Carbon Fiber Reinforced Silicon Carbide Research Articles

Notch sensitivity of C/C-SiC composite evaluated by flexural tests

The notch effects on the mechanical behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (C/C-SiC) was studied. The in-plane (IP) and out-of-plane (OP) flexural properties of notched and unnotched samples with fiber orientations (0°, 45° and 60°) were determined through 3-point-bending (3PB) and single notched beam (SENB) tests. Despite the significant difference in bending modulus, the strength depends only slightly on the fiber orientation and loading direction, which could be explained through the uneven distribution of SiC-matrix within the block-like structure of C/C-SiC. This unique micro-structure also leads to a relatively constant value of notch sensitivity in the IP direction, and the sensitivity to the notch is relatively low for all tested C/C-SiC specimen configurations. Furthermore, due to the large differences of fracture mechanism, the work of fracture (WOF) in the IP direction is significantly smaller than in the OP direction for all fiber orientations.

Experimental and numerical studies on low-velocity impact of laminated C/SiC structures

Laminated C/SiC(carbon fiber reinforced silicon carbide composites) has the complicated nature of composite failure which include cracks for void defects at the meso and micro scales, complex cracks propagation of tunnel cracks, matrix cracks, delaminations and fiber cracks, orthotropic, and pseudoplastic behavior. It has technical challenge to solve all of them for complicated-mechanics problems by using multi-scale methodology. This paper focused tackling it by a model that lies between macro and meso scales, and proposed a new conceptual 3D FE-PDM(Finite Element - Progressive Damage Method). 3D FE-PDM was validated by the experiments of low-velocity impact of 2D C/SiC and 3D needled C/SiC. Damage initiation and evolution were controlled by strain in order to preventing stress chaos which could occur as cracks leading local stress relief. The multi-linear constitutive relations were adopted in orthotropic directions. The coupled effects of stresses between in-plane and out-of-plane were computed by adding damage coefficients into stiffness matrix. Cohesive Zone Method was used for delamination. The PDM approach was introduced for the 3D elements for intralaminar and cohesive elements for the interfaces. A parametric inversion methodology was put forward to determine the model parameters iteratively by comparing simulation results with the load-time curves, damage CT details of the experiments. Validation implies that, with small number of parameters, 3D FE-PDM is able to predict damage initiation of each phase knee, damage evolution, and load–displacement curve with good convergence for the low-velocity impact case. 2D woven and 3D needled non-woven C/SiC both have impact energy threshold and different damage evolution types.

In-situ joining of carbon fiber reinforced silicon carbide composite to Ni-based single-crystal superalloy by active unidirectional casting technology

Aiming to join large-scale Cf/SiC with a complex joining structure to SC CMSX-6 superalloy, a novel active unidirectional casting technology was developed to in-situ form a joint with satisfactory bonding strength. The integrity of the single crystal (SC), interfacial structure, phase formation, and high-temperature mechanical property were studied. The results demonstrated successful formation of a complete CMSX-6 SC structure with a crystallographic orientation deviation of 13.2° from the (001) direction, joined with Cf/SiC. A gradient reaction interlayer composed of γ/γ΄ matrix, AlN, Cr3C2, and TiMoC2 phases was formed. The maximum tear strength of the joining interface reached 32.9 MPa at 750 °C, approximately 2.5 times larger than the interlaminar bonding strength of Cf/SiC. This satisfactory mechanical property was attributed to the pinning effect resulting from the infiltration of molten CMSX-6 into Cf/SiC and reduced thermal stresses facilitated by the formed gradient bonding interface.

Processing-microstructure correlations in material extrusion additive manufacturing of carbon fiber reinforced ceramic matrix composites

