Thermal Contraction Research Articles

A comprehensive review of residual stresses in carbon steel welding: formation mechanisms, mitigation strategies, and advanced post-weld heat treatment techniques

Abstract Residual stresses are critical factors influencing the service performance, reliability, and durability of welded carbon steel joints. These stresses can affect the joint, susceptible to brittle fracture, fatigue failure, and stress corrosion cracking, particularly within the heat-affected zone (HAZ). These stresses result from uneven thermal expansion and contraction during welding, with thicker plates and constrained configurations being more susceptible. Post-weld heat treatment (PWHT) assumes a critical function in mitigating these stresses by tempering martensitic structures, refining microstructures, and enhancing mechanical properties such as toughness and ductility. This review examines the mechanisms driving residual stress formation, evaluates the effectiveness of PWHT techniques, and highlights advanced methodologies like neutron diffraction, computational modeling, and hybrid welding processes. While PWHT significantly alleviates residual stresses, complete stress elimination remains unattainable, emphasizing the need for innovative strategies such as hybrid welding methods, computational modeling, and advanced heat treatments. This work integrates metallurgical principles with experimental findings to provide a strategy for enhancing the performance and reliability of welded joints in critically demanding industrial applications.

Structurally and electronically driven uniaxial negative thermal expansion in BaIrO3.

Negative thermal expansion is known to exist in a range of structure types but is extremely rare in hexagonal perovskites. Here we demonstrate that BaIrO3 displays negative linear thermal expansion in the direction of its face-shared IrO6 trimers, and apparent zero volume thermal expansion below 100 K. We present evidence that this anomalous thermal expansion is driven by an unusual form of rigid body phonon behaviour governed by the effective trimer valence state and therefore has structural and electronic components to the underlying mechanism.

Thermal expansion and thermodynamic properties of Janus WSSe monolayer: A first-principles study

Materials with Janus structure play an important role in the emerging family of 2D materials. In this paper, based on a quasi-harmonic approach, the elastic, thermal expansion, and related thermodynamic properties of Janus WSSe monolayer are investigated by using first-principles calculations. For comparison, WS2 and WSe2 monolayers are studied as well. The linear thermal expansion coefficients of the three monolayers exhibit isotropy as their isotropic structures. All three monolayers show negative thermal expansion behavior at low temperatures (T < 30 K), with very small magnitudes. The value of the largest magnitude of negative thermal expansion is −0.376 × 10−6 K−1, contributed by the Janus WSSe monolayer. The linear thermal expansion coefficients also change from negative to positive as the temperature increases. This is consistent with macroscopic Grüneisen parameters. Remarkably negative values of the macroscopic Grüneisen parameter directly lead to negative thermal expansion at low temperatures. The linear thermal expansion coefficient of Janus WSSe is between those of WS2 and WSe2. The 2D bulk modulus has an important effect on the thermal expansion of three monolayers.

Managing negative linear compressibility and thermal expansion through steric hindrance: a case study of 1,2-bis(4'-pyridyl)ethane cocrystals.

Multicomponent crystals have great scientific potential because of their amenability to crystal engineering in terms of composition and structure, and hence their properties can be easily modified. More and more research areas are employing the design of multicomponent materials to improve the known or induce novel physicochemical properties of crystals, and recently they have been explored as materials with abnormal pressure behaviour. The cocrystal of 1,2-bis(4'-pyridyl)ethane and fumaric acid (ETYFUM) exhibits a negative linear compressibility behaviour comparable to that of framework and metal-containing materials, but overcomes many of their deficiencies restricting their use. Herein ETYFUM was investigated at low temperature to reveal negative thermal expansion behaviour. Additionally, a cocrystal isostructural with ETYFUM, based on 1,2-bis(4'-pyridyl)ethane and succinic acid (ETYSUC), was exposed to high pressure and low temperature, showing that its behaviour is similar in nature to that of ETYFUM, but significantly differs in the magnitude of both effects. It was revealed that the minor structural difference between the acid molecules does not significantly affect the packing under ambient conditions, but has far-reaching consequences when it comes to the deformation of the structure when exposed to external stimuli.

