Thermal Expansion Curves Research Articles

Tuning the thermo-mechanical synergies effect of solid oxide fuel cells with negative thermal expansion NdMnO3 in La0.6Sr0.4Co0.2Fe0.8O3-δ-based symmetric electrode

Solid oxide fuel cells (SOFCs) are efficient and clean energy conversion devices, but one of the major challenges for their marketization is the instability of different component materials under high temperature operating conditions. The existence of a certain internal stress gradient between materials with different thermal expansion characteristics in the process of SOFCs from low temperature assembly to high temperature use is the main reason of this instability, leading to the inability of SOFCs to repeat start-stop and the rapid decay of long-term stability performance. To improve these problems, a creative concept of fuel cell interface overall regulation is proposed, simplifying the complex interface between different components of SOFCs into a unified and adjustable quasi-zero difference thermal expansion interface. The composite of high catalytic activity electrode material and high stability negative thermal expansion material is used for electrolyte support structure symmetrical cell, which makes the whole cell “sandwich” structure thermally and mechanically compatible. As a concept verification, the classic high catalytic performance electrode material La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), Gd0.2Ce0.8O2-δ (GDC) and NdMnO3 (NM) negative thermal expansion material with high chemical stability and mechanical stability were composited in equal proportions to form LSCF@GDC&NM electrode as the symmetrical electrode. After equal proportion compositing, the thermal expansion curve of LSCF@GDC&NM material can highly coincide with the thermal expansion curve of GDC, making the single cell with LSCF@GDC&NM electrode can withstand 25 power thermal cycles without significant performance decay, achieving 442 mW cm−2 at 800 °C and maintaining stably for 140 h without any degradation. These results show that using negative thermal expansion material to regulate electrode strategy is expected to make a whole zero difference thermal fuel cell configuration.

Influence of Thermally Aged Underfill on Flip-Chip Packages

Underfill material plays a crucial role in flip-chip package reliability, thus it necessary to accurately understand the mechanical properties. The material itself is nonlinear and is dependent on degree of cure, temperature, strain rate and thermal aging, among others. In this work, two underfill materials were characterized for thermal expansion and viscoelastic properties over a wide temperature range. A second set of each material was thermally aged through flip-chip processing steps and 250 thermal cycles and then characterized. Temperature dependent thermal expansion and timetemperature dependent moduli curves were generated to represent each material type. These material models were then implemented into a nonlinear finite element model of a flip-chip package to evaluate package stress interaction through processing steps and thermal cycling. The influence that each underfill material had with and without thermal aging was analyzed with respect to typical package failure mechanisms.

Carbide precipitation during tempering of hybrid steel 60

The effects of carbide precipitation on mechanical performance of Hybrid Steel 60, known as a novel bearing steel, have not been investigated. In this study, the austenite transformation temperatures of Hybrid Steel 60 during heating were revealed by the thermal expansion curve. The temperature and effective activation energy of the second phase precipitation were determined by the differential scanning calorimetry (DSC) curve. Different solid solution structures after austenitization were detected using various cooling rates. The solubility temperature was determined based on hardness and residual austenite content. The carbides precipitated at the peak temperature were qualitatively identified using XRD. It was discovered that the temperature points Ac1 and Ac3 of the steel were 786 °C and 864 °C, respectively. In addition, the effect of solid solution temperature on quenching hardness is minimal, while the cooling rate has a greater impact on hardness, reaching a peak at 5 °C s−1. The primary carbide phase in Hybrid Steel 60 is the M7C3 and VC. When the temperature ranges from 500 °C to 550 °C, M23C6 begins to precipitate. As a result, after tempering at 525 °C, the hardness peak value reached 566 HV.

Secondary Phase Precipitation in Fe-22Mn-9Al-0.6C Low-Density Steel during Continuous Cooling Process.

