High Temperature Capability Research Articles

Recrystallisation behaviour and mechanical properties of a novel Re-containing nickel-base superalloy

ABSTRACTA newly developed heavily alloyed polycrystalline nickel-base superalloy containing rhenium and intended as a structural material for turbine discs in gas turbine engines has been studied. Homogenisation and heterogenisation heat treatments were developed for the as-cast superalloy, which led to improving the hot workability as compared to that of as-cast material. electron backscatter diffraction analysis of samples isothermally compressed at temperatures near the solvus temperature showed that continuous dynamic recrystallisation occurred in the superalloy leading to the formation of refined recrystallised structure. These results were used for the development of canned forging processing under quasi-isothermal conditions. The superalloy subjected to canned forging followed by aging exhibited superior high strength and high-temperature capability, while retaining reasonable ductility as compared to known disc superalloys.

A miniaturized spectrometer for NMR relaxometry under extreme conditions

With the advent of integrated electronics, microfabrication and novel chemistry, NMR (Nuclear Magnetic Resonance) methods, embodied in miniaturized spectrometers, have found profound uses in recent years that are beyond their conventional niche. In this work, we extend NMR relaxometry on a minute sample below 20 μL to challenging environment of 150 °C in temperature and 900 bar in pressure. Combined with a single-board NMR spectrometer, we further demonstrate multidimensional NMR relaxometries capable of resolving compositions of complex fluids. The confluence of HTHP (high-pressure high-temperature) capability, minimal sample volume, and reduced sensor envelop and power budget creates a new class of mobile NMR platforms, bringing the powerful analytical toolkit in a miniaturized footprint to extreme operating conditions.

Growth Kinetics and Isothermal Oxidation Behavior of Aluminide Pack Coatings on a Multiphase Mo–Si–B Alloy

Refractory metal alloys, such as Mo–Si–B systems, can extend high-temperature capability more than commercial Ni-based superalloys, but Mo–Si–B alloys require surface coatings to improve their poor oxidation resistance. In this study, aluminide coating layers were created on Mo–3Si–1B (wt%) alloys by pack cementation with NH4Cl, Al and Al2O3 powder. The aluminide coating layers consisted of MoAl4, Mo3Al8, and precipitates. The growth kinetics of the coating layers were estimated by identifying diffusion behaviors. The aluminide coating layer growth constant (k0) was estimated as ~ 741.3 μm/h0.5, and the activation energy (Q) for the growth of the diffusion coating layer was evaluated as ~ 44.2 kJ/mol for the examined coating temperatures of 800, 900 and 1000 °C. The thicknesses of the coating layers calculated by an estimated kinetic equation were compared with the experimental results. The coating layer successfully protected the Mo–Si–B substrate during isothermal oxidation at 1400 °C under an air atmosphere. The growth kinetics of the coated layer and oxidation behaviors were discussed in terms of microstructural analyses.

Stackable SiC Embedded Ceramic Packages for High Voltage and High Temperature Power Electronics Applications

Abstract This paper encompasses the development of a high voltage and high temperature capable package for power electronic applications based on the embedding of SiC (silicon carbide) semiconductor devices in ceramic circuit carrier such as direct bonded copper (DBC) substrate. By sealing the semiconductor devices into DBC substrates, high temperature, high voltage and high current capability as well as high corrosion resistance can be achieved compared to state-of-the-art PCB (printed circuit board) embedding technology. The power devices are attached with high temperature stable solder and sinter material, and are surrounded by thermal conductive ceramic and high temperature capable potting materials that enable the complete package to operate at 250 °C or above. Furthermore, the single embedded packages can be stacked together to multilevel DBC topologies with increased voltage blocking characteristics. Thus, current limits of PCB and LTCC (low-temperature co-fired ceramic) based multilayer solutions are exceeded and will be confirmed in the course of this study. This package is designed to carry out the maximal performance of SiC and future WBG (wide band-gap) devices. It is a promising solution for applications in harsh ambient environment such as aerospace and turbine, geothermal well logging, down hole-well oil & gas, but also applicable for HEV/EV (hybrid electric/electric vehicle) and energy conversion.

Development of a high-temperature micromechanics stage with a novel temperature measurement approach.

