Difference In Thermal Expansion Coefficients Research Articles

Phase-field modeling and n-point polytope characterization of nanostructured protuberances formed during vapor-deposition of phase-separating alloy films

The formation of surface features, such as grooves, protruding grains, or hillocks, in vapor-deposited phase-separating films is typically attributed to internal residual stresses arising due to a difference in thermal expansion coefficients of the film and the substrate. Even though such protuberances are typically observed on the film’s surface, the current understanding of how interfacial energies and surface contact angles influence this nanostructural evolution is very limited. In view of this knowledge gap, we adopt a three-dimensional phase-field approach to numerically investigate the role of seed morphology and contact angles on the morphological evolution of surface protuberances in phase-separating alloy films. Film nanostructures are quantified using a statistical morphological descriptor, namely, n-point polytope functions, which provides a host of insights into the kinetic pathways while unraveling a hidden length scale correlation present at all contact angles. Finally, we also apply this characterization technique on previously reported micrographs of Cu–Ta and Cu–Mo–Ag films to highlight similarities between our simulation-based findings with those obtained from co-deposition experiments.

A potential ZrO2 doped scandium tantalite ceramics for thermal/environmental barrier coating material

Despite scandium tantalite (ScTaO4) has great potential application for thermal/environmental barrier coating system, it is necessary to reduce the thermal expansion coefficient difference between them to lower the thermal stress in practical applications. In this paper, (ZrO2)x-(ScTaO4)1-x (x = 0.1, 0.2) material was prepared by doping ZrO2 into scandium tantalite ceramics, and its thermal expansion coefficient and calcium–magnesium–alumino-silicate (CMAS) corrosion behavior were studied. After the CMAS corrosion experiments of (ZrO2)x-(ScTaO4)1-x material, the phase composition and microstructures of samples were detected by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. The main results show that the alloying effect of ZrO2 doping can reduce the thermal expansion coefficient of ScTaO4 and then alleviate the thermal expansion coefficient difference in thermal/environmental barrier coating system. Besides, Zr4+ ions are separated from (ZrO2)x-(ScTaO4)1-x lattice by molten CMAS under high-temperature corrosion condition and (ZrO2)x-(ScTaO4)1-x material is decomposed into ScTaO4 and t-ZrO2 finally. In addition, only t-ZrO2 is defected in the corrosion products without other crystal type of ZrO2 in the XRD results of the corrosion products, which indicate that ScTaO4 can increase high-temperature phase stability of t-ZrO2 and prevent phase transformation from t-ZrO2 to m-ZrO2.

The Effect of Thin Interfacial Layer on the Mechanical Properties of Metal/Zerodur Heterogeneous Bonding

Heterogeneous bonding between metals and ceramics is of significant relevance to a wide range of applications in the fields of industry, defense, and aerospace. Metal/ceramic bonding can be used in various specific part applications such as vacuum tubes, automotive use of ceramic rotors, and rocket igniter bodies. However, the bonding of ceramic to metal has been challenging mainly due to (1) the low wettability of ceramics, on which the adhesion of molten adhesive bonders is limited and (2) the large difference between the coefficients of thermal expansion (CTE) of the two dissimilar bonded materials, which develops significant mechanical stresses at the interface and potentially leads to mechanical failures.Vapor-phase deposition is a widely used thin film processing technique in both academic research laboratories and manufacturing industries. Since vapor phase coatings do not require wettability or hydrophobicity, a uniform and strongly adherent layer is deposited over virtually any substrate, including ceramics.In this presentation, we report on the effect of vapor phase-deposited interfacial metal layers on the mechanical properties of bonding between stainless steel and Zerodur (lithium aluminosilicate-based glass ceramic). Direct-current magnetron sputtering was utilized to deposit various thin interfacial layers containing Ti, Cu, or Sn. In addition, to minimize the unfavorable stress at the bonded interface due to the large CTE difference, a low temperature allow solder, that can be chemically and mechanically activated at temperatures of approximately 200 °C, was used. The solder is made from a composite of Ti-Sn-Ce-In. A custom-built fixture and universal testing machine were used to evaluate the bonding strength in shear, which was monitored in-situ with LabView throughout the measurement. The shear strength of the bonding between stainless steel and Zerodur was systematically characterized as a function of interfacial metal and metal processing temperature during sputter depositions. Maximum shear strength of the bonding of 4.36 MPa was obtained with Cu interfacial layers, compared to 3.53 MPa from Sn and 3.42 MPa from Ti adhesion promoting layers. These bonding strengths are significantly higher than those (~0.05 MPa) of contacts without interfacial reactive thin metals. The fracture surface microstructures are presented as well. It was found that the point of failure, when Cu interfacial layers were used, was between the coated Cu film and alloy bonder. This varied from the Sn and Ti interfacial layers where the main point of failure was between the interfacial film and Zerodur interface. The findings of the effect of thin adhesion promoting metal layers and failure behaviors may be of importance to some metal/ceramic heterogeneous bonding studies that require high bonding strength and low residual stresses at the bonding interface.The authors gratefully acknowledge the financial support of the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS.

