Temperature In Harsh Environments Research Articles

Mechanical Loading Effect on Stress States and Failure Behavior in Thermal Barrier Coatings

Under service conditions, apart from the harsh temperature environment, mechanical loading also seriously affects the life of thermal barrier coatings (TBCs). A comprehensive understanding of the combined effects of thermo-mechanical loads can help to further reveal the failure mechanism of TBCs. In this work, a portion of a thin-walled circular pipe is intercepted for numerical analysis, and the interface is simplified as a sinusoidal curve. The dynamic growth of thermally grown oxide (TGO) is included into the model. A cohesive model is used for interfacial cracking analysis. The results show that the effects of tensile and compressive loads on the normal stress of the coating are not significant, while the effect on the shear stress of the coating is more obvious. In addition, the in-phase load will delay the occurrence of interfacial failure behavior, while an out-of-phase load can promote the failure. These results will help to better understand the effects of the coupling of mechanical and temperature loads and to provide support and guidance for the design of new TBCs structures in the future.

Thermal and fracture analysis of collinear interface cracks in graded coating systems under ramp-type heating

Ceramic based thermal barrier coatings are extensively employed to shield critical engineering components from harsh temperature environments, where the typical Fourier's law may not be able to provide an accurate assessment of the physical process. This work adopts a more generalized heat conduction approach to reveal the thermal and fracture interaction mechanism of two collinear interface cracks in orthotropic functionally graded thermal coating systems by dual-phase-lag theory. The heating rate of the imposed thermal loading on the exterior bounding surface is modeled by ramp-type function, where the ramping period is comparable to the certain time spent for building the local thermal equilibrium within composites. The methods of Fourier transform and Laplace transform in conjunction with the singular integral equations are applied to solve the complex transient thermoelastic problem. Parametric investigations are conducted to investigate the impacts of ramping time, thermal lags, nonhomogeneous parameters, and crack spacing on the thermal and fracture characteristics. According to the maximum hoop stress criterion, higher fracture risk is discovered with the approaching of collinear interface cracks.

Feasibility study on electrically conductive joining of MoSi2 electrodes for spark plugs

AbstractDespite the often outstanding functional as well as (high temperature‐) mechanical properties of ceramics, their usage is often limited due to their inherent brittleness. This also compromises the joining with metals, which is often indispensable for engineering applications. In this context, electrically conductive ceramics like MoSi2 are promising materials for the application as electrodes where high temperatures in harsh environments are present (e.g., in spark plugs for large gas engines). Due to the difficult joining of the respective materials, long‐term experiments are thereby often still pending. In this work, adhesive bonding, brazing, tungsten inert gas‐, and resistance welding were performed to evaluate their applicability for generating electrically conductive as well as mechanically reliable joints between MoSi2 and Inconel 600, aiming to utilize MoSi2 electrodes in spark plugs. Fractographic analyses are performed to understand cracks associated with the high (thermo‐) mechanical stresses. Additionally, a finite element model was set up for a deeper understanding of the observed fracture behavior. While adhesive bonding is acceptable for short‐term experiments at low temperatures, brazing and resistance welding may qualify for fast and reliable manufacturing of spark plugs with ceramic electrodes.

Highly-Accurate Temperature-Compensated Pneumatic Measurement Using Piezoresistive Pressure Sensor

Pneumatic cylinder is known as one of the major transmission power sources in either machinery or automation operation. However, the sensor used in the pneumatic measurement is sensitive to harsh temperature environments. For this reason, a high precision pneumatic measurement using piezoresistive pressure sensor with temperature compensation is proposed in this paper. The pneumatic signal is read and amplified via A/D converter of the microprocessor. The relationship of pneumatic signal maximum level over temperature influence is also built up for a compensation purpose. A human-machine interface (HMI) with the computer is designed for real-time accurate calibration via RS-485. Based on a current loop transmitter, the measured pneumatic signal can be converted into an industrial standard (i.e., 4-20mA output). The experimental results verify that the proposed system can achieve an accurate measurement outcome below 0.5% error in both HMI and output current under a variety of temperature conditions.

