Tunable Thermal Expansion Research Articles

Enhanced thermal buckling resistance of folded graphene reinforced nanocomposites with negative thermal expansion: From atomistic study to continuum mechanics modelling

Materials with tunable negative thermal expansion (NTE) are of crucial importance in engineering applications. Currently, the route to achieving large tunability for the coefficient of thermal expansion (CTE) in metal matrix composites (MMCs) is very limited. This paper develops folded graphene (FGr) structures to engineering the CTE of MMCs by embedding the FGr into a copper (Cu) matrix through the molecular dynamics (MD) method. Moreover, the present work investigates the thermal buckling resistance capability of the NTE material composite beam using the classical Euler-Bernoulli beam theory and Ritz method. Atomistic studies based on the MD simulations show that the CTE of FGr/Cu nanocomposite can be effectively tuned by mechanical prestress and temperature, especially within the range from 200 K to 400 K. By using the origami-patterned FGr designed herein, the maximum negative and positive CTEs can reach approximately −95.42 × 10−6 K−1 and 56.32 × 10−6 K−1 under the prestress of 1000 MPa at 300 K and 200 K, respectively. More importantly, the quantitative relationship of the temperature- and prestress-dependent material properties of the FGr/Cu composites are built. Based on the built material model, the FGr/Cu composite beam exhibits considerably improved thermal buckling performance than the pristine graphene/Cu beam.

Nano-precipitation leading to linear zero thermal expansion over a wide temperature range in Ti22Nb

Certain cold-worked martensitic Ti-alloys exhibit tunable linear thermal expansion along a specific sample direction. These intriguing properties are related to the anisotropic thermal expansion of the orthorhombic αʺ martensite. However, the tailored expansion obtained in this way is limited to the single-phase martensitic temperature field, below the reverse transformation of martensite into austenite. Here, we demonstrate that the orthorhombic αʺiso formed by diffusion can also regulate the thermal expansion using a prototypical Ti22Nb alloy. More importantly, the temperature range in which the tailored linear thermal expansion occurs is enormously broadened relative to the cold-worked martensitic alloy. We clarify the formation path of nano-sized αʺiso during thermal cycling and resolve the crystallographic relationship with the parent phase. These findings provide new routes for designing low/negative thermal expansion Ti-alloys with large operating temperature ranges.

Spray‐dried sol‐gel glass‐ceramic powders based on the tunable thermal expansion of quartz and keatite solid solutions

AbstractLithium aluminosilicate glass‐ceramic powders were synthesized by the heat treatment of spray‐dried sol‐gel glassy nanobeads, obtaining quartz solid solution (Qss) and keatite solid solution (Kss) crystals. Their composition ranged between 75 mol% SiO2 and pure silica along the spodumene join. The metastable crystals displayed tunable coefficients of thermal expansion ranging from +30 × 10−6 to −2.7 × 10−6 K−1 at room temperature, as obtained from their crystallographic characterization. The solid solution boundaries of Kss could be extended to 85 mol% SiO2. Concurrently, X‐ray diffraction measurements performed in situ at high temperature and at cryogenic conditions confirmed the known linear shift of the high‐low quartz inversion temperature upon increasing Al+Li doping. The obtained results qualify aerosol synthesis as a very versatile method for the production of glass‐ceramic powders in the LAS system.

Design optimization of multifunctional metamaterials with tunable thermal expansion and phononic bandgap

Metamaterials have been extensively investigated owing to their unusual properties. However, the design of multifunctional metamaterials requires further investigation. This study focused on the design of three-dimensional (3D) metamaterials to achieve tunable negative thermal expansion and phononic bandgap properties. First, the independent continuous mapping (ICM) topology optimisation method was applied to create metamaterial microstructures with negative thermal expansion properties based on the multi-scale asymptotic homogenisation theory. Secondly, the conceptual structure from the topology optimisation was reconstructed and parameterized to achieve the desired phononic bandgap widths under negative thermal expansion, using a surrogate model-based optimisation method. Both the negative coefficient of thermal expansion and phononic bandgaps were verified through numerical simulations. The results reveal that, by selecting appropriate parameters, the designed metamaterials can have both a negative coefficient of thermal expansion and a maximum bandgap width ratio. The proposed method provides an important reference for the rational design of multifunctional metamaterials.

