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Journal ArticleDOI

Processing maps for hot deformation of α2 aluminide alloy Ti-24Al-11Nb

01 Mar 2002-Journal of Materials Science (Kluwer Academic Publishers)-Vol. 37, Iss: 6, pp 1197-1201
Abstract: Using the test data of α2 titanium aluminide alloy Ti-24Al-11Nb with microstructural observations, studies are made to examine the flow localization concepts as well as the simplified metallurgical stability criterion for delineating the regions of flow instabilities in the processing maps. The optimum hot working conditions for the material are suggested.

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Topics: Aluminide (61%), Titanium aluminide (58%), Hot working (53%)
Citations
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Journal ArticleDOI
Arash Jenab1, A. Karimi Taheri2Institutions (2)
Abstract: The hot deformation characteristics of 7075 aluminum alloy (AA7075) are investigated by means of hot compression tests carried out in the temperature range of 200–450 °C and strain rate range of 0.0003–1 s−1. Two novel processing maps based on flow localization parameter and enhanced DMM are developed and compared with conventional DMM results. It is observed that processing maps based on flow localization parameter can be used successfully to predict AA7075 thermomechanical behavior. Also, the comparison of the DMM results indicates that the new approach to calculate DMM power dissipation efficiency and instability criteria corresponds better with experimental observations. The occurrence of dynamic recrystallization is probable in the temperature range of 400–450 °C and strain rates of lower than 0.001 s−1. Moreover, the alloy demonstrated a wide range of flow instabilities at temperatures lower than 300 °C and all strain rates tested where the occurrence of dynamic strain ageing is suggested at this domain. However, the most efficient temperature range to deform the alloy is suggested as 300–350 °C at strain rates lower than 0.001 s−1.

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55 citations


Journal ArticleDOI
Abstract: Gamma titanium alumindes are intermetallics, which have very narrow working range. Hot isothermal working is the most suitable process for hot working of alloy. Accordingly, hot isothermal compression test is carried out on reaction synthesized and homogenized titanium aluminide alloys at different temperatures and strain rates using Gleeble thermomechanical simulator. Three alloys of Ti48Al2Cr2Nb0.1B (atom%) have been used in the study. Stress–strain data obtained from the test has been used to construct processing map, which indicates the safe and unsafe working zone. Strain rate sensitivity and Zener–Hollomon parameter has been calculated. Further, constitutive equations have been generated and verified. It is found that alloy has good workability in the temperature range of 1223–1423 K at strain rates of 0.01–0.001 s −1 . In this range of parameters, the alloys nearly follow the constitutive equations.

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33 citations


Journal ArticleDOI
Guoliang Ji1, Fuguo Li1, Qinghua Li1, Huiqu Li  +1 moreInstitutions (1)
Abstract: Using the flow stress data obtained from the compression tests in the temperature ranges of 800–1200 °C and at strain rate ranges of 0.01–50 s −1 , the processing map of Aermet100 steel was developed based on a simple instability condition applicable to a general flow stress versus strain rate curve at any strain and temperature. Deformation mechanisms in the stable and unstable regimes were verified with the microstructure observations. The optimum hot processing windows of Aermet100 steel are at temperature ranges of 1025–1200 °C and at strain rate ranges of 0.03–15 s −1 , in which dynamic recrystallization occurs with a peak efficiency of power dissipation of 38%. The instability regimes I and II occur at low temperature ranges of 800–975 °C, and at strain rate ranges of 0.1–6 s −1 and 4.5–33 s −1 , respectively. While the instability regime III occurs at high temperature ranges of 950–1200 °C and at high strain rate ranges of 15–50 s −1 . These instability regimes, whose microstructural manifestations such as cracks, shear bands and twin kink bands are detrimental to the mechanical properties of components, need to be avoided during hot processing of Aermet100 steel.

