High Thermal Expansion Coefficient Research Articles

Study on the removal behavior of constituent phases of SiCp/Al composites by ultrasonic vibration-assisted milling

SiCp/Al composites are widely used in aerospace, optical devices, electronic devices and other fields due to their excellent properties such as wear resistance, high specific strength and low thermal expansion coefficient. Due to the difference between the constituent phases of SiCp/Al composites and the high hardness of SiC particles, conventional milling (CM) leads to problems such as poor processing quality and severe tool wear. Ultrasonic vibration-assisted milling (UVAM) can achieve high-quality cutting of SiCp/Al composites. However, the relationship between constituent phases (SiC particles, Al matrix) and tool under ultrasonic vibration is complex and the research depth is insufficient. This paper focuses on the study of the interaction between the constituent phase of SiCp/Al composites and the tool in UVAM. The formation process of residual cutting zone and material removal mechanism in ultrasonic machining were analyzed, and the influence of ultrasonic vibration on the removal mechanism of SiCp/Al composites was explored from the aspects of tool cutting speed and tool kinetic energy. A three-dimensional micro-cutting model of SiCp/Al composite multi-particles was established, and the interaction between constituent phases and tool during cutting under different ultrasonic amplitude conditions was analyzed by finite element method and combined with a series of experiments. The results show that the introduced ultrasonic vibration increases the kinetic energy of the tool and improves the tool's ability to damage SiC particles and Al matrix. Compared with CM, UVAM significantly reduces surface pits, scratches, and SiC particle crushing defects, and the surface roughness Sa is reduced by 32.33 %. Tool wear is relieved, and the wear of the back tool face is reduced by 22.31 % at most. At the same time, the resultant milling force is also decreased 32.76 %. In short, the research in this paper is of great significance to improving the high-quality processing of SiCp/Al composites.

The influence of the elemental valence on the thermophysical properties of high entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings for thermal barrier application

Commercial yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are no longer sufficient for the stringent demands in the high operating temperature and excellent thermophysical properties of the high-performance gas turbines and aviation engines. High entropy ceramics, distinguished by their superior thermophysical properties, have risen as a potential substitute for TBCs. However, the realm of atmospheric plasma spraying (APS) in the creation of these advanced TBCs remains relatively unexplored. In this work, three distinct high-entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings were developed through the meticulous alteration of spraying power. The effects of spraying power on the microstructure, valence states of constituent elements and thermophysical properties of the coatings were deeply investigated. The results indicated that all the as-sprayed coatings exhibit a defect fluorite structure. Spraying power does have a significant impact on the thermophysical properties of the coatings. With the decrease in spraying power, the thermal conductivity of the coatings shows a progressive reduction, whereas the coefficient of thermal expansion (CTE) exhibits a gradual increase. This trend is closely related to valence states of constituent elements in the coatings. The resulting coating exhibits a low thermal conductivity of 0.54 W⋅m-1⋅K-1, a high CTE of 11.22×10-6·K-1 and a superior phase stability at elevated temperatures.

Optimization of the Thickness Ratio and Roll-Bonding Parameters of Bimetallic Ti/Al Rod for Bending-Dominated Negative Thermal Expansion Metamaterials

Roll-bonding has rarely been applied to prepare rods for negative thermal expansion metamaterials (NTEMs). Parameters for quantitatively assessing the isotropy and cyclic thermal stability of the thermal expansion coefficient α of NTEMs are lacking. Here, the Ti-to-Al thickness ratio in bimetallic rods for “cross-shaped” node bending-dominated NTEMs was optimized using a general model proposed in the literature. The finite element method was used to determine the optimal initial thickness ratio of the billet, as well as the reduction ratio and rolling temperature. NTEMs were prepared with roll-bonded Ti/Al rods and Ti nodes. A relatively high thermal expansion coefficient was obtained when the thickness ratio of the 7075 Al alloy of the rods was in the range of 0.56–0.60. The optimized roll-bonding process to meet this thickness ratio was as follows: a rolling temperature of 400 °C, a reduction ratio of 50%, and TA1 Ti and 7075 Al billet thicknesses of 0.5 mm and 1.5 mm, respectively. The isotropy and cyclic thermal stability ratios were proposed to quantitatively assess the isotropy and cyclic thermal stability of the NTEMs. These results help to expand the preparation and evaluation methods for NTEMs.

