Cube texture formation of Ni9.3W alloy substrates:preparation by optimized deformation sequence and anneal process
College of Materials Science and Engineering,Beijing University of Technology
作者简介:*Hong-Li Suo e-mail:honglisuo@bjut.edu.cn;
收稿日期:19 December 2015
基金:financially supported by the National Municipal Natural Science Foundation (Nos.51571002,51171002);the Beijing Municipal Natural Science Foundation (Nos.2132011,2172008);the Doctoral Program of Higher Education of Special Research Fund (No.20121103110012);Beijing Municipal Natural Science Foundation B Type(No.KZ201310005003);the Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges under Beijing Municipality (No.IDHT20130510);
Cube texture formation of Ni9.3W alloy substrates:preparation by optimized deformation sequence and anneal process
Fa-Xue Peng Hong-Li Suo Lin Ma Hui Tian Min Liu Jing Liu Dan Yu Yi-Chen Meng
College of Materials Science and Engineering,Beijing University of Technology
Abstract:
The Ni9.3 W alloy with no ferromagnetism and high yield strength is one of the most promising textured substrate materials for coated conductors,but its low stacking fault energy makes it difficult to obtain a strong cube texture by traditional rolling methods and recrystallization anneals.This paper introduces four-time static recoveries during the rolling process.Rolled tapes with80 μm in thickness were obtained by applying various deformation sequences between static recoveries to study their effects on the cube texture formation in Ni9.3 W alloy substrates.The results show that rising gradient deformation sequence is an advantageous way to obtain a higher amount of cube texture,its content increases by 29.2%compared to that of traditional deformation sequence.The effect of the new recrystallization annealing process on the cube texture formation was analyzed.It is shown that the cube texture content increases with anneal temperature increasing in one-step anneal,but decreases again at higher anneal temperature.Two-step anneal could effectively improve the cube texture content,which could be further enhanced by extending holding time during the first-step anneal.However,too long holding time leads to the decrease in cube texture content.Finally,Ni9.3 W alloy substrates with a cube texture content of ~90.0 vol%(<15°) are obtained by optimized two-step anneal.
Keyword:
Ni9.3W substrates; Deformation sequence; Anneal process; Cube texture;
Received: 19 December 2015
1 Introduction
The second generation of coated conductor based on YBa2Cu3O7-x (YBCO) is considered to be a promising superconducting material with wide application prospects and a high potential of industrial application,owing to its high critical current density and low irreversible field
2 Experimental
The Ni9.3W alloy casting ingot was prepared by vacuum induction melting from pure nickel (99.9%) and tungsten(99.9%).After melting,the casting ingot was hot-forged at1200℃to obtain a square rod of 15 mm×20 mm.Subsequently,an ingot of 15 mm×20 mm×25 mm was cut from the Ni9.3W alloy rod as-obtained for subsequent experiments.The ingot was homogenized at 1200℃for24 h,rolled to 8 mm in thickness and submitted to recrystallization anneals at 900℃for 1 h.Then,the ingot was subpided into four samples with 8 mm in thickness(named as Samples 1,2,3 and 4,respectively).Sample 1was submitted to the traditional deformation way:The sample was cold-rolled directly to 80μm without any static recovery during the rolling process.Four-time static recoveries (550℃,2 h) were introduced in the subsequent rolling process for Samples 2,3 and 4.The deformation sequences between static recoveries of four samples are not same.The deformation reduction mentioned in this study is relative reduction,e.g.,the sample thickness before every static recovery is related to that of the last static recovery.More details of the four samples’deformation sequences are shown in Table 1.
The four samples were cold-rolled from 8 mm to 80μm,with reduction ratios of~5%per pass and total deformation reduction of~99%.Then,the cube texture was formed in the four substrates at 1100℃for 2 h.The effect of the deformation sequence on the cube texture formation was analyzed by measuring the cube texture performance to obtain optimized rolling deformation sequence.On this basis,the effect of recrystallization anneal process on the cube texture formation was taken into consideration.First,the anneal temperature was raised by a series of annealing processes (1150℃,2 h;1200℃,2 h;1250℃,2 h).Two-step anneal was then carried out to improve the cube texture content.The effect of different holding time (0.5,1.0,1.5 and 2.0 h) during the first-step anneal on the cube texture formation was studied,when the temperature was700℃.The second-step anneal was introduced at 1150℃for 2 h.Optimized parameters of the first anneal step were obtained by measuring the cube texture performance.Then,the temperature of the second-step anneal was increased to obtain a higher cube texture content.Finally,Ni9.3W alloy substrates with high cube texture content were obtained by optimized two-step anneal.