Estimation of metal state in molten production processes using electromagnetic tomography with fast integrated processing

This paper presents imaging of copper slag solidification processes using electromagnetic tomography (EMT). It describes key components of the measurement system including a sensor that can operate in the harsh temperature environments. An integrated process tomography system is detailed that includes the main processing unit, i.e. a field programmable gate array and other front end circuitries. It is capable of delivering a wide excitation signal frequency ranging from 0.1 Hz to 500 kHz and a fast speed of 131 frames s−1 with a typical signal-to-noise ratio of 66 dB–95 dB. Measurement trials were conducted on a molten converter slag solidification process where the copper slag changes from the molten state to solidification state during the cool-down for more than an hour. The phenomenon in which the disorderly distributed metal gradually forms solid and permeable object was observed, which can indicate the status of the process. This is the first report of observing such a process using an EMT system. Moreover location-based convergence analysis has been carried out in the imaging space and useful new insights have been gained for the copper production process, which would be difficult to obtain otherwise. Verification and calibration using x-ray diffraction and scanning electron microscope indicate the viability of the EMT-based measurement method.

Graphene Ionogel Ultra-Fast Filter Supercapacitor with 4V Workable Window and 150 °C Operable Temperature.

The filtering capacitor plays an essential role in the ever-increasing electronics for current stability in complicated environments. However, because of the low specific capacitance and bulky volume, current filtering devices have difficulty satisfying the harsh temperature environment and small size for supercomputers, electric vehicles, aircraft and so on. Therefore, an ultra-fast electrochemical capacitor is developed on the basis of vertically oriented graphene iongel electrodes (GI-EC), which demonstrates excellent alternate current line-filtering performance with both hot tolerance of up to 150 °C and a wide voltage window of 4V. Because of the particularly oriented graphene nanosheets induced fast ion transport, this ionic electrochemical capacitor displays a high areal specific energy density of 1784 µFV2 cm-2 with a phase angle of -80.0° (120Hz) at 150 °C, which is greater than most of the reported electrochemical capacitors. Moreover, it can filter arbitrary waveforms to smooth direct current signals and works well with a wide frequency range from 10 to 104 Hz. The easy integration of GI-ECs in series or parallel can also further deliver desired capacitances or high voltages. The GI-EC with high-rate performance, wide voltage window, and high-temperature adaptability presents a great promise for universally applicable filtering capacitors.

Influence of substrate temperature on the microstructure of YSZ films and their application as the insulating layer of thin film sensors for harsh temperature environments

Thin film sensors are employed to monitor the health of hot-section components of aeroengine intelligence (for instance, blades), and electrical insulating layers are needed between the metal components and thin film sensors. For this purpose, the electrical insulation characteristics of an yttria-stabilized zirconia (YSZ)/Al2O3 multilayer insulating structure were investigated. First, YSZ thin films were deposited by DC reactive sputtering at various substrate temperatures, and the microstructural features were investigated by scanning electron microscopy and X-ray diffraction. The results indicate that the micromorphology of the YSZ thin film gradually became denser with increasing substrate temperature, and no new phases appeared. The compact and uniform topography of the YSZ thin film improved the insulation properties of the multilayer insulating structure and enhanced the adhesion of the thin film sensors. In addition, the electrical insulation properties of the YSZ/Al2O3 multilayer insulating structure were evaluated via insulation resistance tests from 25 to 800 °C, in which the YSZ thin film was deposited at 550 °C. The results show that the insulation resistance of the multilayer structure increased by an order of magnitude compared with that of the conventional Al2O3 insulating layer, reaching 135 kΩ (5.1 × 10−6 S/m) at 800 °C. Notably, the insulation resistance was still greater than 75 kΩ after annealing at 800 °C for 5 h. Finally, the shunt effect of the YSZ/Al2O3 multilayer insulating structure was estimated using a PdCr thin film strain gauge. The relative resistance error was 0.24%, which demonstrates that the YSZ/Al2O3 multilayer insulating structure is suitable for thin film sensors.

Long-period fiber grating based on inner microholes in optical fiber.

A new, to the best of our knowledge, type of long-period fiber grating based on inner microholes in an optical fiber core is proposed and demonstrated. The device is fabricated by first using a femtosecond laser to write a series of vertical short line structures in the core of a single-mode fiber, followed by discharge of the short line areas with a fusion splicer. Owing to the high temperature generated, the line structure rapidly expands and forms an inner microhole. The device is found to have good high temperature sustainability up to 1000°C, with a sensitivity of approximately 13 pm/°C and its strain and bending sensitivities are approximately -1.57 pm/µɛ and -5.198 dB/m-1, in the ranges of 0-800 µɛ and 0-0.77 m-1, respectively. It is expected that the device can contribute to the multi-parameter sensing and detection of high temperature in harsh environments.

