Low Thermal Expansion Research Articles

Failure analysis on the abnormal cracking of Si3N4 ceramic substrates for SiC power modules in new energy vehicles

Si3N4 ceramic with good thermal conductivity, high mechanical strength and low thermal expansion coefficient is an advanced thermal management material which has been applied to new energy vehicles. At present, with the rapid development of the electric driving technology for new energy vehicles, Si3N4 ceramic has been gradually used in SiC power modules so as to efficiently achieve the functions of heat dissipation, insulation and voltage resistance. Due to its important role in the power conversion process, the reliability of Si3N4 ceramic was vital, and any factor that might lead to its premature failure must be attached importance to. In this paper, a case about abnormal cracking of Si3N4 ceramic substrates during the high and low temperature cycling tests was reported. To solve this problem, various characterization methods were conducted to analyze the density, thermal conductivity, flexural strength, phase structure, morphology characteristics. Finally, through comprehensive analysis, the root cause that resulted in abnormal cracking of Si3N4 ceramic substrates was determined and meanwhile corresponding countermeasures were also proposed. Hopefully, the achievements of this paper will have positive significance for upgrading the quality of Si3N4 ceramic substrates and improving the service reliability of power modules.

Refinement of the Manufacturing Route and Evaluation of the Reinforcement Effect of MAX Phases in Al Alloy Matrix Composite Materials

Microwave Assisted Self-propagating High-temperature Synthesis (MASHS) was used to prepare open-porous MAX phase preforms in Ti-Al-C and Ti-Si-C systems, which were further used as reinforcements for Al-Si matrix composite materials. The pretreatment of substrates was investigated to obtain open-porous cellular structures. Squeeze casting infiltration was chosen to be implemented as a method of composites manufacturing. Process parameters were adjusted in order to avoid oxidation during infiltration and to ensure the proper filling. Obtained materials were reproducible, well saturated and dense, without significant residual porosity or undesired interactions between the constituents. Based on this and the previous work of the authors, the reinforcement effect was characterized and compared for both systems. For the Al-Si+Ti-Al-C composite, an approx. 4-fold increase in hardness and instrumental Young's modulus was observed in relation to the matrix material. Compared to the matrix, Al-Si+Ti-Si-C composite improved more than 5-fold in hardness and almost 6-fold in Young's modulus. Wear resistance (established for different loads: 0.1, 0.2 and 0.5 MPa) for Al-Si+Ti-Al-C was two times higher than for the sole matrix, while for Al-Si+Ti-Si-C the improvement was up to 32%. Both composite materials exhibited approximately two times lower thermal expansion coefficients than the matrix, resulting in enhanced dimensional stability.

Fabrication of low thermal expansion Fe–Ni alloys by in-situ alloying using twin-wire arc additive manufacturing

The binary Fe–Ni system offers alloys with notably low linear coefficients of thermal expansion (CTE), contingent upon their Ni content. In this respect twin-wire arc additive manufacturing (T-WAAM) presents the opportunity of in-situ alloying through the simultaneous feeding of two metal wires into a weld pool to obtain desired alloy compositions. This study aims to deposit a graded wall with Ni contents targeted at 42, 46, and 52 wt% in the building direction of the wall, along with a block comprising of 46 wt% Ni, employing the T-WAAM approach. The results show effective incorporation of additional Ni into the weld pool and geometrically stable weld beads in the continuous metal transfer mode during the T-WAAM process. This mode led to the defect-free and chemically stable deposition of the graded wall and the block with average Ni contents of 42.3 ± 1.1, 45.8 ± 1.4, 52.6 ± 0.8 wt%, and 46.4 ± 0.9 wt%, respectively. The measured Curie temperatures of the as-deposited alloys and the mean CTE values of alloy 46 were found to be comparable to the commercial alloys. In summary, this study validates the feasibility of in-situ deposition of low thermal expansion alloy compositions, thereby enabling the possibility of on-demand thermal expansion properties.

