Tensile Behavior of SiC Fiber-Reinforced γ-TiAl Composites Prepared by Suction Casting

doi:10.1007/s40195-020-01170-5

Abstract

Abstract:

The process of preparing SiC fiber-reinforced γ-TiAl composites by the conventional methods is difficult and complicated due to the high reactivity, high melting point and poor deformability of γ-TiAl alloys. In this work, suction casting, a promising method for preparing SiC_f/TiAl composite, had been attempted. In the process, γ-TiAl alloy melt was introduced rapidly into a mold within pre-arranged fibers that were coated with additional layer of titanium alloy. This simple method successfully prevented serious reactions between the alloy melt and the fibers which remained intact during the solidification process. The interfacial reaction layer was observed by optical microscopy, scanning electron microscopy (SEM). The interfacial reaction products were identified by transmission electron microscopy (TEM). Tensile tests of the matrix alloy and composites were performed at room temperature and 800 °C. The results exhibited that the tensile strength of SiC_f/γ-TiAl composite was higher than that of the matrix alloy at both room temperature and 800 °C. At room temperature, tensile strength of SiC_f/γ-TiAl composite was increased by about 7% (50 MPa), whereas a double increase in tensile strength 14% (100 MPa) was obtained at 800 °C. The titanium alloy coating on the fiber not only prevented the serious interfacial reaction between the γ-TiAl alloy melt and the SiC fiber, but also played a role in delaying the propagation of cracks in the matrix to the fiber at 800 °C. The fracture mechanism of the composite was analyzed by fracture metallographic analysis.

Key words: Suction casting, SiC_f/γ-TiAl composite;, Interfacial reaction, Tensile strength, Fracture mechanism

Yingying Shen, Qing Jia, Xu Zhang, Ronghua Liu, Yumin Wang, Yuyou Cui, Rui Yang. Tensile Behavior of SiC Fiber-Reinforced γ-TiAl Composites Prepared by Suction Casting[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(7): 932-942.

Figures/Tables 12

Fig. 1 Cross section of the fiber coated with titanium alloy used in this work

Fig. 2 a Schematic diagram of the suction casting process used to prepare the composite, b the arrangement of fibers in the mold

Fig. 3 a Optical micrograph of fiber distribution and microstructure of the γ-TiAl matrix alloy on the cross section of the composite, b SEM image showing microstructure of the TiAl matrix alloy prepared by suction casting (white lines indicate the lamellar orientation)

Fig. 4 Interface reaction layer of the composite: a interface morphology between the fiber and the γ-TiAl matrix, b morphology of interface reaction layer between the fiber and titanium alloy coating

Fig. 5 Microstructure of interface reaction layer of the composite under TEM and selected area electron diffraction (SAED) patterns of the products (I: fine-grain TiC layer, and II: coarse-grain TiC layer)

Table 1 Tensile properties of TiAl alloys and SiCf/TiAl composites at different temperatures

	Sample number	R_p0.2 (MPa)	R_m (MPa)	A (%)
TiAl matrix alloy at room temperature	1	-	648	0.20
	2	-	658	0.12
	3	-	646	0.10
SiC_f/TiAl composite at room temperature	4	-	722	0.14
	5	-	682	0.19
	6	-	707	0.20
TiAl matrix alloy at 800 °C	7	615	713	1.0
	8	541	658	1.0
	9	551	693	1.0
SiC_f/TiAl composite at 800 °C	10	591	777	1.0
	11	651	807	2.0
	12	588	814	3.0

Fig. 6 Typical stress-strain curves of the composite and TiAl matrix alloy under different temperatures

Fig. 7 Fracture surfaces of the different samples: a TiAl matrix alloy at room temperature, b SiCf/TiAl composite at room temperature, c TiAl matrix alloy at 800 °C, d SiCf/TiAl composite at 800 °C.

Fig. 8 Fracture surface of sample 3 (the straight line represents the crack growth trace)

Table 2 Strength of composites estimated by the rule of mixture

	Room temperature	800 °C
\({V}_{\mathrm{f}}\) (%)	1.8	1.8
\({\sigma }_{\mathrm{f}}\) (MPa)	3500	3150
\({\sigma }_{\mathrm{m}}\) (MPa)	650	688
\({\sigma }_{\mathrm{comp}}\) (MPa)	701	732

Fig. 9 Fracture morphologies at room temperature of a matrix alloy, b fibers in the composite, c crack propagation directly from the matrix toward the fiber, d crack deflection along the interface layer, e locally enlarged view of the surface of the fiber pullout, flocally enlarged view of the interfacial reaction layer

Fig. 10 Fracture morphologies at 800 °C of a matrix alloy, b fibers in the composite, c broken fibers on the fracture surface, d interface debonding along the interface layer, e locally enlarged view of the interfacial reaction layer, f interface debonding between the SiC and the tungsten core

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