Constructing a novel controllable interface structure through the anchoring effect of α-cyclodextrin at cryogenics to enhance and toughen the mechanical properties of epoxy resin

The fracture toughness of an epoxy resin (EP) often decreases under cryogenic conditions, primarily because of performance degradation caused by molecular chain freezing. In this study, a high-tensile-strength and high-fracture-toughness EP-based nanocomposite (EP/CPN–CuO) was synthesized using α-cyclodextrin (α-CD) for anchoring. The α-CD immobilized flexible linear polymers grafted onto the surface of CuO nanorods (NRs) with negative thermal expansion within a novel interface with the EP. The composite exhibited enhanced mechanical properties because the α-CD effectively hindered the curling of polymer chain segments and considerably improved the chemical bonding between the EP and CuO. Experimental results demonstrated the enhanced mechanical performance of EP/CPN–CuO under cryogenic conditions compared with that of other materials reported in the literature. EP/CPN-CuO-2.0 exhibited a tensile strength of 111.40 MPa, a Young’s modulus of 6.67 GPa, and a fracture toughness of 2.69 MPa·m1/2, marking increases of 67.4 %, 10.8 %, and 100.7 % compared to pure EP. Thus, this study effectively resolved the trade-off between the tensile strength and fracture toughness of an EP under cryogenic conditions, providing a new pathway for the widespread application of EPs in cryogenic environments.

Effect of Fe-doping on magnetic structures and “spin-lattice-charge” strong correlation properties in Mn3Sn1-xFexC compounds

The influences of Fe-doping on the magnetic structure, correlated lattice variation, and electronic transport of the antiperovskite compounds Mn3Sn1-xFexC have been reported for the first time. The results indicate that Fe-doping is effective in altering the magnetic behaviors in the Mn3Sn1-xFexC compounds. The magnetic phase transition point (TC) initially shifts to lower temperatures at low Fe-doping concentrations and then increases to higher temperatures at higher Fe-doping levels. This change is accompanied by the development of macroscopic ferromagnetism in the compound, which is essentially due to the emergence of a new canted ferrimagnetic phase named MCF, revealed by neutron powder diffraction (NPD). By virtue of the Fe-doping effect on the magnetism, the regulation of the negative thermal expansion (NTE) behavior and the abrupt change of resistivity in Mn3SnC are also realized. Based on these results, a magnetic phase diagram for the Mn3Sn1-xFexC series is established. This work not only provides a method for effective regulation of magnetic ordering but also strengthens our understanding of strongly correlated physical properties.

A series of metamaterials exhibiting negative thermal expansion inspired by leaflet pattern in compound leaf

A series of metamaterials exhibiting negative thermal expansion inspired by leaflet pattern in compound leaf

Synthesis and phase purity of the negative thermal expansion material ZrV2O7

Synthesis of pure, homogeneous, and reproducible materials is key for the comprehensive understanding, design, and tailoring of material properties. In this study, we focus on the synthesis of ZrV2O7, a...

Spin state modulation and kinetic control of thermal contraction in a [Fe2Co2] discrete Prussian blue analogue.

