Interfacial Reaction and Thermal Stability of the SiCf/TiAl Composites
SHEN Yingying1,2, ZHANG Guoxing1, JIA Qing1(), WANG Yumin1, CUI Yuyou1, YANG Rui1()
1.Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2.School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Cite this article:
SHEN Yingying, ZHANG Guoxing, JIA Qing, WANG Yumin, CUI Yuyou, YANG Rui. Interfacial Reaction and Thermal Stability of the SiCf/TiAl Composites. Acta Metall Sin, 2022, 58(9): 1150-1158.
SiC-fiber-reinforced γ-TiAl composite materials are promising for high-temperature structural applications owing to their excellent mechanical properties. However, the interfacial reaction of the composites during subsequent high-temperature processing and service is unstable as elements continue to diffuse around the interfacial reaction layer at high temperatures, and more interfacial reaction products are generated. When excessive brittle reaction products are generated, they have detrimental effects on the mechanical properties of the composites. Therefore, to better design and control the interfacial reaction, it is particularly important to study the formation and growth of the complex interfacial products of the composites. In this study, the formation mechanism of interfacial reaction products and thermal stability of SiCf/TiAl composites were investigated by thermal exposure for different time. First, the SiCf/TiAl composites were prepared by suction casting. Next, the specimens were examined by SEM and TEM to investigate the element diffusion and composition of the interfacial reaction products of the as-prepared composites. The interfacial reaction products in the as-prepared composites were mainly composed of a fine equiaxed TiC layer near a carbon layer and a coarse equiaxed TiC layer near a titanium alloy coating. Then, the thermal exposure was conducted at 800oC to investigate the growth of the interfacial reaction products and thermal stability of the interfacial reaction layer. The results show that the thickness of the interfacial reaction layer increased with heat exposure time. Meanwhile, interfacial stratification was observed during the growth of the interface reaction layer. Further, the growth kinetics curve of the reaction layer was drew according to the thickness of the reaction layer with time, and the interfacial reaction growth rate was determined. According to the morphology and TEM analysis results, the interfacial reaction layer was divided into four layers after 200 h thermal exposure, unlike in the as-prepared state. From the fiber side to matrix side, fine-grained TiC, coarse-grained TiC, (Ti, Zr)5Si4, and Ti3Sn + Ti2AlC layers, respectively, were observed. Finally, the formation mechanism of the interfacial reaction products and element diffusion of SiCf/TiAl composites under different conditions were studied, the interfacial stratification occurred during thermal exposure because some TiC participated during the formation of Ti2AlC.
Fig.1 Schematic of the cross section of the SiC fiber coated with titanium alloy
Fig.2 Cross-section SEM image of SiCf/TiAl composite prepared by vacuum suction casting
Fig.3 SEM image and EDS line scanning results of as-processed SiCf/TiAl composites from the fiber to the matrix (Area I is the interfacial reaction layer, area II is the titanium alloy coating, area III is the transition layer between the titanium alloy coating and the matrix alloy, and area IV is the TiAl matrix alloy)
Fig.4 TEM images of the reaction products and the corresponding selected area electron diffraction (SAED) patterns of as-prepared SiCf/TiAl composite (a) TEM image of SiC fiber and interfacial reaction layer and corresponding SAED patterns ((b) local enlarged view of the interfacial reaction products and corresponding SAED patterns
Fig.5 SEM images of interfacial reaction layer and matrix of SiCf/TiAl composite after thermal exposure at 800oC for 25 h (a), 50 h (b), 100 h (c), 150 h (d), and 200 h (e)
Thermal exposure time / h
Thickness of the interfacial reaction layer / μm
Thickness of the carbon layer / μm
25
1.312
2.003
50
1.376
1.982
100
1.472
1.912
150
1.573
1.897
200
1.620
1.869
Table 1 Thicknesses of interfacial reaction layer and carbon layer of SiCf/TiAl composite after thermal exposure at 800oC for different time
Fig.6 Interfacial reaction kinetic curves of SiCf/TiAl composites at 800oC (t—thermal exposure time)
Element
Point A
Point B
Mass fraction
Atomic fraction
Mass fraction
Atomic fraction
C
16.20
42.66
3.61
12.50
Al
3.29
3.85
9.64
14.86
Si
2.78
3.13
0.47
0.69
Ti
74.66
49.26
79.84
69.30
Cr
0.50
0.30
0.39
0.31
Zr
1.21
0.42
1.71
0.78
Nb
0.00
0.00
0.09
0.04
Mo
0.18
0.06
0.37
0.16
Sn
1.17
0.31
3.89
1.36
Table 2 EDS analysis results of points A and B in Fig.5e
Fig.7 TEM image of the reaction products and the corresponding SAED patterns after thermal exposure at 800oC for 200 h (I—fine-grained TiC layer, II—coarse-grained TiC layer, III—(Ti, Zr)5Si4 layer, IV—Ti3Sn + Ti2AlC layer)
Fig.8 Schematic of the formation and growth of interfacial reaction products during thermal exposure
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