled equiaxed grain microstructure with metastable fcc-WC1-x as the majority phase in the surface layer (~2 μm). Thereafter, a subsequent tempering process was applied to the HCPEB-irradiated cemented carbide specimens and the nano equiaxed grains in the surface layer were gradually transferred into nano-scaled fibrous microstructure. Phase transformation was investigated using thermo-gravimetric analysis differential scanning calorimetry (TGA-DSC), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Analysis showed that the fibrous nano structure resulted from the decomposition of WC1-x at 600-700 ºC via fcc-WC1-x → hex-WC + hcp-W2C. After the 2-staged process, the surface microhardness was greatly improved.

Miniaturized Thermal Monitoring Module With CO₂ Laser Ablated Microfluidic Device for Electrochemically Validated DNA Amplification

Polymerase chain reaction (PCR) is the gold standard method to amplify deoxyribonucleic acid (DNA) fragments. Several methods have been used to miniaturize and integrate PCR to execute in a microfluidic platform. A continuous-flow-based microfluidic PCR device permits the required rapid thermal cycling and multiplexing, which are hard to realize in a benchtop PCR or microchamber PCR. This work aims to develop a microfluidic PCR platform using a custom-made Internet of Things (IoT)-enabled portable thermal monitoring module. The microfluidic device was fabricated on polymethyl methacrylate (PMMA) using a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser. Apart from 30 serpentine cycles, the PCR microchannel also had initial denaturation and final elongation regions to enhance the overall amplification. As a proof-of-application, rat GAPDH gene, with a fragment size of 594 base pair, has been amplified on the miniaturized platform. Furthermore, the agarose gel electrophoresis technique was used to separate the DNA molecules validated using a gel-doc system. Subsequently, the acquired results were quantitatively compared with the conventional thermocycler using ImageJ software. Furthermore, this was also validated with electrochemical DNA detection using differential pulse voltammetry (DPV). The results from the smart low-power device showed promising performance for the nucleic acid amplification process while reducing the overall amplification time and achieving benchmarked efficiency.

Development of Various Solid Oxide Cell Technology and Stack Platforms at Nexceris, LCC

With over 25 years of experience in solid oxide fuel cell (SOFC) materials, components and stack development, Nexceris has been rapidly expanding the technology portfolio. Development in Fuel Cell Materials, FlexCell and ChromLok technology are only a few examples. Stack testing capability up to 5 kW has been developed. Modular high-performance stack platforms that accommodate cells from 40 cm2 to 250 cm2 are being utilized, depending on customer requirements and system needs.Recently, Nexceris expanded its R&D efforts into solid oxide electrolysis cell (SOEC) technology. Initial performance of -1.5 A/cm2 and 500-hour durability tests at 1.3-1.4 V and 800 °C in short stacks show promising platform for further SOEC performance and durability improvements. Besides anode- and electrolyte- supported cell development, metal-supported cells (MSCs) have also been successfully developed at Nexceris and scaled to 250 cm2. The structure, performance and durability of MSCs are being continuously improved. Short 5-cell stacks are currently being demonstrated and the results will guide further stack development. A wide range of cell and stack technology developed at Nexceris provides capability to tailor cells and stacks based on user applications, whether those include continuous non-interrupted stationary operation or dynamic operation such as rapid thermal and redox cycling in mobile applications.

Improved grain structure prediction in metal additive manufacturing using a Dynamic Kinetic Monte Carlo framework