Liquid silicon infiltration is a cost-effective manufacturing route for carbon fiber reinforced silicon carbide (C/C-SiC)11C/C-SiC: carbon fiber reinforced silicon carbide, which is a ceramic matrix composite with high specific stiffness associated with damage tolerance. To reduce the cost-intensive machining while improving the geometric freedom of design, a processing route for C/C-SiC based on material extrusion additive manufacturing was investigated. Filament-based material extrusion was applied to manufacture green bodies made of short carbon fiber reinforced polyetheretherketone (PEEK)22PEEK: polyetheretherketone. Additionally, a thermo-oxidative crosslinking step, which is assumed to be a function of the specific surface area, was introduced prior to pyrolysis to prevent the re-melting of PEEK. Via computer-aided image analysis, the influence of process parameters during material extrusion on the green bodies’ specific surface area were investigated using statistical design of experiments. It was shown that it is possible to selectively adjust the specific surface area by modifying the microstructure of the carbon fiber reinforced green bodies and hence the shrinkage during pyrolysis, the liquid silicon infiltration kinetics as well as the phase composition of the obtained C/C-SiC. The understanding of the processing-microstructure correlations enabled an improvement of the mechanical properties. With a layer height of 0.1 mm, an infill density of 100% and a printing direction of ± 45°, a flexural strength of 80.3 ± 6.7 MPa was measured.

Effect of tool wear on machining quality in milling Cf/SiC composites with PCD tool

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have great application potential in aerospace. But their high hardness and anisotropy cause rapid tool wear during machining, which affects machining quality and efficiency. However, tool wear mechanisms in milling Cf/SiC composites are still unclear. There is a lack of research on the relationship between tool wear and cutting performance. In this paper, milling experiments on 2.5D Cf/SiC composites were conducted using polycrystalline diamond (PCD) cutters. The tool wear mechanisms and effect of tool wear on surface roughness, milling force, burr damage, surface microstructure and chips were explored. The results show that abrasive wear caused by chips continuously scraping tool material and diamond particle fragmentation and falling off caused by sprouting and expansion of cracks inside grain were primary causes of tool failure. The formation mechanism of burr damage was analyzed. It was proved that the peak radius of cutting edge Rpeak and flank wear VB could reflect cutting capabilities. It was found that increasing flank wear had regrinding effects on the cutting edge, which affects the peak radius. The degree of burr damage was related to these two parameters. Tool wear changed the surface formation mechanism. Before tool wear, carbon fibers were primarily removed through the micro-brittle fracture, with low surface roughness. The flank face and chips scratched the workpiece like abrasive grains after tool wear, leaving scratches on the surface and increasing surface roughness from 1.27 μm to 2.25 μm.

Additive manufacturing of continuous carbon fiber-reinforced silicon carbide composite by fused filament fabrication and precursor infiltration pyrolysis

Continuous fiber reinforced silicon carbide composites (Cf/SiC) are known for their advantages such as high strength, high modulus, high thermal conductivity, and low density. In this paper, we propose an integrated Cf/SiC preparation and processing process. The continuous carbon fiber-reinforced resin matrix composite green parts were processed by fused filament fabrication, and then ceramicized by precursor infiltration pyrolysis process. The processing parameters of the green parts, the performance of the green-part specimens, the phase evolution in the post treatment, and the performance of Cf/SiC samples were investigated. The infill line distance (ILD) had a huge influence on the mechanical properties of green parts and Cf/SiC. The bending strength of the green parts and the Cf/SiC specimens increased with the decrease in ILD. The maximum bending strength of 169.48 MPa and 155.83 MPa was achieved for the carbon fiber/polyethylene terephthalate glycol (Cf/PETG) and polylactic acid (Cf/PLA) green parts, respectively. The highest bending strength of 47.73 MPa of the Cf/SiC material was obtained with the Cf/PLA green parts, while the bending strength of 93.79 MPa was obtained for the Cf/SiC with Cf/PETG green parts. The increase in mechanical properties was believed to result from the pyrolyzed carbon brought by PETG and the increase of the equivalent fiber density within the single layer after a larger nozzle size was used.

Novel approach for ceramic matrix composites – Cf/PEEK hybrid yarn-based C/C-SiC

To fabricate a C/C-SiC (Carbon fiber-reinforced Silicon Carbide) with favorable mechanical properties via the Liquid Silicon Infiltration process, it is crucial to focus on the first fabrication step, the creation of a CFRP (carbon fiber-reinforced plastic). Hence, the selection of a fitting polymer is essential. Besides thermosets, thermoplastics can be used as matrix material. Nevertheless, the high melt viscosity of thermoplastics leads to problems regarding the fiber bundle infiltration. This study shows for the first time that this problem can be avoided by using C/C-SiC based on a novel short fiber Cf/PEEK fiber hybrid yarn. The yarn was warm pressed into a CFRP, pyrolyzed and infiltrated with C/C-SiC. The product of each processing step was characterized with a focus on the analysis of the microstructure. Additionally, for the C/C-SiC, three-point bending tests were conducted. Those results were simular compared to reference literature.

