3D Visualization of Top Surface Structure and Pores of 3D Printed Ti-6Al-4V Samples Manufactured with TiC Heterogeneous
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INTRODUCTION
ADDITIVE manufacturing (AM), which is commonly referred to as 3D printing, is the process of fabricating objects layer by layer from 3D numerical models, as opposed to traditional subtractive manufacturing technologies. AM is classified into the following seven disciplines[1–3]: (1) Powder bed fusion, (2) Binder jetting, (3) Directed energy deposition, (4) Sheet lamination, (5) Vat photopolymerization, (6) Material extrusion, and (7) Material jetting. Among these, the most popular processes for the AM of metals are powder bed fusion including selective laser melting (SLM)[4–7] and laser metal deposition.[4,8,9] The rapid cooling rates and directional solidification mean that metals produced by AM have structures, microstructures, and 3D multiscale architectures that differ from their cast and wrought counterparts. For example, the local solidification of small melt pools during AM can result in epitaxial growth and the formation of columnar grains as heat is primarily extracted through the previously manufactured (solidified) layer, often across a steep thermal gradient.[10–13]
YOSHIMI WATANABE, MASAFUMI SATO, TADACHIKA CHIBA, and HISASHI SATO are with the Department of Physical Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan. Contact e-mail: [email protected] NAOKO SATO and SHIZUKA NAKANO are with the Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan. Manuscript submitted June 18, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Microstructural evolution during the SLM method using conventional Ti-6Al-4V powder is illustrated in Figures 1(a) through (c).[14,15] A consequence of repeated melting and deposition under a thermal gradient is the epitaxial growth of Ti-6Al-4V to form coarse primary columnar b-Ti grains.[16,17] In addition, solidstate b-grain growth is caused by the high-temperature thermal cycles associated with layer-by-layer manufacturing, as shown in Figure 1(b). As a result, the microstructure of the AMed sample has large and elongated grains with texture oriented parallel to the building direction, as shown in Figure 1(c). However, this epitaxial growth does not necessarily correlate to enhanced mechanical performance in all situations.[18] Moreover, unwanted porosity caused by incorrect processing parameters or manufacturing conditions, surface roughness, and other surface defects are other problems to be overcome. Meanwhile, the equiaxed grain structure of Al alloy castings ensures uniform mechanical properties, reduced ingot cracking, improved feeding to eliminate shrinkage porosity, the distribution of secondary phases and microporosity on a fine scale, and improved machinability and cosmetic features.[19] One of the methods to obtain the equiaxed grain structure of Al alloy castings involves the addition of grain refiners, such as Al-Ti alloy, Al-Ti-B alloy, and Al-Ti-C alloy systems containing Al3Ti, TiB2, and TiC particles.[20–24] In these refiners, the Al3Ti, TiB2, and TiC pa
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