Secondary phase precipitation in Fe-22Mn-9Al-0.6C low-density steel was investigated during a continuous cooling process with different cooling rates through a DIL805A thermal expansion dilatometer, and the changes in microstructures and hardness by different cooling rates were discussed. The results showed that the matrix of the Fe-22Mn-9Al-0.6C was composed of austenite and δ-ferrite; moreover, the secondary phases included κ-carbide, β-Mn and DO3 at room temperature. The precipitation temperatures of 858 °C, 709 °C and 495 °C corresponded to the secondary phases B2, κ-carbide and β-Mn, respectively, which were obtained from the thermal expansion curve by the tangent method. When the cooling rate was slow, it had enough time to accommodate C-poor and Al-rich regions in the austenite due to amplitude modulation decomposition. Furthermore, the Al enrichment promoted δ-ferrite formation. Meanwhile, the subsequent formation of κ-carbide and β-Mn occurred through the continuous diffusion of C and Mn into austenite. In addition, the hardness of austenite was high at 0.03 °C/s due to the κ-carbide and β-Mn production and C enrichment, and it was inversely proportional to the cooling rate. It can be concluded that the presence of κ-carbide, DO3 and β-Mn produced at the austenitic/ferrite interface when the cooling rate was below 0.1 °C/s resulted in κ-carbide and β-Mn precipitating hardly at cooling rates exceeding 0.1 °C/s, which provides a guideline for the industrial production of Fe-Mn-Al-C low-density steel in the design of the hot working process.

Archaeometric characterization of pottery from the Houjiazhai site (ca. 7.3-5.7 ka BP), Anhui Province, China.

A combination of polarized light microscopy (PLM), X-ray diffraction (XRD), X-ray fluorescence (XRF), neutron activation analysis (NAA) and thermogravimetry (TG) was used on the pottery from the Houjiazhai site in Anhui, China. The analytical data demonstrate that the clay raw material of the Houjiazhai pottery clay was ordinary fusible clay. Phase I pottery consisted of shell-tempered pottery (with a high CaO content), plant-tempered pottery (with a high P2O5 content), and sand-tempered pottery. The pottery body of Houjiazhai was composed of quartz, feldspars, and minor amounts of mica. In addition, the shell-tempered pottery contains calcite. The results of the NAA analysis suggest that the samples from the two phases have the same place of production. The presence of calcite in the mixture indicates that the firing temperature for shell-tempered pottery from Phase I should not exceed 800 °C, while the thermal expansion curve shows that clay pottery from Phase II could reach 900 °C. Houjiazhai people have made progress in temperature control technology and can fire pottery with higher temperatures.

Aluminum-based ceramic/metal composites with tailored thermal expansion fabricated by spark plasma sintering.

We have devised a moderate temperature spark plasma sintering route for preparing aluminum matrix composites which possess tailored coefficients of thermal expansion (CTEs) in combination with tunable electrical and thermal conductivities. Due to its isotropic negative thermal expansion over a wide temperature range, cubic-phase ZrW2-xMoxO8 (x = 0.0, 1.0) is an ideal secondary phase for metal matrix composites with suitable CTEs. In this study, high-density ZrW2O8/Al and ZrWMoO8/Al composites containing 30-70 vol% Al were fabricated using spark plasma sintering. X-ray diffraction analysis indicated that the composites were composed of a thermally-stable cubic phase at temperatures as high as 873 K for ZrW2O8 and 773 K for ZrWMoO8, without any orthorhombic high-pressure phase derived from the large thermal mismatch between the ceramic and metal during sintering. The thermal expansion curves of the ZrW2-xMoxO8/Al composites were consistent with the predictions made using the Rule-of-Mixtures. The CTEs could be controlled from negative to positive and even close to zero by simply varying the volume fraction of aluminum. Similarly, the thermal and electrical conductivity of the ZrW2-xMoxO8/Al composites increases with increasing Al content, which is thought to be mainly related to the contribution of the free electron conduction path of Al in the composites.

Constitutive Equation for the Hot Deformation and Microstructure Evolution of 12Cr‐F/M Steel

Ferrite/martensite steel is an important material candidate for nuclear reactor claddings owing to its excellent mechanical properties and radiation resistance. In particular, the hot deformation behavior of 12Cr‐ferritic/martensitic (12Cr‐F/M) steel is crucial for the fabrication of cladding tubes, and experiments performed in a wide temperature range could reveal the possible thermal deformation behavior of 12Cr‐F/M steel during tube fabrication. Herein, hot compression experiments of 12Cr‐F/M steel are conducted with strain rates and deformation temperatures ranging from 0.005 to 5 s−1 and 750 to 1200 °C, respectively. According to the thermal deformation flow and thermal expansion curves of the alloy, the Arrhenius‐type constitutive equations before and after the phase transformation of 12Cr‐F/M steel are established, taking 950 °C as the critical point. The results show that for a strain rate of 0.5 s−1, the cooling intensity increases gradually with the deformation temperature. The ferrite transforms into a mixed structure of ferrite and pearlite and finally transforms into martensite. At 950 °C, the degree of austenitization of the alloy increases with the strain rate, and the texture changes from cubic to brass.