This work describes a Dynamic Kinetic Monte Carlo numerical modeling framework that can predict the microstructure of metals during powder bed fusion (PBF) and directed energy deposition (DED) additive manufacturing (AM) while considering significant variations in thermal history and heat accumulation that occur during the build. Although the conventional Kinetic Monte Carlo (KMC) method is well-established, it does not accommodate variation in the spatial domains of the melt pool (MP) and heat affected zone (HAZ) with time. Thus, the predicted microstructure remains relatively similar even over large AM build domains. While the existing KMC approach may suffice over spatial regions in which the MP and HAZ remain relatively unchanged, this circumstance is largely contrary to what experimentalists have recently found when imaging different regions in PBF and DED AM builds, thus raising issues with scalability and versatility of the method. The Dynamic KMC framework proposed in this work addresses these concerns by implementing discretized, spatially-varying MP and HAZ at every time increment during the grain structure prediction. The new framework operates in two stages; stage one establishes the 3D spatial MP and HAZ dimensions using either thermal finite element (FE) simulation or through experimental 3D thermal imaging; stage two subsequently integrates these time-varying MP and HAZ dimensions into the KMC algorithm at every time increment during the build. Thus, the Dynamic KMC framework captures the effects that rapid thermal cycles and heat accumulation have on grain nucleation and growth. The method is demonstrated through a case study involving a thin-walled Inconel 625 structure made by the selective laser melting (SLM) type of laser-based powder bed fusion (PBF-LB). The numerically predicted microstructures at various regions and scan layers within the build show strong agreement with experimentally observed trends reported in literature. Significant variations in grain morphology predicted by the Dynamic KMC framework can, according to specific thermal histories, provide investigators with new capabilities in assessing mechanical property variations across different regions of AM parts. • A Dynamic Kinetic Monte Carlo (KMC) framework for microstructure prediction in metal additive manufacturing is demonstrated. • Microstructure evolution is captured based on dynamic melt pool and heat affected zone behavior due to 3D heat accumulation. • Microstructure results using the novel framework for a thin-walled Inconel 625 SLM build agree with experimental observation. • More realistic microstructures in laser-based powder bed fusion and directed energy deposition can therefore be predicted.

Fusing MEMS technology with lab-on-chip: nanoliter-scale silicon microcavity arrays for digital DNA quantification and multiplex testing

We report on the development of a microfluidic multiplexing technology for highly parallelized sample analysis via quantitative polymerase chain reaction (PCR) in an array of 96 nanoliter-scale microcavities made from silicon. This PCR array technology features fully automatable aliquoting microfluidics, a robust sample compartmentalization up to temperatures of 95 °C, and an application-specific prestorage of reagents within the 25 nl microcavities. The here presented hybrid silicon–polymer microfluidic chip allows both a rapid thermal cycling of the liquid compartments and a real-time fluorescence read-out for a tracking of the individual amplification reactions taking place inside the microcavities. We demonstrate that the technology provides very low reagent carryover of prestored reagents < 6 × 10−2 and a cross talk rate < 1 × 10−3 per PCR cycle, which facilitate a multi-targeted sample analysis via geometric multiplexing. Furthermore, we apply this PCR array technology to introduce a novel digital PCR-based DNA quantification method: by taking the assay-specific amplification characteristics like the limit of detection into account, the method allows for an absolute gene target quantification by means of a statistical analysis of the amplification results.

Martensite tempering kinetics: Effects of dislocation density and heating rates

In this study, the combined effect of dislocation density and rapid thermal cycling on the tempering kinetics of fully martensitic steel has been investigated by straining the sheets to different deformation levels. It was found that the strain-induced dislocations created more nucleation sites for carbide precipitation, and decreased carbide growth time. Strain-enhanced precipitation caused the carbide morphology to change from elongated to small quasi-spherical precipitates. Plastic deformation also accelerated the decomposition of carbides and film-like retained austenite in the as-received martensite laths. After tempering the deformed martensite had higher microhardness than tempered unstrained martensite, resulting from finer and semi-coherent precipitates, a high retained dislocation density, and the presence of untempered and partially tempered martensite blocks.

Core-Shell Beads as Microreactors for Phylogrouping of E. coli Strains.

Multiplex polymerase chain reaction (PCR) is an effective tool for simultaneous detection of target genes. Nevertheless, their use has been restricted due to the intrinsic interference between primer pairs. Performing several single PCRs in an array format instead of a multiplex PCR is a simple way to overcome this obstacle. However, there are still major technical challenges in designing a new generation of single PCR microreactors with a small sample volume, rapid thermal cycling, and no evaporation during amplification. We report a simple and robust core-shell bead array for a series of single amplifications. Four core-shell beads with a polymer coating and PCR mixture were synthesized using liquid marble formation and subsequent photo polymerization. Each bead can detect one target gene. We constructed a customised system for thermal cycling of these core-shell beads. Phylogrouping of the E. coli strains was carried out based on the fluorescent signal of the core-shell beads. This platform can be a promising alternative for multiplex nucleic acid analyses due to its simplicity and high throughput. The platform reported here also reduces the cycling time and avoids evaporation as well as contamination of the sample during the amplification process.