Exploring the structural stability and related physical properties of FePt2 alloys

The current work presents a theoretical study of the physical properties of several FePt2 ordered structures through first-principles calculations, including structural, magnetic, electronic, mechanical, phonon and thermal properties. The structural stabilities are certified by the enthalpies of formation, elastic constants, and phonon dispersion relationships. The tetragonal I4/mmm structure is energetically favorable compared to other types FePt2 structures including Cmcm, Immm, P63/mmc and P4/nmm structures. The electronic density of states and the contributions of each d-orbital electron to the magnetic moment are analyzed to understand their magnetism. The bulk modulus B values of these FePt2 structures are similar, but the Young's modulus E and shear modulus G as well as the elastic anisotropy are quite different. The thermal properties at finite temperature are estimated by the quasi-harmonic approximation. The I4/mmm structure has higher isothermal bulk modulus, lower thermal expansion coefficient and weaker thermal expansion anisotropy, which is more suitable for high temperature applications than other structures. Also, the sequence of thermal expansion anisotropy is P4/nmm > Immm > Cmcm > I4/mmm (≈P63/mmc).

Designing high thermally stable deep red phosphors based on low thermal expansion coefficients for optical applications.

Mn4+-activated oxide phosphors with low cost and unique luminescent properties have been considered as a promising candidate for various optical applications, while the search for high thermal stable red-emitting phosphors is still a huge challenge. In our work, we find and unveil the relationship between luminescence thermal quenching behavior and thermal expansion coefficients (α/10-6 K-1) based on double-perovskite niobate phosphors Ca2LnNbO6:Mn4+ (Ln3+ = Y3+, Gd3+, La3+, or Lu3+). It can be concluded that the phosphors with low thermal expansion coefficients contribute to high thermal stability. Subsequently, Ca2LuNbO6:Mn4+ accomplishes accurate temperature testing and high-CRI white light-emitting diodes. Thus, a thermal expansion coefficient strategy is a new guide to select the appropriate substrate with high thermal stability for an Mn4+-activated emitter.

Ultra-high performance hafnium-based capacitors: Synergistic achievement of high dielectric constant and low leakage current

The relationship between the dielectric constant and leakage current of materials often exhibits a negative correlation. However, to sustain Moore's Law, the semiconductor industry necessitates novel materials that simultaneously possess a high dielectric constant and low leakage current, meeting the shrinking demands of electronic components. In this study, a high-performance hafnium-based thin film capacitor achieved through the collaborative effects of bottom electrode engineering and ion doping. Tungsten (W) as the bottom electrode, with its chemically inert nature and low thermal expansion coefficient, proves advantageous in improving interface quality and promoting the generation of the high-k phase in HfO2. Concurrently, yttrium (Y) ion doping contributes to stabilizing the high-k phase of HfO2, reducing non-lattice oxygen, and enhancing the disorderliness of the dielectric thin film. By synergistically integrating these factors, the hafnium-based thin film capacitor achieves a high dielectric constant of 36.6 while maintaining minimal leakage current (Electric field ∼ 6 MV/cm, J ∼ 10−8 A/cm2) and a high charge storage capacity (Urec ∼ 104.4 J/cm³). These research findings open a promising pathway for the development of novel hafnium-based materials with broad applicability and exceptional dielectric performance.

Investigation of Drilling Holes in CFRP for Aircraft Using cBN Electroplated Ball End Mill Using Helical Interpolation Motion

Investigation of Drilling Holes in CFRP for Aircraft Using cBN Electroplated Ball End Mill Using Helical Interpolation Motion

Effect of sodium gluconate addition on anomalous codeposition of electroplated nickel-iron alloys