Table 1 Experimental details of relative reduction/%
The rolling texture of the rolled substrates was calculated using orientation distribution functions (ODFs)measured in step of 5°from 0°to 75°by X-ray diffractometer (XRD,Bruker D8 Advance,CuKα)
3 Results and discussion
3.1 Deformation sequences
Figure 1 shows the contents of the rolling texture components in the four samples of Ni9.3W alloy substrates rolled to 80μm.It can be easily seen that Sample 1 has the most Brass orientation content,reaching 37.18 vol%(<15°,the same below),while the contents of S orientation and copper orientation are the lowest among all samples,being29.41 vol%and 6.18 vol%,respectively,which is disadvantageous for the cube texture formation
Fig.1 Contents of main rolling textures for Ni9.3W tapes rolled to80μm
Subsequent recrystallization anneals were performed at1100℃for 2 h for the four kinds of substrates.EBSD maps and comprehensive properties of annealed substrates are shown in Figs.2 and 3.It can be easily seen that the cube texture content of Sample 3 is higher with respect to other samples.In addition,the amount of low-angle grain boundaries (LAGB) and twin boundaries (∑3) of Sample 3is superior to that of other samples.It must be noted that the cube texture content of Sample 3 increases by29.2 vol%,11.1 vol%and 14.1 vol%,respectively,compared to those of Samples 1 and 4.In order to confirm the result,the four samples rolled to 80μm were annealed under higher temperature further (1150℃,2 h;1200℃,2 h).The results show that higher cube texture content is still obtained by Sample 3 with respect to other samples.Thus,the rising gradient deformation sequence (Sample 3)is a favorable way to the formation of cube texture ofNi9.3W alloy substrates.
For Sample 2,high cube texture content is not obtained.Possibly,the reason may be that static recovery is only a process of stress release and it is not a good choice that Sample 2 was rolled to 80μm by applying the same deformation sequence due to too low SFE
Fig.3 Properties of Ni9.3W substrates after annealing at 1100℃for2h
Fig.2 EBSD maps of annealed Ni9.3W substrates (1100℃,2 h):a Sample 1,b Sample 2,c Sample 3 and d Sample 4 (TD,transverse direction;RD,rolling direction)
3.2 Optimizing of anneal process
Since Ni9.3W alloy has a lower SFE,Ni9.3W alloy substrates of a high cube texture content are not easy to be obtained after traditional anneal.From the above studies,optimized rolling deformation processing (Sample 3:the rising gradient deformation sequence) is obtained.However,higher cube texture content is not obtained after the recrystallization anneal at 1100℃for 2 h.Therefore,to further improve the cube texture content of Ni9.3W alloy substrates,the recrystallization anneal process must be carefully studied for Sample 3.This paper describes the optimization study of the recrystallization anneal process.The cube texture content is optimized by improving the temperature of one-step recrystallization anneal process to increase the cube texture content of the Ni9.3W alloy substrates.Figure 4 shows the cube texture content of Ni9.3W alloy substrates after one-step recrystallization anneal at various temperatures.It can be easily seen that the cube texture content first increases and then decreases at higher recrystallization anneal temperature,and the cube texture content reaches its highest value of 79.3%(<15°) at1200℃,being optimized.Since recrystallization anneal is a process of thermal activation,it is related to the thermal activation energy outside
Fig.4 Content of cube texture for Ni9.3W substrates after annealing at different temperatures
Many studies have shown that two-step anneal processes are favorable to the formation of cube texture
In order to continually improve the cube texture content of Ni9.3W alloy substrates,the temperature of the secondstep anneal was further increased to obtain a higher amount of cube texture (1200,1250 and 1300℃).Figures 5 and 6show EBSD maps and properties of Ni9.3W alloy substrates after two-step anneal,respectively.It can be easily seen that the cube texture content of Ni9.3W alloy substrate reaches~90.0 vol%(<15°) when the temperature of second-step anneal is 1250°C,and its LAGB andΣ3 contents are superior,being 72.3 vol%and 11.1 vol%,respectively.When the anneal temperature is enhanced to1300℃,the content of cube texture declines due to the occurrence of the secondary recrystallization.At this temperature,inpidual grains grow abnormally
Table 2 Properties of annealed Ni9.3W substrates
Fig.5 EBSD maps of Ni9.3W substrates after annealing at a 1200℃,b 1250℃and c 1300℃
Fig.6 Properties of Ni9.3W substrates after annealing at different temperatures
4 Conclusion
For Ni9.3W alloy substrates,the rising gradient deformation sequence could effectively improve its cube texture content which increases by 29.2%compared to that of traditional deformation sequence.The cube texture content increases with anneal temperature increasing in one-step anneal,but decreases again at higher anneal temperature.Two-step anneals effectively improve the cube texture content of Ni9.3W alloy substrates,which could further be enhanced by extending the holding time during the firststep anneal.However,too long holding time would also lead to the decrease in cube texture content.Finally,Ni9.3W alloy substrates with a cube texture content of~90.0 vol%(<15°) are obtained by optimized two-step anneal processes.
参考文献
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