The study of mechanical properties of materials at high temperatures at the microstructural length regime requires dedicated setups for testing. Despite the advances in the instrumentation in these setups over the last decade, further optimization is required in order to extend the temperature range well-beyond 600 °C. Particularly, an improvement of the contact temperature measurement is required. A design with a novel approach of temperature measurement with independent tip and sample heating is developed to characterize materials at high temperatures. This design is realized by modifying a displacement controlled room temperature microstraining rig with the addition of two miniature hot stages, one each carrying the sample and indenter tip. The sample reaches temperatures of >600 °C with a 50 W diode laser system. The stages have slots for the working sample as well as a reference sample on both ends for precise temperature measurements, relying on the symmetry of the stage toward the ends. The whole setup is placed inside a custom-made steel chamber, capable of attaining a vacuum of 10-4 Pa. Alternatively, the apparatus can be operated under environmental conditions by applying various gases. Here, the unique design and its high temperature capabilities will be presented together with the first results of microtension experiments on freestanding copper thin films at 400 °C.

Design Challenges of SiC Devices for Low- and Medium-Voltage DC-DC Converters

Silicon carbide (SiC) devices are considered as key enablers for the development of highly efficient and compact dc-dc converters for low- and medium-voltage applications. Besides their high temperature capability and low conduction losses, they provide superior switching characteristics.This paper emphasizes design challenges of SiC devices in the low- and medium-voltage range arising from their fast switching speeds. First, detailed measurement results on the switching characteristics of 1200 V SiC devices and different leakage inductances are presented. The results are assessed with regard to the switching losses as well as the transient voltage and current overshoots. The impact on the switching behavior as function of leakage inductances is shown. The leakage inductances also influence the resonance frequency of the power module and dc-dc converters. This is a crucial design aspect to determine the size of the EMI filters. Its significance is demonstrated based on an 800 V dc-dc converter using commercially available SiC MOSFETs. Furthermore, zero-voltage switching is emphasized to reduce the impact of the module parasitic elements on the switching behavior. The performance of 10 kV SiC MOSFETs in a medium-voltage dc-dc converter shows, however, that a significant amount of commutation energy is required to ensure a successful soft-switching transition.

Solidification of niobium-silicide-based alloys during laser additive manufacturing process

Niobium silicide-based composites, in the application of gas turbine blades, promise significant efficiency improvements compared to current Ni-based alloys. The higher temperature capability would allow the engine to run at a higher temperature than that of current alloys, increasing engine efficiency. Nb-Si based composites possess a lower density, due to the presence of ceramic phases such as Nb5Si3 and/or Nb3Si. This would reduce the weight of the rotating blades. However, improvements in certain properties, such as room temperature toughness and oxidation resistance are needed.This study focuses on the manufacturability aspect of the powder feeding laser additive manufacturing (LAM) process to engineering Nb-Si based alloy samples. LAM has the advantage of forming near-net shapes without the use of expensive cores and moulds for the reactive Nb-Si melt. Fine microstructure and even chemical composition distribution with reduced macro-segregation are obtained. With the use of power feeding system, new Nb-Si based alloys are LAMed with varying atomic composition. Microstructures of the LAMed alloys will be presented, and the relationship between the microstructure and the alloy chemistry will be reported.

Fabrication of mullite ceramic-supported carbon nanotube composite membranes with enhanced performance in direct separation of high-temperature emulsified oil droplets

The direct treatment of high-temperature oil-in-water (O/W) emulsions is a challenging energy-saving water treatment issue for membrane technology, where thermally resistant separation membranes are required. This work proposes the rational design and facile fabrication of a thermally resistant mullite-CNT (carbon nanotube) composite membrane with a hierarchical structure for the high-temperature direct removal of tiny oil droplets from O/W emulsions. CNTs were grown in situ on/inside robust mullite ceramic hollow fibers by chemical vapor deposition (CVD), where hydrogen gas was produced as by-product with a concentration as high as 5.5% at 600 °C. After structural characterization, the high-temperature separation capability of mullite-CNT composite ultrafiltration membranes was assessed. The membranes exhibited excellent performance with high oil rejection of 100%, 99.99%, 99.99% and 99.99% and increased initial permeate fluxes from 6.5, 9.7, 12.8–15.7 L m−2 h−1 at the investigated temperatures of 25, 50, 80 and 100 °C. A simple cleaning method using dilute aqueous NaOH without energy consumption was used to effectively accomplish membrane regeneration. Our results indicate that ceramic-CNT membrane is promising for highly efficient direct separation of high-temperature O/W emulsions without the necessity of including a cooling process, thus providing recovered hot water with intensive energy saving in practical industrial applications.