Quantification of Performance Variation and Crack Evolution of Bond-Wire Interconnects Under Harsh Temperature Environments by S-Parameter Analysis

Electrical interconnects play important roles in both the performance and reliability of integrated circuits. As the operating frequency has increased and products have been exposed to harsh environments such as temperature extremes and thermal cycling, it has become essential to quantify the thermal effects on the reliability of such circuits. In particular, the effects on the signal transmission performance of the interconnects and the evolution of cracks caused by thermo-mechanical stresses need to be investigated. This study proposes that both research goals can be accomplished by S-parameter analysis alone. First, the performance variation was experimentally quantified by in situ measurements of S21 (an indicator of signal transmission performance) on bond-wire test vehicles at static temperatures between -60 °C and 120 °C. An impedance model of the interconnect was developed focusing on thermal expansion effects and it predicted the performance variation of the interconnect successfully at the given temperatures. Second, the results of ex situ measurements of S11 (an indicator of return signal) obtained using a test vehicle under thermal cycling were compared with scanning electron microscopy images of crack propagation in the interconnect. In the crack initiation phase, a resonance peak occurred on the S-parameter pattern and the peak moved toward lower frequencies as the crack propagated until failure. SPICE simulations using a suggested impedance model of the cracked interconnect confirmed the experimental results. In addition, this study demonstrates that monitoring the resonant frequency in the S-parameter pattern as a prognostic factor can predict the initiation and evolution of cracks earlier and is more sensitive than the conventional dc resistance measurement method.

Effect of Elevated Temperatures on SAC305 Solder Alloy Thermal Interface Material in a Microelectronic Assembly

In microelectronics assemblies, Thermal Interface Materials (TIMs) are vital to the reliability of the devices in operation. Some electronic devices operate in elevated temperature environments such as military and industrial applications. Hence, the need to evaluate the reliability of such devices at elevated temperatures. Tin-Silver-Copper lead-free solder TIMs have been used during the assembly process of some electronic devices operating under harsh temperature environments. In this study, the reliability of SAC305 lead-free solder TIM was considered at elevated temperatures ranging from 100 oC to 200 oC at 25 oC interval, and aged for about an hour. ANSYS finite element analysis software was employed for the design and evaluation of SAC305 lead-free solder model. The findings of the investigation demonstrated that the higher the harsh temperature environment, the lower the reliability of the SAC305 solder TIM. In addition, the highest fatigue life (36735 or 4.2 years) was recorded at 100 oC, while 200 oC recorded the lowest fatigue life (1014 or 0.12 years). The fatigue life is an indication of the lifespan of the TIM when in operation. This research will be beneficial to engineers assembling microelectronic products. Keywords— elevated temperature; fatigue life; microelectronics; reliability; SAC305 solder

Fabrication and applications of polyimide nano-aerogels

Nano-aerogels have been used in various fields due to their ultralow density, ultrahigh porosity and ultralow thermal conductivity. However, common nano-aerogels with poor thermal stability are scarcely used in high- and low-temperature environments. Polyimide (PI) nano-aerogels that are developed from PIs can meet the requirements and have been studied in recent years, especially in the field of deep space exploration. In this review, we discuss the current state of the fabrication, classification, methods of improving properties and fields of application of the PI nano-aerogels. As one of the best materials with outstanding comprehensive properties under harsh temperature environments, PI nano-aerogels will play important roles in technology in the future.

A Thermal Drift Compensation Method for Precision Sensors Considering Historical Temperature State

This article proposes a compensation method for precision sensors considering historical temperature states, which can significantly reduce the thermal drift of the sensors during rapid temperature change process. A typical differential eddy current sensor (ECS) measuring displacement is used as an example to explain the principle. By analyzing the source of thermal drift of the ECS, it is proved that time history of temperature change will also affect the output of the ECS. In this article, the temperature response characteristics of the sensing head of the ECS are obtained by the lumped capacitance method, and the output of the ECS is compensated by convolution operation. Experimental results show that the temperature coefficient of the ECS during a temperature change process is depressed from 34.62 to 1.64 nm/°C with this method, and it is also less than 1/4 of 7.70 nm/°C which is obtained with direct compensation using current temperature value. Furthermore, this method is expected to function efficiently for any precision sensor in complex and harsh temperature environments.