Thermal properties of fluoride fiber Bragg gratings at high to cryogenic temperatures.

The thermal sensitivity of fiber Bragg gratings (FBGs) is extensively employed in diverse industrial and scientific applications. FBGs lie at the core of flexible, low-cost, and highly precise sensors, featuring stability in harsh environments and distributed sensing capability. This study assesses the thermal properties of FBGs in fluoride fibers within a temperature range of 4-373 K. Despite having higher thermal expansion coefficients, FBGs in the near-IR wavelength range do not exhibit high sensitivity at room or higher temperatures. However, the pronounced enhancement of their thermal sensitivity at longer Bragg wavelengths shows the potential for sensing applications in the light of the fluoride glass extended transmission range up to 4-5.5 µm. Most importantly, employing FBGs inscribed in fluoride fibers enables the further expansion of fiber-based sensors to cryogenic environments, as they exhibit a detectable sensitivity of 0.5-1.7 pm/K below 50 K. Overall, the exposure to low temperatures provides valuable information on glass stability and physical parameters, which is beneficial for the further development of photonic systems based on fluoride fibers.

Continuously tunable negative pressure for engineering high-symmetry nanocrystalline phases

In this work, the phenomenon of strain induced by a mismatch in thermal expansion coefficients between a thin film and its substrate is harnessed in a new context, replacing the canonical planar support with a three-dimensional (3-D), nanoconfining scaffold in which we embed a material of interest. In this manner, we demonstrate a general approach to exert a continuously tunable, triaxial, tensile strain, defying the Poisson ratio of the embedded material and achieving the exotic condition of "negative pressure." This approach is hypothetically generalizable to materials of low modulus and high thermal expansion coefficient, and we use it here to achieve negative pressure in perovskite-phase CsPbI3 embedded within the cylindrical pores of anodic aluminum oxide membranes. Through controlled thermal hysteresis, the perovskite crystal structure can be continuously tuned toward higher symmetry when confined in a scaffold with pore size <40 nm, in contrast with the symmetry-reducing action of any other mechanical perturbation. We use this effect to control the octahedral rotation angle that is critical to the remarkable photovoltaic attributes of halide perovskites. Under hundreds of megapascals of apparent negative pressure, the bandgap tunability is observed to follow the same quantitative trend observed for hydrostatic positive pressure, exploring the negative pressure region and demonstrating the relative dominance of bond stretching effects over average octahedral rotation angle on electronic structure. This study reveals and quantifies the structural and electronic consequences of 3D tensile strain present by design and provides a framework for understanding adventitious strain present in all nanocomposite materials.

Preparation and optimization of La0.6Sr0.4Fe1-yCoyO3-δ cathodes for intermediate temperature solid oxide fuel cells

It is shown in this work that a synthetic route based on the auto-combustion of an ethylene glycol-metal nitrate polymerized gel precursor can be efficiently used to easily produce a range of La0.6Sr0.4Fe1-yCoyO3-δ nanopowders at moderate temperatures. We have been able to determine on air-sintered samples the effect of sintering temperature on the microstructure. At sintering temperatures as low as 1100 to1200 °C, grains are well defined with a uniform round spherical morphology and have a homogeneous sub-micrometer size distribution showing a highly densified microstructure. The electronic conductivity and thermal expansion coefficients (TEC) of sintered LSFC samples have been determined according to the variation of Fe/Co composition. Both measures clearly increase with the Co content. These materials also must exhibit chemical stability with electrolytes, most commonly used for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this way, the material as obtained is optimized in terms of chemical homogeneity and good stoichiometric control, microstructural characteristics of sintered samples, and finally the adequate Cobalt content to avoid high TEC mismatch with other components of the SOFC. This is a crucial issue as it causes an important thermo¬mechanical stress; promote extensive microcraking and significant performance degradation. Finally, these cathodes must exhibit acceptable electrochemical parameters for use in IT-SOFC.

