Microstructure Characterization and Fracture Toughness of Laves Phase-Based Cr-Nb-Ti Alloys

doi:10.1007/s40195-015-0227-7

Abstract

Abstract:

Three Laves phase-based alloys with nominal compositions of Cr₂Nb-xTi (x = 20, 30, 40, in at%) have been prepared through vacuum non-consumable arc melting. The results show that the microstructures of Cr₂Nb-(20, 30) Ti alloys are composed of the primary Laves phase C15-Cr₂(Nb,Ti) and bcc solid solution phase, while the microstructure of Cr₂Nb-40Ti alloy is developed with the eutectic phases C15-Cr₂(Nb,Ti)/bcc solid solution. The measured fracture toughness of ternary Laves phase C15-Cr₂(Nb,Ti) is about 3.0 MPa m^1/2, much larger than 1.4 MPa m^1/2 for binary Laves phase Cr₂Nb. Meanwhile, the fracture toughness of Cr₂Nb-xTi (x = 20, 30, 40) alloys increases with increasing Ti content and reaches 10.6 MPa m^1/2 in Cr₂Nb-40Ti alloy. The eutectic microstructure and addition of Ti in Cr₂Nb are found to be effective in toughening Laves phase-based alloys.

Key words: Laves phase-based alloys, Microstructure characterization, Fracture toughness, Crack propagation, Fracture

Yun-Long Xue, Shuang-Ming Li, Hong Zhong, Lai-Ping Li, Heng-Zhi Fu. Microstructure Characterization and Fracture Toughness of Laves Phase-Based Cr-Nb-Ti Alloys[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(4): 514-520.

Figures/Tables 8

Fig. 1 XRD patterns of Laves phase-based Cr2Nb-xTi (x = 20, 30, 40) alloys

Fig. 2 SEM micrographs of Laves phase-based Cr2Nb-xTi (x = 20, 30, 40) alloys: a sample B20; b sample T20; c sample B30; d sample T30; e sample B40; f sample T40

Table 1 EDS results and volume fractions of Laves phase C15-Cr2(Nb,Ti) in Cr2Nb-Ti (x = 20, 30, 40) alloys

Sample	Composition (at%)			Phase	Fraction of Cr₂(Nb,Ti) (vol%)
Sample	Ti	Cr	Nb	Phase	Theo.	Exp.
B20	10.7-11.4	54.3-56.8	31.5-33.4	C15-Cr₂(Nb,Ti)	68	89
B20	32.2-33.7	22.7-23.6	42.9-44.4	Nb-rich bcc		89
T20	8.9-9.4	55.3-58.4	31.8-33.2	C15-Cr₂(Nb,Ti)		81
T20	32.1-33.9	19.4-20.5	44.8-46.5	Nb-rich bcc		81
B30	16.5-17.6	54.3-56.8	24.8-25.9	C15-Cr₂(Nb,Ti)	53	69
B30	39.4-41.9	28.4-29.5	28.6-29.7	Ti-rich bcc		69
T30	15.7-16.4	55.8-57.6	25.5-26.7	C15-Cr₂(Nb,Ti)		64
	27.1-28.7	24.3-25.7	42.3-45.9	Nb-rich bcc
	70.4-76.3	15.4-16.7	8.9-9.7	Ti-rich bcc
B40	21.2-22.9	53.9-56.8	19.7-20.8	C15-Cr₂(Nb,Ti)	34	56
B40	54.8-58.3	9.8-11.2	29.7-31.7	Ti-rich bcc		56
T40	19.2-21.8	54.3-57.9	18.9-20.5	C15-Cr₂(Nb,Ti)		54
T40	56.6-58.8	10.4-10.9	30.2-32.4	Ti-rich bcc		54

Fig. 3 TEM results of the eutectic in arc-melted Cr2Nb-40Ti alloy: a bright-field image of the eutectic; b SAD pattern of the bcc solid solution at position A; c SAD pattern of the C15-Cr2(Nb,Ti) at position B

Fig. 4 Fracture toughness of Laves phase-based Cr2Nb-xTi (x = 20, 30, 40) alloys inserted with the typical indentation produced on single Laves phase Cr2(Nb,Ti)

Fig. 5 Crack propagations in Laves phase-based Cr2Nb-xTi (x = 20, 30, 40) alloys: a sample B20; b sample T20; c sample B30; d sample T30; e sample B40; f sample T40

Fig. 6 Low-magnification fracture surfaces of Laves phase-based Cr2Nb-xTi (x = 20, 30, 40) alloys: a sample B20; b sample T20; c sample B30; d sample T30; e sample B40; f sample T40

Fig. 7 High-magnification fracture surfaces of Laves phase-based Cr2Nb-xTi (x = 20, 30, 40) alloys: a sample T20; b sample T30; c sample T40

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