Effect of solid-state phase transformation on residual stress of selective laser melting Ti6Al4V

Residual stress in selective laser melting (SLM) is one of the key challenges in terms of precision control, success rate and the performance of deposited components. Ti6Al4V belongs to α+β titanium alloy, the residual stress of selective laser melted (SLMed) Ti6Al4V component maybe affected by solid-state phase transformation result from complex thermal history of SLM. In the present study, effect of solid-state phase transformation on residual stress of SLM Ti6Al4V was investigated. A coupled modeling method of thermo-metallurgical-mechanical considering solid-state phase transition is provided and validated by microstructure observation and residual stress measurements. Then the solid-state phase transformation strain was neglected in the validated model, the computed residual stress is used to investigate the effect of solid-state phase transformation strain on residual stress by comparing with experimental measurements. In addition, the influence of the difference in yield strength and thermal expansion coefficient between the original phase and the transition phase on the residual stress is discussed. It has been found that the residual stress of SLMed Ti6Al4V is related to the direction, the longitudinal residual stress is about twice transverse, and they are all tensile stresses. The microstructure and residual stress predicted by the simulation are in good agreement with the experimental measurements. The microstructure of SLM Ti6Al4V is mainly composed of martensite α', and the average error between the predicted longitudinal stress and measurement is 2.1%. The solid-state phase transformation has a stress relaxation effect during the SLM Ti6Al4V, predicted longitudinal and transverse residual stress exceeds the experimental measurement by up to 80.7% and 53.9%, when neglecting the solid-state phase transformation strain. The influence of the solid-state phase transformation of SLM Ti6Al4V on the residual stress is mainly determined by the volume change between the solid-state phases.

Determining thermal stresses in asphalt concrete by the method of computer simulation

The main destructions of asphalt concrete pavement are rut, transverse cracking, fatigue failures, peeling, etc. When the pavement cools, lowtemperature damages can occur for various reasons. The sources of damages that cause such failures are not well studied, so this problem is relevant. Goal. The aim of this work was to determine the stress-strain state inside the volume of asphalt con-crete during cooling on the basis of a two composite three-dimensional model using the method of computer simulation in response to the changing structured bitumen properties. Methodology. The method of finite element analysis of the stress-strain state of the composite material was used. The material is represented by a three-dimensional (3D) model pro-posed by prof. B.S. Radovsky. Results. The finite element analysis method was used to calculate the average thermal stresses in asphalt concrete during cooling in accordance with increase of viscosity of bitumen section, which is located in asphalt concrete in a structured state. This consideration is realized on the basis of changes in a number of bitumen properties in the contact zone, in particular, the changes in the glass transition temperature. It is shown that the thermal stresses that occur during cooling by limiting the movement of asphalt concrete in the construction reach the strength values at negative temperatures, which can be used to estimate the temperature of crack formation in asphalt concrete under the condi-tion of its action in pavement (Tcr). The values of these stresses depend on the cooling rate, the bitumen content, its viscosity and structure. Originality. For the first time, it was found numerically that in the sample of asphalt concrete, which is free from restriction of movements, there are internal thermal stresses during cooling due to the difference of bitumen thermal expansion coefficients and stone materials. These stresses are up to 87 percent of the average thermal stresses that occur in the compressed sample. Practical value. The possibility of rapid estimation of thermal stresses with the possibility of predicting low-temperature cracks in asphalt concrete is shown.