Effect of SiC addition on the high-frequent cyclic ablation of C/C-AlSi composites

Components such as pistons in high-power diesel engines and barrels of rapid-fire weapons are often exposed to cyclic impacted high-temperature combustion. C/C-AlSi composites exhibit exceptional mechanical property, good particle erosion resistance and remarkable short-term anti-ablation ability. However, the cyclic ablation of the composite was primarily dominated by thermal stress damage between the alloy matrix and the carbon skeleton. In this study, SiC was utilized to mitigate such failures. C/C-SiC-AlSi composites were prepared by slurry impregnation method, and C/C-AlSi composites were also carried out for parallel comparison. The results indicate that the SiC and resin-carbon hybrids in the prepared composites are evenly distributed between the carbon fibers and the aluminium alloy matrix. Furthermore, the C/C-SiC-AlSi composites exhibit a greater density, a higher coefficient of thermal expansion and a better resistance to high frequent cyclic ablation. The mass ablation rate and linear ablation rate of the C/C-AlSi composites and the C/C-SiC-AlSi composites gradually decrease with increasing ablation time. When the ablation time is 200 s, the mass ablation rates of C/C-AlSi composite and C/C-SiC-AlSi composite are 0.20 mg/s and 0.12 mg/s, respectively. Compared to the two composites, the mass ablation rate of C/C-SiC-AlSi composite is reduced by approximately 40 %. The ablated morphologies indicated that the addition of SiC particles alleviated the thermal stress on the carbon skeleton and the alloy matrix, resulting in reduced mechanical damage.

Synergistic effect of pre-induced dislocations and ZrB2 on mechanical and thermal properties of Al/SiC composite

Al/SiC composites are considered promising materials for electronic packaging and thermal management systems, because of their high strength, low CTE, and high thermal conductivity. Despite of promising characteristics, these composites often come at the cost of ductility. To address these issues, varying content of ZrB2 was incorporated in Al/3 wt% SiC composite to fabricate high performance hybrid composites via powder metallurgy. Subsequently, the microstructure evolution, thermophysical, and mechanical properties were investigated in a systematic way. The result shows that the pre-induced dislocations were characterized in Al/3 wt% SiC/0.5 wt% ZrB2 composite, which was further quantitatively estimated by XRD peak broadening analysis. The synergistic effect of pre-induced dislocations and grain refinement brought on by ZrB2 contributed to increase hardness, elongation to fracture, and thermal conductivity, significantly. Most specifically, the hardness, ultimate tensile strength (UTS), elongation to fracture, and ultimate compressive strength (UCS) of Al/3 wt% SiC/0.5 wt% ZrB2 composite were increased to 25.9 %, 33.0 %, 245.8 %, and 32.2 %, respectively, when compared to Al/3 wt% SiC composite. In addition, thermal conductivity was increased to 226.9 W/m.K (53.7 %) and coefficient of thermal expansion (CTE) was slightly decreased, while linear thermal expansion remained consistent in the temperature range of 25–200 °C. The thermophysical properties of hybrid Al/3 wt% SiC/0.5 wt% ZrB2 composite enhanced due to the high thermal conductivity of ZrB2, grain refinement, and stabilization effect of dislocations on the thermal expansion. Therefore, it can be stated that the addition of ZrB2 have a positive influence on the hardness, strength and elongation to fracture while maintaining high TC. These promising characteristics making them appealing materials for electronic packaging and thermal management systems.

A Series of Ultra-low Permittivity ALaP4O12 (A = Li, Na, K) Metaphosphate Microwave Dielectric Ceramics for Ultra-wideband Dielectric Resonant Antenna Application.