Metamaterials with a controllable thermal-mechanical stability: Mechanical designs, theoretical predictions and experimental demonstrations

Mechanical metamaterials with tunable thermal expansion are of increasing interest due to their capability for matching the thermal expansion of surrounding components to maintain high-level thermal-mechanical stability upon a temperature change and show their promising applications in the fields of flexible electronics, aerospace, MEMS, and precision instruments. Though numerous of studies on metamaterials with zero thermal expansion of coefficient (CTE) has been developed to access these demands, the experimentally demonstrated designs with a remarkable zero CTE value (e.g. <0.5 ppm/K) still remain a challenge. In this paper, a design concept of metamaterial capable of offering a tailorable CTE, especially the excellent thermal-mechanical stability, is systematically studied, whose underlying mechanism is the conversion of thermal-induced deflection of bilayer beams (in Al and Ti) into unusual, effective thermal expansion or shrinkage of metamaterials. Notably, the experimentally demonstrated CTE of this metamaterial is 0.42 ppm/K, which is the unprecedented zero CTE result as compared to the previously reported studies. The theoretical model for CTE and elastic modulus of this design, which is verified by FEA and experiments, provides a clear understanding of relationships between configuration parameters and effective thermal and mechanical performances. Combined theoretical predictions, FEA, and experimental studies demonstrate the capability of this metamaterial to serve as a design platform for devices or components that require excellent thermal-mechanical stability.

Tailoring thermal expansion coefficient from positive through zero to negative in the compositional crossover alloy Ti50(Pd40Cr10) by uniaxial tensile stress

The precision control of thermal expansion is of fundamental interest and desirable for applications that require materials to retain their shape at different temperatures. In the present study, we propose that the thermal expansion coefficient can be tuned by uniaxial external stress for a single material embedded with nanoclusters, if the formation, growth or alignment of the nanoclusters depends on the external stress. We demonstrate the idea in a prototype alloy (Ti50(Pd40Cr10)) located at the compositional crossover region between martensite and strain glass in the temperature-composition phase diagram of Ti50(Pd50−xCrx). Its thermal expansion coefficient varies linearly from positive, through zero to negative values with increasing uniaxial tensile stress within 200 K ~ 300 K. The phase field simulations show that the volume fraction of nanoscale martensite variant favored by the external stress increases with stress, producing extra strain and compensating for the contraction of the austenite matrix on cooling. The degree of compensation leads to different thermal expansion coefficients. Such a tunable thermal expansion behavior occurs only in the crossover compositions between martensite and strain glass, providing a design recipe for searching new systems with similar behavior.

Microstructure evolution and its influence on the thermal expansion of La(Fe0.79Al0.21)13 alloy prepared by arc-melting

NaZn13-type La(Fe1−xAlx)13 alloys show tunable thermal expansion. However, whether the arc-melted alloys contain secondary phase, which can obviously influence the thermal expansion, is still unclear. Facing to this question, we take arc-melted La(Fe0.79Al0.21)13 as an example and investigate its microstructure evolution. The as-cast ingot consists of NaZn13, α-Fe and amorphous La-rich phases. Their size and distribution are different at different positions, indicating the existence of microstructure segregation. During annealing,NaZn13 phase grows up through a reaction between α-Fe and amorphous La-rich phases, but a single-phase sample still can’t be obtained even after 15-days-annealing. Nonuniformly distributed α-Fe phase, which is a result of microstructure segregation, exists in the NaZn13 main phase. Our measurements on different parts of the annealed sample indicate that the thermal expansion is highly related with the local concentration of α-Fe phase.