Superconducting V3Si for quantum circuit applications

V3Si thin films are known to be superconducting with transition temperatures up to 15 K, depending on the annealing temperature and the properties of the substrate underneath. Here we investigate the film structural properties with the prospect of further integration in silicon technology for quantum circuits. Two challenges have been identified: (i) the large difference in thermal expansion coefficient between V3Si and the Si substrate leads to large thermal strains after thermal processing, and (ii) the undesired silicide phase VSi2 forms when V3Si is deposited on silicon. The first of these is studied by depositing layers of 200 nm V3Si on wafers of sapphire and oxidized silicon, neither of which react with the silicide. These samples are then heated and cooled between room temperature and 860 °C, during which in-situ XRD measurements are performed. Analysis reveals a highly non-linear stress development during heating with contributions from crystallization and subsequent grain growth, as well as the thermal expansion mismatch between silicide and substrate, while the film behaves thermoelastically during cooling. The second challenge is explored by depositing films of 20, 50, 100 and 200 nm of V3Si on bulk silicon. For each thickness, six samples are prepared, which are then annealed at temperatures between 500 and 750 °C, followed by measurements of their resistivity, residual resistance ratio and superconducting critical temperature. A process window is identified for silicide thicknesses of at least 100 nm, within which a trade-off needs to be made between the quality of the V3Si film and its consumption by the formation of VSi2.

Optical imaging of surface strain distribution up to 1500°C: Development of micro‐speckle pattern

AbstractMicro‐speckle patterns were fabricated using α‐Al2O3 and SiC micro‐particles for in‐plane strain distribution measurement at temperatures up to 1500°C using an ultraviolet high‐temperature observation system (UV‐HTOS) combined with a digital image correlation (DIC) technique. The experimental results showed that the measured mean surface strains of α‐Al2O3 were in good agreement with the calculated values obtained from thermal expansion coefficient and temperature difference. The proposed speckle pattern could be used for strain distribution measurement without degradation even after heating up to 1500°C. The results also demonstrated that the pattern fabricated in this study is effective to understand the heterogeneous deformation mechanism in composite materials applied in high‐temperature structural components.

Interfacial characteristics and mechanical properties of additive manufacturing martensite stainless steel on the Cu-Cr alloy substrate by directed energy deposition

Copper/steel is a typical bimetal functional material, combining the excellent electrical and thermal conductivity of copper alloy and the high strength and hardness of stainless steel. There has been recent interest in manufacturing copper/steel bimetal by directed energy deposition (DED) due to its layer-by-layer method. However, cracks tend to form on the copper/steel interface because of the great difference in thermal expansion coefficient and crystal structure between copper and steel. In this work, interfacial characteristics and mechanical properties of the copper/steel bimetal were studied from one layer to multilayers. The laser power has a great influence on the Cu element distribution of the molten pool, affecting the crack formation dramatically on the solidification stage. Cracks tend to form along columnar grain boundaries because of the Cu-rich liquid films and spherical particles in the cracks. Crack-free and good metallurgical bonding copper/steel interface is formed at a scanning velocity of 800 mm/min and the laser power of 3000 W. The ultimate tensile strength (UTS) and the break elongation (EL) of the vertically combined crack-free copper/steel bimetal are 238.2 ± 4.4 MPa and 20.6 ± 0.7%, respectively. The fracture occurs on the copper side instead of the copper/steel interface, indicating that the bonding strength is higher than that of the Cu-Cr alloy. The UTS of the horizontally combined crack-free copper/steel bimetal is 746.7 ± 22.6 MPa, which is 200% higher than that of the Cu-Cr alloy substrate. The microhardness is 398.6 ± 5.4 HV at the steel side and is 235.3 ± 64.1 HV at the interface, which is 400% higher than that of the Cu-Cr alloy substrate. This paper advances the understanding of the interfacial characteristics of heterogeneous materials and provides guidance and reference for the fabrication of multi-material components by DED.

