Effect of δ Phase on Microstructure and Hardness of Heat-Affected Zone in TIG-Welded GH4169 Superalloy

doi:10.1007/s40195-018-0861-y

Abstract

Abstract:

The GH4169 superalloy with different content of δ-Ni₃Nb phase was welded by tungsten inert gas welding. A detailed study of microstructure and hardness of heat-affected zone (HAZ) was performed in both as-welded and aged state. The results show that the precipitation of δ phase, especially the intergranular δ phase, can lead to the enrichment of Nb and Mo elements, which promote the formation of γ/Laves eutectic constituent at grain boundaries in HAZ. In as-welded state, the hardness decreases first and then increases (exhibiting a “V” shape) with distance away from fusion line in HAZ, which is governed by grain size. After aging treatment, however, the γ″ phase plays a key role in hardness and leads to the “Λ” shape profiles of hardness in HAZ.

Key words: GH4169 superalloy, TIG(tungsten inert gas) welding, δ phase, γ″ phase, Element enrichment

Tian-Fu Wang , Xin-Jie Di, Cheng-Ning Li, Jia-Mei Wang, Dong-Po Wang. Effect of δ Phase on Microstructure and Hardness of Heat-Affected Zone in TIG-Welded GH4169 Superalloy[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(8): 1041-1052.

Figures/Tables 12

Table 1 Chemical composition of the experimental GH4169 superalloy (wt%)

Ni			Cr			Nb?+?Ta			Mo			Ti			Al			Si			C
52.68			18.81			5.34			3.04			1.05			0.49			0.08			0.03
Mn		S		P			Cu				Co			B		Ta			Fe
0.03	0.001				0.008			0.01		0.01			0.003				<0.01			Bal.

Fig. 1 Four groups of welded superalloys

Table 2 Heat treatment and welding parameters of the samples

Designation	Heat treatment parameters	Welding current, I (A)	Welding voltage, U (V)	Welding speed, v (m/min)
S0	As-received	90	13	0.2
S1	925 °C for 1 h, air cooled	90	13	0.2
S3	925 °C for 3 h, air cooled	90	13	0.2
S9	925 °C for 9 h, air cooled	90	13	0.2

Fig. 2 SEM micrographs of GH4169 in different conditions: a as-received; b 925 °C for 1 h; c 925 °C for 3 h; d 925 °C for 9 h

Fig. 3 a X-ray diffraction spectrums of the pre-welding samples with heat treatment at 925 °C for 1 h, 3 h and 9 h, respectively; b the calculated content of δ phase in different heat treatment samples

Fig. 4 OM and SEM images of HAZs in the four welded samples: a, d, g, j OM images of HAZs in S0, S1, S3 and S9, respectively; b, e, h, k SEM images of Region1 in a, d, g, j, respectively; c, f, i, l SEM images of Region2 in a, d, g, j, respectively

Fig. 5 SEM images and EDS spectrums of δ phase, Laves phase and NbC in S9: a SEM image of δ phase in base metal; b EDS spectrum of δ phase in a; c SEM image of Laves phase in Region1; d EDS spectrum of Laves phase in c; e SEM image of NbC particles in Region1; f EDS spectrum of NbC particles in e

Fig. 6 Grain size distribution and average grain size of Region1 and Region2 in the four welded samples: a grain size distribution of Region1 in the four welded samples; b grain size distribution of Region2 in the four welded samples

Fig. 7 SEM images of HAZs after aging treatment: a Region1 in S0; b Region2 in S0; c Region1 in S9; d Region2 in S9

Fig. 8 Vickers hardness profiles of welded joints (S0-S9) in: a as-welded and b aged condition

Fig. 9 SEM images and EDS elemental distribution maps of S9 in: a base metal, b Region1 and c Region2

Fig. 10 Schematic of the redistribution of Nb (colored black) and Mo (colored light blue) atoms and how the γ/Laves eutectic constituent formed

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