Page 21 - MSAM-1-2

Materials Science in Additive Manufacturing Laser absorption and printability of 90W-Ni-Fe

2. Materials and methods experiment was carried out using a CMT5205 testing
machine with a loading rate of 1 mm/min.
2.1. Powder preparation and LPBF printing
This work utilized the commercial spherical W powder 2.3. Establishment of GO-RT models
and nano-scale Ni and Fe powder as starting materials Numerical simulations in this work were based on
(Figure 1), and an E2000 vertical inverter ball mill the mechanism of LPBF (Figure 2A), and a random
was used to prepare nanoparticle-coated 90W-Ni-Fe function was used to generate powder beds in MATLAB
powders with different morphologies. The W powder (Figure 2B). The geometric information was imported
had a size distribution of D = 8.25 μm, D = 14.41 μm, into the optical design and analysis software FRED to
50
10
and D = 24.25 μm, respectively. The laser absorptivity/ form geometric models. After establishing the geometric
90
reflection of different powders was tested using a models, according to Fresnel formulae, the laser reflection
Shimadzu UV3600 UV-Vis NIR spectrophotometer, behavior was described as [16,22] :
and the morphology of different powders was observed (n 1 / cos) m 2

using a Hitachi S-4800 field emission scanning electron =1- c c 2 (1)
p

microscope (SEM). (n 1 / cos) m c
c
The LPBF printing device was developed by the Nanjing =1- (n cos ) m 2 c (2)
c
University of Aeronautics and Astronautics, and the process s (n cos ) m 2 c
c
details were described in our previous work . High-purity
[21]
argon (99.9%) was used as the protective gas to prevent the where α denotes the absorptivity, θ is the angle of incidence,
formation of oxides, and a chessboard scanning strategy n represents the real part of the complex index of refraction,
c
was employed to reduce heat accumulation during LPBF and m represents the imaginary part of the complex index
c
[14,22]
printing . The LPBF processing parameters of 90W-Ni-Fe of refraction . In this study, the laser refractive behavior
[9]
alloys were laser power of 200 W, scanning speed of of different materials was described by defining the complex
250 mm/s, hatch spacing of 50 μm, and layer thickness of index of refraction (Figure 3). Integrating sphere is one of
30 μm. The length of the LPBF-fabricated single tracks was the laser absorption/reflectivity measurement methods
50 mm, the size of block specimens was 6 mm × 8 mm × (Figure 4A). By the laser absorbance formula:
8 mm, and the length to diameter (L/D) of the compression A=-1 T R- (3)
parts was 1.25 (GB/T 7314-2017). where A denotes the absorption, T is the transmission,
2.2. Microstructure and mechanical properties and R represents the radiation reflection. The transmitted
radiation of metal can be generally regarded as zero .
[8]
The top surface morphologies of 90W-Ni-Fe scanning Therefore, the above equation can be simplified as:
tracks and block specimens were observed using SEM,
and the block specimens were ground and polished A=-1 R (4)
according to the standard metallographic procedures this means the absorption of the laser energy can
and were observed using an XJP-300 optical microscope be calculated using the measured reflectivity [14,22] . After
(OM). The 3D morphology and the surface roughness obtaining a powder bed with indices defined, a spherical
of 90W-Ni-Fe alloys were obtained using a VK-150K 3D analytical surface was established according to the principle
laser microscope imaging system. The microhardness of of integrating sphere. At the same time, a Gaussian
the optimal 90W-Ni-Fe sample was tested using an HXS- distributed optical source similar to the LPBF equipment
1000 AY microhardness tester with a load setting of 1000 g, was loaded above the powder bed (Figure 4B). Subsequently,
and the stress distribution was obtained by a Proto LXRD ray tracing was performed in FRED to investigate the laser
high-speed X-ray residual stress analyzer. The compression absorption behavior (Figure 4C and D).

A B C

Figure 1. SEM images showing the starting powders: W (A), Ni (B), and Fe (C).

Volume 1 Issue 2 (2022) 3 http://doi.org/10.18063/msam.v1i2.11