Invar nickel-iron alloy has been widely applied in the fields of electronics, sensors, communications and optics, due to its low thermal expansion coefficient, high hardness, high ductility and other characteristics according to product requirements. The application in metal stencil during the manufacturing process of active-matrix organic light-emitting diodes is mainly due to their good electrical conductivity and soft magnetic properties. In this study, sodium gluconate is used as a substitute for boric acid in the acidic electroplating of nickel-iron alloys; the concentration ratio of nickel-iron in the plating bath is 2:1. After adding sodium gluconate, the precipitation of nickel varies significantly. The iron content in the weight percentage of the deposited nickel-iron alloy is obviously larger than nickel, even up to 3 times. The whole deposition process is in the state of anomalous codeposition, and the selectivity ratio reaches 3 or more; the nickel-iron alloy deposited by adding sodium gluconate to the plating bath has a great influence on the material properties of the nickel-iron alloy plating, The nickel-iron alloy deposited at -1.4 V exhibits a hardness of approximately 3.17 GPa and a modulus of elasticity about 37.88 GPa. Notably, the resistance to plastic deformation of the alloy deposited in sodium gluconate plating solution (H3/U2=0.022) is significantly higher than that in boric acid plating solution (H3/U2=0.007). The experimental results also show that it has the best ability to resist plastic deformation.

Preparation and performance of alumina/epoxy-siloxane composites: A comparative study on thermal- and photo-curing process

Although epoxy-based composites that consist of inorganic fillers and matrixes are widely used in “conventional” electronic packaging applications due to their excellent insulation and robust properties, they limit their uses in “advanced electronic packaging” which requires enhanced thermal conductivity. However, conventional thermal curing methods for fabrication of epoxy-based composites do not fulfill sufficient thermal conductivity. Herein, we apply photo-induced curing strategy for fabricating alumina-incorporated epoxy-siloxane composites that consist of sol-gel derived siloxane matrix and bimodal sized alumina particles as a thermally conductive filler. We investigate how curing mechanism (thermal- or UV-curing) and varying the ratios of the alumina particles of two different sizes affect the various physical properties. It is found that photo-curing process makes greatly enhanced thermal conductivity, low thermal expansion, and high mechanical robustness compared to thermally-cured composites. As the results, we can achieve significantly enhanced thermal conductivity (>11 W/m K) with high thermal stability and mechanical robustness.

Comparison of the Casimir force between SiC plates with different permittivity models: Lorentz model and Palik data

Accurate calculation of Casimir forces is essential for the development of micro- and nanoelectromechanical systems. Silicon carbide (SiC) is an excellent material for fabricating microsensors due to its high durability, high stiffness, and low thermal expansion. The permittivity of the SiC could be characterized by the Lorentz model or the Palik data. However, the influence of the two models of calculating permittivity on the Casimir force has not been discussed. In this work, we calculate the Casimir force between SiC plates by the Lorentz model and the Palik data, respectively. The Casimir force calculated by the Lorentz model could be 4 times greater than the Palik data for SiC at a gap distance of 10 nm. The difference of the permittivity in the ultraviolet lead to different Casimir forces. This work demonstrates the difference between the two models of permittivity for calculating the SiC-based Casimir force, and provides a reliable base for more accurate Casimir force calculations.

Ultra-high-performance graphene-based bulk materials strengthened by Y-type connection structure

The strategic design and assembly of bulk graphene materials represent a pivotal advancement for harnessing the inherent properties of graphene in practical applications. However, fabricating high-strength graphene-based bulk materials from graphene powders presents a significant challenge, primarily due to interlayer slippage between the graphene layers. Here, a unique Y-type connection structure was found in few-layer graphene synthesized by self-propagating high-temperature synthesis (SHS) and subsequently retained in graphene-based bulk materials prepared by spark plasma sintering (SPS) process. The Y-type connection structure and defect-induced linkages serve to cross-link the graphene-based bulk materials. Consequently, the bulk material exhibited an ultra-high compressive strength, reaching 2.14 GPa, supported by Molecular dynamics (MD) simulations which demonstrated that the Y-type connection structure increases the shear modulus and the load transfer rate. The Y-type connection structure plays a vital role in reinforcing the strength of graphene-based bulk materials, offering valuable insights for the microstructural design and property augmentation of other graphene-derived materials. Besides it’s ultra-high compressive strength, the graphene-based bulk material also performs a low thermal expansion coefficient (0.5 × 10−6 K−1), high electrical conductivity (1.47 × 105 S·m−1) and exceptional EMI shielding capability.

