Study of the Reaction Layer of Ti and Al Dissimilar Alloys by Wire and Arc Additive Manufacturing
TIAN Yinbao,SHEN Junqi (),HU Shengsun,GOU Jian
Tianjin Key Laboratory of Advanced Joining Technology, School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China
Cite this article:
TIAN Yinbao , SHEN Junqi , HU Shengsun , GOU Jian. Study of the Reaction Layer of Ti and Al Dissimilar Alloys by Wire and Arc Additive Manufacturing. Acta Metall Sin, 2019, 55(11): 1407-1416.
The wire and arc additive manufactured Ti/Al dissimilar alloys can be used in the aerospace and automobile industries. For some parts, Ti alloy was replaced by Al alloy, which reduced the weight and cost. The additive manufactured Ti/Al dissimilar alloys had the advantages of two materials and remedied the each other's shortcomings. In this study, TC4 and ER2319 wires were deposited by direct current cold metal transfer (CMT) and variable polarity-CMT+pulse mode, respectively, to realize the wire and arc additive manufacturing for Ti/Al dissimilar alloys. The arc shape, droplet transfer, voltage and current were captured by high speed camera and electrical signal acquisition system. Microstructure and mechanical properties of Ti/Al component were analyzed by OM, SEM, TEM, EDS, hardness test and tensile test. The results showed that the variable polarity-CMT+pulse welding process included the positive pulse periods and negative CMT periods. During the positive pulse periods, the arc concentrated at the end of welding wire. During the negative CMT periods, the heat input was low, which had a cooling effect on component. The reaction layer in the component included the interface layer and transition layer. The thickness of TiAl3 interfacial layer was 10 μm. The hardness of reaction layer was between that of Ti and Al alloys. The crack was formed in the interface layer. The average tensile strength was approximately 65 MPa. All samples fractured in the interface layer. The fracture mode was brittle fracture.
Fig.2 Current and voltage waveforms during the deposition process for the first Al alloy layer (EN-CMT—electrode negative cold metal transfer)
Fig.3 Droplet transfer processes of the first Al alloy layer (Arrows indicate the movement directions of the wire)(a) pulse period (b) EN-CMT period
Fig.4 OM image of Ti/Al wire and arc additive manufacturing (WAAM) component (a), SEM images of areas II (b), III (c) and IV (d) in Fig.4a
Position
Atomic fraction of element / %
Possible phase
Ti
Al
Cu
V
Point 1 in Fig.4b
21.20
77.99
-
0.81
TiAl3
Point 2 in Fig.4c
24.23
74.23
-
1.54
TiAl3
Point 3 in Fig.4d
85.21
11.50
-
3.29
Ti
Point 4 in Fig.5a
20.90
77.79
-
1.31
TiAl3
Point 5 in Fig.5a
-
71.97
28.03
-
Al2Cu
Point 6 in Fig.9b
22.30
76.73
-
0.97
TiAl3
Table 2 EDS analysis results for different positions in the WAAM component
Fig.5 High magnified SEM image of area II in Fig.4a (a) and corresponding element distributions for Al (b), Ti (c) and Cu (d)Color online
Fig.6 TEM analyses of area II in Fig.4a(a) TEM image of net shape phase (b) electron diffraction pattern of circle area in Fig.6a(c) TEM image of long strip phase (d) electron diffraction pattern of circle area in Fig.6c
Fig.7 Schematic of the formation of Ti/Al reaction layer(a) interdiffusion of Ti and Al atoms (b) formation of TiAl3 in area III in Fig.4a(c) formation of TiAl3 and Al2Cu in area II in Fig.4a (d) solidification of Al alloy
Fig.8 SEM image of crack in reaction layer of WAAM component
Fig.9 Low (a) and locally high (b) magnified SEM images of fracture surface
Fig.10 Hardness distributions near the interface layer of WAAM component
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