Computational Assessment of the Efficacy of Oxidation-Resistant Iridium Coatings for Multiple Principal Component Rhenium Substitutes

Rhenium is an advanced engineering material valued for its performance under rapid thermal cycling to high temperatures. Due to rhenium’s high cost, alternatives are actively being sought, and hexagonal close packed multiple principal component alloys consisting of Mo, W, Ta and Ru have been previously identified as a promising candidate. Here we assess whether the use of iridium coatings, a widely adopted approach to limit the oxidation of Re, can also be used with this candidate alloy. Specifically, we quantify, through atomistic computations based on density functional theory, the relative diffusion rates of the constituent elements through the protective Ir coating, which is known to be a dominant failure mechanism.

Rapid thermal annealing of Cr–Si–N, Ta–Si–N, and Zr–Si–N coatings in glass molding atmospheres

Glass molding is widely used for manufacturing high-precision optical elements. Nitride coatings are recommended as protective coatings on glass molding dies. In a die-fixed glass molding system, the molding dies undergo rapid thermal shocks. In this study, near-amorphous Cr–Si–N, Ta–Si–N, and Zr–Si–N coatings with a Si concentration of >14 at.% were prepared. The feasibility of these coatings in the glass molding process was evaluated through rapid thermal cycling annealing in a 15-ppm O2–N2 atmosphere. The cycling annealing test was performed at 270 °C and 580 °C or 600 °C. The heating, holding, and cooling times in the annealing process were 1 min each. The results indicated that Zr–Si–N coatings exhibited superior anti-sticking against SiO2–B2O3–BaO-based glass. The reactions between the nitride coatings and glass were investigated.

Insight into Type IV cracking in Grade 91 steel weldments

In this work, an insight into the premature Type IV cracking was undertaken to clarify its mechanisms in Grade 91 steel pipe weldments. High-resolution microscopy observations of the as-welded heat-affected zone (HAZ) reveal that the commonly recognized fine-grained region susceptible of cracking on the edge of HAZ belongs to the inter-critical HAZ (ICHAZ), rather than the fine-grained HAZ (FGHAZ). Instrumented indentation tests uncover that the ICHAZ is the weakest region across the weld, exhibiting the largest displacement and the lowest hardness in three thermal stages. Localized deformation of matrix grains and high stress triaxiality in the ICHAZ promoted nucleation of creep cavities along grain boundaries. This localized deformation was induced by the creep strength mismatch of matrix grains with different Cr concentrations. Cavity-free regions exhibit a relatively homogenous Cr distribution, whereas, an inhomogeneous Cr distribution is observed in the cavity-containing regions. It is believed that this local Cr inhomogeneity in the ICHAZ is caused by the partial dissolution of Cr-rich M23C6 carbides and an insufficient homogenization during rapid welding thermal cycles.

Observations of Radiation‐Dominated Rapid Cooling of Structures Based on Carbon Nanotubes and Graphene

It is often desirable to cause rapid thermal cycles in isolated systems, and it is convenient to do so by means of radiant heating and cooling. In principle, the rate of heating is arbitrarily increased simply by applying sufficient irradiance. This is not true for cooling, wherein the radiant emittance of a surface is determined by its emissivity and temperature. In an optically thin structure, the cooling rate is determined by the ratio of the material's emissivity to its specific heat, a factor that is expected to be greater in materials with a short characteristic absorption length, such as graphite. Herein, several forms of carbon‐based nanostructures, which have very short thermal radiation attenuation lengths, and are very robust and can withstand the high temperatures required for substantial Planckian thermal radiant emittance, are examined. Rapid cooling times ranging from about 100 μs to 1 ms are observed in structures cooling from a typical high temperature of 1500 K to a low of roughly half that value. Such rapid extreme thermal cycling of isolated materials provides new opportunities, for both research and potentially practical applications.