Stimuli-responsive switchable molecules represent an important category of magnetic materials with significant potential for functional devices. However, engineering complexes with controlled switchability remains challenging due to their sensitivity to lattice interactions. Herein, we report a [Fe2Co2] square complex [FeTp(CN)3]2[Co{(F5-Ph)Py}2]2·2ClO4·4CH3OH·2H2O {1·4CH3OH·2H2O; (F5-Ph)Py = (Z)-N'-(perfluorophenyl) picolinimidamide and Tp = hydrotris(1-pyrazolyl)borate}, tailored with hydrogen bonding (HB) donor and acceptor moieties for effective lattice interactions. The alteration in HB interactions in crystal phases obtained via single-crystal-to-single-crystal (SC-SC) transformation (i.e., 1·4CH3OH·2H2O ↔ 1·2H2O ↔ 1) led to a remarkable change in magnetic properties. Complexes 1·4CH3OH·2H2O and 1 possess [FeII LS(μ-CN)CoIII LS] and [FeIII LS(μ-CN)CoII HS] configurations, respectively. Meanwhile, 1·2H2O demonstrates multi-responsive (thermo-, photo- and pressure) reversible two-step electron transfer coupled spin transition (ETCST) accompanied by thermal contraction and expansion. The complete diamagnetic [FeII LS(μ-CN)CoIII LS] configuration in 1·2H2O was obtained at an intermediate temperature accompanied by thermal contraction, an unusual behaviour observed for the first time in cyanide-bridged systems. Additionally, 1·2H2O displayed temperature-induced excited spin state trapping (TIESST) of ∼70% of the paramagnetic [FeIII LS(μ-CN)CoII HS] configuration at low temperatures. The isothermal relaxation of the thermally trapped paramagnetic state shows a much faster and complete conversion to a diamagnetic state at ∼140 K, compared to the relaxation observed at other temperatures (100-190 K), corroborating the observed unique magnetic behaviour. Hence, this result provides valuable insight into the strategic design of complexes with enhanced and controlled switchability for potential applications such as actuators and sensors.

Tracking anharmonic oscillations in the structure of β-1,3-diacetylpyrene.

A recently discovered β polymorph of 1,3-diacetylpyrene has turned out to be a prominent negative thermal expansion material, with a linear thermal expansion coefficient of -199 (6) MK-1 at room temperature. Its unique properties can be linked to anharmonic oscillations in the crystal structure that can be attributed to several weak C-H...O interactions. The onset and development of anharmonic effects have been successfully tracked over a wide (90-390 K) temperature range using single-crystal X-ray diffraction. Experimental data of sufficient quality combined with Hirshfeld atom refinement of the crystal structures enabled a quantitative analysis of elusive anharmonic effects within the Gram-Charlier formalism. This example highlights that quantum crystallography tools can and should be applied in structural analysis even for data collected at high temperatures as well as of standard (∼0.8 Å) resolution.

Dynamic behavior of ultrasonic frequency pulsed current-assisted gas metal arc welding

Investigating ultrasonic frequency pulsed current (UFPC)-assisted welding is crucial owing to its significant advantages over traditional welding methods, including enhanced weld quality, reduced defects, and increased efficiency. This study elucidated the generation mechanism of arc ultrasonic waves influenced by UFPC through theoretical derivation. A microscopic model of arc plasma under the influence of UFPC was developed, and the equations governing the thermophysical properties of the plasma were theoretically derived and calculated. A three-dimensional numerical simulation model was developed to analyze the dynamic behavior of arc plasma and molten metal in UFPC-assisted gas metal arc welding (UFPC-GMAW). The simulation results revealed that the incorporation of UFPC increased both the maximum arc temperature and plasma velocity, resulting in a conical shape of the arc. Additionally, the maximum arc temperature amplitude decreased from 13.6% in conventional GMAW (C-GMAW) to 9.6% in UFPC-GMAW, indicating improved arc stability. The increase in electromagnetic force led to a higher droplet transfer frequency. Moreover, the weld pool in UFPC-GMAW exhibited greater weld penetration than in C-GMAW. Notably, the variations in maximum arc temperature and velocity were synchronized with UFPC, resulting in localized thermal contraction and expansion within the arc. These changes affected the arc volume and shape, leading to the excitation of ultrasonic waves. The calculated droplet size and transfer frequency were consistent with the experimental results, confirming the reliability of the models. These simulation results provide valuable guidance for engineers in designing UFPC-GMAW technology to achieve high-quality welds.