Behaviors of starches evaluated at high heating temperatures using a new model of Rapid Visco Analyzer ‒ RVA 4800

Rapid Visco Analyzer (RVA) is a reliable viscometer that is commonly utilized to measure the pasting properties of starch. The conventional model of RVA can only determine starch pasting properties at heating temperatures up to 95 °C, which thus cannot evaluate the performance of starch related to high-temperature processing, such as retorting, jet-cooking and extrusion. In this study, RVA 4800 ‒ the latest model of the viscometer having high-temperature capability ‒ was deployed to determine the pasting properties of representative waxy, normal and high-amylose starches of 1.8–69.7% amylose contents at heating temperatures of 95–140 °C. As the temperature increased from 95 to 140 °C, the pasting temperatures and peak viscosities of most waxy and normal starches remained unchanged, but their holding strengths and final viscosities decreased, which could be attributed to thixotropic breakdown and thermal degradation of starch molecules. Consequently, the paste adhesiveness or gel hardness of most waxy and normal starches was reduced at higher temperatures. By contrast, heating at temperatures above 120 °C completely gelatinized wrinkled pea and high-amylose maize starches, allowing the starch granules to swell for viscosity development and subsequent gel formation. Matrix structures of the freeze-dried starch pastes and gels were observed under scanning electron microscope to elucidate how the changes at granular and molecular levels at the tested cooking temperatures influenced the pasting and gelling properties of different starches. This research offered new insights into the relationships between the thermal properties, pasting properties and gelling ability of various starches at heating temperatures of 95–140 °C by using RVA 4800.

Enhanced mechanical properties at 400 °C of carbon fabric reinforced phthalonitrile composites by high temperature postcure

Phthalonitrile resins have received growing attention due to their superior thermal stability and good structural properties required for high temperature applications in aerospace industry etc. In this work, a newly developed phthalonitrile blend resin with an appropriate viscosity for autoclave processing is employed for manufacturing of high quality void-free thick composite panels using MT300 carbon fabrics. In particular, the effects of postcure temperature are systematically examined on their 400 °C mechanical properties required for high temperature structural applications. Dynamic mechanical analysis reveals that the composite postcured at the high temperature of 375 °C exhibits a high glass transition temperature over 450 °C. Mechanical testing results show that the flexural and compressive strengths at room temperature are lowered by the high temperature postcure, but their counterparts at 400 °C are obviously enhanced by the postcure. Moreover, the 400 °C interlaminar shear strength initially decreases but then increases with increasing the postcure temperature. The char retention in nitrogen at 1000 °C is 89% of its initial weight. Consequently, the newly developed phthalonitrile resin is highly promising for manufacturing of thermal resistant polymeric composites for high temperature application in aerospace industry etc. that need composites to have high temperature capabilities.

Improved Proportional Base Driver for SiC BJTs

The benefits of high-power silicon carbide (SiC) bipolar junction transistors (BJTs) in terms of low conduction and switching losses, high-temperature capability, and increased reliability associated with the lack of gate oxide have been partially shadowed by the high-power consumption of its driver. This paper focuses on the optimization of SiC BJT base drivers and presents an innovative design of a proportional base current driver. The driver is a stand-alone system achieving instantaneous tracking of the collector current without the need for a current sensor and can also account for variations of the BJT’s dc current gain with the temperature. Implementation of these two features is realized by sensing the collector–emitter voltage, which is conditioned to be used as a reference voltage for a switching regulator featuring a megahertz synchronous buck converter. This leads to a variable base current that is proportional to the instantaneous collector current for the SiC BJT. The concept is validated using a 1.5-kW boost converter, which shows a significant reduction in power consumed by the driver.

Cylinder pressure sensors for smart combustion control

Abstract. Different sensor concepts for time-resolved cylinder pressure monitoring of combustion engines are realized and evaluated in this paper. We distinguish a non-intrusive form of measurement outside the cylinder, performed by means of a force compression rod from intrusive, real in-cylinder measurement by means of pressure membrane sensors being exposed to the hot combustion process. The force compression rod has the shape of a sine wave with thinner zones equipped with highly sensitive foil strain gauges that experience a relatively moderate temperature level of 120 ∘C. The sensor rod delivers a relative pressure value that may be influenced by neighbour cylinders due to mechanical coupling. For the intrusive sensor type, two different materials for the membrane-type sensor element were simulated and tested, one based on the ceramic zirconia and the other based on stainless steel. Due to the higher thermal conductivity of steel, the element experiences only 200 ∘C while the zirconia element reaches 300 ∘C. Metallic chromium thin films with high strain sensitivity (gauge factor of 15) and high-temperature capability were deposited on the membranes and subsequently structured to a Wheatstone bridge. The pressure evolution can be measured with both types in full detail, comparable to the signals of test bench cylinder pressure sensors. For the preferential steel-based sensor type, a reliable laser-welded electrical connection between the thin films on the membrane and a copper wire was developed. The in-cylinder pressure sensors were tested both on a diesel test bench and on a gas-fired engine. On the latter, an endurance test with 20 million cycles was passed. Reliable cylinder pressure sensors with a minimum of internal components are thus provided. The signals will be processed inside the sensor housing to provide analysis and aggregated data, i.e. mass fraction burned (MFB50) and other parameters as an output to allow for smart combustion control.