Stereolithography additive manufacturing of multi-ceramic triangle structures with tunable thermal expansion

Ceramics and their structures with tunable thermal expansion are deemed necessary to develop. In this study, multi-ceramic structures with tunable thermal expansion, including negative thermal expansion (NTE), zero thermal expansion (ZTE), and positive thermal expansion (PTE), were developed for the first time. Firstly, multi-ceramic triangle structures with tunable thermal expansion were designed based on ZrO2 and Al2O3 ceramics. Then, multi-ceramic triangle structures were fabricated by using the stereolithography additive manufacturing technology. Functionally gradient ceramic (FGC) layers were applied for releasing the thermal mismatch stress among the structure. Finally, the thermal expansion behavior of the multi-ceramic triangle structures were characterized and analyzed by using a homemade thermal expansion testing system. The proposed design, fabrication and characterization methods of multi-ceramic structures with tunable thermal expansion are believed to promote the engineering application.

Copper matrix thermal conductive composites with low thermal expansion for electronic packaging

Reducing thermal expansion and improving thermal conductivity of copper based materials are particularly important for improving thermal stability of electronic packaging materials. Herein, Cu/Sc2W3O12/SiC composite with a moderate coefficient of thermal expansion (CTE) of 8.28 ppm/K and a high thermal conductivity of 287.2 W/m⋅K was successfully prepared by partial replacement of Sc2W3O12 by the nano SiC particles to compensate sacrificial thermal conductivity of the reported Cu/Sc2W3O12 composites using a hot-pressing method. Theoretical calculation and Ashby plot map suggests that this Cu/Sc2W3O12/SiC composite facilitate the best combination between tunable thermal expansion and high thermal conductivity, which may due to that SiC nanoparticles can strengthen the driving force of vacuum hot-pressing sintering and thus lead to more homogeneous microstructure accounting for improved thermal reliability. This work can provide useful insights into the design and synthesis of composites used as packaging material for various semiconductors.

Kondo-Induced Giant Isotropic Negative Thermal Expansion.

Negative thermal expansion is an unusual phenomenon appearing in only a handful of materials, but pursuit and mastery of the phenomenon holds great promise for applications across disciplines and industries. Here we report use of x-ray spectroscopy and diffraction to investigate the 4f-electronic properties in Y-doped SmS and employ the Kondo volume collapse model to interpret the results. Our measurements reveal an unparalleled decrease of the bulk Sm valence by over 20% at low temperatures in the mixed-valent golden phase, which we show is caused by a strong coupling between an emergent Kondo lattice state and a large isotropic volume change. The amplitude and temperature range of the negative thermal expansion appear strongly dependent on the Y concentration and the associated chemical disorder, providing control over the observed effect. This finding opens avenues for the design of Kondo lattice materials with tunable, giant, and isotropic negative thermal expansion.

A novel Ag based sealant for solid oxide cells with a fully tunable thermal expansion

Abstract In this work, we show that a promising sealant for the use in solid oxide fuel cell and electrolysis stacks can be obtained by combing a conventional silver-based braze with eucryptite (LiAlSiO4), a negative thermal expansion coefficient material. The thermo-mechanical properties of the Ag2CuO-LiAlSiO4 system and the microstructure as a function of the LiAlSiO4 content are investigated. By adding 8 wt% of the LiAlSiO4 filler, the coefficient of thermal expansion of the Ag2CuO braze is lowered from 19.6 × 10−6 K−1 to 12.2 × 10−6 K−1 (25–800 °C). The aluminized Crofer 22 H is brazed to the gadolinium-dope ceria electrolyte of the solid oxide cell by employing the composite braze. The obtained joints are defect free and display low leak rates (1.2–1.4 × 10−3 sccm cm−1). The leak rate and structural integrity of the joints are retained after aging tests at 800 °C for 300 h, indicating excellent stability of the sealant.

