EFFECT OF C ON THE RUPTURE PROPERTIES OF SINGLE CRYSTAL SUPERALLOYS
YU Zhuhuan1(), LIU Lin2
1 Department of Materials Science and Engineering, Xi′an University of Science and Technology, Xi′an 710054 2 State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi′an 710072
Cite this article:
YU Zhuhuan, LIU Lin. EFFECT OF C ON THE RUPTURE PROPERTIES OF SINGLE CRYSTAL SUPERALLOYS. Acta Metall Sin, 2014, 50(7): 854-862.
The effects of carbon addition on the solidification microstructure and rupture life were investigated in five different carbon level single crystal superalloys. With the increasing of carbon level, the volume fraction of eutectic decreased markedly and the volume fraction of carbide increased. The carbides mainly distributed in interdendrite zone, when the carbon level was high, there were little carbides in the dendrite core. After heat treatment, coarse γ/γ′ eutectics in interdendrte zone mainly were dissolved, a little γ/γ′ eutectic was not dissolved. Morphologies of carbide became much simpler, the size of carbide decreased, the volume fraction of carbide decreased, and the distribution of carbide became much more dispersion, and the type of carbide became much more variety. Grain and chainlike M23C6 appeared after heat treatment. With the increasing of carbon level, the rupture life of single crystal superalloy increased at first and then decreased, and the rupture life came up to the maximum when the carbon level was 0.045%. SEM observation indicates that the cracks of alloys mainly originate from shrinkage, carbides and eutectics. The change of rupture life was mainly because the un-dissolved eutectic and carbides of alloy which act as the source of cracks. The variation trend of carbide and eutectic was contrary with the increasing of carbon level; therefore, the carbon content should be controlled in the perfect level.
Fund: Supported by National Natural Science Foundation of China (No.51201130), National Basic Research Program of China (No.2010CB631201), Natural Science Foundation of Shaanxi Province (No.2012JQ6005), Startup Project of Doctor Scientific Research of Xi′an University of Science and Technology (No.2011QDJ023) and Fund of the State Key Laboratory of Solidification Processing in NWPU (No.SKLSP201226)
Table 1 Chemical compositions of single crystal superalloys with different carbon additions
(mass fraction / %)
Fig.1 SEM images of alloys with carbon additions of 0.001% (a), 0.006% (b), 0.045% (c), 0.085% (d) and 0.150% (e)
Fig.2 Volume fraction of eutectic and carbide in the alloys with different carbon additions
Fig.3 OM images of dendritic microstructure for alloys after heat treatment with carbon additions of 0.001% (a), 0.006% (b), 0.045% (c), 0.085% (d) and 0.150% (e)
Fig.4 Carbide morphologies of deep etched sample after heat treatment with carbon additions of 0.006% (a), 0.045% (b, c), 0.085% (d, e) and 0.150% (f~h)
Fig.5 Mass fraction of grainy carbide by EDS analysis after heat treatment
Fig.6 Relationships between the rupture life and carbon content
Fig.7 Relationships among the elongation d, shrinkage y and carbon content
Fig.8 Crack morphologies near the fracture with carbon additions of 0.001% (a, b), 0.006% (c, d), 0.045% (e, f), 0.085% (g, h) and 0.150% (i, j)
Fig.9 TEM image (a) and EDS analysis (b) of M6C carbide in the rupture sample with 0.045%C
[1]
Guo J T. Acta Metall Sin, 2010; 46: 513
(郭建亭. 金属学报, 2010; 46: 513)
[2]
Pollock T M, Murphy W H, Goldman W H, Antolokch S D, Stusrud R W, MacKay R A. Superalloys 1992, Warrendale: TMS, 1992: 125
[3]
Liu G, Liu L, Zhang S X, Yang C B, Zhang J, Fu H Z. Acta Metall Sin, 2012; 48: 845
