Thermal Behavior During the Selective Laser Melting Process of Ti-6Al-4V Powder in the Point Exposure Scan Pattern
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IN recent years, titanium alloy has been widely used in industrial applications owing to its attractive combination of high strength and sound corrosion resistance.[1] However, modern titanium alloy parts normally have complex structures and irregular shapes. The PINGMEI TANG, MUJUN LONG, HUAMEI DUAN, SHENG YU, and DENGFU CHEN are with the College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P.R. China. Contact e-mail: [email protected] SEN WANG and SHUQIAN FAN are with the Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, P.R. China and also with the Chongqing Key Laboratory of Additive Manufacturing Technology and Systems, Chongqing 400714, P.R. China. Contact e-mail: [email protected] The contributions of Pingmei Tang and Sen Wang are equivalent. Manuscript submitted May 4, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
conventional processing methods have limited ability to meet the high industrial requirements for titanium alloy parts. Therefore, a novel technology is necessary for titanium alloy to obtain complex parts with good performance. Selective laser melting (SLM) is a promising additive manufacturing (AM) technology because it allows a high degree of design freedom and the preparation of high-performance metal parts.[2–4] The main process of this technology is that components are built up in a layer-by-layer fashion by using a laser beam to selectively melt and consolidate a thin layer of powder.[5] So far, a number of materials, such as Ni-based superalloys,[6] Ti-based alloys,[7] Al-based alloys,[8] steels,[9] and composites,[10] have been used to build parts for aerospace, rapid tooling, automotive, and medical applications. In addition, there have also been many commercial machines developed for the SLM printing process, for instance, EOS GmbH, SLM Solutions
GmbH, Concept Laser GmbH, and AM250.[11] Most of these machines adopt a continuous exposure scan pattern. The work pattern of continuous exposure is that a laser is continuously on as a layer is exposed. Actually, there is another discontinuous exposure scan pattern, which refers to the point exposure scan pattern, as shown in Figure 1. In this pattern, a single point is exposed for some time; then the laser is turned off, repositioned, and the next point is exposed. This pattern allows the AM250 machine to build finer detail features as a static molten pool that is more stable than a dynamic one.[11] Moreover, the point exposure scan pattern is considered to be able to generate more discrete molten pools and, thus, an even higher cooling rate during solidification as compared with the continuous exposure scan pattern.[12] As a result, the point exposure scan pattern has been widely used in the field of AM. Nevertheless, due to the fact that the actual printing process involves many complicated mechanisms, such as convection, diffusion, heat transfer, and mass transfer affected by the operating temperature, some uncontrollable defects, mainly including por
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