Mechanical and thermal expansion behaviour of TiC-reinforced CoCrFeMnNi high entropy alloy prepared by mechanical alloying and spark plasma sintering

ABSTRACT In this study, TiC-reinforced CoCrFeMnNi high-entropy alloy (HEA) composites were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The phase composition, microstructure, mechanical and thermal expansion behaviour of composite HEAs were investigated. The results reveal that the addition of TiC has no effect on the crystal structure, however, the microstructure and mechanical properties show a strong dependency on the TiC content. Compared to the original HEA, the composite HEA shows decreased grain size, resulting in TiC nanoparticles (NPs) retarding grain growth by pinning the grain boundaries. With increasing TiC content from 0 to 4 wt-%, significant increases in the hardness from 410 to 480 HV and compressive yield strength from 680 to 1100 MPa, which is mainly due to the grain boundary and dispersion strengthening effects. Moreover, the thermal expansion curves show linear increments up to 800°C and decrease with increasing TiC content.

Investigation on residual stress of EQ56 high strength steel butt weld

In the welding process of high-strength steel (HSS), the intense temperature change in joints induces the formation of welding residual stress (WRS), which increases the fatigue crack growth rate. Developing an effective finite element (FE) model for accurately predicting the WRS distribution is critical to improve the quality of welded structures. Experimental tests and numerical simulations were carried out to investigate the WRS distribution of EQ56 HSS. The thermal expansion curves at various heating and cooling rates were measured through thermal simulation experiments for achieving the continuous cooling transformation (CCT) diagram of EQ56 HSS. Based on the CCT diagram, the thermo-metallurgical-mechanical (TMM) FE model was developed to consider the influence of solid-state phase transformation (SSPT) on distribution and magnitude of WRS for welded EQ56 HSS joints, as well as material hardening law. Comparison of predicted WRS distribution and experimental data shows that plastic hardening laws of materials significantly affect the precision of WRS distribution, and combined hardening law gives most reliable prediction. The FE model considering SSPT behavior provides more accurate estimation of WRS distribution than those without considering SSPT behavior.

High-temperature behavior of the UV-luminescent sodalite-type natural compound Na8(Al6Si6O24)(HS)2: Comparative study by in situ single-crystal X-ray diffraction and Raman spectroscopy

The in situ single-crystal X-ray diffraction and Raman spectroscopy were performed for a sapozhnikovite Na8(Al6Si6O24)(HS)2, a rare mineral with sodalite-type crystal structure. The crystal chemical analysis and calculation of thermal expansion coefficients based on the refinement of Na8(Al6Si6O24)(HS)2 crystal structures in the temperature range of 300–1273 K show that this sodalite-type compound undergoes: (1) reversible phase transition P4‾ 3n ↔ Pm3‾n at 1223 K, (2) drastic increase of linear expansion coefficient at 1173 K, (3) non-elastic behavior of sapozhnikovite framework after cooling. The temperature dependencies of the unit-cell parameters were divided into two parts and described by quadratic a = 8.911(12) – 0.000018(33)T + 0.000000138(22)T2 (from 300 to 1173 K) and linear a = 7.765(13) + 0.001130(11)T (from 1173 to 1273 K) polynomial functions. Raman spectroscopy data reveal the partial transformations of the extra-framework HS− anion by follows reactions: 6HS–→ S3•– + 3H2S (gas) and 2HS– – 2e → S22− + 2H+. These transformations may cause the observed discontinuity in the thermal expansion curve for sapozhnikovite at 1173 K with drastic increase of linear expansion coefficient and not fully elastic behavior of framework after removal of temperature exposure. After the heat treatment experiments (300–1273 K) the HS− anion restores in the β-cage of sapozhnikovite crystal structure. In the synthetic analogue of sapozhnikovite the heat treatment leads to the irreversible transformation according to the reactions: 2HS– + 2.5O2 (gas) → SO42− + 0.25S4 + H2O (gas) and 2HS– + 3.5O2 (gas) → SO42− + SO2 (gas) + H2O (gas). The orange luminescence of Na8(Al6Si6O24)(HS)2 is stable up to the 1073 K.

