Instantaneous Coefficient Of Thermal Expansion Research Articles

Failure analysis of Al2O3–C–SiO2 slide gate plates during continuous casting based on numerical simulation

The thermo-mechanical and failure behavior of the burning-free Al2O3 –C–SiO2 slide gate plate materials during the steel casting process are investigated. Firstly, the instantaneous coefficient of thermal expansion and the Young's modulus of the slide gate plate materials with different component contents at high temperature are measured. Secondly, a material constitutive model and a concrete damage plasticity mode are established based on the experiments, and adopted to simulate the failure behavior of the burning-free Al2O3–C–SiO2 slide gate plate during casting based on Finite Element Method (FEM) analysis. Results show that temperature gradient in the slide gate plate near the casting hole increased significantly and had a significant influence on cracking. The area near the casting hole of the slide gate plate is under tensile stress conditions, and then changes towards compressive stress conditions. Under those severe thermal stress conditions, crack formation is evaluated and an optimized composite structure of the slide gate plate combining advantages of reducing the risk of cracking and extending the service life is proposed. Moreover, the thermal shock test further verified that the microcrack extension was significantly alleviated due to the SiC distributed in whisker form and formed an interlocking structure in material. This work provides a reliable theoretical and experimental basis for the design and optimization of high performance Al2O3–C–SiO2 slide gate plates.

Study on the anomalous thermal expansion behavior of cold-rolled Ti-34 Nb alloy and its novel tailoring strategy

In this study, we have investigated the anisotropic in-plane thermal expansion behavior of cold-rolled (CR) Ti-34 Nb alloy and its relationship with temperature by means of continuous heating and cyclic heating-cooling thermal expansion measurement methods. A new microscopic model including the morphology of β and martensite (α″) phases, cold rolled textures and α″ content is proposed, which successfully explains the mechanism of anomalous positive thermal expansion of transverse direction (TD) and negative thermal expansion of rolling direction (RD). It is found that the coefficient of thermal expansion (CTE) of CR-Ti-34 Nb alloy is controlled by α″ content. The instantaneous CTEs of TD and RD (absolute value) both increase first and then decrease (nonlinearity) within the temperature range of anomalous thermal expansion, which is attributed to the increase of α″→β transformation rate (temperature increases by 1 °C) with increasing temperature and the significant decomposition of α″ phase above 260 °C. Moreover, we have excluded the influence of the anisotropy of α″ and internal stress on CTE. According to the abovementioned findings, α″ content is adjusted by pre-aging treatment for the first time, and a wide range of CTEs (−33.0 × 10−6 k−1 ~ 0.4 × 10−6 k−1) are obtained in CR-Ti-34 Nb alloy, including a variety of low (−6.3 × 10−6 k−1, −3.3 × 10−6 k−1) and zero (−1.5 × 10−6 k−1, −0.9 × 10−6 k−1, 0.4 × 10−6 k−1) CTEs with a wide temperature window of 275 °C (25 °C ~ 300 °C).

Strengthening the thermal Negative Poisson's ratio structures by SiC chemical vapor infiltration

Negative Poisson's ratio structures exhibit adjustable thermal expansion behavior as the thermal stress can be dispersed or offset by torsion, bending, and tension of the struts. However, the structural stability under cyclic thermal stress significantly determines the long-term durability. Strengthening the Negative Poisson's ratio structure can ensure high thermal and mechanical reliability. The work designed a heat-induced torsional Negative Poisson's ratio structures and fabricated it by 3D printing. For efficient strengthening, the preforms were further densified by chemical vapor infiltration (CVI) of SiC to enhance the reliability. Pores and gaps in the preforms were homogeneously covered and filled by the SiC, enhancing the surface finish and mechanical performance. The heat induced torsion of the structures dispersed the heat flow in one single direction, reducing the thermal stress concentration. The independent thermal expansion change of the structural unit can offset or consume the heat dissipation stress, and further improve the reliability and thermal stability through the densification process. As a result, the 120° twisted structure exhibited an average coefficient of thermal expansion (CTE) of 6. 12 × 10−6/K from room temperature (RT) to 500 °C, and the instantaneous CTE reached the minimum value of 4.01 × 10−6/K at 125 °C. Meanwhile, the load-bearing capacity strengthened significantly, exhibiting the optimized strength of 11.31 MPa and Young's Modulus of 36.44 GPa, revealing a significant improvement than those of preforms, promising for high load-bearing and low expansion application of structure-function integrated low expansion material.

