1. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China 2. Electron Microscopy Center, Chongqing University, Chongqing 400044, China
Cite this article:
Jialin ZHU,Shifeng LIU,Yu CAO,Yahui LIU,Chao DENG,Qing LIU. Effect of Cross Rolling Cycle on the Deformed and Recrystallized Gradient in High-Purity Tantalum Plate. Acta Metall Sin, 2019, 55(8): 1019-1033.
Cross rolling plays an important role in the production of high-quality tantalum (Ta) sputtering targets, which are crucial in achieving thin films for micro-electronic components. However, the effect of the cross rolling cycle on the microstructure homogeneity is always ignored. Therefore, 1 and 2 cycle samples were obtained by a new approach named a 135° cross rolling. The deformation and recrystallization behavior of high-purity Ta plate then was systematically compared between 1 and 2 cross rolling cycles, aiming to elucidate why the increase of cross rolling cycles can effectively ameliorate the microstructure gradient along the thickness direction. XRD results showed that the 2 cycle sample through the thickness consisted of a relatively homogenous {111}<uvw> ([111]//normal direction (ND)) and {100}<uvw> ([100]//ND) fibers while texture distribution was extremely uneven for the 1 cycle sample. The stored energy was quantitatively analyzed by X-ray line profile analysis (XLPA) and it was found that the stored energy across the thickness distributed more homogeneously for the 2 cycle sample. Misorientation characteristics of deformed grains with different rolling cycles were analyzed in detail by visualizing the misorientation angle based on an electron backscatter diffraction dataset. Many well-defined microbands and microshear bands occurred in the {111} grain at the center layer for the 1 cycle sample, while it can be effectively destroyed with the increase of the cross rolling cycle and few peaks occurred in the "point to point" plot. Kernel average misorientation (KAM) and grain reference orientation deviation-hyper (GROD-Hyper) further confirmed their differences. Then, micorband and microshear bands were detailedly characterized by TEM, and the analysis based on relative Schmid factor suggested that the primary slip system activated in the {111} grains led to the formation of microbands in the 1 cycle sample, while multiple slip systems appeared to be activated in the 2 cycle sample and deformation was more uniform. Upon annealing, the remarkably reduced stored energy gap between the {111} and {100} grain as well as the relatively homogeneous deformation microstructure between the surface and center layer for the 2 cycle sample was conductive to synchronous recrystallization together, while the high stored energy as driving force and preferential nucleation sites at the center region led to faster recrystallization for the 1 cycle sample. The recrystallization microstructure was relatively uniform and smaller variation in grain size for the 2 cycle sample through the thickness, which was beneficial to the application of Ta sputtering target. Therefore, the increase of cross rolling cycle can ameliorate the recrystallized kinetics and microstructure of high purity Ta plate.
