EFFECT OF GROWTH ANGLE AND SOLIDIFICATION RATE ON THE FLOATING ZONE STABILITY FOR PROCESSING OF HIGH-TEMPERATURE PURE METALS
LI Shuangming1(), GENG Zhenbo1, HU Rui1, LIU Yi2, LUO Ximing2
1 State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072 2 Kunming Institute of Precious Metals, Kunming 650106
Cite this article:
LI Shuangming, GENG Zhenbo, HU Rui, LIU Yi, LUO Ximing. EFFECT OF GROWTH ANGLE AND SOLIDIFICATION RATE ON THE FLOATING ZONE STABILITY FOR PROCESSING OF HIGH-TEMPERATURE PURE METALS. Acta Metall Sin, 2015, 51(1): 114-120.
The height of floating zone and molten zone instability for five pure metals including Nb, W, Ta, Mo, and Ir with high melting points is investigated using electron beam floating zone method (EBFZM). The results show that the height level of floating zone for these five metals are in order with the sequence of Nb>Mo>W>Ta>Ir. The crystal growth angles for these metals are in the range of 8°~13° and the sample in large size can be developed by EBFZM as the growth angle is found not to be zero. Meanwhile, the actual growth angles are related with the interface growth mechanism. For continuous growth mechanism, the growth angles vary slightly with the solidification rate for rough interface, and for dislocation growth mechanism, the growth angles decrease with increasing the solidification rate. If faceting growth mechanism prevails, the growth angles drop remarkably at a low solidification rate and further increase with increasing the solidification rate. Additionally, by employing EBFZM growth of Ir and Mo pure metals, a solidification rate approaching 1 mm/min is available for controlling the growth angle and the height of floating zone. These calculations fit well with the experimental results of Mo single crystal prepared by EBFZM.
Fig.1 Schematic shapes of a molten floating zone growth of a cylindrical crystal by electron beam floating zone method (EBFZM) (M—melting interface, S—solidification interface, L—liquid metal, a—growth angle, rc—growing crystal radius, h—height of molten zone, R1 and R2—radii of principal curvature, r—axial coordinate, z—vertical coordinate)
(a) upward growth
(b) pulling down growth
Metal
r / (g·m-3)
Tm / ℃
gsl / (mN·m-1)
glv / (mN·m-1)
a / (°)
hmax / mm
Ir
20.00
2443
411
2241
10.6
8.4
Mo
9.34
2620
464
2110
12.7
11.9
Nb
7.83
2468
347
2335
8.4
13.7
Ta
15.00
2950
415
2467
9.7
10.1
W
16.20
3370
510
2676
12.0
10.2
Table 1 Physical parameters for five pure metals with high melting points[13,14]
Fig.2 Relationship of heights of floating zone of Ir, Mo, Nb, Ta, and W with the radius of the floating zone stable growth by EBFZM, and imposed with the Rayleigh′s instability results
Fig.3 Relationship of heights of floating zone of Ir and Mo with the radius of floating zone stable growth by EBFZM as the growth angle does not equal to zero
Fig.4 Crystal growth angles as a function of the solidification rate for Ir (a) and Mo (b) prepared by EBFZM
Fig.5 Heights of floating zone vs the solidification rate of Ir (a) and Mo (b) in diameter of 30 mm prepared by EBFZM at different growth mechanisms
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