Development of Printed Circuit Boards with High Thermal Conductivity and Low Thermal Expansion by Applying Cu-Mo Composite Materials

In recent years, electronic devices are strongly required to be smaller, lighter, and more powerful. As a result, mounted components have become smaller, more powerful, and denser, and the heat generation density on printed circuit boards (PCBs) has increased. Since rising component temperatures can lead to component failure, efficient heat removal from the generated heat has become an urgent issue. Since general PCBs have low thermal conductivity, when high heat dissipation is required, methods to increase the thermal conductivity of PCBs have been employed by increasing the copper (Cu) content in the PCB or by placing an aluminum (Al) alloy in the inner layer. However, while Cu and Al have high thermal conductivity, they also have high coefficients of thermal expansion (CTE) and young’s modulus, and the CTE of a PCB with increased thermal conductivity using these materials is high. If the thermal expansion difference between the PCB and mounted components is large, reliability against heat cycles cannot be obtained. Therefore, we have focused on copper-molybdenum (CuMo) composite materials with high thermal conductivity, high elastic modulus, and low thermal expansion. We have been utilizing Cu-Mo for the development of our PCBs and fabricated multilayered CuMo composite PCBs; therefore, this report will focus on the results regarding thermal characterization of prototype PCBs.

Proton pathways via free volumes: A positron annihilation lifetime spectroscopy (PALS) investigation of proton conductivity in SPEEK-PEG-TMOS composites

This study investigates the ionic conductivity and dielectric properties of SPEEK-PEG-TMOS solid-state polymer electrolytes across a broad frequency spectrum (0.1–1000 kHz). Proton transport mechanisms were explored over an extensive temperature range, and positron annihilation lifetime spectroscopy (PALS) was employed to elucidate the roles of free volumes in the transport mechanism. At elevated temperatures, sulfonic acid groups and free volume defects predominantly govern the conductivity in all polymer electrolytes. PEG incorporation significantly improved proton conductivity at low temperatures, while the presence of TMOS and higher PEG content have elevated conductivity at higher temperatures. Proton conductivity mechanisms at elevated temperatures are influenced by SPEEK's intrinsic proton conductivity, PEG's plasticizing effect, acid-base interactions, and the presence of free volumes. PALS analysis reveals temperature-dependent trends in the o-Ps lifetime, intensity, and free volume fraction, increasing linearly with temperature due to thermal expansion. PEG content modulated this trend, with lower PEG content samples displaying lower thermal expansion slopes, and higher PEG content samples exhibiting more substantial increases in hole-free volume. The o-Ps intensity displayed a temperature-dependent change attributed to PEG's thermal expansion limitations. These insights contributed to a comprehensive understanding of the intricate interplay between PEG content, thermal expansion, and free volume in SPEEK-PEG-TMOS composites. The study has implications for material science applications, particularly in the development of high-temperature, anhydrous proton-conductive systems.

A rapid and precise approach to predicting the cure‐induced warping of T‐shaped composite parts with inconsistent layup

AbstractThis work involved the precise prediction and in‐depth analysis of cure‐induced warping of T‐shaped parts with inconsistent layup. First, the warping mechanism of this kind of part was studied. Then, a finite element analysis (FEA) that considered the parts' structural characteristics and inconsistent layup using the curing mechanical constitutive model was developed to predict the warping. Following verification of the model's accuracy, the effects of material and structural characteristics on warping were investigated. When designing T‐shaped parts, selecting materials with lower thermal expansion coefficients can help minimize warping. Additionally, increasing the radius of the chamfer at the rib and flange connections is also effective. By taking into account the effects of structural parameters and inconsistent layup by using both classical laminated plate theory and artificial neural networks (ANN), a rapid and accurate surrogate model for warping prediction was finally developed. It was discovered that the two‐layer ANN model performed better than the other two models and could predict warping with accuracy and speed. For the parts analyzed in this work, this model is able to identify the fluctuations of warping captured by FEA. Moreover, by defining deviation as the difference between the predicted values of the surrogate model and the FEA, it can be observed that the majority of deviations for the validation set are within ±1.5 mm. This demonstrates that the two‐layer ANN possesses strong generalization ability and high accuracy in predicting warping.Highlights The inconsistent layup could significantly affect the T‐shaped part's warping. Cutting off a part's rib may significantly reduce its warping. A rapid and accurate model for warping prediction was developed. The layup and structure's influence could be identified by the two‐layer ANN.