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27 citations


Journal ArticleDOI
Daosheng Wen1, Youhai Zong1, Yi Wang, Z.Y. Liu1  +1 moreInstitutions (1)
Abstract: High temperature deformation behaviors of the unhydrogenated and hydrogenated Ti-46Al-2V-1Cr-0.3Ni (at%) alloys were investigated in the temperature range 1050–1200 °C and strain rate range 0.001–1 s−1. The flow stress of the hydrogenated alloy was lower than that of the unhydrogenated alloy, which was mainly attributed to hydrogen-promoted lamellar decomposition, twinning and dynamic recrystallization. Processing maps of the unhydrogenated and hydrogenated alloys were constructed. The stability domain of the hydrogenated alloy was enlarged in comparison with that of the unhydrogenated alloy, meaning hydrogen enhanced the hot workability of the Ti-46Al-2V-1Cr-0.3Ni alloy. Hydrogen activated slip systems so that lamellar bending more easily occurred in the hydrogenated alloy, which made inter-lamellar fracture convert into trans-lamellar fracture. Therefore, crack propagation was restrained in the hydrogenated alloy during hot deformation. The critical strain of the hydrogenated alloy was less than those of the unhydrogenated alloy, meaning the dynamic recrystallization occurred earlier in the hydrogenated alloy. γ-phase discontinuous dynamic recrystallization was promoted due to hydrogen addition, leading to a consumption of plentiful dislocations, which restrained continuous dynamic recrystallization to some extent. Hydrogen-promoted discontinuous dynamic recrystallization was mainly attributed to hydrogen-promoted lamellar decomposition, twinning, and hydrogen-decreased stacking fault energy.

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24 citations


Journal ArticleDOI
Shuaixiong Huang1, Xingdong Zhang1, Yun Jiang2, Yurong Jiang1  +4 moreInstitutions (2)
05 Feb 2017-Materials & Design
Abstract: The phase relations in the Ti-Nb-Co system are of great importance for the design of high temperature Ti alloys. The isothermal section of Ti-Nb-Co system at 1000 °C has been established using one diffusion couple supplemented with 13 key alloys. Phase relations and ternary solubility of the binary compounds were determined using electron probe microscopy (EPMA), wave dispersive X-ray spectrometer (WDS) and X-ray diffraction (XRD) techniques. There are 19 two-phase equilibria and 9 three-phase equilibria in the isothermal section at 1000 °C. The determined maximum solubility of Nb in TiCo3, TiCo2 (h), TiCo2 (c), TiCo, Ti2Co were 6.22, 17.21, 2.29, 22.88 and 2.49 at.%, respectively. Nb2Co7, NbCo3, NbCo2, Nb6Co7 dissolves up about 0.33, 17.75, 13.26 and 10.81 at.% Ti, respectively. All of the binary phases have a certain composition range at 1000 °C except Nb2Co7. The phase diagram of Ti-Nb-Co system varied greatly when the temperature raised from 900 °C to 950 °C, but the changes was not so big when temperature increased from 950 °C to 1000 °C.

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18 citations


References
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01 Jan 1985-
Abstract: This book contains over 50 selections. Some of the titles are: Order-disorder behavior of grain boundaries in a two-dimensional model ordered alloy; Dislocation reactions at grain boundaries in Ll/sub 2/ ordered alloys; Creep cavitation in a nickel aluminide; Effects of elastic anisotropy on the anomalious yield behavior of cubic ordered alloys; and Processing technology for nickel aluminides.

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2,121 citations


Book
01 Jan 1963-

1,040 citations




Journal ArticleDOI
Abstract: A simple condition for metallurgical instability, useful in the development of processing maps for analysing high-temperature forming of metals, is suggested following a criterion based on continuum principles as applied to large plastic flow proposed by Ziegler. It can be used for any type of flow stress versus strain rate curve. This criterion has been validated using the flow stress data of a 6061 Al-10 vol% metal matrix composite with microstructural observations. Optimum hot working conditions based on the instability map are suggested for this material.

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31 citations


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