LNG 화물창 정밀 구조해석을 위한 에폭시와 폴리우레탄 접착제 기계적 물성치 분석

As the demand for natural gas that satisfies environmental regulations increases, the quantities of natural gas cargo that carrier can load is also increasing. Natural gas is transported in a liquefied state at -163 ℃ to increase loading efficiency. Among several LNG CCS types, MARK-III types are generally adopted in terms of loading efficiency. The secondary barrier adhesives of the MARK-III, nevertheless, is subjected to tensile stress due to thermal contraction and tension in the environment. In terms of these reasons, local analysis of the adhesive to evaluate the stress state must be carried out. According to previous studies, local analysis is unavailable since material properties for secondary barrier adhesives have not been reported. Thus, in this study, the cryogenic tensile test and coefficient of thermal expansion of epoxy and polyurethane (PU15, PU45), which are most widely used at cryogenic temperatures, were experimentally analyzed. At cryogenic temperature, the mechanical behavior of the polyurethane adhesive was better than epoxy of the adhesive. the joint of FSB and epoxy adhesive of the secondary barrier has the maximum coefficient of thermal expansion difference at 25 ℃ and minimum at –150 ℃, respectively.

의료전자기기 적용을 위한 Epoxy 솔더 접합부의 신뢰성 평가

In this study, the bonding characteristics of epoxy solder joints for the manufacture of highly reliable medical electronic devices were investigated. A total of 2000 cycles of thermal shock tests were performed by simulating the heat generation of electronic devices on specimens manufactured using eutectic solders (SAC305 and Sn58Bi) and epoxy solders (SACE and Sn58BiE). After the thermal shock, the formation of internal cracking owing to the difference in the thermal expansion coefficients of dissimilar material solder joints and the deterioration of the bonding properties of the solder joints was analyzed. Consequently, in the case of the epoxy solder, the epoxy was cured outside the solder joint, suppressing thermal stress owing to a difference in thermal expansion coefficients and suppressing the internal cracking of the solder joint, thereby improving the bonding characteristics of the solder joint.

Effects of Zn x Mn1−x S buffer layer on nonpolar AlN growth on Si (100) substrate

Thin film growth of Zn x Mn1−x S on a Si (100) substrate by sputtering was investigated for nonpolar AlN film growth on Si (100) substrate. The Zn x Mn1−x S buffer layer reduces the large differences in thermal expansion coefficient and lattice constants between AlN and Si. Although the solubility of ZnS in MnS is less than 5% at 800 °C in bulk form, the insertion of a room-temperature MnS layer between Zn x Mn1−x S and Si enabled (100)-oriented cubic-Zn x Mn1−x S film growth even at x = 9.5%, which is a metastable phase and a phase separation region in bulk form. On the (100)-oriented cubic Zn x Mn1−x S film, nonpolar AlN growth was achieved by sputtering. Furthermore, X-ray photoelectron spectroscopy measurements revealed that the Zn x Mn1−x S film improved the stability of the AlN/Zn x Mn1−x S interface. Zn x Mn1−x S has the potential to enable nonpolar AlN growth on large-diameter Si (100) substrates.