The employment of ultra-low permittivity materials in the configuration of antennas has been demonstrated to augment the antenna bandwidth and diminish signal delay effectively. This study presents three ultra-low permittivity metaphosphate microwave dielectric ceramics (MWDCs). The ALaP4O12 (A = Li, Na, K) metaphosphate ceramics, which all belong to the monoclinic crystal system, exhibit extremely low permittivity (εr ≈ 5) and excellent quality factor (Q·f > 10,000 GHz) at a low sintering temperature (T < 950 °C). Terahertz time-domain spectroscopy indicates that the εr of ALaP4O12 at terahertz frequencies is comparable to that observed in the microwave band and its value remains stable over an extensive frequency range. Furthermore, the relationship between the crystal structure and the dielectric properties of ALaP4O12 has been analyzed through the lens of chemical bond theory. The highest Q·f value observed for LiLaP4O12 can be attributed to the high chemical bond strength and stability of its crystal structure. The lowest ionic polarizability per unit volume is exhibited by NaLaP4O12, which results in the lowest pore-corrected permittivity. The thermal expansion of the chemical bonds within KLaP4O12 is considerable, resulting in the highest coefficient of thermal expansion. Finally, the performance of a LiLaP4O12-based dielectric resonator antenna (DRA) excited by slot-coupled microstrip lines was designed and optimized by using different ceramic radius-to-height (RH) ratios. It was found that when the RH ratio of DRA reached 1.85, both the fundamental mode (HEM11δ) and the higher-order mode (HEM12δ) of DRA were simultaneously excited. The two modes overlap significantly, resulting in an ultra-wideband (UWB) of 46.8% (bandwidth = 7.93 GHz). Concurrently, the maximum radiation efficiency and gain of the DRA, obtained from the simulation, are 97.9% and 7.92 dBi, respectively. The findings of this study may inform the investigation of ultra-low permittivity phosphorus-based MWDCs and UWB DRAs.

Development of Interpenetrating Phase Structure AZ91/Al2O3 Composites with High Stiffness, Superior Strength and Low Thermal Expansion Coefficient

Development of Interpenetrating Phase Structure AZ91/Al2O3 Composites with High Stiffness, Superior Strength and Low Thermal Expansion Coefficient

Negative Thermal Expansion Realized by an Incomplete Bimaterial Ring

Incomplete bimaterial ring (a circular ring with a gap) capable of producing negative macroscopic thermal expansion is proposed and its behavior is analyzed. The ring exhibits negative thermal expansion (NTE) (in the plane of the ring) when the outer ring has higher thermal expansion coefficient than the inner one. When the thermal expansion coefficients are equal (monomaterial incomplete ring), the effective (macroscopic) planar thermal expansion becomes zero. (The complete thermal expansion will be positive but small.) It is the presence of the gap which is the basis of this thermal behavior. Similar effect can be achieved by spring or spiral structures where the role of the gap is played by the open ends. These structures will have higher stiffness than the incomplete bimaterial ring. The thermal expansion of the ring is characterized by the effective (macroscopic) coefficient of linear thermal expansion. The effective coefficient of linear thermal expansion depends on the temperature increase, making the thermal expansion nonlinear. Planar and 3D NTE structures are considered.

Effect of filer content on the thermal characteristics of underfill materials for Ball-Grid-Array component package

High-density integration and fast processing speed in the semiconductor industry have increased heat generation in electronic devices. Underfill materials, known for their high thermal conductivity and low coefficient of thermal expansion (CTE), offer a potential solution to dissipate heat and improve device reliability. In this study, we investigate the effect of filler content on the thermal reliability of underfill materials for ball grid array (BGA) component packaging. Mainly, we investigate the thermal conductivity, CTE, and mechanical properties of different filler contents of Al2O3 and Al2O3–BN hybrid underfills to facilitate heat dissipation and improve device reliability. The thermal conductivity of the underfill materials was evaluated by measuring the surface temperatures of underfill molded flip-chip light-emitting diodes (FCLEDs). The mechanical properties and thermo-mechanical reliability of the underfill materials were evaluated via a three-point bending test of the underfill packaged BGA components after the thermal shock test. The results showed that optimizing underfill properties based on specific application environments is crucial for obtaining enhanced thermal reliability and mechanical properties of underfill packaged BGA components.

