Ti2AlNb alloys are considered as a potential structural material for high temperature applications like gas turbine engine components due to their high specific strength and good creep resistance. In this work, pre-alloyed powder of Ti-22Al-24Nb-0.5Mo (atomic fraction, %) was prepared by an electrode induction melting gas atomization process and powder metallurgy (PM) alloys was made through a hot isostatic pressing (HIPing) route. PM Ti-22Al-24Nb-0.5Mo rings and plates were welded by electron beam welding (EBW). The microstructure of the welded joints was investigated by OM, SEM, EPMA and X-ray tomography. The effect of post-weld heat treatments (PWHT) on the microhardness, tensile properties and rupture lifetime at 650 ℃, 360 MPa of the welding joint of PM Ti-22Al-24Nb-0.5Mo plate was also studied. The results show that the HIPing temperature will affect the porosity distribution of PM Ti-22Al-24Nb-0.5Mo alloys. The PM Ti-22Al-24Nb-0.5Mo rings HIPed at 1030 ℃ after 980 ℃, 2 h, vacuum furnace cooling show good weldability. The fusion zone (FZ), heat affected zone (HAZ) and base metal (BM) of welded joints show homogeneous chemical composition. The microstructures of FZ, HAZ and BM are different while the microhardnesses of FZ, HAZ and BM show no obvious differences. Tensile and stress rupture lifetime testing specimens all fracture in the FZ. It is found that there are a certain number of micro-porosity in the FZ of the welded joints. However, the porosity reduces after PWHT, which will improve the high temperature ductility and rupture properties of the PM Ti-22Al-24Nb-0.5Mo welded joints.
Fig.1 Rings (a) and plate (b) of powder metallurgy Ti-22Al-24Nb-0.5Mo alloys after electron beam welding
Fig.2 Schematics of the specimens of as-welded powder metallurgy Ti-22Al-24Nb-0.5Mo alloys for tensile tests (a) and rupture lifetime tests at 650 oC and 360 MPa (b) (unit: mm, FZ—fusion zone)
Fig.3 SEM images of Ti-22Al-24Nb-0.5Mo pre-alloyed powders in full view (a) and high-magnification of Fig.3a (b)
Fig.4 XRD spectrum of Ti-22Al-24Nb-0.5Mo pre-alloyed powder
Fig.5 Micro- porosity distribution of PM Ti- 22Al- 24Nb-0.5Mo alloys under different HIP temperatures[11]
Sample
Al
Nb
Mo
O
N
H
Ar
Ti
Pre-alloyed powder
10.4
41.3
0.92
0.065
0.0021
0.0006
<0.0005
Bal.
As-HIPed compact
10.3
41.4
0.90
0.065
0.0100
0.0010
<0.0005
Bal.
Table 1 Chemical compositions of Ti-22Al-24Nb-0.5Mo pre-alloyed powders and as-HIPed compacts (mass fraction / %)
Fig.6 OM images (a, b) and corresponding X-ray inspections (c, d) of as-welded joints of the HIPed (a, c) and heat-treated (b, d) Ti-22Al-24Nb-0.5Mo alloys
Fig.7 The microstructure (a), Al distribution (b) and Nb distribution (c) of as-welded powder metallurgy Ti-22Al-24Nb-0.5Mo alloys joints (HAZ—heat affected zone, BM—base metal)
Fig.8 Microhardness distributions of powder metallurgy Ti-22Al-24Nb-0.5Mo alloys joints at as-welded state (a) and as-welded + PWHT state (b) (PWHT—post-weld heat treatment)
Sample
T / oC
Rm / MPa
δ / %
L / h
Rm1/Rm2
Fracture location
BM
20
1072
10.0 12.0
25
- -
- -
650
743
As-weld
20
978
4.0
0.3
94%
Joint
650
680
-
93%
Joint
As-weld+HT1
20
710
- 6.0
3
69% 92%
Joint Joint
650
675
As-weld+HT2
20
948
3.0
3
92%
Joint
650
660
12.0
90%
Joint
As-weld+HT3
20
941
4.0
5
91%
Joint
650
590
6.0
81%
Joint
Table 2 Mechanical properties of powder metallurgy Ti-22Al-24Nb-0.5Mo alloys electron beam welded joints
[1]
Banerjee D, Gogia A K, Nandi T K, Joshi V A.Acta Metall, 1988; 36: 871
[2]
Wang Z, Cao L, Liu R C, Liu D, Cui Y Y, Yang R.Acta Metall Sin, 2013; 49: 1487
[2]
(王震, 曹磊, 刘仁慈, 刘冬, 崔玉友, 杨锐. 金属学报, 2013, 49: 1487)
[3]
Boehlert C J, Majumdar B S, Seetharaman V, Miracle D B.Metall Mater Trans, 1999; 30A: 2305
[4]
Zhang S Z.PhD Dissertation, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 2004
[4]
(张尚洲. 中国科学院金属研究所博士学位论文, 沈阳, 2004)
[5]
Hu D, Wu X, Loretto M H.Intermetallics, 2005; 13: 914
[6]
Wang Y.PhD Dissertation, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 2011
Deng Y H, Guan Q, Tao J, Wu B, Wang X C.Acta Metall Sin, 2015; 51: 1111
[14]
(邓云华, 关桥, 陶军, 吴冰, 王西昌. 金属学报, 2015; 51: 1111)
[15]
Guo R P. Master Thesis, Northeastern University, Shenyang, 2014
[15]
(郭瑞鹏. 东北大学硕士学位论文, 沈阳, 2014)
[16]
Guo R P, Xu L, Wu J, Yang R, Zong B Y. Mater Sci Eng, 2015; A639: 327
[17]
Wang S G, Wang S C, Zhang L.Acta Metall Sin, 2013; 49: 897
[17]
(王绍钢, 王苏程, 张磊. 金属学报, 2013; 49: 897)
[18]
Xu L, Wu J, Cui Y Y, Yang R.In: Kim Y W, Smarsly W, Lin J P, Dimiduk D, Appel F eds., Gamma Titanium Aluminide Alloys 2014, Warrendale, PA: TMS, 2014: 195
[19]
Liu X W, Su Y Q, Luo L S, Li K, Dong F Y, Guo J J, Fu H Z.Int J Hydrogen Energy, 2011; 36: 3260
[20]
Li W B, Easterling K E.Powder Metall, 1992; 35: 47
[21]
Xu L, Guo R P, Bai C G, Lei J F, Yang R.J Mater Sci Technol, 2014; 30: 1289
[22]
Wu J, Xu L, Guo R P, Lu Z G, Cui Y Y, Yang R.Mater Res Innovations, 2015; 19(sup9): 46
[23]
Kou S. WeldingMetallurgy.2nd ed . Canada: John Wiley &Sons, 2003: 27
[24]
Boehlert C J.Metall Mater Trans, 2001; 32A: 1977
[25]
Boehlert C J, Miracle D B.Metall Mater Trans, 1999; 30A: 2349
