1. State Key Laboratory of Advanced and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China 2. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
ZHAO Xu,SUN Yuan,HOU Xingyu,ZHANG Hongyu,ZHOU Yizhou,DING Yutian. Effect of Orientation Deviation on Microstructure and Mechanical Properties of Nickel-Based Single Crystal Superalloy Brazing Joints. Acta Metall Sin, 2020, 56(2): 171-181.
Ni-based single crystal superalloy has excellent high temperature properties, which is the main materials for aero-engine turbine blade. In order to improve the yield strength of single crystal blades, the reliable bonding technology has become an increasingly indispensable key technology in the process of producing single crystal blades. However, there is inevitably an orientation deviation in the bonded single crystal component, owing to its shape complexity and randomness during assembly in the practice of bonding single crystal components. The CMSX-4 single crystal superalloy with the orientation combination of 0°+0°, 0°+45° and 0°+90° were brazed by Ni-based filler alloy at 1210 ℃ for 30 min and carried out ageing heat treatment. The effect of base material orientation combination on the microstructure was analyzed by SEM, EBSD and EPMA. The mechanical properties of joints after bonding and ageing treatment were tested. The result indicates that the microstructures and phase compositions of three orientation combination joints were similar in the filler alloy zone, consisting of γ-Ni, γ′, γ+γ′ eutectic, M3B2 type boride, CrB, nickel-silicon compound and γ-Ni+Ni3B+CrB ternary eutectic phase. The melting point depressant B in the filler alloy is not diffused significantly to the base material, and no brittle compound phase is precipitated in the diffusion affected zone of the joint. After ageing treatment, elements diffusion is uniform and brittle precipitates are reduced, and the continuous grain boundary can be observed at the center of the joint when the base material on both sides of the joint has orientation deviation. The testing results of mechanical properties show that the base material orientation deviation has no distinctly effect on the room and high temperature tensile properties of the joint. However, the tensile strengths of the joint at room and high temperature both reduce with orientation deviation after ageing treatment, but the degree of orientation deviation has no obvious influence on the tensile strength of the joint. The fracture of the three joints occurs in the filler alloy zone.
Table 1 Compositions of CMSX-4 single crystal superalloy and JSSNi60A Ni-based braze alloy (mass fraction / %)
Fig.1 Schematic of specimen for brazed bonding (The axial direction of the specimen 1 is parallel to [001] and specimen 2 is deviated from [001] by θ angle; θ=0°, 45° and 90°, respectively)
Fig.2 Dimension diagram of tensile specimen (unit: mm)
Fig.3 SEM images of 0°+0° orientation combination single crystal superalloy brazed joint(a) integrated joint (b) diffusion aftected zone (I) (c) interface bonding zone (II) (d) filler alloy zone (III)
Zone
Ni
Cr
Co
W
Mo
Al
Ti
Ta
Nb
Si
B
Ⅰ
62.8
10.6
12.4
3.2
-
5.4
0.9
2.3
2.1
0.3
-
Ⅱ
63.2
12.5
10.2
3.5
-
4.3
1.3
0.8
2.2
0.5
1.5
Table 2 Compositions of the 0°+0° orientation combination single crystal superalloy brazed joint in Fig.3 (atomic fraction / %)
Fig.4 Back scattered electron (BSE) images of each phase in filler alloy zone(a) γ-Ni, γ', γ+γ' eutectic, M3B2 and CrB boride (b) Ni-Si compound and γ-Ni+Ni3B+CrB ternary eutectic phase
Phase
Ni
Cr
Co
W
Mo
Al
Ti
Ta
Nb
Si
B
M3B2
24.2
13.5
6.3
15.2
4.6
-
0.7
1.3
0.7
-
32.8
CrB
5.9
39.6
4.5
7.8
8.3
-
1.6
1.6
1.8
-
28.9
γ-Ni
60.3
12.1
10.4
3.2
-
7.4
1.4
1.6
2.7
0.9
-
γ′
66.4
4.3
8.3
1.4
0.8
6.7
4.5
1.4
2.0
4.2
-
γ+γ′
61.7
9.8
9.4
1.8
-
9.4
2.8
1.7
0.6
2.8
-
M3Si
50.7
1.6
7.2
-
-
-
0.9
-
14.8
22.5
2.3
γ-Ni+Ni3B+CrB
52.9
8.4
8.8
4.3
1.7
2.1
5.2
-
1.3
2.4
12.9
Table 3 Compositions of each phase in filler alloy zone in Fig.4 (atomic fraction / %)
Fig.5 SEM images of three orientation deviation single crystal superalloy brazed joints(a) 0°+0° (b) 0°+45° (c) 0°+90°
Fig.6 SEM (a~c) and EBSD (d~f) images of three orientation deviation single crystal superalloy brazed joints(a, d) 0°+0° (b, e) 0°+45° (c, f) 0°+90°
Fig.7 SEM images of three orientation deviation single crystal superalloy brazed joints before (a~c) and after (d~f) heat treatment(a, d) 0°+0° (b, e) 0°+45° (c, f) 0°+90°
Fig.8 SEM (a~c) and EBSD (d~f) images of three orientation deviation single crystal superalloy brazed joints after heat treatment(a, d) 0°+0° (b, e) 0°+45° (c, f) 0°+90°
Fig.9 Schematics of formation mechanism and heat treatment process of brazed joint with orientation deviation(a) heating (b) holding (c) brazing joint (d) heat treatment joint
Fig.10 Tensile strengths of three orientation deviation single crystal superalloy brazed joints at room temperature
Fig.11 Longitudinal section OM images of tensile fracture path of three orientation deviation single crystal superalloy brazed joints (a~c) and heat treatment joints (d~f) at room temperature(a, d) 0°+0° (b, e) 0°+45° (c, f) 0°+90°
Fig.12 Tensile strengths of three orientation deviation single crystal superalloy brazed joints at high temperature (980 ℃)
Fig.13 Longitudinal section OM images of tensile fracture path of three orientation deviation single crystal superalloy brazed joints (a~c) and heat treatment joints (d~f) at high temperature (980 ℃)(a, d) 0°+0° (b, e) 0°+45° (c, f) 0°+90°
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