Simulation of thermal stress predictions for NiTi coating on a stainless-steel substrate using thermal plasma spraying

Thermal stresses arise during the thermal plasma spraying of composite coatings, influenced by the differing thermophysical properties of the substrate and coating materials. This study focuses on a thick coating with a top NiTi layer and a base stainless steel (AISI 304) substrate, along with an epoxy carrier layer. Initially, the substrate is stress-free at the deposition temperature of 1400 °C. Once the coating is applied, the carrier layer activates at 150 °C, introducing thermal stresses before cooling to room temperature (20 °C). Using COMSOL Multiphysics, we examine stress distribution within the assembly at both 150 °C and room temperature. The model treats the thick plate as a two-dimensional solid, with layers assumed to be isotropic and linear elastic. The higher coefficient of thermal expansion in the substrate (17.3 × 10⁻⁶) compared to the coating (11 × 10⁻⁶) results in tensile stresses in the substrate and compressive stresses in the coating.

Synergetic effect of diamond particle size on thermal expansion of Cu-B/diamond composite

Diamond particles reinforced Cu matrix (Cu/diamond) composites have promising applications for heat dissipation of high-power electronic devices because of their high thermal conductivity and suitable coefficient of thermal expansion. The effect of diamond particle size on thermal conductivity has been addressed; however, the effect of diamond particle size on thermal expansion still needs to be clarified. In this study, Cu-B/diamond composites with various diamond particle sizes ranging from 66 μm to 701 μm were fabricated to assess the impact of diamond particle size on the thermal expansion behavior. The composites exhibit low and adjustable coefficient of thermal expansion (CTE) values of 4.58–6.63 × 10−6 K−1, which align with 4–8 × 10−6 K−1 of widely employed semiconductors. The CTE of the Cu-B/diamond composites first decreases and then increases with increasing diamond particle size, which arises from a synergetic effect of interfacial bonding strength and matrix strengthening effect. As the diamond particle size is smaller than 272 μm, the interfacial bonding strength rises with increasing particle size, enabling the diamond particles to restrain the expansion of the Cu matrix more effectively and to reduce the CTE. As the diamond particle size exceeds 272 μm, the dislocation density in the Cu matrix continually decreases with increasing particle size, reducing the strength increment in the Cu matrix and increasing the CTE. The effect of thermal cycling on the thermal expansion of the Cu-B/diamond composites was also investigated, and all the composites show an increase in the CTE after 100 thermal cycles. Notably, the composite with 272 μm diamond particle size exhibits the lowest CTE increment. It shows a CTE value of 5.29 × 10−6 K−1 after thermal cycling, still compatible with the semiconductors for electronic packaging applications.

High-pressure synthesis, crystal structure and anisotropic thermal/compressive behaviors of pseudo-ternary (V,Cr,Mo)P4

Pseudo-ternary CrP4-type (V,Cr,Mo)P4 was successfully synthesized at the conditions of 4 GPa and 900 °C by using a large volume multi-anvil-type press. SEM-EDS and STEM analyses revealed that the synthesized pseudo-ternary (V,Cr,Mo)P4 contains almost equimolar amounts of transition metals. The lattice parameters and unit cell volume of (V,Cr,Mo)P4 yield the average value of its end-members. The low-temperature (133 K–333 K) in-situ synchrotron XRD measurements demonstrated that the c-axis showed the highest coefficient of thermal expansion, followed by the b-axis and the a-axis. These thermal behaviors are the same as the binary end-members and pseudo-binary (V,Cr)P4. While from the high-pressure (P < 10 GPa) in-situ synchrotron XRD measurements, it was found that (V,Cr,Mo)P4 showed no phase transition and compression behaviors in which the c-axis was more compressible than the other two axes (b and a) and the b-axis was slightly compressible more than the a-axis. The zero-pressure bulk modulus of 106 (1) GPa and 122.1 (7) GPa were obtained for (V,Cr)P4 and (V,Cr,Mo)P4, respectively. MoP6 octahedral is highly distorted in comparison with VP4 and CrP4, thus the incorporation of MoP4 greatly yields incompressible behaviors of CrP4-type phosphides with respect to temperature and pressure.