Double Glow Plasma Nitriding Pretreatment of TiAlN-Coated TA15 Alloy for Enhancement of Bonding Strength and Mechanical Properties

As a classic hard coating, titanium aluminum nitride (TiAlN) coating is widely applied in the aviation field due to its extremely high hardness and strength. Unfortunately, the large difference in hardness and thermal expansion coefficient between the coating and the substrate could also lead to the reduction of bonding force. In this paper, Double-glow plasma nitriding (DGPN) pretreatment followed by RF magnetron sputtering was used to prepare DGPN-TiAlN coating on the surface of TA15 alloy. The adhesion and the bearing capacity of DGPN-TiAlN coating is characterized by scratch and indentation tests. The gradient hardness support and stress transition effect of the nitriding layer are significant, and the bonding strength of TiAlN coating and the substrate are significantly improved. In addition, the high temperature wear resistance and erosion resistance of DGPN-TiAlN coating were detected through high-temperature wear tests and sand erosion tests. At 500 °C, the surface of DGPN-TiAlN coating formes a dense Al2O3 lubricating film with good adhesion, and the friction coefficient is lower than that of TiAlN coating. Under different erosion speeds and erosion angles, the erosion rate of DGPN-TiAlN coating is lower than that of TiAlN coating, and the coating surface defects are less.

Brass/Invar bimetal by explosive welding

Thermostatic bimetals (thermobimetals) are materials consisting of layers with different coefficients of thermal expansion. The layer with a higher coefficient of thermal expansion is called active, with a lower—passive. Invar (Ni-Fe alloy) is mainly used as the passive layer and brass (Cu-Zn alloy) as the active layer. Strong adhesion of the layers along the entire length is one of the main requirements for all grades of thermobimetals. In this study, an Invar/brass thermobimetal plate was obtained by explosive welding (EW). The plate was subjected to metallographic, ultrasonic, and mechanical examination. Scanning electron microscope (SEM) showed that the weld interface had the form of uniform waves over its entire surface. Also, melted zones in the crests and troughs of the waves were observed. Energy-dispersive spectroscopy (EDS) line scanning showed that the melted zones consisted of a disordered Cu–Zn–Fe–Ni solid solution (predominately, of Zn and Cu) and undissolved Invar particles. The average microhardness of the melted zones was 350 HV. A 3-mm-wide strengthened zone along the weld interface was observed. The average tear strength of the Invar/brass weld joint was 550 MPa, which is higher than that of the individual initial metals. The bending testing has shown that the thermobimetal plate is resistant to delamination, which indicates the satisfactory quality of the weld joint. Based on the results obtained from this study, it can be concluded that EW can be used to produce high-quality Invar/brass thermobimetal plates.

Method of combining thermal homology theory with a genetic algorithm for the design and optimization of precise submillimeter-wave antennas.

It is a common problem in precise submillimeter-wave telescopes that thermal deformation coupling between major subsystems results from materials with different coefficients of thermal expansion or at different temperatures. Here, the method of combining thermal homology theory with a genetic algorithm (CTHTGA) is proposed for the design and optimization of large precise submillimeter-wave antennas. The CTHTGA method has two key steps: (1) design of the structure of the antenna according to thermal homology theory; and (2) structural optimization based on the genetic algorithm. It has the ability to solve the problem of thermal deformation coupling well and to ensure sufficient rigidity. As an application, CTHTGA was used in the design and optimization of a 1.2 m submillimeter-wave telescope. The results showed that the CTHTGA method, compared to the previous design of a 1.2 m antenna, not only dramatically decreases the impact of thermal deformation coupling but gives the designed antenna sufficient stiffness and smaller gravity deformation. Moreover, other things being equal, a method of combining thermal homology theory with zero-order and a first-order compound optimization algorithm is used to quantitatively validate the CTHTGA method. As the results suggest, the overall performance of the CTHTGA is, to the best of our knowledge, better than that of the latter method.