Investigation on the dislocation, thermal and mechanical properties, and crystal growth stress of Zr:GdTaO4 scintillator

The dislocation, thermal and mechanical properties, and crystal growth stress of the new heavy scintillator Zr:GdTaO4 (Zr:GTO) grown by the Czochralski method were systematically studied. The chemical etching experiment exhibits that the dislocation morphology of Zr:GTO is quadrilateral, whose causes were explained by the surface energy of the crystal faces calculated with the first principle. The thermal diffusivities of Zr:GTO along <1 0 0> and <0 0 1> directions are similar to each other and larger than that along <0 1 0> direction. The thermal expansion coefficient of Zr:GTO crystal along the crystalline axis presents a large anisotropic feature. And the thermal expansion curves demonstrate that the phase of Zr:GTO is transformed at 1650 K, which suggests that its annealing temperature should be lower than 1650 K to avoid crystal cracking. The thermal and mechanical properties are anisotropic, which causes the crystal to crack during growth and cooling. The thermal stress of Zr:GTO crystal during the growth and cooling stages was studied by numerical simulation for the first time. The results indicate that the thermal stress results in seed bending and cracking near the interface of the iridium rod and the crystal seed, and the crystal seed should be as short as possible to reduce thermal stress. Meanwhile, the cooling rate after crystal growth was optimized numerically. For Zr:GTO crystal with a size of Ø25 mm × 30 mm, uniform cooling for 48 h may be optimal. All the obtained results are of great significance for the growth and applications of high-quality Zr:GTO scintillator.

Experimental Investigation on the Inhomogeneities of Transverse Microstructure and Internal Stress of High‐Strength Low‐Alloy Hot‐Rolled Strip

Herein, the evolution of transformation in the width direction of high‐strength low‐alloy hot‐rolled strip is studied by using thermomechanical simulation, and the temperature, microstructure, and internal stress are correlated based on electron backscatter diffraction data. The temperature and time range of the transverse transformation are determined based on the thermal expansion curve. The results show that the transformation at the edge of the steel plate ends earliest and that at the plate center begins at the latest; only 31.9% austenite undergoes transformation at the plate central by the end of laminar cooling. The fraction of transformed austenite at the plate center is the least throughout the laminar cooling process. The proportion of small grains (within the grain size range of 0–4 μm), mean, and variant coefficient of grain sizes at the plate edge are 75%, 4 μm, and 1.29, respectively. In contrast, those values of the central region are 66%, 4.4 μm, and 1.05, respectively. The correlation between temperature and internal stress evolutions is established. It is demonstrated that the internal stress increases monotonically with the average transformation rate.

THERMAL STABILITY AND THERMAL EXPANSION BEHAVIOR OF AlFeCoNiCu AS-CAST HIGH-ENTROPY DUAL-PHASE ALLOY

This work is devoted to the thermal stability and thermal expansion of dual-phase AlFeCoNiCu as-cast high-entropy alloy of equiatomic composition. The mix FCC + BCC phases is in AlFeCoNiCu high entropy alloy. According to characterized by EDS-analysis, Fe and Co are almost uniformly distributed in both phases in comparison with other elements. The BCC phase is rich in Ni and Al, and the FCC phase is Cu. Our measurement results of hardness and elastic modulus values for inter dendrites (FCC phase) and dendrites (BCC phase) of as-cast AlFeCoNiCu alloy showed the difference between there. Hardness values for inter dendrites and dendrites: 3.4±0.4GPa and 4.1±0.6GPa. Elastic modulus values for inter dendrites and dendrites: 130.5±2.0GPa and 166.5±5.6GPa. The thermal stability of the phases presented in AlFeCoNiCu as-cast high-entropy alloy has been studied with dilatometry and differential scanning calorimetry (DSC). The DSC thermogram shows an endothermic peak at 1000K. The coefficient of thermal expansion (CTE) curve shows linear increment from room temperature up to 1370K from (10.6 ± 0.3)×10-6K−1 to (27.7 ± 0.3) ×10-6K−1. The CTE temperature curve also shows the peak at 1000K. The peaks in the CTE temperature and the DSC curve suggest a phase transformation with increasing temperature up to~1000K.