A temperature compensation method for fiber Bragg gratings using negative thermal expansive β-eucryptite packaging

Abstract Fiber optic sensing measurements hold significant potential for various applications, but temperature compensation of fiber Bragg grating (FBG) remains a formidable challenge. This paper introduces the utilization of β-eucryptite as an encapsulation material for FBG, exploiting its negative thermal expansion property to achieve temperature compensation. A two-point adhesive sealing technique was employed to affix FBG to the β-eucryptite substrate. While bare FBG and sensors encapsulated in 7075 aluminum alloy served as comparison. Experimental outcomes reveal that the FBG encapsulated in β-eucryptite exhibits temperature sensitivities of 1.67 pm °C−1 within the temperature ranges of −30 °C to 150 °C. In contrast, bare FBG and sensor encapsulated with 7075 aluminum alloy display temperature sensitivities of 10.46 pm °C−1 and 37.31 pm °C−1, respectively. The use of β-eucryptite for sensor encapsulation effectively reduces the temperature sensitivity of FBG. This temperature compensation method is straightforward yet promising and has great potential in aerospace and precision instrument measurement.

Thermal Enhanced Near-Infrared Upconversion Luminescence in Y2Mo4O15:Yb/Nd with Uniaxial Negative Thermal Expansion.

Thermal quenching (TQ) of luminescence presents a significant barrier to the effective use of optical thermometers in high-temperature applications. Herein, we report a novel uniaxial negative thermal expansion (NTE) phosphor, Y2-2x-2yMo4O15:xYb,yNd, synthesized by a solid-state reaction. Under 980 nm laser excitation, it exhibits excellent thermally enhanced near-infrared (NIR) upconversion luminescence (UCL) performance. The UCL intensities of Nd3+ at 573 K were enhanced by 396-fold (750 nm), 57.6-fold (810 nm), and 7.6-fold (882 nm), respectively, compared with that of room temperature. In situ temperature-dependent X-ray diffraction and steady- and transient-state spectra are used to reveal thermal expansion behavior and luminescence mechanism in detail. The thermal enhancement of NIR UCL is attributed to the synergistic effect of increased radiative transition probability due to the anisotropic thermal expansion of the crystal and the enhanced energy transfer (ET) efficiency resulting from uniaxial shrinkage and the phonon-assisted process. Based on the luminescence intensity ratio (LIR) of the thermally coupled energy levels (4F7/2/4F3/2), the target sample achieved ultrahigh sensitivity (Sr = 3.0% K-1 at 298 K) with high repeatability over the entire temperature range. This study not only provides a fresh perspective for achieving thermal enhancement of NIR UCL phosphors using uniaxial negative thermal expansion materials but also presents a novel approach for developing NIR UCL optical thermometers with outstanding temperature performance.

Methylammonium Lead Iodide across Physical Space: Phase Boundaries and Structural Collapse.

Hybrid perovskites exhibit complex structures and phase behavior under different thermodynamic conditions and chemical environments, the understanding of which continues to be pivotally important for tailoring their properties toward improved operational stability. To this end, we present for the first time a comprehensive neutron and synchrotron diffraction investigation over the pressure-temperature phase diagram of the paradigmatic hybrid organic-inorganic perovskite methylammonium lead iodide (MAPbI3). This ambitious experimental campaign down to cryogenic temperatures and tens of kilobars was supported by extensive ab initio molecular dynamics simulations validated by the experimental data, to track the structural evolution of MAPbI3 under external physical stimuli at the atomic and molecular levels. These combined efforts enable us to identify the mechanisms underpinning structural phase transitions, including those exhibiting negative thermal expansion across the boundary between the cation-ordered low-temperature phase and the dynamically disordered high-pressure cubic phase. Our results bring to the fore how pronounced octahedral distortions at high pressures ultimately drive the structural collapse and amorphization of this material.