The tunable negative thermal expansion covering a wide temperature range around room temperature in Sn, Mn co-substituted Mn3ZnN

Based on anti-perovskite Mn3ZnN, the negative thermal expansion (NTE) temperature can be effectively broadened via co-substituting Sn, Mn. Using optimized components, the room-temperature NTE effect covering a wide temperature range can be realized. Both the competing ferromagnetic order from Mn and local lattice disorder from Sn should be the reason for the physical origination of the broadening of the NTE temperature. By compositing with epoxy, the low thermal expansion could be achieved around room temperature, which exhibits great potential in the field of electronic packaging.

Large and tunable negative thermal expansion induced by a synergistic effect in M2II[MIV(CN)8] Prussian blue analogues.

Designing negative thermal expansion (NTE) materials with a larger NTE coefficient and a wider temperature window is a great challenge nowadays, leading to the limitation of existing NTE materials such that only about 150 kinds of NTE materials have been discovered since 1996. Here, using first-principles calculations combined with the quasi-harmonic approximation (QHA), we find that the synergistic effect of different vibrational modes can significantly enhance the NTE in open framework compounds. We systematically investigate the NTE properties of the M2IIMIV(CN)8 (MII = Ni, Co, Fe, and Mn; MIV = Mo and W) family, which is the first kind of Prussian blue analogues (PBAs) with a 2D and 3D topology structure, to explore the synergistic enhancement effect in NTE. We reveal that both the optical modes of the rotational motion of [W(CN)8] and [Ni(NC)4] rigid units and the low frequency acoustic modes of the transverse vibration contribute significantly to the NTE. Furthermore, the coefficients of NTE increase monotonously with increasing ionic radius upon substituting Ni in M2IIW(CN)8 with Co, Fe, or Mn, respectively. Analyzing the vibrational modes of the substituted systems indicates that the dramatic changes in NTE originate from a highly synergistic effect, in which all the frequencies of these NTE modes have the same trend, i.e. the lower the frequencies, the larger the coefficient of NTE. This work clearly presents a synergistic mechanism of enhancing NTE in PBA materials, and sheds light on designing new materials with better properties.

Micro-structured medium with large isotropic negative thermal expansion.

A challenge in nano- and micro-mechanics is the realization of innovative materials exploiting auxetic behaviour to tailor thermal expansion properties. For this purpose, a new class of micro-structured media possessing an extremely wide range of tunable (positive, negative or even zero) thermal expansion is proposed and analytically and experimentally assessed. For this class of isotropic Mechanical-Auxetic Thermal-Shrinking media, the effective coefficient of thermal expansion is explicitly linked to two microstructural variables via a simple relation, allowing the design with desired values. The theoretical predictions for the negative thermal properties are fully validated by the experimental and numerical outcomes. The simplicity of the proposed structure makes the design useful for the production of a new generation of advanced media, with applications ranging from micromechanical devices to large civil and space structures.

Lightweight cellular metal composites with zero and tunable thermal expansion enabled by ultrasonic additive manufacturing: Modeling, manufacturing, and testing

In aerospace applications, variations of temperature caused by changing environmental conditions or generation of heat is a common problem. The resulting thermal strains cause separation and alignment errors in optical systems, and stresses due to mismatches of thermal expansion at material interfaces cause failure of components and structures. Because minimizing weight, cost, and lead time are also critical requirements, lightweight, easily machined metals are attractive for aerospace applications, but these materials all have substantial coefficients of thermal expansion. Previous work has shown that the superposition of two metals with dissimilar coefficients of thermal expansion in periodic cellular configurations can result in a composite material with zero effective thermal expansion. However, fabrication of these material architectures typically is either impossible or requires manual assembly. Here, we propose methods to design and fabricate cellular metal composites with tunable thermal expansion and optimized specific stiffness that can be manufactured at useful scales entirely with automated methods. Samples were manufactured with ultrasonic additive manufacturing and computer-controlled machining, and thermal expansion was measured optically. The results demonstrate the practical fabrication of cellular metal composites with zero or negative thermal expansion in one direction, tunable thermal expansion in a second direction, and structural performance indices competitive with the indices of conventional aerospace alloys.