Preparation of Li2O–Al2O3–SiO2–B2O3（LASB）glass-ceramic with low thermal expansion coefficient from spent hydrogenation catalysts and crystallization kinetics

The recovery of spent hydrogenation catalysts occupies advantages in both alleviating environmental burden and resource shortage. Whereas, the development of conventional hydrometallurgical recovery of molybdenum (Mo) and nickel (Ni) from spent MoNi/Al2O3 catalysts has been limited by the numerous processes and the accompanying generation of waste liquids and residues. Herein, A new recycling route for the preparation of spent hydrogenation catalysts with low thermal expansion coefficients (CTE) was proposed, which has the advantages of short process, green environment and high value utilization. The Li2O–Al2O3–SiO2–B2O3 (LASB) parent glass containing Mo and Ni were obtained by melting with different contents of the spent catalysts. The thermal expansion coefficient of the glass was minimized to 6.08 × 10−6/°C at an addition of 25 wt% of the spent catalysts. Moreover, according to the crystallization peak in DTA curve, glass-ceramics were prepared by one-step crystallization heat treatment at different crystallization temperatures. The main crystalline phase of the glass-ceramic precipitated by heating at 685 °C is β-quartz (Li2Al2Si3O10), which gives the glass-ceramics the lowest coefficient of thermal expansion (0.96 × 10−6/°C) of glass-ceramic as well as the maximum density (2.45 g/cm3) and Vickers hardness (705.8 Hv). Furthermore, the activation energy (354.65 ± 17.42) kJ/mol) and Avrami index (5.39) associated with crystallization were extracted from the fitting of different theoretical model, indicating the three-dimensional crystallization of the LASB glass-ceramics. This technology provides a waste-to-material strategy for hazardous waste and a clean production route for the preparation of the functional glass-ceramics.

Interfacial Stability between High-Entropy (La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 and Yttria-Stabilized Zirconia for Advanced Thermal Barrier Coating Applications

(La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEZ) has shown considerable promise as a novel thermal barrier coating material for temperatures exceeding 1300 °C. This study systematically investigates the interfacial stability of (La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 with yttria-stabilized zirconia (YSZ), which is of paramount importance for its application in double-layer thermal barrier coatings. Our findings highlight that rare earth elements with a smaller radius diffuse more easily into the YSZ lattice, resulting in a broader diffusion zone. Simultaneously, the incorporation of rare earth elements into the YSZ lattice inhibits tetragonal-to-monoclinic phase transformation. Compared to La2Zr2O7/YSZ, HEZ/YSZ demonstrates superior high-temperature stability, which could be attributed to the higher fracture toughness and lower thermal expansion coefficient of HEZ, the absence of t-m transformation and the formation of a continuous gradient diffusion layer that minimizes interface stress. This study offers a practical strategy for designing materials for durable double-layer thermal barrier coating systems.

Bioepoxy based advanced lightweight hybrid composites from hemp fibers: Towards greener production

Over the past few decades, the widespread use of composite materials has become prominent, particularly following the industrial revolution. In response to environmental concerns, natural fiber polymer composites have found extensive applications, notably in the automotive industry and various versatile applications. However, pure natural fiber polymer composites face challenges in matching the performance of synthetic fiber-reinforced polymer composites. To address this issue, natural fibers are hybridized with synthetic fibers to enhance the performance characteristics. In this study, hemp fibers were hybridized with Innegra fibers through a stacking sequence and subjected to weathering. Both the weathered and unweathered composites underwent mechanical, thermal, and viscoelastic analysis to assess their performance under harsh environmental conditions. The mechanical analysis revealed that the tensile strength of the composite with Innegra as the skin layer was 76.56 MPa, reducing to 67.73 MPa after the weathering process. The flexural strength showed values of 111.01 MPa and 101.61 MPa before and after the weathering process, respectively. Thermomechanical analysis indicated that pure hemp composites exhibited lower thermal expansion at 1.45%, with the composite featuring hemp fibers in the outer layer performing better at 2.34% compared to hybrid composites. Additionally, SEM images demonstrated good interfacial adhesion between fibers and the matrix. Overall, the results suggest that the developed composites have the potential for use in lightweight semi structural applications.