Design of an acoustic sensor for fission gas release characterization devoted to JHR environment measurements

Among numerous research projects devoted to the improvement of the nuclear fuel behaviour knowledge, the development of advanced instrumentation for in-pile experiments in Material Testing Reactor is of great interest. In the frame of JHR reactor, new requirements have arisen creating new constraints. An acoustic method was tested with success during a first experiment called REMORA 3 in 2010 and 2011, and the results were used to differentiate helium and fission gas release kinetics under transient operating conditions. This experiment was leading at OSIRIS reactor (CEA Saclay, France). The maximal temperature during the irradiation test was about 150 °C. [1], [2]. We have developed thick film transducers produced by screen-printing process. They offered a wide range of possible application for the development of acoustic sensors and piezoelectric structure for harsh temperature environment measurements [3]. We proposed a screen-printed modified Bismuth Titanate piezoelectric element on alumina substrate allowing acoustic measurements [4] for JHR environment. In this paper we will focus on the mechanical design of the new sensor. This acoustic sensor is composed of an acoustic element for generation and detection of acoustic waves propagating into a cavity filled with gaz. We will detail the choice of piezoelectric materials, the thickness of the different layers, the cavity shapes, the electrical connections, the means of assembly of the different parts. Theoretical and experimental results will be given. All that point will be discussed in terms of acoustic sensor sensitivity versus dimensional constraints, in the case of a high temperature range working.

Investigation on a novel polysilylaryl-enyne/Ca0.7La0·2TiO3 composite with an ultra-high dielectric constant and excellent temperature resistance

This article reports a novel category of thermosetting composite prepared by compounding a high temperature resistant polysilylaryl-enyne (PSAE) resin with different volume fractions (vol%) of high dielectric constant Ca0·7La0·2TiO3 (CLT) ceramics. The microstructure, dielectric properties and thermal properties of the PSAE/CLT composites were fully investigated. The results show that the PSAE/CLT composite with an ultra-high dielectric constant and low dielectric loss (εr = 23.0 and tanδ = 3.4 × 10−3, at 10 GHz) was obtained when the filler volume fraction reached 60%. Meanwhile, the coefficient of thermal expansion of the composite was reduced to 15.1 ppm/°C which could match copper foils. And a high thermal conductivity of 0.918 W/(m·K) could be obtained at 60 vol% filler loading. The glass transition temperatures of the PSAE/CLT composites were over 450 °C which indicate that all the PSAE/CLT composites have an excellent temperature resistance. The novel PSAE/CLT composite has important application prospect in high-frequency communication under a harsh temperature environment.

Reliability of Sub-20 nm Black Phosphorus Trench (BP-T) MOSFET in High-Temperature Harsh Environment

In this work, the high-temperature reliability of the Black Phosphorus Trench (BP-T) MOSFET device has been analyzed. When the temperature is very high (500 K), the proposed device (BP-T-MOSFET) shows very high reliability with less effects in the device performance. The device is also calibrated with the experimental data. All the simulation has been performed using ATLAS-3D device simulator. BP-T-MOSFET shows high-temperature reliability in terms of reduced sub-threshold current, hot-electron injection gate current, and impact ionization substrate current. Further, higher switching ratio (Ion/Ioff), electron mobility, and electron velocity have also been observed owing to the electrical properties of black phosphorus used in the trench gate which shows the potential in a high-temperature environment. Owing to trench structure and electrical properties of black phosphorus, BP-T-MOSFET has significant device efficiency and low leakage currents at high temperatures which prove as highly shrieked MOS device applications in harsh temperature environment.

Composition gradient (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 film with improved dielectric, piezoelectric and ferroelectric temperature stability

Lead-free (1-x)Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 (BZT-BCT) possesses comparable piezoelectric constant with lead zirconate titanate (PZT), but its poor temperature electric performances stability and low Curie temperature limit its application. Here we designed composition graded BZT-BCT films with improved temperature stability of piezoelectric, ferroelectric, and dielectric performances over a wide temperature range, and the d33 reaches 21 pm/V with hysteresis loop even at 180 °C, which is far above the Curie temperature of BZT-BCT ceramic and BZT-0.5BCT film. The excellent temperature stability is ascribed to the lattice distortion and strain gradient in the grains caused by ions diffusion, and could suppress phase transition. This work could bring forward a feasible design for dielectric/piezoelectric/ferroelectric devices operating in harsh temperature environment.

