Deformation Behavior and Microstructure Evolution of Powder Metallurgy Ti6Al4V Alloy During Hot Compression
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JMEPEG https://doi.org/10.1007/s11665-019-04166-0
Deformation Behavior and Microstructure Evolution of Powder Metallurgy Ti6Al4V Alloy During Hot Compression Ronge Liu, Baoyu Wang, Junling Li, Weiping Ma, and Shushan Hu (Submitted January 23, 2019; in revised form April 20, 2019) In order to determine appropriate workability parameters for cross-wedge rolling products of powder metallurgy (PM) Ti6Al4V alloys, thermal compression experiments were carried out within the temperature range of 850-1050 °C, the strain rate range of 0.1-10 s21, and with a height decrease of 60%. The compression deformation behavior was investigated. A strain-compensated constitutive model was established based on the flow stress curves corrected by the friction, which can predict the flow behaviors under the entirety of the experimental deformation conditions. Moreover, the processing map was developed, and stable and unstable deformation regimes were established. The microstructure analysis illustrated that globularization and dynamic recrystallization were the main deformation mechanisms. The porosity of the compressed samples was greatly reduced and influenced by the temperature and strain rate. Considering the material flow stress, hot processing map, microstructure and porosity, the appropriate hot deformation parameters for PM Ti6Al4V alloy preforms are suggested. Keywords
constitutive model, microstructure, porosity, powder metallurgy, processing map, Ti6Al4V titanium alloy
1. Introduction Ti6Al4V is a typical a + b titanium alloy that provides the excellent properties required for structural parts in the aviation and energy fields (Ref 1). However, the high costs of refining and processing limit its extensive application. To reduce the manufacturing cost and expand its scope of application, powder metallurgy (PM) fabrication of titanium alloys has developed rapidly in recent years (Ref 2–8). For powder metallurgy, the initial powder is a significant factor that should be considered. Typically, it includes a prealloyed powder and blended elemental powder (Ref 9). Compared with prealloyed powders, the use of blended elemental powders with a simple process (cold pressing and sintering) is a feasible and cost-effective method for manufacturing near-net shaped parts. However, with a blended elemental powder process, there is a potential risk of not being completely densified. The residual porosity has an important influence on the performance of components. Secondary operations, such as forging (Ref 6, 10), extrusion (Ref 7, 11) and hot isostatic pressing (Ref 5), have Ronge Liu and Shushan Hu, School of Mechanical Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, China; and Ordos Institute of Technology, Ordos 017000, China; Baoyu Wang, Junling Li, and Weiping Ma, School of Mechanical Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, China. Contact e-mails: [email protected], [email protected], [email protected]
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