Transition of in-plane compressive strength and failure mechanism of 2D-C/SiC: Influence of off-axis loading angle and loading rate

In this study, the in-plane compressive behavior of two-dimensional plain-woven carbon fiber-reinforced silicon carbide composite (2D-C/SiC) was investigated using on- and off-axis compression experiments under both quasi-static and dynamic loading conditions. The failure mechanisms were elucidated through in-situ observations and microanalysis-based methods. As the loading angle increased from 0 to 45°, stress–strain curves exhibited stronger nonlinearity, and the in-plane compressive strength decreased by 50.2% and 41.1% under quasi-static and dynamic loading conditions, respectively. The failure mechanism shifted from fiber-dominant to interface- and matrix-dominant as the loading angle increased, which was responsible for the strength degradation and intensified nonlinearity in curves. A positive strain rate effect on the in-plane compressive strength attributed to the interface enhancement and multiple crack propagation was identified. Additionally, owing to the competition between the dynamic strengthening and damage aggravation effects, the strain-rate sensitivity factors increased with the loading angle up to 30° and then decreased at 45°.

On understanding the mechanical properties and damage behavior of Cf/SiC composites by indentation method

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have the advantages of high temperature resistance, wear resistance, low density, high hardness as well as specific strength. They have been applied extensively in hot-end components of aerospace and braking systems of trains. Nevertheless, grappling with the anisotropy, non-homogeneity, and weak interlayer bonding of Cf/SiC composites presents a major challenge for achieving efficient and low-damage processing. This paper is primarily intended to investigate comprehensively the mechanical properties and damage behavior of Cf/SiC composites by nanoindentation and Vickers indentation tests. The behaviors of indentation damage on the longitudinal section of fiber (LSF), the cross-section of fiber (CSF) and matrix under different loads and the deflection mechanism of matrix crack were analyzed. The findings reveal a pronounced anisotropy between the radial and axial orientations of the fiber, and plastic deformation exists in the matrix. Furthermore, the matrix has the largest hardness and elastic modulus, while the LSF displays the lowest values among the composites. The main forms of indentation damage on the LSF are fiber crack, fiber peel off, fiber cocked up and squamous crack. The main manifestations of indentation damage on CSF are fiber crushing and fiber debonding, with the total surface damage area being comparatively limited. The fiber orientation and interface are influential factors in the crack propagation path of matrix. Notably, the fibers effectively inhibit the crack propagation of the matrix. This investigation provides valuable theoretical guidance for the formation mechanism and suppression strategy of machining damage in Cf/SiC composites.

Large-scale material extrusion-based additive manufacturing of short carbon fibre-reinforced silicon carbide ceramic matrix composite preforms

ABSTRACT Large-scale short carbon fibre-reinforced silicon carbide (Csf/SiC) ceramic matrix composites (CMCs) have important applications in the field of aerospace engineering. This study proposed the use of material extrusion based additive manufacturing to fabricate large-scale C sf/SiC CMC preforms. In this paper, we determined how the key material extrusion parameters, including solid loading, nozzle diameter and layer height impact the stability of the additively manufactured C sf/SiC CMCs. The solid loading significantly influenced the stability of the C sf/SiC CMCs, and the slurry with 50 vol.% solid loading was better for additive manufacturing. The layer height played a significant role in the void formation in CMCs. It was appropriate for structure retention to set the layer height as 60–75% of the nozzle diameter. The effect of angle from vertical on the stability of out-of-plane structure was also investigated. When the angle was over 40o, the out-of-plane structure additively manufactured without supports tended to collapse. Large-scale C sf/SiC CMC preforms with out-of-plane structures were finally successfully fabricated. This study is believed to provide some fundamental understanding for the fabrication of large-scale fibre-reinforced ceramic matrix composites.