Fabrication of Sr-feldspar/cordierite and Sr-feldspar/Sr-osumilite composites through sintering of Mg–Sr-cordierite and borosilicate glass for electronic applications

The main objective of this study is to fabricate composite materials having excellent thermal, mechanical and electrical properties for thermal and electronic applications. In this work, strontium feldspar-containing composites (Sr-feldspar/cordierite and Sr-feldspar/Sr-osumilite) were prepared by solid-state sintering of SrO-containing cordierite (MgSrAl4Si5O18)/borosilicate glass powder mixtures. The phase composition, physical properties and microstructure of sintered composites were investigated by X-ray diffraction technique, water displacement method and scanning electron microscope, respectively. Moreover, the thermal expansion coefficient, hardness, and electrical properties were also measured. The results of X-ray patterns revealed the crystallization of Sr-feldspar and cordierite in the composites that contain up to 20% borosilicate glass. On the other hand, the composites that include more than 20% glass, displayed the crystallization of Sr-feldspar and Sr-osumilite with little amount of cristobalite. The bulk density values of sintered composites were decreased from 2.41 to 1.84 g/cm3 with increasing the amount of added glass. The microhardness values were increased from 519 to 710 kg/mm2 with increasing the glass content. Low thermal expansion coefficient (2.65 × 10−6, 2.22 × 10−6, 3.45 × 10−6 and 4.26 × 10−6 K-1 for C0, CG91, CG73, CG55, respectively) and low dialectic constant (7–8.5) were obtained for the prepared composites.

Influence of Transition Metals on the Development of Semiconducting and Low Thermal Expansion TiO2-Borosilicate Glasses and Glass Ceramics

This current investigation represents as well as discusses in detail the characterization of the thermal, mechanical, as well as electrical characteristics of titanium-based borosilicate glasses doped transition metal ions (3d) in addition to their corresponding glass–ceramics. The building structural units of the as-prepared glasses together with their glass – ceramic were characterized by the FTIR technique. FTIR spectra reveal characteristic silicate and borate groups vibrations, some of the TiO4 units are formed beside (TiO6) groups. The progressive enhancement in microhardness and thermal expansion values was recorded for glass – ceramic state that occurred as a result of the crystallization of nano-sized crystals throughout the glass matrix. The estimated electrical parameters which include permittivity (ε'), dielectric loss (ε''), AC conductivity (σac) capacitance (C), and dielectric loss demonstrated a distinctive variation in their values in accordance with the type of transition metal and /or the applied frequency. The prepared glass–ceramic was found to be suitable for use in electronics and solar cell applications based on its overall thermal and electrical properties.

SiC skeleton‐reinforced highly oriented graphite with good thermophysical and electromagnetic shielding properties

AbstractThe design of multifunctional materials with good thermophysical and electromagnetic shielding properties is desirable to overcome overheating and electromagnetic interference (EMI) in electronic devices. In this study, three‐dimensional (3D) continuous SiC skeleton‐reinforced highly oriented graphite flake (GF@SiC) composites were fabricated by combining molten salt synthesis, heat treatment, and spark plasma sintering. When the SiC content was higher than 9 vol.%, a 3D continuous SiC skeleton was formed, which effectively constrained the cross‐plane thermal expansion of the GF@SiC composites. Highly oriented GFs endowed the composites with good thermal conductivity (TC) along the basal plane and effective EMI shielding in the X‐band. The composites with SiC concentrations of 9 vol.% exhibited an optimal comprehensive performance with a high TC of 322 W/m/K in the basal plane direction, a low thermal expansion value of 10.5 × 10−6/K in the through‐plane direction, and EMI shielding effectiveness of 36 dB. Our strategy provides a promising and practical approach for realizing graphite‐based composites to meet the current demands for electronic devices.