Abnormal thermal expansion behaviour and phase transition of laser powder bed fusion maraging steel with different thermal histories during continuous heating

Although maraging steel materials have been widely used in the laser powder bed fusion (LPBF) process, there are few reports on the behaviour of thermal expansion, which is an important indicator for materials used in machinery, moulds, aerospace, new material development, etc. The unique process of LPBF causes the difference in performance between LPBFed parts and their traditional counterparts. In this regard, thermal expansion is an important factor for phase transition investigation. In this study, a highly sensitive computer-controlled dilatometer was used to systematically study the thermal expansion behaviour along different orientations during continuous heating and corresponding phase transition. The scanning electron microscope, electron backscatter diffraction and microhardness testing were used to study the fine cellular/columnar structures, martensite lath, textures and formation mechanism of precipitates in the as-built and heat-treated samples. The results show an abnormal thermal expansion behaviour and phase transition during continuous heating for both samples with different building directions. For the as-built and direct ageing-treated OX samples (parallel to the building direction), the first step reversion of martensite to austenite is much stronger than the second step. After solution treatment and solution+ageing treatment, both OX and OZ (perpendicular to the building direction) samples display similar thermal expansion curves and a typical two-step martensite-to-austenite reversion. The increase of the austenite phase during the heating process leads to a quick shrinkage with a negative coefficient of thermal expansion (CTE) in the solution-treated and solution+ageing-treated OX samples. However, a very small shrinkage with a positive CTE appears in the as-built and direct ageing-treated OZ samples. Overall, the as-built and ageing-treated samples show differences in phase transition due to precipitation behaviour.

The Effect of Stress on Ferrite Transformation During the Continuous Annealing of DP780 High-Strength Steel

Continuous cooling transformation curves for DP780 high-strength steel were drawn by combining measured thermal expansion curves, microstructures and hardness values. Annealing experiments for DP780 highstrength steel under three different stresses of 0 MPa, 10 MPa and 20 MPa were carried out using Gleeble 3500, and a transformation kinetics model of austenite to ferrite was established by considering the effect of stress at low cooling rates. Then, based on the finite element platform and secondary development, the continuous annealing process of DP780 high-strength steel under various stress states was simulated. The results show that the applied stress has significant effects on the ferrite transformation of DP780 high-strength steel. With increasing tensile stress, the transformation plasticity of ferrite becomes more obvious. The simulation results coincide with the measurement. It is thus proven that the numerical model can correctly reflect the deformation and transformation laws during the heat-treatment process and lay a foundation for further numerical simulations of the heat-treatment process of high-strength steel.

Flux Growth and Properties of Volatile Bromine-Containing UV Nonlinear Optical Crystal K3B6O10Br

A UV Nonlinear optical (NLO) crystal is one of the key devices in all-solid-state laser technology, and borate halides show outstanding potential due to their abundant structural diversity and short UV cut-off edges. In this article, the sizable UV NLO crystal of K3B6O10Br (KBOB) has been grown with lead-containing and lead-free fluxes systems using the high-temperature top-seeded solution growth (TSSG) method. Energy Dispersive X-ray Spectroscopy (EDS) and transmittance spectra illustrate the influence of Pb2+ ions on the transmittance properties and laser-induced damage threshold (LDT). The thermal property, namely, thermal expansion, thermal conductivity, and thermal diffusivity curves, were characterized. Moreover, a small variation of thermal refractive indexes was analyzed to illustrate the advantage of KBOB in the application for temperature-fluctuated specific regions.