Properties of SiC‐Si made via binder jet 3D printing of SiC powder, carbon addition, and silicon melt infiltration

AbstractWe report the physical and mechanical properties of ceramic composite materials fabricated by binder jet 3D printing (BJ3DP) with silicon carbide (SiC) powders, followed by phenolic resin infiltration and pyrolysis (IP) to generate carbon, and a final reactive silicon melt infiltration step. After two phenolic resin infiltration and pyrolysis cycles; porosity was less than 2%, Young's modulus was close to 300 GPa, and the flexural strength was 517.6 ± 24.8 MPa. However, diminishing returns were obtained after more than two phenolic resin infiltration and pyrolysis cycles as surface pores in carbon were closed upon the formation of SiC, resulting in reaction choking and residual‐free carbon and porosity. The instantaneous coefficient of thermal expansion of the composite was found to be independent of the number of phenolic IP cycles and had values of between 4.2 and 5.0 ppm/°C between 300 and 1000℃, whereas the thermal conductivity was found to have a weak dependence on the number of phenolic IP cycles. While the manufacturing procedures described here yielded highly dense, gas impermeable, siliconized SiC composites with properties comparable to those of bulk siliconized silicon carbide processed according to conventional techniques, BJ3DP enables the manufacture of objects with complex shape, unlike conventional techniques.

Processing and properties of SiC composites made via binder jet 3D printing and infiltration and pyrolysis of preceramic polymer

AbstractThe effect of polymer infiltration and pyrolysis (PIP) cycles with polycarbosiloxane on the microstructure, air leak rate, and properties of SiC composites manufactured by a combination of binder jet 3D printing and PIP is reported. The density, Young's modulus and flexural strength of disk‐shaped components increased with the number of PIP cycles. In the case of density, it increased from 2.05 g/cm3 in one PIP cycle to 2.33 g/cm3 after three PIP cycles, while values of flexural strength and Young's modulus at room temperature after three PIP cycles reached 66.8 ± 2.5 MPa and 69.5 ± 2.8 GPa, respectively. Conversely, the air leak rate was found to decrease with number of PIP cycles, and it reached a value of 4 mbar‐L/s after three cycles. The instantaneous coefficient of thermal expansion of the composite was found to change minimally with the number of PIP cycles and had a value of 4 ± 1.2 ppm/°C between 200°C and 1000°C. Thermal conductivity was found to increase with number of PIP cycles and to decrease with temperature. For example, after three PIP cycles it was found to change from 6.72 ± 0.08 to 6.98 ± 0.08 W/mK at 25°C and 7.36 ± 0.08 to 7.96 ± 0.08 W/mK at 300°C. These values were lower than those of crystalline SiC because of the amorphous nature of the matrix and the presence of pores and cracks.

Dilatometric model for determining the formation of austenite during continuous heating in medium carbon steel

A model was developed to predict the formation of austenite and dilatometric behavior during continuous heating in AISI 1045 steel, which has an initial microstructure composed of ferrite and pearlite. The model is proposed in two parts based on the heating rate and steel behavior to estimate the volume fraction of austenite during continuous heating. The first part of the transformation model is based on the diffusive model from Johnson–Mehl–Avrami–Kolmogorov at a heating rate interval of 0.083–0.383 °C s−1. The kinetic parameters k and n of the Avrami equation were considered to be dependent on the heating rate. In the second part of the model, the non-isothermal transformation rate model from Johnson–Mehl–Avrami–Kolmogorov was used for a heating rate interval of 0.383–1 °C s−1. The dilatometric behavior before and after austenite formation was associated with the instantaneous coefficient of thermal expansion for each phase or microconstituent present in the steel and during transformation, which was estimated using the volume fraction of austenite and a phase mixing rule. The dilatometric model considers a stage for homogenization of carbon into austenite based on an exponential diffusive model. A dilatometric curve analysis technique was used to determine the kinetic parameters, the instantaneous coefficient of thermal expansion, and the critical temperatures of the AISI 1045 steel. Finally, the model was validated by comparing its predictions with the dilatation deformation obtained in an experiment.