A focused review on the tribological behavior of C/SiC composites: Present status and future prospects

Silicon carbide-based ceramic matrix composites have received extensive attention in recent years. Many excellent reviews have reported on the tribological behavior of carbon fiber-reinforced carbon and silicon carbide dual matrix (C/C-SiC) composites. However, a systematic overview of the tribological properties of carbon fiber-reinforced silicon carbide (C/SiC) composites does not exist. This review focuses on C/SiC composites and summarizes the key factors, including internal factors (constituent content, graphitization process, material structure and fiber direction), and various test conditions (pressure and speed, dry and wet, temperature, and counterparts) that affect their tribological behavior. Their wear mechanisms under different conditions are elaborated. Finally, some potential future development directions for improving the performance of C/SiC composites are proposed to provide high-quality ceramic matrix composites for engineering applications. These directions include structural modification, matrix modification, coating technology, laser surface texturing, and material genome method.

Additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic composites

AbstractA material extrusion (MEX) technology has been developed for the additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic (Cf/SiC) composites. By comparing and analyzing the rheological properties of the slurries with different compositions, a slurry with a high solid loading of 48.1 vol% and high viscosity was proposed. Furthermore, several complex structures of Cf/SiC ceramic composites were printed by this MEX additive manufacturing technique. Phenolic resin impregnation–carbonization process reduces the apparent porosity of the green body and protects the Cf. Finally, the reactive melting infiltration (RMI) process was used to prepare samples with different Cf contents from 0 to 2 K (a bundle of carbon fibers consisting of 1000 fibers). Samples with Cf content of 1 K show the highest bending strength (161.6 ± 10.5 MPa) and fracture toughness (3.72 ± 0.11 MPa·m1/2) while the thermal conductivity of the samples with the Cf content of 1 K reached 11.0 W/(m·K). This study provides a strategy to prepare Cf/SiC composites via MEX additive manufacturing and RMI.

Design of discrete-edge polycrystalline diamond tool and its cutting performance in milling Cf/SiC composites

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites are used extensively in many fields because of their superior properties, such as high specific strength and high specific modulus. However, Cf/SiC composites are typically difficult to machine materials due to their high hardness and anisotropy. Its machining easily leads to high cutting force, short tool life, and poor surface quality. The tool structure shows a significant impact on the cutting performance, which can further affect the cutting force and surface quality. In this study, a novel polycrystalline diamond (PCD) tool with discrete-edge structure was designed for milling Cf/SiC composites, which was devised with tiny microgrooves on the peripheral edge, and the geometric parameters were optimized by finite element simulation method. The cutting performance of the designed discrete-edge PCD tool in milling of Cf/SiC composites was studied. Cutting force, machined surface quality, tool wear mechanisms, and tool life were comprehensively investigated. Comparative experiments were also carried out with conventional straight-edge PCD tools by using identical cutting parameters. The cutting force when using the discrete-edge PCD tool gradually decreased with increasing cutting speed. The machined surface roughness Sa reached 3.5 μm at cutting speed of 125 m⋅min−1 with the discrete-edge tool. Surface defects in terms of fiber pullout, debonding, and cavities were reduced by the discrete-edge tool. The life of the discrete-edge PCD tool was 1.875 times that of the conventional PCD tool. The study illustrates that the cutting performance of the designed discrete-edge PCD tool is better than that of the conventional straight-edge PCD tool.

Microstructural tailoring, mechanical and thermal properties of SiC composites fabricated by selective laser sintering and reactive melt infiltration

Poor flowability of printable powders and long preparation cycles are the main challenges in selective laser sintering (SLS) of chopped carbon fiber reinforced silicon carbide composites (SiC composites) with complex structures. In this study, we develop an efficient and novel processing route in the fabrication of lightweight SiC composites via SLS of phenolic resin (PR) and C_f powders with the addition of α-SiC particles combined with one-step reactive melt infiltration (RMI). The effects of α-SiC addition on the microstructural evolution of the C_f/SiC/PR printed bodies, C_f/SiC/C green bodies, and derived SiC composites were investigated. The results indicate that the added α-SiC particles play an important role in enhancing the flowability of raw powders, reducing porosity, increasing the reliability of the C_f/SiC/C green bodies, and contributing to improving the microstructure homogeneity and mechanical properties of the SiC composites. The maximum density, flexural strength, and fracture toughness of the SiC composites are 2.749±0.006 g×cm⁻³, 266±5 MPa, and 3.30±0.06 MPa·m^1/2, respectively. The coefficient of thermal expansion (CTE) of the SiC composites is approximately 4.29×10⁻⁶ K⁻¹ from room temperature (RT) to 900 °C, and the thermal conductivity is in the range of 80.15-92.48 W·m⁻¹·K⁻¹ at RT. The high-temperature strength of the SiC composites increase to 287±18 MPa up to 1200 °C. This study provides a novel as well as a feasible tactic for the preparation of high-quality printable powders as well as lightweight, high strength, and high thermal conductivity SiC composites with complex structures by SLS and RMI.

