Microstructure and Mechanical Properties of Long Ti-6Al-4V Rods Additively Manufactured by Selective Electron Beam Melti
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INTRODUCTION
INTEREST in additive manufacturing (AM) of titanium (Ti) alloys continues to grow rapidly worldwide, especially for aerospace and biomedical applications.[1–6] Although much effort has been made to establish the processing-microstructure-property relationships for additively manufactured (AMed) Ti alloys,[7,8] there are still a number of unanswered S.L. LU, Ph.D Candidate, is with the School of Materials and Metallurgy, Northeastern University, Shenyang 110819, P.R. China and with the State Key Laboratory of Porous Metal Materials, Northwest Institute for Nonferrous Metal Research, Xi’an 710016, P.R. China, and also with the Centre for Advanced Materials Processing and Manufacturing, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, QLD 4072, Australia. H.P. TANG, Professor, Y.P. NING, Graduate Student, and N. LIU, Junior Engineer, are with the State Key Laboratory of Porous Metal Materials, Northwest Institute for Nonferrous Metal Research. Contact e-mail: [email protected] D.H. STJOHN, Professor, is with the Centre for Advanced Materials Processing and Manufacturing, School of Mechanical and Mining Engineering, The University of Queensland. M. QIAN, Professor, is with the Centre for Additive Manufacturing, School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, VIC 3001, Australia. Contact e-mail: [email protected] Manuscript submitted March 3, 2015. Article published online May 30, 2015 3824—VOLUME 46A, SEPTEMBER 2015
important questions, particularly for the AM of Ti alloy samples or parts from a deep powder bed. Two such concerns are microstructure inhomogeneity and hidden defects. They apply to the AM processes by both SEBM and selective laser melting (SLM), which are the two premier powder-bed-based metal AM processes. They are similar but differ in a number of aspects including the melting environment, requirements for powder size, preheating temperatures, and therefore the as-built microstructure, mechanical properties, and surface finish.[3–5] The SEBM-based AM process was first made available to the manufacturing industry by the Arcam AB Company (Sweden) in 2002.[9] The process is particularly suited to the AM of Ti alloys due to the high vacuum building chamber used, which alleviates the pick-up of oxygen and nitrogen from the building environment during AM (the oxygen content of the used powder still increases[3]). To date, the process has proved to be competent in the manufacturing of small Ti alloy samples or parts with excellent mechanical properties and consistency while requiring no post-AM heat treatment (which is in contrast to those AMed by SLM).[3] As a result, it is being increasingly adopted by industry. For instance, more than 40,000 titanium acetabular cups made by the process had been METALLURGICAL AND MATERIALS TRANSACTIONS A
implanted by April 2014 and globally this accounts for about 2 pct of the production of acetabular cups.[10] However, what is missing from a research perspective is that, to the authors’
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