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Research Papers

Selective Laser Melting Additive Manufacturing of Hard-to-Process Tungsten-Based Alloy Parts With Novel Crystalline Growth Morphology and Enhanced Performance

[+] Author and Article Information
Dongdong Gu

College of Materials Science and Technology,
Nanjing University of Aeronautics and
Astronautics (NUAA),
Yudao Street 29,
Nanjing 210016, China;
Institute of Additive Manufacturing (3D Printing),
Nanjing University of Aeronautics and
Astronautics (NUAA),
Yudao Street 29,
Nanjing 210016, China
e-mail: dongdonggu@nuaa.edu.cn

Donghua Dai, Wenhua Chen, Hongyu Chen

College of Materials Science and Technology,
Nanjing University of Aeronautics and
Astronautics (NUAA),
Yudao Street 29,
Nanjing 210016, China;
Institute of Additive Manufacturing (3D Printing),
Nanjing University of Aeronautics and
Astronautics (NUAA),
Yudao Street 29,
Nanjing 210016, China

1Corresponding author.

Manuscript received June 22, 2015; final manuscript received November 23, 2015; published online March 28, 2016. Assoc. Editor: Z. J. Pei.

J. Manuf. Sci. Eng 138(8), 081003 (Mar 28, 2016) (11 pages) Paper No: MANU-15-1305; doi: 10.1115/1.4032192 History: Received June 22, 2015; Revised November 23, 2015

Selective laser melting (SLM) additive manufacturing (AM) of hard-to-process W-based parts with the addition of 2.5 wt.% TiC was performed using a new metallurgical processing mechanism with the complete melting of the high-melting-point powder. The influence of SLM processing parameters, especially laser scan speed and attendant laser fluence (LF), on densification behavior, microstructural development, and hardness/wear performance of SLM-processed W-based alloy parts was disclosed. The densification response of SLM-processed W-based parts decreased both at a low LF of 10.7 J/mm2, caused by the limited SLM working temperature and wetting characteristics of the melt, and at an excessively high LF of 64 J/mm2, caused by the significant melt instability and resultant balling effect and microcracks formation. The laser-induced complete melting/solidification mechanism contributed to the solid solution alloying of Ti and C in W matrix and the development of unique microstructures of SLM-processed W-based alloy parts. As the applied LF increased by lowering laser scan speed, the morphologies of W-based crystals in SLM-processed alloy parts experienced a successive change from the cellular crystal to the cellular dendritic crystal and, finally, to the equiaxed dendritic crystal, due to an elevated constitutional undercooling and a decreased thermal undercooling. The optimally prepared W-based alloy parts by SLM had a nearly full densification rate of 97.8% theoretical density (TD), a considerably high microhardness of 809.9 HV0.3, and a superior wear/tribological performance with a decreased coefficient of friction (COF) of 0.41 and a low wear rate of 5.73 × 10−7 m3/(N m), due to the combined effects of the sufficiently high densification and novel crystal microstructures of SLM-processed W-based alloy parts.

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Figures

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Fig. 1

Schematic of SLM equipment used in the present study (a) and SLM procedures for producing bulk-form parts (b)

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Fig. 2

XRD spectra over a wide range of 2θ = 30–120 deg showing constitutional phases of SLM-processed W-based alloy parts using different SLM processing parameters: (a) LF = 10.7 J/mm2, v = 300 mm/s, (b) LF = 16 J/mm2, v = 200 mm/s, (c) LF = 32 J/mm2, v = 100 mm/s, and (d) LF = 64 J/mm2, v = 50 mm/s

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Fig. 3

Typical surface morphologies (FE-SEM) of SLM-processed W-based alloy parts at different SLM processing parameters, revealing the variation of densification behaviors: (a)LF = 10.7 J/mm2, v = 300 mm/s, (b) LF = 16 J/mm2, v = 200 mm/s, (c) LF = 32 J/mm2, v = 100 mm/s, and (d) LF = 64 J/mm2, v = 50 mm/s

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Fig. 4

High-magnification surface morphologies (FE-SEM) of SLM-processed W-based alloy parts under various SLM processing conditions, showing typical features of the solidified liquid front in laser scanned tracks: (a) LF = 10.7 J/mm2, v = 300 mm/s, (b) LF = 16 J/mm2, v = 200 mm/s, (c) LF = 32 J/mm2, v = 100 mm/s, and (d) LF = 64 J/mm2, v = 50 mm/s

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Fig. 5

Effects of laser scan speed and resultant LF on densification levels of SLM-processed W-based alloy parts

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Fig. 6

Characteristic microstructures (FE-SEM) on the etched cross sections of SLM-processed W-based alloy parts using different SLM processing parameters, showinglaser-controlled crystallization features of W-based crystals: (a) LF = 10.7 J/mm2, v = 300 mm/s, (b) LF = 16 J/mm2, v = 200 mm/s, (c) LF = 32 J/mm2, v = 100 mm/s, and (d) LF = 64 J/mm2, v = 50 mm/s. Typical microstructure of SLM-processed pure W part at LF of 32 J/mm2 is provided for a comparison purpose (e).

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Fig. 7

Morphological change of W-based crystals during SLM with the increase of LF

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Fig. 8

Microhardness (a), COF (b), and wear rate (c) of SLM-processed W-based alloy parts at different LFs

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Fig. 9

Typical morphologies (FE-SEM) of worn surfaces of SLM-processed W-based alloyparts at various SLM processing parameters: (a) LF = 10.7 J/mm2, v = 300 mm/s, (b) LF = 16 J/mm2, v = 200 mm/s, (c) LF = 32 J/mm2, v = 100 mm/s, and (d) LF = 64 J/mm2, v = 50 mm/s

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