Unraveling Superior Elasticity and Controlled Thermal Expansion in Trigonal MBO3 (M=Al, Ga) with Isolated [BO3] Group: A Theoretical Perspective

AbstractA comprehensive theoretical investigation employing density functional theory explores the electronic structure, temperature‐dependent elasticity, thermodynamic properties, and chemical bonding of trigonal MBO3 (M=Al, Ga) with isolated [BO3] groups. The results uncover MBO3 (M=Al, Ga) as indirect semiconductors with superior mechanical stability, characterized by greater resistance to volume compression over shear deformation. Their elasticity exhibits relatively weak temperature dependence, suggesting excellent thermal stability. Thermodynamic analysis predicts that GaBO3 has a higher thermal expansion coefficient than AlBO3, approximately 2.1×10−5 K−1 and 1.8×10−5 K−1 at 300 K, respectively. Significantly, the overall thermal expansion coefficients of GaBO3 and AlBO3 are lower compared to other borate materials containing isolated [BO3] groups. Chemical bonding insights reveal that GaBO3′s larger thermal expansion is attributed to its larger atomic displacement parameters and weaker Ga−O bond strength. This research positions MBO3 (M=Al, Ga) as prime candidates for optical device applications due to their well‐characterized elasticity and controlled thermal expansion.

Structure and tribological behavior of a polyetherimide/polytetrafluoroethylene matrix filled with negative thermal expansion zirconium tungstate particles

Thermal expansion mismatch stresses may be a reason for premature failure of sealing and bearing components made of polymer composites that are rubbed against metallic surfaces at elevated temperatures. It is of particular importance for polymer matrix composites loaded with anti-friction inclusions of polytetrafluoroethylene (PTFE) that possesses high coefficient of thermal expansion. In this regard, a study was undertaken to elucidate the effect of the thermal mismatch on wear and friction of amorphous polyetherimide (PEI) matrix loaded with either polytetrafluoroethylene (PTFE) particles (i) or PTFE particles covered with negative thermal expansion zirconium tungstate (ZT) α-ZrW2O8 (ii) at temperatures 23 °C, 120 °C and 180 °C. The ball-on-disk testing scheme was used according to standard with AISI 52100 steel balls rubbed against a polymer composite disks at normal force P = 5 N and sliding velocity V = 0.3 m/s. The PEI/PTFE/ZT composite demonstrated a tendency for wear rate (WR) reduction in sliding at 120 °C and 180 °C as compared to corresponding WR enhancement on the PEI/PTFE. The rationale is provided that the ZT additive effectively reduced thermal expansion of the PTFE in the PEI matrix and thus improved wear resistance of the composite. New thermal expansion-controlled wear and friction instability mechanism has been proposed and discussed.

Thermophysical properties of Yb3+-doped nonstoichiometric gadolinium zirconate ceramics