Fiber orientation effects on grinding characteristics and removal mechanism of 2.5D Cf/SiC composites

Carbon fiber reinforced silicon carbide (Cf/SiC) composites are widely used in aerospace for their excellent mechanical properties. However, the quality of the machined surface is poor and unpredictable due to the material heterogeneity induced by complex removal mechanism. To clarify the effects of fiber orientation on the grinding characteristics and removal mechanism, single grit scratch experiments under different fiber orientations are conducted and a three-phase numerical modelling method for 2.5D Cf/SiC composites is proposed. Three fiber cutting modes i.e., transverse, normal and longitudinal, are defined by fiber orientation and three machining directions i.e., MA (longitudinal and normal), MB (longitudinal and transverse) and MC (normal and transverse), are selected to investigate the effect of fiber orientation on grinding force and micro-morphology. Besides, a three-phase cutting model of 2.5D Cf/SiC composites considering the mechanical properties of the matrix, fiber and interface is developed. Corresponding simulations are performed to reveal the micro-mechanism of crack initiation and extension as well as the material removal mechanism under different fiber orientations. The results indicate that the scratching forces fluctuate periodically, and the order of mean forces is MA > MC > MB. Cracks tend to grow along the fiber axis, which results in the largest damage layer for transverse fibers and the smallest for longitudinal fibers. The removal modes of transverse fibers are worn, fracture and peel-off, in which normal fibers are pullout and outcrop and the longitudinal fibers are worn and push-off. Under the stable cutting condition, the change of contact area between fiber and grit leads to different removal modes of fiber in the same cutting mode, and the increase of contact area results in the aggravation of fiber fracture.

Synergistic reinforcement effects of ZrB2 on the ultra-high temperature stability of Cf/SiC composite fabricated by liquid silicon infiltration

A carbon fiber-reinforced silicon carbide (Cf/SiC) composite was fabricated with ZrB2 via the liquid silicon infiltration (LSI) method. A prepreg was prepared by impregnating the phenolic resin with the ZrB2 powder. The as-LSIed composites were tested for 5 min with an oxyacetylene torch to evaluate their ablation and oxidation properties under an ultra-high temperature environment. The ZrB2 powders and SiC matrix between carbon fiber bundles generated a dense ZrO2-SiO2 layer, which inhibited further oxygen diffusion into the composite and minimized the ablation and oxidation of the carbon fibers. Weight loss and linear ablation rate were further reduced with the addition of ZrB2 to the Cf/SiC composite; moreover, the synergistic effect of ZrB2 and SiC reinforced the ablation properties with increased ZrB2 content. ZrB2 also reduced the amount of residual silicon, which was detrimental to the mechanical properties of Cf/SiC composite.

Enhancing the machinability of Cf/SiC composite with the assistance of laser-induced oxidation during milling

Carbon fiber-reinforced silicon carbide matrix (Cf/SiC) composites have been widely used in aerospace for its superior properties. However, due to high hardness, heterogeneity, and anisotropy, many problems such as machining damage, low process efficiency, and rapid tool wear are encountered in machining Cf/SiC composite. In this study, laser-induced oxidation-assisted milling (LOAM), as novel hybrid machining process, was proposed to enhance machinability of Cf/SiC composites. Pulsed laser was used to induce reaction between Cf/SiC composites and oxygen. Easily removable loose and porous oxides were produced, which were simultaneously removed with milling tool, leading to improved material removal rate and tool life. Oxidation mechanisms and influences of laser parameters on oxidation behavior of Cf/SiC composite were studied. Conventional milling (CONV) without the assistance of laser was also performed on Cf/SiC composite for comparative analysis. Milling force, tool wear, and surface quality were studied in detail. Under laser irradiation, Cf/SiC composite was modified into metamorphic-layer that consisted of oxide layer and transition layer. Material irradiated with laser got melted, vaporized, and then reacted with oxygen, producing oxide. Oxide layer was formed due to the accumulation of oxide. Increasing laser energy density boosted oxidation reaction and increased the thickness of oxide layer. In contrast, increase in laser scanning speed decreased thickness of oxide layer. Results show that cutting force was extremely low and no tool wear occurred during milling oxide layer, indicating significant enhancement in machinability. Abrasive wear mainly occurred on flank face when milling transition layer. Surface damages, for instance fiber fracture and matrix fragmentation, were significantly contained by LOAM. Surface roughness Sa obtained via LOAM was 9.5 μm, which was lower than that obtained by CONV (35 μm). This study indicates that LOAM can achieve high-efficiency processing, low-defect surface, and prolonged tool life when machining Cf/SiC composite.

