Influence of Filler on the Microstructure, Mechanical Properties and Residual Stresses in TIG Weldments of Dissimilar Titanium Alloys

doi:10.1007/s40195-021-01236-y

Abstract

Abstract:

The influence of titanium alloy (Ti-5Al-2.5Sn) and commercially pure titanium (cpTi) as fillers on dissimilar pulsed tungsten inert gas weldments of Ti-5Al-2.5Sn/cpTi was investigated in terms of microstructure, mechanical/nano-mechanical properties, and residual stresses. A partial martensitic transformation was observed in the weldments for all the welding conditions due to high heat input. The microstructure evolved in the FZ/cpTi interfacial region was observed to be the most sensitive to the proportion of α stabilizer in the filler alloy. Furthermore, the addition of filler alloy improved the tensile properties and nano-mechanical response of the weld joint owing to the increased volume of metal in the weld joint. As compared to the Ti-5Al-2.5Sn wire, the use of cpTi filler wire proved to be better in terms of energy absorbed during tensile and impact tests, tensile strength and ductility of the dissimilar welds. An asymmetrical residual stresses profile was observed close to the weld centerline, with high compressive stresses on the Ti-5Al-2.5Sn side for both the weldments obtained with and without filler wires. This was attributed to mainly the low thermal conductivity of Ti-5Al-2.5Sn. The presence of residual stresses also influenced the nano-hardness profile across the weldments.

Key words: Titanium alloys, Dissimilar welding, Nano-indentation, Residual stresses, Tungsten inert gas (TIG) welding, Microstructure

Massab Junaid, Fahd Nawaz Khan, Tauheed Shahbaz, Haris saleem, Julfikar Haider. Influence of Filler on the Microstructure, Mechanical Properties and Residual Stresses in TIG Weldments of Dissimilar Titanium Alloys[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(10): 1395-1406.

Figures/Tables 18

Table 1 Parameters for dissimilar pulsed TIG welding of Ti-5Al-2.5Sn/cPTi

S. No.	Current (A)		Pulse width (ms)		Voltage (V)	Welding speed (mm/min)	Filler alloys
S. No.	Primary	Background	High	Low	Voltage (V)	Welding speed (mm/min)	Filler alloys
1	32	16	8	4	10	32.5	-
2	32	16	8	4	10	32.5	cpTi
3	32	16	8	4	10	32.5	Ti-5Al-2.5Sn

Fig. 1 Physical appearance of the weldments with a no filler, b Ti-5Al-2.5Sn filler wire, c cpTi filler wire

Fig. 2 Microstructures of the two base metals: a Ti-5Al-2.5Sn, b cpTi

Fig. 3 Microstructures of FZ in the Ti-5Al-2.5Sn/cpTi dissimilar alloy weldments with a no filler, b Ti-5Al-2.5Sn filler wire, c cp-Ti filler wire

Fig. 4 Microstructures of HAZ toward Ti-5Al-2.5Sn side in the Ti-5Al-2.5Sn/cpTi dissimilar alloy weldments with a no filler, b Ti-5Al-2.5Sn filler wire, c cp-Ti filler wire

Fig. 5 Microstructures of HAZ toward cpTi side in the Ti-5Al-2.5Sn/cpTi dissimilar alloy weldments with a no filler, b Ti-5Al-2.5Sn filler wire, c cp-Ti filler wire

Fig. 6 Microhardness profiles across the Ti-5Al-2.5Sn/cPTi weld joints for different conditions of fillers

Fig. 7 Stress-strain curves of the smooth tensile specimen of Ti-5Al-2.5Sn/cpTi weld joint for different conditions of filler material

Table 2 Stress-strain characteristics of the smooth tensile testing of Ti-5Al-2.5Sn/cpTi weld joints

Sample	Maximum load (N)	Energy at break (J)	Extension at break (mm)
No filler wire	3658	4	2
Ti-5Al-2.5Sn filler wire	3668	15	5
cpTi filler wire	3757	21	7

Fig. 8 Stress-strain curves of the notch tensile specimen of Ti-5Al-2.5Sn/cpTi weld joint for different conditions of filler material

Table 3 Stress-strain characteristics of notch tensile specimen of Ti-5Al-2.5Sn/cpTi weld joint

Sample	Maximum load (N)	Energy at break (J)	Extension at break (mm)
No filler wire	5248	10	3
Ti-5Al-2.5Sn filler wire	5600	16	3
CP-titanium filler wire	5896	29	6

Fig. 9 SEM fractographs of the fractured surfaces of double notch tensile specimens of Ti-5Al-2.5Sn/cpTi dissimilar weldments with a no filler, b Ti-5Al-2.5Sn filler, c cpTi filler

Fig. 10 Nano-indentation load-depth curves of the base materials: a Ti-5Al-2.5Sn, b cp-Ti

Fig. 11 Nano-indentation load-depth curves of the weldments without filler material: a HAZ of Ti-5Al-2.5Sn side, b FZ, c HAZ of cpTi side

Fig. 12 Nano-indentation load-depth curves of the weldments obtained using Ti-5Al-2.5Sn wire filler: a HAZ of Ti-5Al-2.5Sn side, b FZ, c HAZ of cpTi side

Fig. 13 Nano-indentation load-depth curves of the weldments obtained using cpTi wire filler: a HAZ of Ti-5Al-2.5Sn side, b FZ, c HAZ of cpTi side

Table 4 Summary of the nano-mechanical properties of the Ti-5Al-2.5Sn/cPTi weld joint for different conditions of filler

S. No.	Type of filler	Nano-hardness (GPa)					Elastic modulus (GPa)
		BM cpTi	HAZ cpTi side	FZ	HAZ of Ti-5Al-2.5Sn side	BM Ti-5Al-2.5Sn	HAZ of cpTi side	FZ	HAZ of Ti-5Al-2.5Sn side
1	No filler	2.0 ± 0.3	2 ± 0.1	3 ± 0.1	5 ± 0	4.5 ± 0.4	120 ± 9	128 ± 3	145 ± 4
2	cpTi		2 ± 0.4	3.6 ± 0.8	4 ± 0		123 ± 7	134 ± 4	140 ± 9
3	Ti-5Al-2.5Sn		2 ± 0.5	4 ± 0.3	4 ± 0		113 ± 3	139 ± 1	136 ± 5

Table 5 Longitudinal and transverse residual stresses in the Ti-5Al-2.5Sn/cPTi weld joint for different conditions of filler

S. No.	Type of filler	Depth (mm)	Longitudinal residual stresses (MPa)		Transverse residual stresses (MPa)
S. No.	Type of filler	Depth (mm)	cpTi side	Ti-5Al-2.5Sn side	cpTi side	Ti-5Al-2.5Sn side
1	No filler	0.1	63	130	89	85
1	No filler	0.7	30	- 43	46	20
2	cpTi	0.1	- 2	- 53	107	61
2	cpTi	0.7	- 35	- 23	74	150
3	Ti-5Al-2.5Sn	0.1	99	- 177	69	- 148
3	Ti-5Al-2.5Sn	0.7	56	- 169	18	- 111

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