Controllable thermal expansion and magnetic structure in Er2(Fe,Co)14B intermetallic compounds

Tunable thermal expansion from negative, to zero, to positive with a wide temperature range in Er2(Fe,Co)14B intermetallic compounds.

Tunable near-zero thermal expansion in the C-doped La(Fe, Si)13 compounds at cryogenic temperatures

The controllable thermal expansion property gives us a method to design materials with desirable coefficient of thermal expansion. In this paper, we report a tunable zero thermal expansion (ZTE) in C-doped La(Fe, Si)13 compounds over a wide operation-temperature window (77–260 K). The effects of the interstitial C atoms on the thermal expansion and magnetic properties of the LaFe10.0Si3.0Cx (x = 0, 0.2, 0.3, 0.4) compounds were respectively investigated. The further magnetic analysis indicates that the ZTE behaviors of this La(Fe, Si)13-based compounds are attributed to the changes of magnetic exchange couplings because of the introduction of interstitial C atoms.

Tunable Thermal Expansion from Negative, Zero, to Positive in Cubic Prussian Blue Analogues of GaFe(CN)6.

The achievement of controlling thermal expansion is important for open-framework structures. The present work proposes a feasible way to adjust the coefficient of thermal expansion continuously from negative to positive via inserting guest Na+ ions or H2O molecules into a GaFe(CN)6 framework. The guest ions or molecules have an intense dampening effect on the transverse vibrations of CN atoms in the -Ga-N≡C-Fe- linkage, especially for the N atoms. This study demonstrates that electrochemical or redox intercalation of guest ions will be an effective way to tune thermal expansion in those negative thermal expansion open-framework materials induced by low-frequency phonons.

Investigation on Thermal Properties of CuO–ZnO Nanocomposites

Nanocomposites have attracted the attention of scientists and engineers for their tunable properties and extended applications. ZnO has been used as a dominant candidate for solar cell, gas sensing and piezoelectric applications. Addition of CuO can enhance the solar absorption capacity of ZnO nanostructures. In the present work, nanocomposites of CuO–ZnO have been synthesized from copper sulphate and zinc acetate by sol gel. The annealing temperature was varied at 200, 400 and 600 °C to study the temperature dependence on morphology and thermal properties. The samples were characterized by XRD, SEM and FTIR. It was found that the crystallite size increased, when temperature was increased from 200 to 600 °C. Increase in temperature showed decreased CuO phase and tunable thermal expansion of the composite (0.0115–0.0025/°C).

Continuous and reversible atomic rearrangement in a multifunctional titanium alloy

Linear elastic Hookean solids can be strong but become brittle in general as their strength-to-modulus ratio is higher about 1/100 due to the well-known inverse strength-ductility relationship. Combined with the first-order reversible martensitc transformation, they can be functional but their mechanical and functional properties are sensitive to temperature, for example, superelasticity and zero/negative thermal expansion are limited in a narrow temperature range of about 100 Kelvin. Here we report a group of titanium alloys which are strong, ductile, flexible together with superelasticity and tunable thermal expansion from positive, via zero, to negative across a wide temperature range from below 4.2 K to 625 K. This is attributed to its nonlinear elasticity obeying a high-order Hooke's law due to a continuous and reversible atomic rearrangement at a large scale up to phase transition strain. Such novel mechanism distinguishes completely from the previous elastic and martensitic mechanisms ruled by Poisson ratio and sharp crystal structure change, respectively. We demonstrate that the atomic-level mechanism is organized adaptively by a nanoscale compositional modulation, which is created by a spinodal decomposition. These findings pave a way to design new solids through a nanoscale periodical distribution in chemistry.