Experimental investigation on interlaminar and in-plane shear damage evolution of 2D C/SiC composites using acoustic emission and X-ray computed microtomography

Carbon fiber-reinforced silicon carbide composites (C/SiC) are widely used in lightweight aerospace structures for thermal protection due to its excellent mechanical properties. The low interfacial shear strength of the composites decreases its performance and limits its application. To investigate the shearing performance of C/SiC composite, interlaminar shear and in-plane shear tests were conducted. Real-time X-ray micro-computed tomography (XCT) non-destructive testing technology is an effective method for damage analysis of composite materials. The damage mechanisms of 2D plain weave C/SiC composites prepared by chemical vapor infiltration process under interlaminar shear loading are investigated using the combination of XCT and acoustic emission detection system. The in-situ XCT results reveal the damage visualization mechanisms of the composites and the damage evolution process including matrix damage, interfacial debonding and fiber fracture. The failure mechanisms and morphology of the shear effect for 2D plain weave C/SiC were analysed.

Corrosion behavior and failure mechanism of SiC whisker and c-AlPO4 particle-modified novel tri-layer Yb2Si2O7/mullite/SiC coating in burner rig tests

The corrosion behavior of environmental barrier coatings (EBCs) directly affects the service life and stability of ceramic matrix composite (CMC) structural parts in the aero-engines. The silicon carbide (SiC) whisker toughening phase and c-AlPO4 bonding phase are firstly used to improve the service life of novel tri-layer Yb2Si2O7/mullite/SiC EBCs in the burner rig test. The formation of penetrating cracks in Yb2Si2O7/mullite/SiC coating caused the failure of coating at 1673 K. The SiC whiskers in mullite middle coating significantly inhibited the formation of penetrating cracks in Yb2Si2O7/mullite/SiC coating, and efficiently prevented the oxidation of carbon fiber reinforced silicon carbide (Cf/SiC) samples for 360-min thermal cycles (24 times) with a weight loss of 6.19×10−3 g·cm−2. Although c-AlPO4 particles further improved the service life of SiCw-mullite (SM) coating, the overflow of POx gas aggravated the formation and expansion of cracks in the Yb2Si2O7 outer coating, and caused the service life of overall Yb2Si2O7/c-AlPO4-SiCw-mullite (ASM)/SiC coating to be slightly lower than that of Yb2Si2O7/SM/SiC coating. This study guides the design of modified tri-layer EBCs with long service life in high-temperature and high-speed gas environment.

Interfacial heat transfer characteristics and thermal expansion behavior of heterostructure materials in arc-heated wind tunnel

Structural ceramics such as carbon fiber reinforced silicon carbide (C/SiC) are of great importance for supersonic aircraft, where thermal-mechanical coupling behavior of materials affects the service performance of structural ceramics. In order to advance the understanding of the high temperature thermal-mechanical coupling behavior of heterostructure materials (one typical type of structural ceramics), we adopted here an optical observation system to visualize the variation of the gap width between heterostructure materials in arc-heated wind tunnel test. The variation of the gap width (decreasing and then volatility increasing) was observed during the test. Numerical simulation shows that thermal conduction and thermal expansion between the substrate and specimens play a critical role in the evolution of the gap width, as evidenced by the experiments. Additionally, the variation of the gap width under various conditions was given and a one-dimensional unsteady thermodynamic model of double-layer plate was established to reveal the gap evolution mechanism of heterostructure materials. The results of theoretical model agree well with numerical simulation.