Fig.1 Sketch maps of 135° clock rolling employed in this study (RD—rolling direction) (a) the first cycle (b) the second cycle
Rolling cycle
Rolling pass
Entrance thickness
Exit thickness mm
Rolling gap geometry
Strain per pass
Total rolling reduction
mm
h-1
%
%
First cycle
1
20.0
17.2
2.01
14.00
14.0
2
17.2
14.7
2.22
14.53
26.5
3
14.7
12.6
2.37
14.28
37.0
4
12.6
10.8
2.56
14.28
46.0
5
10.8
9.3
2.72
13.89
53.5
6
9.3
8.0
2.95
13.98
60.0
7
8.0
6.9
3.15
13.75
65.5
8
6.9
6.0
3.29
13.04
70.0
Second cycle
9
6.0
5.3
3.31
11.67
73.5
10
5.3
4.7
3.46
11.32
76.5
11
4.7
4.2
3.55
10.64
79.0
12
4.2
3.8
3.54
9.52
81.0
13
3.8
3.5
3.36
7.89
82.5
14
3.5
3.2
3.66
8.57
84.0
15
3.2
3.0
3.23
6.25
85.0
16
3.0
2.8
3.45
6.67
87.0
Table 1 Rolling scheme of 1 and 2 cycle samples, respectively
Fig.2 Macrotextures along the thickness direction for cross rolling Ta plate with 1 (a1~a3) and 2 (b1~b3) cycles (Fmax—maximum orientation distribution function (ODF) density)Color online(a1, b1) surface layer (a2, b2) quarter layer (a3, b3) center layer
Rolling cycle
Position
Diffraction plane
Yhkl[21,22,23]
vhkl[21,22,23]
Br
Ba
Ehkl
GPa
J·mol-1
First cycle
Surface
(200)
145.517
0.316
0.185
0.100
3.997
(222)
387.931
0.362
0.318
0.140
5.037
Quarter
(200)
145.517
0.316
0.179
0.100
3.636
(222)
387.931
0.362
0.302
0.140
4.425
Center
(200)
145.517
0.316
0.218
0.100
6.192
(222)
387.931
0.362
0.453
0.140
11.469
Second cycle
Surface
(200)
145.517
0.316
0.190
0.100
4.306
(222)
387.931
0.362
0.312
0.140
4.804
Quarter
(200)
145.517
0.316
0.186
0.100
4.058
(222)
387.931
0.362
0.295
0.140
4.166
Center
(200)
145.517
0.316
0.197
0.100
4.753
(222)
387.931
0.362
0.326
0.140
5.356
Table 2 Orientation-dependent stored energy of 1 and 2 cycle samples at different thicknesses by XLPA
Fig.3 Orientation image maps (OIMs) of 1 (a, b) and 2 (c, d) cycle samples at the surface (a, c) and center layer (b, d) (ND—normal direction, MSB—microshear band)Color online
Fig.4 Misorientation profiles along the scanning lines S1 and S2 in Fig.3a (a), C1 and C2 in Fig.3b (b), S3 and S4 in Fig.3c (c), C3 and C4 in Fig.3d (d)
Fig.5 OIMs (a1~d1), grain reference orientation deviation-hyper (GROD-Hyper) (a2~d2) and kernel average misorientation (KAM) (a3~d3) maps of {111} and {100} grains at the surface and center layer for 1 and 2 cycle samplesColor online(a1~a3) 1 cycle, surface (b1~b3) 1 cycle, center(c1~c3) 2 cycles, surface (d1~d3) 2 cycles, center
Fig.6 OIMs of 1 and 2 cycle samples annealed at 1050 ℃ for 5 min (a1~d1), 10 min (a2~d2), 30 min (a3~d3), 60 min (a4~d4) and 120 min (a5~d5)Color online(a1~a5) 1 cycle, surface (b1~b5) 1 cycle, center(c1~c5) 2 cycles, surface (d1~d5) 2 cycles, center
Fig.7 Grain size distributions of 1 (a) and 2 (b) cycle samples annealed at 1050 ℃ for 120 min
Fig.8 Micro-hardness curves of 1 (a) and 2 (b) cycle samples annealed at 1050 ℃ for different time
Texture
0°
135°
270°
405°
540°
γ fiber
(60°, 55°, 45°)
(195°, 55°, 45°)
(330°, 55°, 45°)
