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Materials (Basel). 2019 Apr 12;12(8). pii: E1204. doi: 10.3390/ma12081204.

Morphological Development of Sub-Grain Cellular/Bands Microstructures in Selective Laser Melting.

Liu X1, Zhou X2,3, Xu B4, Ma J5, Zhao C6, Shen Z7,8, Liu W9.

Author information

1
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. liuxihe.pku@gmail.com.
2
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. dr_zhouxin@foxmail.com.
3
Science and Technology on Plasma Dynamics Laboratory, Air Force Engineering University, Xi'an 710038, China. dr_zhouxin@foxmail.com.
4
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. xuben@mail.tsinghua.edu.cn.
5
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. ma-jing@mail.tsinghua.edu.cn.
6
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. zhaocc819@mail.tsinghua.edu.cn.
7
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. zhijian.james.shen@mmk.su.se.
8
Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden. zhijian.james.shen@mmk.su.se.
9
School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China. liuw_tsinghua@126.com.

Abstract

In this paper, single-layer and bulk 316 L selective laser melting (SLM) experiments were conducted, fine submicron-scale geometric symmetrical cellular (hexagonal, pentagonal and square), elongated cellular and bands solidification morphologies were found in the laser-melt top surface. Meanwhile, morphological developed sub-grain patterns with quasi-hexagonal cellular, elongated cellular and bands structures (size ~1 μm) coexisting inside one single macro-solidified grain were also identified. This demonstrated the transitions from quasi-hexagonal-cells to elongated cells/bands, and transitions reverse, occurred in the whole bulk under some circumstances during SLM. Based on the experimental realities, these morphologies are formed by the local convection and Bénard instabilities in front of the solid/liquid interface (so-called mushy zones) affected by intricate temperature and surface tension gradients. Quasi-hexagonal cellular convective fields are then superimposed on macro-grain solidification to form the sub-grain patterns and micro-segregations. This explanation seems reasonable and is unifying as it can be expanded to other eutectic alloys with face center cubic (FCC) prevenient phase prepared by SLM, e.g., the Al-Si and Co-Cr-Mo systems.

KEYWORDS:

Bénard-Marangoni-instability; rapid solidification; selective laser melting; sub-grain microstructures; thermocapillary convection

PMID:
31013811
DOI:
10.3390/ma12081204
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