Low thermal conductivities and high thermal expansion coefficients are desirable for rare-earth zirconate thermal barrier coating materials. Introduction of cation doping and adjustment of the nonstoichiometry are efficient methods for enhancing the thermophysical characteristics of materials. Herein, the thermophysical properties of Yb3+-doped nonstoichiometric gadolinium zirconate ceramic materials were investigated using first-principles calculations and solid-state reaction techniques. As the Yb3+ content increases, additional cations enter the interstitial spaces (for excess Gd3+ gadolinium zirconate) and form vacancy defects (for excess Zr4+ gadolinium zirconate), which serve as phonon scattering centres to decrease the thermal conductivity. When Yb3+ is doped at the same concentration, gadolinium zirconate with excess Zr4+ exhibits a lower thermal conductivity. Specifically, Gd1.875Yb0.25Zr2.125O7 shows the lowest minimum thermal conductivity of 1.133 W/(m⸱K) (according to the Clark model) and 1.241 W/(m⸱K) (according to the Cahill model). In addition, the experimental results also suggest that the optimal content of Yb3+ is 0.25 excess Zr4+ gadolinium zirconate, which has the lowest intrinsic thermal conductivity of 1.037 W/(m⸱K) at 1300 K. Moreover, the thermal expansion coefficient of the Yb3+-doped excess Gd3+ nonstoichiometric material is greater than that of the doped excess Zr4+ material, this is due to the greater electronegativity difference between Yb3+ and Zr4+ than that between Yb3+ and Gd3+ and the lower binding energy of Gd-O than that of Zr-O. The experimental results and the calculated results are in good agreement. The aim of this work is to enhance the thermophysical characteristics of gadolinium zirconate ceramics for use as thermal barrier coating materials.

Thermal cycling property of the novel Hf6Ta2O17/YSZ TBCs prepared by atmospheric plasma spraying technology

Hf6Ta2O17, with low thermal conductivity, high thermal expansion coefficient, and excellent fracture toughness, was a promising candidate ceramic top coat material of thermal barrier coating (TBC). A novel Hf6Ta2O17/YSZ double ceramic top coat prepared by atmospheric plasma spraying (APS) was applied to study the role of the microstructure and mechanical property on the thermal cycling property at 1200 °C. Results show that the rapid decomposition of Hf6Ta2O17 occurred during the spraying process. As the increased spraying power, more HfO2 phases were observed in the Hf6Ta2O17/YSZ TBCs. Besides, the porosity of the Hf6Ta2O17 ceramic top coat decreased with the increased spraying power, resulting in the elastic modulus of the Hf6Ta2O17 ceramic top coat enhancement. The highest cycles at 1200 °C were obtained for the Hf6Ta2O17/YSZ TBCs with the lowest elastic modulus and least HfO2 phases, and were twice as long as the cycles of the single YSZ TBCs. The chemical reaction between HfO2 and Hf6Ta2O17 might have contributed to the cracking of the Hf6Ta2O17/YSZ TBCs. This work provides a new option for the preparation and development of the ternary oxides by APS.

The effect of carbon fiber length on the thermal expansion of fiber‐reinforced particulate hybrid composites

AbstractThermal expansion of materials is a critical factor influencing their dimensional stability. This study explores the regulation of thermal expansion in composite materials through the incorporation of carbon fibers and zirconium tungstate particles. The influence of fiber length on the thermal expansion behavior of these composites was investigated. The investigation reveal that the variation in the relative elongation ratio (dl/L0) of the carbon fiber‐reinforced zirconium tungstate composites is nonlinear, characterized by an initial increase, subsequent decrease, and a final resurgence. Notably, an increase in fiber length results in a mitigated rate of increase in the (dl/L0) ratio. Furthermore, composites fabricated with shorter fibers exhibit a higher coefficient of thermal expansion (CTE). Upon elevating the temperature to 250°C, the CTE for composites reinforced with 100 and 500 mesh carbon fibers escalate to 24.5 × 10−6/K and 74.6 × 10−6/K, respectively. These values represent an 8% and 116% enhancement relative to those measured at 50°C.Highlights The thermal expansion properties are improved by adding carbon fiber and ZrW2O8 nanoparticles. Utilizing fiber lengths ranging from 100 to 500 mesh effectively diminishes the CTE. The Cf‐ZrW2O8/9621 composite exhibits non‐linear behavior in its dl/L0 ratio. Within the range, longer fibers are more beneficial for reducing the CTE.