Analysis of the optimal heat treatment temperature for AlNiCo-based semi-hard magnetic materials based on temperature-dependent yield strength prediction model

To improve the starting characteristics of permanent magnet hysteresis motors, AlNiCo-based on semi-hard magnetic materials (ASMM) is proposed. The microstructural design is carried out by combining the advantages of soft magnetic composites (SMCs) and AlNiCo8 while choosing BaTiO3 with the negative thermal expansion property to eliminate the voids. The material composition as well as the range of heat treatment temperatures are determined by the phase transition kinetics. The temperature-dependent yield strength prediction model considering stress-equivalent magnetic fields is then developed. The model establishes the quantitative relationship between yield strength, ambient temperature, magnetostriction coefficient, elastic modulus, and Poisson's ratio. The comparisons between the model and experiments are made. It can be obtained that the yield strain is related to the microstructure and morphology, and the optimum heat treatment temperature is 680°C under the condition of ensuring the highest yield strength. This method can be used to optimize the parameters of the material preparation process and provide a reference for the optimized design of high-speed and ultra-high-speed motors.

Long-term alpine summit vegetation cover change: Divergent trajectories driven by climate warming and fire

ABSTRACT Alpine summit vegetation, the highest point of species geographical distributions, is vulnerable to climate change (thermal niche contraction), and there is evidence of change in Northern Hemisphere summits. However, summits are experiencing multifaceted change due to warming and increasing fire frequency. Little is known about how these factors are affecting alpine summit vegetation. We used a revisitation approach to capture the long-term (eighteen years) dynamic changes in Australian alpine plant summit community patterns and to understand the mechanisms of change. We found that vegetation change was influenced by climate and moderated by site-specific factors. There was increased shrub cover over time; however, summit vegetation was largely stable unless disturbed. Fire-disturbed summits experienced higher instability in their vegetation cover over time. Linear mixed-effect models indicated that as time since fire increased and the growing degrees accumulated, there was a strong positive effect on forb and graminoid cover and a negative effect on shrub cover. Forb cover was higher at cooler, wetter, higher-elevation summits. These findings indicate the multifaceted nature of change that must be accounted for in alpine vegetation studies. We show that alpine summit vegetation will respond multidirectionally to a warming climate and changing fire regimes, with outcomes likely contingent on life history characteristics.

Negative Thermal Expansion Behavior Enabling Good Electrochemical‐Energy‐Storage Performance at Low Temperatures

AbstractMetal‐ion batteries (such as lithium‐ion batteries) are very popular energy‐storage devices nowadays. However, low temperatures cause their poor electrochemical kinetics and performance, significantly limiting their wide applications in cold environments. Here, we propose that electrochemical energy‐storage materials with negative‐thermal‐expansion (NTE) behavior can enable good low‐temperature electrochemical performance, which becomes a new strategy to tackle the low‐temperature issues of metal‐ion batteries. LiTi2(PO4)3 (LTP) with an a‐direction thermal expansion coefficient of −1.1×10− K−1 is used as a model material. As the temperature decreases, the transverse vibration of O atoms not only increases the transverse distances among O atoms connected to Li/Ti atoms, but also widens the Li+‐transport channels and enlarges the Li+‐insertion sites along the [12 ] direction, which are mainly controlled by the lattice parameter a. Consequently, carbon‐coated LTP (C–LTP) retains good electrochemical performance at −10 °C, including fast Li+ diffusivity (84 % of that at 25 °C), large capacity (96 % of the theoretical capacity), and superior rate capability (83 % capacity retention at 5 C vs. 0.5 C). Moreover, the more open crystal structure of LTP at the lower temperature allows smaller maximum unit‐cell‐volume expansion, resulting in better cycling stability of C–LTP at −10 °C (96.8 % capacity retention over 1000 cycles at 2 C).

Negative Thermal Expansion Behavior Enabling Good Electrochemical-Energy-Storage Performance at Low Temperatures.