Effect of Volume Fraction Whiskers on Tensile and Thermal Expansion Properties of Mg2B2O5 Whisker-reinforced Aluminum Composite

This paper prepared magnesium borate whisker reinforced aluminum matrix composites by extrusion casting, and studied the effects of the volume fraction of the reinforced phase on the mechanical properties, thermal expansion properties and microstructure of the composites. The test results show that the reinforced magnesium borate whisker in the composite can be uniformly dispersed in the aluminum matrix to improve the strength. With the increase of the volume fraction, the strength of the composite material increases and the plasticity decreases. When the whisker volume fraction is 30%, the strength of the composite material reaches the maximum, with its tensile strength reaching 244 MPa and elastic modulus 107.6 GPA. When the whisker volume fraction is 20%, the composite has the best plasticity and the fracture elongation is 0.47%. The thermal expansion curve of the composite shows that the increase of whisker volume fraction will reduce the thermal expansion coefficient of the composite.

Investigation on structure and properties of nitride-tin-boron-fluorophosphate glass for low-temperature sealing

Glass with composition of 45 P2O5–53SnF2–2B2O3 (mol%) was prepared by using the one-step melt quenching method. The effect of nitrogen on tin-boron-fluorophosphate glass was investigated. Full characterizations have been carried out by the XRD and FTIR, as well as by the XPS spectroscopies. Infrared results reflected that intensity of the P = O bonds and bridging oxygen declined since the oxygen was replaced by nitrogen. XPS results suggested transformation in the bond type of glass network. The new P-N and P = N bonds was proved to exist in structure. Differential scanning calorimetry (DSC) of glass showed that the transition temperature increased with the increasing NH4H2PO4 content. Similar tendency was observed in results of thermal expansion curves (TEC), Tf =160.1℃. The weight loss of bulk glass decreased as the concentration of NH4H2PO4 increased. This work proves that the nitride tin-boron-fluorophosphate with satisfied properties has potential to be low-temperature sealing material.

Study on Mechanical and Thermal Expansion Properties of Oxide Coated Magnesium Borate Whiskers Reinforced Aluminum-based Composite

The surface of magnesium borate whiskers was coated with oxide coatings of different components by chemical precipitation method, and magnesium borate whisker-reinforced aluminum-based composites were prepared by squeeze casting method. The compressive deformation resistance of the prefabricated whisker and the tensile and thermal expansion properties of the composite were tested. The experimental results show that the oxide coating can effectively improve the anti-deformation ability of the whisker preform, and the whisker preform prepared by MgO and Al2O3 coating has better strength, and the compressive strength at room temperature reaches 0.98 MPa and 0.96 MPa. The composite material prepared by Al2O3 coated whiskers has the highest room temperature tensile strength of 263 MPa, and the composite material prepared by ZnO coated whiskers has the lowest room temperature tensile strength of 224 MPa. The thermal expansion curve of the composite material shows that as the temperature increases, the thermal expansion coefficient of the composite material gradually increases, and the thermal expansion coefficient of the composite material decreases slightly after a temperature cycle.

Thermal stability and thermal expansion behavior of FeCoCrNi2Al high entropy alloy

Present work reports the thermal stability and thermal expansion behavior of dual-phase FeCoCrNi2Al HEA prepared by Mechanical Activated Synthesis and consolidated by hot pressing. The thermal stability of the phases present in FeCoCrNi2Al HEA has been extensively studied using in-situ high-temperature X-ray diffraction (HT-XRD) in conjunction with dilatometry and differential scanning calorimetry (DSC). The DSC thermogram shows a single endothermic peak at 1430 °C (1703 K) which belongs to the melting point of the alloy. HT-XRD and dilatometry experiments were carried out from room temperature to 1000 °C (1273 K). HT-XRD study has shown that the room temperature FCC + BCC (face-centred cubic + body-centred cubic) phases remains stable up to 1000 °C (1273 K). Although the amount of BCC phase has increased above 800 °C (1073 K), no additional phase formation was observed in HT-XRD. The coefficient of thermal expansion (CTE) curve shows linear increment up to 1000 °C (1273 K) with a slight change in slope beyond 800 °C (1073 K). Theoretical CTE was computed using the lattice parameter of the FCC phase, obtained from HT-XRD, as a function of temperature and compared with experimental CTE. Third-order polynomial equation was fitted to the experimental CTE data and the constants were evaluated which can be used to predict the coefficient of thermal expansion of the alloy.