Microstructure and Mechanical Properties of Electron Beam Welded Titanium Alloy Ti-6246

doi:10.1016/j.jmst.2016.10.007

Abstract

Abstract:

Electron beam welding (EBW) was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk. The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstructure observations indicated that there existed plenty of thin needle-like α platelets studding in the matrix of the columnar β grains in the as-welded fusion zone (FZ). Post-weld heat treatment (PWHT) led to the precipitation of small secondary α platelets in the β matrix in heat affected zone and FZ. The thickness and the density of α platelets increased as the temperature of PWHT increased from 545 to 645 °C. The microhardness across the Ti-6246 EBW joint exhibited a nonuniform distribution. The hardness increased with the decrease of distance to the weld center, and reached the maximum of 467 HV in FZ when PWHT was carried out at 595 °C. All the weldments tested with tension were fractured at the base material (BM) and exhibited a ductile fracture mode. The major deformation barrier in BM was the platelet α/β interfaces, however, the major deformation barrier in FZ was found to be β grain boundaries and secondary α/β interfaces. The BM with thicker platelet α phases had lower strength than the other two zones in the joint, and the BM deformed first and led to fracture in this zone.

Key words: Electron beam welding, Ti-6246, microstructure, Mechanical properties

Guoqiang Wang, Zhiyong Chen, Jinwei Li, Jianrong Liu, Qingjiang Wang, Rui Yang. Microstructure and Mechanical Properties of Electron Beam Welded Titanium Alloy Ti-6246[J]. J. Mater. Sci. Technol., 2018, 34(3): 570-576.

Figures/Tables 13

Fig. 1. Microstructure of as-received base material Ti-6246.

Fig. 2. Locations of FZ in the tested specimens with tension of Ti-6246 weldment.

Fig. 3. Macrostructure of the Ti-6246 alloy weldment (OM).

Fig. 4. Microstructure of the FZ of as-welded Ti-6246 weldment: (a) SEM; (b) TEM, and SAED analysis (inset).

Fig. 5. Microstructure of HAZ of as-welded Ti-6246 weldment: (a) near-HAZ, (b) far-HAZ.

Fig. 6. XRD patterns of as-welded FZ and FZ under different PWHT conditions.

Fig. 7. Microstructure of weldment after PWHT: (a) BM after 545 °C/8 h/AC, (b) BM after 645 °C/8 h/AC, (c) far-HAZ after 545 °C/8 h/AC, (d) far HAZ after 645 °C/8 h/AC, (e) near-HAZ after 545 °C/8 h/AC, (f) near HAZ after 645 °C/8 h/AC, (g) FZ after 545 °C/8 h/AC, (h) FZ after 645 °C/8 h/AC.

Fig. 8. Microhardness across weldments in different conditions: (a) as-welded, (b) PWHT at 545 °C,8 h, AC, (c) PWHT at 595 °C,8 h, AC, (d) PWHT at 645 °C, 8 h, AC.

Table 1 Room tensile properties of the weldment and base material of Ti-6246 alloy

Specimen details	PWHT	YS_0.2% (MPa)	UTS (MPa)	Elongation (%)	Failure location
Weldment	545 °C/8 h/AC	1109	1185	7.5	BM
	545 °C/8 h/AC	1119	1185	4.5	BM
	595 °C/8 h/AC	1096	1170	9.0	BM
	595 °C/8 h/AC	1109	1177	4.0	BM
	645 °C/8 h/AC	1066	1133	9.5	BM
	645 °C/8 h/AC	1079	1142	6.5	BM
As-received base material		1066	1165	17.5	—
As-received base material		1066	1162	16.5	—

Fig. 9. Pseudo-binary section through a β isomorphous phase diagram[21] and location of Ti-6246 alloy.

Table 2 Room tensile properties of simulated-HAZ and FZ

Simulated-HAZ (S-HAZ)	Solution treatment	Cooling method	Ageing treatment	YS_0.2% (MPa)	UTS (MPa)	Elongation (%)
S-HAZ-1	900 °C, 1 h	AC	595 °C, 8 h, AC	1290	1377	10.0
		AC	595 °C, 8 h, AC	1294	1378	9.0
		WQ	595 °C, 8 h, AC	1387	1494	5.5
		WQ	595 °C, 8 h, AC	1379	1456	7.0
S-HAZ-2	920 °C, 1 h	AC	595 °C, 8 h, AC	1284	1390	8.5
		AC	595 °C, 8 h, AC	1292	1391	8.5
		WQ	595 °C, 8 h, AC	1448	1511	0.5
		WQ	595 °C, 8 h, AC	1447	1484	0.5
S-HAZ-3	950 °C, 1 h	AC	595 °C, 8 h, AC	—	1302	—
		WQ	595 °C, 8 h, AC	—	1213	—
		WQ	595 °C, 8 h, AC		1291
FZ after ageing treatment at 595 °C, 8 h, AC				—	1208	—
FZ after ageing treatment at 595 °C, 8 h, AC				—	1122	—

Fig. 10. Typical stress-strain curve of tensile samples extracted from S-HAZ and FZ.

Fig. 11. SEM fractographs of weldment and FZ of tensile specimens: (a) weldment PWHTed at 545 °C, (b) weldment PWHTed at 595 °C, (c) weldment PWHTed at 645 °C, (d) FZ PWHTed at 595 °C, (e) enlarged area of (d).

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