Metal-ion batteries (such as lithium-ion batteries) are very popular energy-storage devices nowadays. However, low temperatures cause their poor electrochemical kinetics and performance, significantly limiting their wide applications in cold environments. Here, we propose that electrochemical energy-storage materials with negative-thermal-expansion (NTE) behavior can enable good low-temperature electrochemical performance, which becomes a new strategy to tackle the low-temperature issues of metal-ion batteries. LiTi2(PO4)3 (LTP) with an a-direction thermal expansion coefficient of -1.1×10- K-1 is used as a model material. As the temperature decreases, the transverse vibration of O atoms not only increases the transverse distances among O atoms connected to Li/Ti atoms, but also widens the Li+-transport channels and enlarges the Li+-insertion sites along the [12 ] direction, which are mainly controlled by the lattice parameter a. Consequently, carbon-coated LTP (C-LTP) retains good electrochemical performance at -10 °C, including fast Li+ diffusivity (84 % of that at 25 °C), large capacity (96 % of the theoretical capacity), and superior rate capability (83 % capacity retention at 5 C vs. 0.5 C). Moreover, the more open crystal structure of LTP at the lower temperature allows smaller maximum unit-cell-volume expansion, resulting in better cycling stability of C-LTP at -10 °C (96.8 % capacity retention over 1000 cycles at 2 C).

A Smart Slippery Surface with Reversible Dynamic Temperature Responsiveness for Long‐Term Controllable Anti‐Icing

AbstractRecently, slippery liquid‐infused porous surface (SLIPS) is widely utilized for anti‐icing. Nevertheless, a major challenge hindering the practical applications of SLIPS is the depletion of lubricating oil, significantly deteriorating its deicing performance. Given that super‐slippery effects are not required during most non‐icing periods, this research introduces a novel dynamic wettability‐adjustable SLIPS anti‐icing coating inspired by the nepenthes. This coating‐comprising modified diatomaceous earth and soft silicone rubber‐releases lubricating oil only when temperatures fall below −2 °C, thus exhibiting super‐slippery characteristics and effectively preventing icing. The porous modified diatomaceous earth retains lubricating oil for prolonged periods and facilitates its controlled release under external forces. The high elasticity and strength of the soft silicone rubber endow the coating with thermal expansion and contraction capabilities, enabling the active absorption and release of lubricating fluid in response to temperature variations. This coating, prepared using a straightforward strategy, demonstrates an ice adhesion strength and an oil loss rate of less than 23 kPa and 13%, respectively, after 50 icing/de‐icing cycles. These findings highlight the remarkable performance of the coating, providing valuable insights for achieving long‐term anti‐icing on the external surfaces of equipment in extreme working conditions.

Crystallographic assessment and thermal expansion fine‐tuning of quartz solid solutions in the ZnO–MgO–Al2O3–SiO2 system

AbstractGlass powders with compositions within the ZnO–MgO–Al2O3–SiO2 system (without the addition of nucleating agents) were synthesized by spray‐drying and carefully crystallized to obtain stuffed quartz solid solutions (Qz‐ss). The substitution of Zn by Mg causes an increase in the crystallization temperature and the composition of Qz‐ss varies during their formation, highlighting a nonisochemical precipitation with respect to the parent glass. A change from a low‐temperature modification of Qz‐ss to a high‐temperature modification was visible for Qz‐ss containing 80 or 90 mol% SiO2. The high‐temperature modification of Mg‐ and (Zn,Mg)‐Qz‐ss displays negative thermal expansion for SiO2 content equal to 90 mol%, but a positive one for 80 and 67 mol%. In contrast, the high‐temperature modifications of Zn‐Qz‐ss show a negative thermal expansion for the three SiO2 contents studied. The properties of (Zn,Mg)‐Qz‐ss containing 67 mol% SiO2 cannot be predicted by a linear interpolation between Zn‐Qz‐ss and Mg‐Qz‐ss. A (Zn,Mg)‐Qz‐ss with zero thermal expansion was crystallized by modulating SiO2 content and Mg/Zn ratio.