(105°, 55°, 45°)
(240°, 55°, 45°)
{111}<011>
{111}<341>
{111}<211>
{111}<314>
{111}<011>
(90°, 55°, 45°)
(225°, 55°, 45°)
(0°, 55°, 45°)
(135°, 55°, 45°)
(270°, 55°, 45°)
{111}<112>
{111}<143>
{111}<110>
{111}<413>
{111}<112>
θ fiber
(0°, 0°, 45°)
(135°, 0°, 45°)
(270°, 0°, 45°)
(45°, 0°, 45°)
(180°, 0°, 45°)
{001}<110>
{001}<100>
{001}<110>
{001}<010>
{001}<110>
(45°, 0°, 45°)
(180°, 0°, 45°)
(315°, 0°, 45°)
(90°, 0°, 45°)
(225°, 0°, 45°)
{001}<010>
{001}<110>
{001}<100>
{001}<110>
{001}<010>
Table 3 Orientation evolution with rolling direction
Fig.9 TEM images and corresponding SAED patterns (insets) showing the dislocation morphologies of 1 (a, b) and 2 (c, d) cycle samples in {111} grain (a, c) and {100} grain (b, d) (MBs—microbands, CBs—cell blocks)
Rolling cycle
position
Point
Euler angle (φ1, φ, φ2)
Maximum (SM)
Secondary (SS)
? / %
First cycle
Surface-{111}
P1
(358.82, 36.219, 49.918)
0.4317
0.3962
8.2233
P2
(1.6153, 35.251, 47.642)
0.4251
0.3924
7.6923
P3
(3.5297, 35.013, 46.584)
0.4219
0.3954
6.2811
Surface-{100}
P1
(97.475, 36.196, 2.1378)
0.2836
0.2677
5.6064
P2
(97.253, 36.315, 3.9174)
0.2844
0.2695
5.2391
P3
(97.851, 36.060, 3.2431)
0.2871
0.2693
6.1999
Center-{111}
P1
(203.06, 39.914, 17.290)
0.4657
0.3956
15.0526
P2
(201.92, 40.490, 17.615)
0.4663
0.3926
15.8052
P3
(201.61, 40.022, 18.037)
0.4675
0.3956
15.3796
Center-{100}
P1
(277.21, 20.078, 87.222)
0.3669
0.3375
8.0130
P2
(278.54, 20.308, 86.565)
0.3690
0.3344
9.3766
P3
(279.73, 20.075, 85.354)
0.3702
0.3337
9.8595
Second cycle
Surface-{111}
P1
(178.23, 33.425, 48.046)
0.4269
0.4063
4.8254
P2
(177.25, 32.668, 48.757)
0.4305
0.4113
4.4599
P3
(176.55, 33.356, 48.129)
0.4247
0.4091
3.6731
Surface-{100}
P1
(284.72, 32.614, 74.052)
0.3013
0.2841
5.7085
P2
(287.28, 31.133, 72.346)
0.3068
0.2907
5.2477
P3
(285.63, 31.163, 73.580)
0.3051
0.2887
5.3752
Center-{111}
P1
(38.471, 44.421, 2.9263)
0.4078
0.3766
7.6508
P2
(38.870, 44.086, 2.0842)
0.4073
0.3790
6.9481
P3
(39.115, 43.609, 1.7601)
0.4089
0.3773
7.7280
Center-{100}
P1
(103.58, 34.267, 86.929)
0.3067
0.2931
4.4343
P2
(102.67, 34.886, 88.888)
0.3044
0.2885
5.2233
P3
(102.64, 35.064, 88.995)
0.3037
0.2869
5.5317
Table 4 Euler angle, the maximum and secondary Schmid factors and the relative Schmid factor (?) of some points
Fig.10 ? for 696 points selected from lines L1 and L2 in Fig.5a1 (a), L3 and L4 in Fig.5b1 (b), L5 and L6 in Fig.5c1 (c) and L7 and L8 in Fig.5d1 (d)
Fig.11 Band contrast distributions of {111} and {100} grains at the surface (a, c) and center layer (b, d) for 1 (a, b) and 2 (c, d) cycle samples
Rolling cycle
Position
Grain orientation
Qi(gi)
Qmax
Qmin
Hi / (J·mol-1)
First cycle
Surface
{100}
86.5
121.5
13.5
3.241
{111}
76.5
109.5
22.5
3.793
Center
{100}
82.5
119.5
18.5
3.663
{111}
63.5
125.5
14.5
5.586
Second cycle
Surface
{100}
96.5
130.5
23.5
3.178
{111}
93.5
128.5
29.5
3.535
Center
{100}
91.5
126.5
20.5
3.302
{111}
87.5
126.5
18.5
3.611
Table 5 Local stored energies in {111} and {100} grains at the surface and center layer by EBSD
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