ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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 , Volume 55 Issue 6 Previous Issue    Next Issue
 Select Microstructure and Tensile Property of TC4 Alloy Produced via Electron Beam Rapid Manufacturing Zheng LIU,Jianrong LIU,Zibo ZHAO,Lei WANG,Qingjiang WANG,Rui YANG Acta Metall Sin, 2019, 55 (6): 692-700.  DOI: 10.11900/0412.1961.2019.00007 Abstract   HTML   PDF (10313KB) ( 551 ) Electron beam rapid manufacturing (EBRM) is one of the 3D printing technologies. The main attractions of EBRM technology are its high efficiency and economy in fabricating large, complex near net shape components dielessly and only needing limited machining. In general, the microstructure and texture of titanium alloy can play a significant role in determining its mechanical behaviors. In the present work, the microstructure, texture and tensile property of TC4 alloy produced by electron beam rapid manufacturing (EBRM) are investigated. Results show that the microstructure is comprised of columnar prior β grains that orient parallel to the building direction. The width of the columnar β grains increased rapidly at the initial several build layers, and the subsequent increase rate of the width of the columnar β grains tends to slow down. Fine α lamellae with gradient size are observed inside the columnar prior β grains, which occur because the alloy experiences different complex thermal histories during the EBRM-produced process. The size of α lamellae tends to decrease with the increase of build layers. The XRD result shows that the TC4 alloy has a typical α phase texture, (the c-axes are either concentrated at about 45° or are perpendicular to the building direction). At the same time, the <$10\bar{1}0$> poles are relative to random distribution. For the tensile samples along the electron beam scanning direction, the yield strengths do not show significant change with the increase of build layers, but the tensile strengths increase. The ductility of the alloy also has an upward trend, despite of a slightly decreasing ductility in the top sample. The tensile samples at the bottom of the alloy (10 mm and 20 mm away from the substrate) have similar work hardening exponents, which are lower than the top sample. The top sample shows the highest work hardening exponent. This difference in the tensile properties can be highly attributed to the gradient microstructure. The alloy also presents obvious anisotropy in tensile strength. The tensile sample along the 45° direction has a higher strength than the sample along the X direction, while the tensile sample along the Z direction shows the lowest strength. This anisotropic strength is strongly associated with the α phase texture. When the loading direction is 45° to the building direction, most of the c-axes of α phase are about parallel to the loading direction, showing a "hard" orientation, leading to a higher strength than other oriented samples. Conversely, when the loading direction is along the building direction, most of the α phase present a "soft" orientation, resulting in lower strength compared to the tensile samples along the 45° or the X direction.