# Cyclic Thermal Shock Damage Behavior in CVI SiC/SiC High-Pressure Turbine Twin Guide Vanes

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## Abstract

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_{2}. When the thermal shock temperature increased from 1400 to 1450 and 1480 °C, the spalling area of the basin and the back region of the guide vane did not increase significantly, but the delamination occurred at the tenon, upper surface of the guide vane near the trailing edge of the guide vane. Through the X-ray Computed Tomography (XCT) analysis for the guide vanes before and after thermal shock, there was no obvious damage inside of guide vanes. The oxidation of SiC coating and the formation of SiO

_{2}protects the internal fibers from oxidation and damage. Further investigation on the effect of thermal shock on the mechanical properties of SiC/SiC composites should be conducted in the future.

## 1. Introduction

^{TM}SiC fiber-reinforced polymer impregnation and pyrolysis (PIP) SiC matrix, Nextel

^{TM}312 fiber-reinforced chemical vapor infiltrated (CVI) SiC matrix, and Nicalon

^{TM}SiC fiber-reinforced CVI SiC matrix) using the water-quench technique. The damage of matrix cracking and delamination induced by thermal shock was determined using the flexure testing and dynamic resonance measurement. Udayakumar et al. [12] investigated the effect of thermal cycling of 2D plain-woven SiC/SiC composites on the mechanical properties, e.g., the proportional limit stress, percentage elongation, fracture toughness, and interfacial bonding strength. Zhang et al. [13] investigated the effect of thermal cycles between 900 and 300 °C in air atmosphere on the tensile properties of 2.5D woven C/SiC composite. The composite can retain the tensile strength within 40 thermal cycles. On the fractured surface, extensive fiber’s pullout appeared, indicating the weakening of the bonding strength at the fiber/matrix interface subjected to thermal cycles. Yang and Liu [14] performed cyclic thermal shock test on the oxide/oxide CMCs. The thermal aged CMCs under cyclic thermal shocks showed a rapid decrease in the elastic modulus compared to the original CMCs. Absi and Glandus [15] developed an improved method for the severe thermal shock testing method of ceramcis by water quenching. Jiao et al. [16] performed water quenching thermal shock tests on SiC/SiC guide vanes with different laminates and evaluated the defects in the vanes and thermal shock performance. For the unidirectional laminate SiC/SiC guide vane, the thermal shock resistance is the worst, and the fracture of the guide vane occurs after 10 thermal shocks; however, for the orthogonal laminates, the guide vane possesses better thermal shock resistance with more than 30 thermal shocks. Boccaccini [17] predicted the critical temperature difference for the thermal shock resistance oof different fiber-reinforced CMCs. Li [18,19] analyzed the thermal fatigue damage evolution in fiber-reinforced CMCs, and predicted the tensile stress-strain curves of different CMCs after thermal fatigue loading. Yang et al. [20] developed a damage constitutive model for thermal shocked Oxide/Oxide CMCs. However, in the research mentioned above, the cyclic thermal shock damage behavior in fiber-reinforced CMC components has not been investigated.

## 2. Fabrication of SiC/SiC Twin Guide Vanes and Cyclic Thermal Shock Experimental Procedure

#### 2.1. Fabrication of SiC/SiC Twin Guide Vanes

^{3}. To protect the SiC fiber and adjust the thermal misfit between the fiber and the matrix, the PyC interphase was deposited on the surface of the fiber using the chemical vapor deposition (CVD) method. The CVD temperature was approximately 900–1100 °C using the Ar as the protective gas. The deposition time is approximately 20–50 h and the thickness of the interphase is approximately 300–500 μm. After deposition of the interface, the SiC matrix was deposited on the fiber’s preform using the CVI method at approximately 1100–1400 °C. The deposition furnace was vacuumized to 20–50 kPa, 60–100 L/min H

_{2}gas was used as carrier gas, the precursor gas flow rate of SiC matrix was 100–500 L/min, and the single deposition time was 100–150 h. When the density of the material was more than or equal to 2.5 g/cm

^{3}, the densification process was completed. The surface of the SiC/SiC guide vane was then deposited the SiC coating using the CVD method at approximately 1000 °C. Figure 1 shows the photograph of the SiC/SiC twin guide vanes observed under X-ray Computed Tomography (XCT).

#### 2.2. Cyclic Thermal Shock Experimental Procedures

## 3. Experimental Results and Discussion

#### 3.1. Surface Temperature Distribution for the SiC/SiC Twin Guide Vane under Thermal Shock Test

#### 3.2. Damage Analysis of SiC/SiC Twin Guide Vanes during Thermal Shock Test

_{2}on the surface of SiC/SiC guide vane due to high temperature oxidation under high temperature environment.