The Importance of Establishing a Very High-Temperature Radiation Thermometry Measurement Capability at the National Metrology Institute of South Africa (NMISA)

The ITS-90 scale above the Silver (Ag) point is realized using a standard linear radiation thermometer by measurement at a reference point which is an Ag, Gold (Au), or Copper (Cu) point. The fixed...

On the development of uniaxially‐oriented PET tapes for weaving, woven tape fabrics, and their applications

This article reports the development of weavable, uniaxially‐oriented PET tape, and woven‐tape fabric. Fabric from uniaxially‐oriented polypropylene (PP) tape has been commercially produced since the 1960s, and it is the dominant material for flexible industrial packaging, carpet backing, geotextiles and self‐reinforced composites. Attempts had been made over the same period to produce similar poly(ethylene terephthalate) (PET) tape fabric, knowing that it would offer superior performance over PP due to PET's higher stiffness and strength, lower creep, abrasion resistance, and higher temperature capability. However, these attempts could not be translated into industrial production because the PET tapes had a tendency to splinter when subjected to sudden pulls and twists in the weaving loom. This was solved here by blending polymeric additives such as 2% polycarbonate (PC) and 2% linear low‐density polyethylene (LLDPE). Transmission electron microscopy of the oriented tapes showed the 2% PC formed a profusion of nano ellipsoids that adhered well to the PET matrix, and these prevented axial cracks from running through in a brittle manner. The LLDPE formed larger domains with poorer adhesion, but it imparted resistance to splitting from twists and axial folding. The combination of PC and polyolefin imparted a synergistic toughening of the tape. POLYM. ENG. SCI., 59:E120–E132, 2019. © 2018 Society of Plastics Engineers

A Novel One-Transistor Dynamic Random-Access Memory (1T DRAM) Featuring Partially Inserted Wide-Bandgap Double Barriers for High-Temperature Applications.

These days, the demand on electronic systems operating at high temperature is increasing owing to bursting interest in applications adaptable to harsh environments on earth, as well as in the unpaved spaces in the universe. However, research on memory technologies suitable to high-temperature conditions have been seldom reported yet. In this work, a novel one-transistor dynamic random-access memory (1T DRAM) featuring the device channel with partially inserted wide-bandgap semiconductor material toward the high-temperature application is proposed and designed, and its device performances are investigated with an emphasis at 500 K. The possibilities of the program operation by impact ionization and the erase operation via drift conduction by a properly high drain voltage have been verified through a series of technology computer-aided design (TCAD) device simulations at 500 K. Analyses of the energy-band structures in the hold state reveals that the electrons stored in the channel can be effectively confined and retained by the surrounding thin wide-bandgap semiconductor barriers. Additionally, for more realistic and practical claims, transient characteristics of the proposed volatile memory device have been closely investigated quantifying the programming window and retention time. Although there is an inevitable degradation in state-1/state-0 current ratio compared with the case of room-temperature operation, the high-temperature operation capabilities of the proposed memory device at 500 K have been confirmed to fall into the regime permissible for practical use.

Microstructure and mechanical properties of a novel polycrystalline rhenium-containing nickel-based disc superalloy subjected to hot forging

A newly developed heavy alloyed polycrystalline nickel-based superalloy SDZhS-15 containing rhenium and intended as a structural material for turbine discs in gas turbine engines has been studied. Multiple homogenization and heterogenization heat treatment was developed for the superalloy to improve its hot workability. The heat treated workpieces were subjected to single-step hot forging under quasi-isothermal conditions at temperatures slightly below the γ′ solvus temperature followed by air cooling and ageing. As a result, sound forgings with an inhomogeneous, partially recrystallized microstructure were produced. The obtained forgings were used for preparation of specimens for mechanical testing. The new superalloy showed superior high strength and high temperature capability, while retaining reasonable ductility in comparison with currently known disc superalloys.