Determination on the Coefficient of Thermal Expansion in High-Power InGaN-based Light-emitting Diodes by Optical Coherence Tomography

The coefficient of thermal expansion (CTE) is a physical quantity that indicates the thermal expansion value of a material upon heating. For advanced thermal management, the accurate and immediate determination of the CTE of packaging materials is gaining importance because the demand for high-power lighting-emitting diodes (LEDs) is currently increasing. In this study, we used optical coherence tomography (OCT) to measure the CTE of an InGaN-based (λ = 450 nm) high-power LED encapsulated in polystyrene resin. The distances between individual interfaces of the OCT images were observed and recorded to derive the instantaneous CTE of the packaged LED under different injected currents. The LED junction temperature at different injected currents was established with the forward voltage method. Accordingly, the measured instantaneous CTE of polystyrene resin varied from 5.86 × 10−5 °C−1 to 14.10 × 10−5 °C−1 in the junction temperature range 25–225 °C and exhibited a uniform distribution in an OCT scanning area of 200 × 200 μm. Most importantly, this work validates the hypothesis that OCT can provide an alternative way to directly and nondestructively determine the spatially resolved CTE of the packaged LED device, which offers significant advantages over traditional CTE measurement techniques.

Thermal expansion behavior of new Co-based alloys and implications for coatings

Abstract The thermal expansion behavior of five γ′-(L12) containing Co-based superalloys was measured using push-rod dilatometry. These results were analyzed to determine the mean coefficient of thermal expansion (CTE), the instantaneous CTE, and γ′-solvus temperature of the alloys. The CTE was found to depend strongly on the γ′-solvus temperature. In turbine applications, these alloys will be part of a multilayer system that generates thermal stresses due to the CTE mismatch between the components. To investigate this phenomenon, the CTE data was incorporated into a thermo-mechanical model to calculate the energy release rate (ERR) for the delamination of coatings from these alloys. The ERR of a thermally grown oxide (TGO) formed on the bare and bond coated Co-based alloys was determined as a function of superalloy and bond coat CTE. The ERR of a thermal barrier coating (TBC) was evaluated as a function of temperature, superalloy CTE, and coating thickness. The ERR was found to be about 1.5 × greater in Co-based superalloys compared to Ni-based superalloys cooled from T = 1100 °C to ambient. Strategies for reducing the driving force for delamination are discussed.

Effect of pyrochemical chloride waste loading on thermo-physical properties of borosilicate glass bonded Sr-chloroapatite composites

Borosilicate glass (BSG) bonded composites of Sr-chloroapatite (SrApCl) and its simulated pyrochemical waste loaded compositions were synthesized by solid state reaction route. These compositions were characterized by XRD and SEM. Percentage (%) thermal expansion of the composites was measured by high temperature XRD (HT-XRD) and dilatometry. 10–16 wt.% waste loaded composites show minor variations in % linear expansion at 298–900 K. The composite with 10 wt.% waste loading and without BSG encapsulation exhibited slightly higher % of expansion compared to other compositions above 700 K. The coefficient of thermal expansion (αm) measured by HTXRD and dilatometry are found to be of the same order of magnitude. The % expansion measured by dilatometry shows higher values for waste loaded compositions compared to SrApCl; whereas values measured by HTXRD show a decreasing trend with respect to pristine SrApCl. The instantaneous coefficient of thermal expansion (αi) is used to determine the glass transition temperature (Tg) of the glass-bonded composites from the dilatometry data. The αi measured by HTXRD for the composites ranges from 2.40(1) × 10−7 to 9.51(2) × 10−6 K−1 along a-axis, 9.28(1) × 10−8 to 7.68(1) × 10−6 K−1 along c-axis and. αm measured by dilatometry ranges from 3.80(1) × 10−7 to 13.14(1) × 10−6 K−1.

Thermal expansion behavior of Ni–Al2O3 composites with particulate and interpenetrating phase structures: An analysis using finite element method

The thermal expansion behavior of Ni–Al2O3 composites was investigated up to 700°C using object-oriented finite-element method (OOF). Composites having particulate structure and interpenetrating phase structure (IPC) were studied. Three samples of each type of composite structure, with 40%, 60% & 80% Nickel, reinforced in Alumina were studied. In the present work, the instantaneous coefficient of thermal expansion (CTE) was predicted using OOF and thermo-elastic models of Kerner & Turner and the results were compared with the experimental values reported in literature.The CTE of metal–matrix composites is significantly influenced due to the presence of voids & the plastic deformation of matrix. Composites with porous microstructure were modeled as three phase composites containing nickel, alumina and porosity and the percentage of porous phase was obtained. The thermal stresses resulting due to the CTE mismatch of constituents, were analyzed by plotting the thermal stress contours.

