Effect of Build Orientation on Mechanical Properties and Microstructure of Ti-6Al-4V Manufactured by Selective Laser Mel
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TRODUCTION
COMPARED with conventional ‘‘subtraction manufacturing’’ techniques, ‘‘additive manufacturing’’ (AM) is a near net shaping technique that eliminates many restrictions on design freedom and simplifies the preparation of complex parts.[1] These advantages make AM popular in the medical, aerospace, and automotive fields.[2,3] Although selective laser melting (SLM) has been rapidly developed as an AM method, the end product does not always meet the requirements of engineering quality standards. In this regard, the unique conditions during the SLM process give rise to some problems. Large temperature gradients cause rapid solidification, (solidification rates between 0.1 and 5 m/seconds[3]) resulting in non-equilibrium microstructures and residual stress. Furthermore, variations in the process parameters strongly influence the microstructure, density, and surface quality of the final product.[4]
SHUBIN REN, YUHONG CHEN, TINGTING LIU, and XUANHUI QU are with the Beijing Advanced Innovation Center for Materials Genome Engineering, Institute for Advanced Materials and Technology, University of Science and Technology, Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted December 27, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Therefore, a thorough understanding of the mechanical properties of SLM materials is necessary before such rapid manufacturing techniques can be applied to critical load-bearing parts. The as-deposited SLM Ti-6Al-4V is a high-strength, low-ductility alloy; its residual stress, the fine acicular a¢ martensitic microstructure, and porosity are responsible for its low ductility.[5] In recent years, many successful studies have sought to improve performance by optimizing the SLM process or improving microstructure through heat treatment.[6–9] Also, due to the directionality of the process, studies related to improving the performance of SLM Ti-6Al-4V have found that the build orientation of the sample strongly affects its properties. For example, Vilaro et al.[10] studied the effect of heat treatment and sample orientation on the microstructure and mechanical properties of SLM Ti-6Al-4V and found that a horizontal sample exhibited higher strength and ductility than a vertical sample. They attributed the mechanical properties difference between vertical and horizontal sample to the manufacturing defects. Simonelli et al.[5] investigated the effect of different building directions on the mechanical properties and fracture modes of SLM Ti-6Al-4V and found that the fabrication direction affects the tensile properties, particularly the ductility and the defects were also believed to be the main cause of performance difference. Carroll et al.[11] believed that the anisotropy of
Ti-6Al-4V prepared by the direct energy deposition (DED) is mainly attributed to the relative orientation of a grain boundary and load, which is consistent with the results reported in DED Ti-6Al-4V,[12] SLM Ti-6Al-4V,[13] wire arc additive manufactured Ti-6Al-4V,[14] and electron beam melted (
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