An interconnection method based on Sn-coated Ni core-shell powder preforms for high-temperature applications

A die-attach material based on an Sn-coated Ni core-shell powder with a high re-melting temperature can be used for high-temperature applications. The outer Sn layers of the Sn-coated Ni particles possess a low melting point of 232 °C and can be completely converted into a Ni3Sn4 intermetallic compound with a high re-melting point of 794.5 °C after reflowing at a low temperature of 250 °C for 40 min. This die-attach material exhibits an excellent high-temperature operational capability, with a high shear strength of 40.2 MPa at 500 °C. The coefficient of thermal expansion (CTE) of the reflowed preform is between those of SiC and Cu, which is highly beneficial for mitigating the stress caused by the CTE mismatch between these materials. In addition, the thermal conductivity of the bondline is sufficiently high for heat dissipation during operation.

A Scalable, High-Throughput, and Environmentally Benign Approach to Polymer Dielectrics Exhibiting Significantly Improved Capacitive Performance at High Temperatures.

High-temperature capability is critical for polymer dielectrics in the next-generation capacitors demanded in harsh-environment electronics and electrical-power applications. It is well recognized that the energy-storage capabilities of dielectrics are degraded drastically with increasing temperature due to the exponential increase of conduction loss. Here, a general and scalable method to enable significant improvement of the high-temperature capacitive performance of the current polymer dielectrics is reported. The high-temperature capacitive properties in terms of discharged energy density and the charge-discharge efficiency of the polymer films coated with SiO2 via plasma-enhanced chemical vapor deposition significantly outperform the neat polymers and rival or surpass the state-of-the-art high-temperature polymer nanocomposites that are prepared by tedious and low-throughput methods. Moreover, the surface modification of the dielectric films is carried out in conjunction with fast-throughput roll-to-roll processing under ambient conditions. The entire fabrication process neither involves any toxic chemicals nor generates any hazardous by-products. The integration of excellent performance, versatility, high productivity, low cost, and environmental friendliness in the present method offers an unprecedented opportunity for the development of scalable high-temperature polymer dielectrics.

Effects of PCB power layouts design on switching transient performance of SiC MOSFETs

This paper investigates the effects of Printed Circuit Board (PCB) layouts design of power stage on the switching transient performance of SiC MOSFETs-based Bidirectional Switching Power Pole (BSPP). SiC MOSFETs have compelling merits such as low power losses, high breakdown voltage, high thermal conductivity, high operating temperature capabilities, and excellent reverse recovery characteristics. To realize those features, it is challenging to design PCB layers for the power stage with low parasitic inductance to achieve high switching speed operation with an acceptable amount of ringing and overshoot in the switching transient waveforms. Therefore, this work introduced critical PCB design keys to achieving low parasitic inductance as well as symmetrical switching transient performance for both high and low side SiC MOSFETs based BSPP. A broad coupled traces method is used to design the PCB power traces with a minimum parasitic inductance for given geometric dimensions. Mathematical formulas are used to calculate the parasitic inductance of the PCB prototypes. The formulas purely depend on the geometric dimensions of the PCB layers and the thermal expansion coefficient of the substrate material. Cadence simulation tools are used to verify the parasitic inductance calculations of the experimental PCB prototypes by comparing both experimental and simulation switching transient performances.

Environmentally benign non-fluoro deep eutectic solvent and free-standing rice husk-derived bio-carbon based high-temperature supercapacitors

Deep eutectic solvents (DESs) have been emerging as newer environmentally benign electrolytes for energy storage devices with the high-temperature operational capability. For the first-time, we propose ethylene glycol and tetrapropylammonium bromide based non-fluoro DESs as electrolytes for the supercapacitor. Different compositions of DESs were also evaluated. Also, the high-temperature operational capability of the proposed electrolytes was evaluated with the free-standing microporous commercial activated carbon (AC) and mesoporous rice husk-derived bio-activated carbon (Bio-AC). The maximum cell voltages of 1.3 V and 1.0 V are identified for AC and Bio-AC based supercapacitors, respectively at 25 °C. The specific capacitances of both AC and Bio-AC electrodes are ∼100 F g−1 at 0.1 A g−1. The proposed DES electrolyte can be operated at the maximum temperature of 115 °C, which is higher than the previously reported DESs (80 °C). The specific capacitance increases with increasing temperature, and the maximum specific capacitance of an electrode is 172 F g−1 at 115 °C for Bio-AC supercapacitor. Excellent long-term stability is noted after 10,000 cycles at 25 °C and 115 °C for both AC and Bio-AC supercapacitors. The supercapacitors here may be practically used in high-temperature applications.