Flexible PTFE/MXene/PI soft electrothermal actuator with electromagnetic-interference shielding property

In recent years, soft electrothermal actuators (ETAs) have attracted great concern because of their potential applications in biomimetic intelligent devices, soft robotics and aerospace engineering. However, achieving the simultaneous optimization of low-voltage actuation, ultrafast preparation and highly integrated functionality are main challenges to the development of ETAs. Herein, a flexible, hydrophobic, mechanically robust and electromagnetic-interference (EMI) shielding PTFE/MXene/PI soft ETA is constructed through a very simple and fast “cutting and sticking” method by taping PTFE and PI tapes onto the surface of MXene film. The commercially available PTFE and PI tapes endow PTFE/MXene/PI sandwich structure with ideal mechanically robustness and hydrophobic self-cleaning function, thus it can work in different environments. Remarkably, PTFE/MXene/PI sandwich structure shows an outstanding EMI shielding ability with the maximum SET value of 44 dB owing to the high electrical conductivity of MXene film. More importantly, the PTFE/MXene/PI sandwich actuator can bend from PTFE side toward PI side under the electrical stimulus, because the excellent electrothermal MXene layer is sandwiched between the two tapes with large difference in thermal expansion coefficients. Under a 6 V low voltage, the actuator can generate heat energy with the maximum saturation temperature of 110 °C and large bending deformation with the maximum bending angle of 122° within 40 s. Interestingly, the PTFE/MXene/PI structure can be designed and manufactured in different shapes and configurations upon actuation, such as the “S” shape and four-finger gripper. At last, a smart shielding curtain with the combination of actuation properties and EMI shielding performance is finally developed as a principle of concept, which further indicates the multifunctional PTFE/MXene/PI ETA can be widely applied in smart EMI shielding system and soft robotic devices.

Study of designable coefficient of thermal expansion in cellular structures

In this work, a model of cellular structures in thermal fields has been established based on methods of material mechanics, structural mechanics and thermodynamics. Cellular structures have different deformation behaviors in thermal environment with different coefficients of thermal expansion (CTE), the desirable equivalent coefficient of thermal expansion (ECTE) of cellular structures can be achieved by introduce members with different CTEs. Three different configurations are proposed to study the relationship between ECTE and geometrical configuration. The results show that: desirable ECTE can be obtained by designing configuration shape of cellular structures, inclined angle of members and positions of different CTE materials.

Stress distribution at the AlN/SiC heterointerface probed by Raman spectroscopy

We grow AlN/4H-SiC and AlN/6H-SiC heterostructures by physical vapor deposition and characterize the heterointerface with micro-scale resolution. We investigate the spatial stress and strain distribution in these heterostructures using confocal Raman spectroscopy. We measure the spectral shifts of various vibrational Raman modes across the heterointerface and along the entire depth of the 4H- and 6H-SiC layers. Using the earlier experimental prediction for the phonon-deformation potential constants, we determine the stress tensor components in SiC as a function of the distance from the AlN/SiC heterointerface. Despite the fact that the lattice parameter of SiC is smaller than that of AlN, the SiC layers are compressively strained at the heterointerface. This counterintuitive behavior is explained by different coefficients of thermal expansion of SiC and AlN when the heterostructures are cooled from growth to room temperature. The compressive stress values are maximum at the heterointerface, approaching 1 GPa, and relax to the equilibrium value on the scale of several tens of micrometers from the heterointerface.

Spark plasma sintering of B4C and B4C-TiB2 composites: Deformation and failure mechanisms under quasistatic and dynamic loading

Spark plasma sintering (SPS) was employed to consolidate powder specimens consisting of B4C and various B4C-TiB2 compositions. SPS allowed for consolidation of pure B4C, B4C-13 vol.%TiB2, and B4C-23 vol.%TiB2 composites achieving ≥99 % theoretical density without sintering additives, residual phases (e.g., graphite), and excessive grain growth due to long sintering times. Electron and x-ray microscopies determined homogeneous microstructures along with excellent distribution of TiB2 phase in both small and larger-scaled composites. An optimized B4C-23 vol.%TiB2 composite with a targeted low density of ∼3.0 g/cm3 exhibited 30–35 % increased hardness, fracture toughness, and flexural bend strength compared to several commercial armor-grade ceramics, with the flexural strength being strain rate insensitive under quasistatic and dynamic loading. Mechanistic studies determined that the improvements are a result of a) no residual graphitic carbon in the composites, b) interfacial microcrack toughening due to thermal expansion coefficient differences placing the B4C matrix in compression and TiB2 phase in tension, and c) TiB2 phase aids in crack deflection thereby increasing the amount of intergranular fracture. Collectively, the addition of TiB2 serves as a toughening and strengthening phase, and scaling of SPS samples show promise for the manufacture of ceramic composites for body armor.