Thermal shock resistance behavior of auxetic ceramic honeycombs with a central crack or an edge crack

In this paper, the thermal shock resistance of an auxetic ceramic honeycomb plate is studied based on the fracture mechanics concept for the cases of a central crack or an edge crack. The transient temperature field and transient thermal stress field are obtained for both auxetic and non-auxetic structures. The relationship between the thermal stress intensity factor (TSIF) and the internal cell angle, crack length and time is determined and the critical temperature for the initiation of crack propagation is predicted. Results show that compared with the non-auxetic ceramic honeycombs which are at an internal cell angle of 30°, the critical temperature of the auxetic ceramic honeycombs whose cell are orientated at an angle of −30° increases by 78.5% and the TSIF at the crack tip decreases by 40%, respectively. Hence, the auxetic structures have better thermal shock resistance. This study indicates that auxetic ceramic honeycombs have significant potential applications in harsh temperature environments.

Ultrastable and Low-Noise Self-Compensation Method for Circuit Thermal Drift of Eddy Current Sensors Based on Analog Multiplier

This article proposes a self-temperature compensation method based on an analog multiplier, which reduces the circuit thermal drift by more than an order of magnitude. An ac bridge eddy current sensor (ECS) is used as an example to analyze the thermal drift of the circuit in detail, and the basic principle of the compensation method is expounded. A high-precision ECS prototype is manufactured and tested. Results show that the temperature coefficient of the circuit in the prototype is decreased from 243 to 5 ppm/°C with this technique. This self-compensation method is simple, effective, and universal. Furthermore, this technique has a unique advantage for high-bandwidth and high-precision sensors and can work efficiently in complex and harsh temperature environments.

Stable ferroelectric properties of Hf0.5Zr0.5O2 thin films within a broad working temperature range

The ferroelectric properties of 20 nm Hf0.5Zr0.5O2 (HZO) thin films has been investigated in a wide temperature range from 100 K to 450 K. The remnant polarization of HZO thin films decreases slightly from 24.6 μC cm−2 (100 K) to 17.9 μC cm−2 (450 K), indicating a robust temperature stability. The capacitors also exhibit excellent endurance properties up to 109 cycles at 100 K and 300 K, and their endurance cycles slightly degrades to 108 at an elevated temperature of 450 K. The results show that HZO ferroelectric thin films have great potential for future emerging memory applications in various harsh temperature environments.

Well‐Aligned Hierarchical Graphene‐Based Electrodes for Pseudocapacitors with Outstanding Low‐Temperature Stability

AbstractThe relatively poor performance stability of pseudocapacitors over a wide temperature window (i. e. temperature stability), particularly at low temperatures, hinders their practical applications. Here, well‐aligned hierarchical pseudocapacitive electrodes are fabricated, featuring run‐through channels in a graphene network (GN) as ion‐buffering reservoirs, open inter‐sheet channels between vertical graphene nanosheets (VGNSs) for fast ion transport and MnO2 nanopetals on VGNSs for efficient interfacial pseudocapacitive reactions. With reduced ion diffusion length and charge‐transfer resistance as well as improved ion‐transport rate, the capacitance of pseudocapacitive electrodes decreases from 541 to 490 F g−1 at 1 A g−1 as the temperature drops from 25 to 0 °C, revealing a high capacitance retention of 90.7 %. Furthermore, the specific capacitance of a symmetric device based on the hierarchical electrodes at −30 °C maintains 80.8 % of the room‐temperature capacitance. Such outstanding temperature stability is comparable to the state‐of‐the‐art electric double‐layer capacitors. Importantly, 86.0 % of capacitance is retained after repeated heating and cooling at temperatures ranging from −30 to 60 °C for 5000 cycles. Asymmetric supercapacitors with the hierarchical architecture in the positive electrode exhibit stable performance over a wide temperature range. These results demonstrate the rationality of the electrode design for practical energy storage applications in harsh temperature environments.