## 4. Summary and Conclusions

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- The temperature in the middle of the leading edge of the left guide vane is the highest. The temperature at the basin region decreased from the leading edge to the trailing edge, and the temperature of the trailing edge was the lowest. The temperature at the trailing edge and leading edge of the right guide vane is the highest, and the temperature of the middle region is the lowest. The temperature of the basin region is higher than that of the back region of the guide vane.
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- Before the thermal shock test, the surface of turbine guide vane is smooth. After 100 cycles, large spalling areas appeared on the leading edge and back region, which were the spalling of SiC sealing coating on the surface of SiC/SiC guide vane. After 400 cycles, the spalling area of the coating at the basin and back region of the guide vane is more than 30%, and the whole guide vane becomes gray under the action of high temperature gas, due to the formation of SiO
_{2}on the surface of SiC/SiC guide vane under high temperature environment. When the thermal shock test temperature was raised to 1450 °C, the spalling area of the basin and the back region of the guide vane did not increase significantly, but the delamination occurred at the tenon of the guide vane. When the thermal shock test temperature was increased to 1480 °C and the holding time increased from 30 to 60 s, the spalling area of the basin and back region of the guide vane did not increase significantly, but a new delamination phenomenon appeared on the upper surface of the guide vane near the trailing edge.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**The photograph of SiC/SiC twin guide vanes observed under XCT (

**a**) Front view; and (

**b**) Back view.

**Figure 3.**(

**a**) Front view of the guide vane; (

**b**) Top view of the guide vane; (

**c**) Front view of the fixture; and (

**d**) Top view of the fixture.

**Figure 5.**Surface temperature distribution for the twin guide vanes under thermal shock test at the target temperature of T = 1400 °C (

**a**) Basin area of the left guide vane; and (

**b**) Back area of the right guide vane.

**Figure 6.**The temperature change with time for different measurement spots during thermal shock test (

**a**) Left guide vane; and (

**b**) Right guide vane.

**Figure 7.**Surface temperature distribution for the twin guide vanes under thermal shock test at the target temperature of T = 1480 °C (

**a**) Basin area of the left guide vane; and (

**b**) Back area of the right guide vane.

**Figure 8.**The temperature change with time for five different measurement spots during thermal shock test of left guide vane.

**Figure 9.**Thermal shock damage of SiC/SiC twin guide vane at target temperature of T = 1400 °C for leading edge at (

**a**) N = 100, (

**b**) N = 200, (

**c**) N = 300, and (

**d**) N = 400, the basin region at (

**e**) N = 100, (

**f**) N = 200, (

**g**) N = 300, and (

**h**) N = 400, and the back region at (

**i**) N = 100, (

**j**) N =200, (

**k**) N = 300, and (

**l**) N = 400.

**Figure 10.**Thermal shock damage of SiC/SiC twin guide vane at target temperature of T = 1450 °C for leading edge at (

**a**) N = 100, (

**b**) N = 200, and (

**c**) N = 300, the basin region at (

**d**) N = 100, (

**e**) N = 200, and (

**f**) N = 300, and the back region at (

**g**) N = 100, (

**h**) N = 200, and (

**i**) N = 300.

**Figure 11.**Thermal shock test of SiC/SiC twin guide vane at target temperature of T = 1450 °C at N = 300.

**Figure 12.**Thermal shock damage of SiC/SiC twin guide vane at target temperature of T = 1480 °C with the hold time of t = 30 s for leading edge at (

**a**) N = 100, and (

**b**) N = 200, the basin region at (

**c**) N = 100, and (

**d**) N = 200, and the back region at (

**e**) N = 100, and (

**f**) N = 200.

**Figure 13.**Thermal shock damage of SiC/SiC twin guide vane at target temperature of T = 1480 °C with the hold time of t = 60 s for leading edge at (

**a**) N = 100, and (

**b**) N = 200, the basin region at (

**c**) N = 100, and (

**d**) N = 200, and the back region at (

**e**) N = 100, and (

**f**) N = 200.

**Figure 14.**Thermal shock test of SiC/SiC twin guide vane at target temperature of T = 1480 °C at N = 200 (

**a**) New delamination occurred at the trailing edge; and (

**b**) New delamination observed under XCT.

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**MDPI and ACS Style**

Liu, X.; Guo, X.; Xu, Y.; Li, L.; Zhu, W.; Zeng, Y.; Li, J.; Luo, X.; Hu, X.
Cyclic Thermal Shock Damage Behavior in CVI SiC/SiC High-Pressure Turbine Twin Guide Vanes. *Materials* **2021**, *14*, 6104.
https://doi.org/10.3390/ma14206104

**AMA Style**

Liu X, Guo X, Xu Y, Li L, Zhu W, Zeng Y, Li J, Luo X, Hu X.
Cyclic Thermal Shock Damage Behavior in CVI SiC/SiC High-Pressure Turbine Twin Guide Vanes. *Materials*. 2021; 14(20):6104.
https://doi.org/10.3390/ma14206104

**Chicago/Turabian Style**

Liu, Xiaochong, Xiaojun Guo, Youliang Xu, Longbiao Li, Wang Zhu, Yuqi Zeng, Jian Li, Xiao Luo, and Xiaoan Hu.
2021. "Cyclic Thermal Shock Damage Behavior in CVI SiC/SiC High-Pressure Turbine Twin Guide Vanes" *Materials* 14, no. 20: 6104.
https://doi.org/10.3390/ma14206104