Lattice thermal expansions of NpN, PuN and AmN

Lattice parameters of NpN, PuN and AmN were measured by a high temperature X-ray diffraction method from room temperature up to 1478 K. Linear thermal expansions of these TRU nitrides were determined as a function of temperature. The average coefficients of linear thermal expansion from 293 to 1273 K were 8.8, 11.1 and 11.2 × 10 −6 K −1 for NpN, PuN and AmN, respectively. The instantaneous coefficient of thermal expansion either at 293 or at 1273 K against the reciprocal decomposition temperature under 1 atm of nitrogen showed a linear relationship for TiN, ZrN, HfN, UN, NpN and PuN. Based on this relationship, the decomposition temperature of AmN was roughly predicted to be 2700 K.

Thermal expansion behaviour of aluminum matrix composites with densely packed SiC particles

Abstract The coefficient of thermal expansion (CTE) of Al-based metal matrix composites containing 70 vol.% SiC particles (AlSiC) has been measured based on the length change from room temperature (RT) to 500 °C. In the present work, the instantaneous CTE(T) of AlSiC is studied by thermo-elastic models and micromechanical simulation using finite element analysis in order to explain abnormalities observed experimentally. The CTE(T) is predicted according to analytical thermo-elastic models of Kerner, Schapery and Turner. The CTE(T) is modelled for heating and cooling cycles from 20 °C to 500 °C considering the effects of microscopic voids and phase connectivity. The finite element analysis is based on a two-dimensional unit cell model comparing between generalized plane strain and plane stress formulations. The thermal expansion behaviour is strongly influenced by the presence of voids and confirms qualitatively that they cause the experimentally observed decrease of the CTE(T) above 250 °C.

Instantaneous Coefficient of Thermal Expansion Determined by Temperature-modulated Dilatometry

Thermal expansion coefficients of Cu-Zn alloy, nickel and iron around the critical temperatures (structural or magnetic order-disorder transition) were measured by a push-rod type dilatometer (DIL) using modulated temperature profile. The temperature correction procedures were established from the experimental conditions measured at many frequencies. As a result, a multi-frequency temperature-modulated dilatometric experiment was established.

A computer study of the thermomechanical deformation behavior of a duplex steel

Specimens of ferritic-austenitic duplex steels with an anisotropic microstructure undergo irreversible length changes even under pure thermal cycling conditions. This unexpected behavior is due to the different coefficients of thermal expansion of ferrite and austenite which, upon thermal cycling, can generate stresses in the phases exceeding their yield strength. In this report, results of an extended elasto-plastic analysis of the thermomechanical deformation behavior of the duplex steel are presented. In addition to thermal loading, external tensile stresser smaller than the yield strength of the two phases are exerted on the microstructure. A full thermal cycle 900°C–20°C–900°C is analysed. The instantaneous coefficient of thermal expansion of the duplex steel depends on the applied load. It is shown that the combination of thermal and mechanical loads causes irreversible deformations. The amount of these deformations depends on the applied load. The deformations are identified as plastic deformations since the volume of the considered body is the same at the beginning and the end of the thermal cycle.

Viscosity of Dental Porcelains in Glass Transition Range

Changes in the viscosity of dental porcelain as a function of temperature are the controlling factor determining incompatible stresses in porcelain-fused-to-metal restorations. A new method was used to estimate viscosity using a viscoelastic analytical model that considers the relation between the heating rate and deformation temperature (Td) of dental porcelain with stress applied during heating. The activation energy of viscous flow and the viscous constant in the Arrhenius equation were calculated for six kinds of commercial body and opaque porcelains. The effect of the heating rate on the instantaneous coefficient of thermal expansion was also measured. Tg onset was graphically determined using data on thermal deformation and agreed well with the strain point as defined by viscosity. The data gathered in this study was also compared to the experimental results of previous works by others.

On nonlinear temperature‐dependence of thermal strain

AbstractFinite element calculation and the nonlinear temperature‐dependence of thermal strain are reviewed using basic principles. An approach for thermal strain calculation based on an instantaneous coefficient of thermal expansion, material description, is presented for incremental finite element analysis. The approach is then related to the current calculation method which uses a reference‐dependent mean expansion coefficient. Implications of the alternative approaches are discussed, and the principles are applied to actual expansion data for an epoxy. The paper is written to aid finite element analysts and code developers on thermal strain calculation.