The Influence of Top and Bottom Metal Electrodes on Ferroelectricity of Hafnia

In recent years, several experimental approaches have been adopted to study and understand the mechanism and improve the ferroelectricity of fluorite-type hafnia-based ferroelectric materials. In this regard, significant efforts have been made to elucidate the role of top electrode and bottom electrode (TE and BE) materials in defining the ferroelectricity in such systems, especially in terms of induced mechanical tensile stress by these materials during the process of annealing. However, the effect of the electrode material was not investigated both at TE and BE, and despite numerous efforts, there is still a lack of accurate and systematic understanding. In this report, we have carried out a systematic investigation on the effect of TE and BE materials having different coefficient of thermal expansion (CTE), by changing the electrode material one at a time, both at the top and bottom. The influence of the TE was confirmed using [TE/Hf0.5Zr0.5O2(HZO)/TiN] structure in which the BE was fixed as TiN, and the influence of the BE was confirmed using [TiN/HZO/BE] structure by fixing TiN as the TE. As revealed by polarization versus electric field and residual stress analysis, smaller CTE of the electrode was found to result in higher tensile stress in the HZO films during the annealing process, facilitating the formation of higher ferroelectric o-phase and thereby resulting in greater ferroelectricity. Although the influence of TE and BE on the ferroelectric property of HZO films was found to show similar trends according to the CTE value of the electrodes, the influence of TE on the ferroelectric property of the HZO capacitors is found to be mainly due to the variation in the induced mechanical tensile stress; pulse switching measurement and X-ray photoelectron spectrometer (XPS) analysis suggest that in case of BE, both the induced mechanical tensile stress and the interfacial dead layer were found to play a significant part. As a result, BE was found to have a greater influence on ferroelectricity of the HZO capacitors when compared with that of TE. The highest remnant polarization of 48.2 and $58.7~\mu \text{C}$ /cm2 was obtained for W with the lowest of CTE of $4.5\times 10^{-6}/^{\circ }\text{C}$ in both the configurations. The results obtained in this article are expected to provide a new way out to optimize the interface quality and ferroelectricity in HZO-based capacitors.

Thermal Shock Behavior of Twill Woven Carbon Fiber Reinforced Polymer Composites

In the current research, the effect of cyclic temperature variation on the mechanical and thermal properties of woven carbon-fiber-reinforced polymer (CFRP) composites was investigated. To this, carbon fiber textiles in twill 2/2 pattern were used as reinforced phase in epoxy, and CFRPs were fabricated by vacuum-assisted resin-infusion molding (VARIM) method. Thermal cycling process was carried out between −40 and +120 °C for 20, 40, 60 and 80 cycles, in order to evaluate the effect of thermal cycling on mechanical and thermal properties of CFRP specimens. In this regard, tensile, bending and short beam shear (SBS) experiments were carried out, to obtain modulus of elasticity, tensile strength, flexural modulus, flexural strength and inter-laminar shear strength (ILSS) at room temperature (RT), and then thermal treated composites were compared. A dynamic mechanical analysis (DMA) test was carried out to obtain thermal properties, and viscoelastic properties, such as storage modulus (E’), loss modulus (E”) and loss factors (tan δ), were evaluated. It was observed that the characteristics of composites were affected by thermal cycling due to post-curing at a high temperature. This process worked to crosslink and improve the composite behavior or degrade it due to the different coefficients of thermal expansion (CTEs) of composite components. The response of composites to the thermal cycling process was determined by the interaction of these phenomena. Based on SEM observations, the delamination, fiber pull-out and bundle breakage were the dominant fracture modes in tensile-tested specimens.