MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF TC1 ALLOY FABRICATED BY PLASMA ARC COLD HEARTH MELTING DURING ROLLING PROCESS
LIU Mengying1, CHANG Hai1(), XU Feng2, XU Zhengfang2, YANG Zhao2, WANG Ning2, GAN Weimin3, FENG Qiang1,4()
1 National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083 2 Baosteel Special Metals Co., Ltd., Shanghai 200940 3 Helmholtz-Zentrum Geesthacht, Out Station at FRM2, Garching, Germany, 85747 4 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083
Cite this article:
LIU Mengying, CHANG Hai, XU Feng, XU Zhengfang, YANG Zhao, WANG Ning, GAN Weimin, FENG Qiang. MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF TC1 ALLOY FABRICATED BY PLASMA ARC COLD HEARTH MELTING DURING ROLLING PROCESS. Acta Metall Sin, 2015, 51(3): 341-348.
Plasma arc cold hearth melting (PAM) is an effective technology to produce high purity titanium alloy ingots which are widely used in aeronautic and astronautic industries. To date, the development of PAM in our country is still at initial stage. It is necessary to investigate the melting parameters of PAM and the following thermal mechanical processing of the ingots fabricated by PAM. In this study, the TC1 alloy ingots casted by PAM were cogged at b transus temperature and then rolled by unidirectional rolling and cross rolling in the a+b phase field. The typical widmanstatten structure of cast-ingots turned to transformed b morphology after cogging at b transus temperature in which the a phases forms in smaller colonies of laths. After the unidirectinal rolling in the a+b phase field, the a colonies were distorted and the a laths re-arranged along the rolling direction, while they had weaker directivity after cross rolling. The sheets rolled by both unidirectional and cross rolling showed typical prismatic texture. After annealing treatment below the b transus temperature, the a phases turned to equiaxial morphology. The ambient yield strength of the sheet in transverse direction was significantly higher than in rolling direction, which could be attributed to the strong prismatic texture introduced by hot rolling process.
Fund: Supported by National Natural Science Foundation of China (No.51201006) and Programme of Introducing Talents of Discipline to Universities (No.B12012)
Fig.1 Schematic of tensile testing specimen (unit: mm) (a) and important directions on the rolled sheet (b)
Fig.2 Low (a) and high (b) magnified typical OM images of TC1 ingot fabricated by plasma arc cold hearth melting (PAM)
Fig.3 Low (a) and high (b) magnified typical OM images of TC1 sheet on the RD-TD plane after breakdown rolling
Fig.4 Typical OM images of TC1 sheets on the RD-TD (a, c) and RD-ND (b, d) planes after unidirectional rolling (UR) (a, b) and cross rolling (CR) (c, d) (Insets show the high magnified images)
Fig.5 Typical OM images of TC1 sheets on the RD-TD (a, c) and RD-ND (b, d) planes after UR (a, b) and CR (c, d) and then annealed at 750 ℃ for 30 min with cooling in air
Fig.6 {0002} (a) , {1010} (b) and {1120} (c) pole figures of a phase in TC1 ingot after breakdown rolling
Fig.7 {0002} (a, d), {1010} (b, e) and {1120} (c, f) pole figures of a sphase after UR (a~c) and CR (d~f)
Rolling mode
Sample position
Yield strength MPa
Ultimate strength MPa
Elongation %
UR
RD
621±3
733±3
18.1±5.2
TD
747±9
755±8
15.6±0.1
CR
RD
661±18
763±8
17.4±3.0
TD
745±6
761±5
21.1±4.3
Table 1 Ambient tensile properties of TC1 sheets along RD and TD directions after UR and CR
Rolling mode
Sample position
Yield strength MPa
Ultimate strength MPa
Elongation %
UR
RD
561±4
671±10
31.7±0.2
TD
655±8
673±9
31.3±0.4
CR
RD
524±24
667±2
26.1±1.0
TD
642±9
686±3
25.4±0.1
Table 2 Ambient tensile properties of TC1 sheets along RD and TD directions after UR and CR and then annealed at 750 ℃ for 30 min with cooling in air
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