Selective laser melting of high-performance pure tungsten: parameter design, densification behavior and mechanical properties

Figures & data

Figure 1. SEM morphology (a) and size distribution (b) of the pure tungsten powder.

Table 1. Physical parameters used for theoretical calculation in laser parameters design.

Physical parameter	Unit	Value
Density/ρ	kg·m^−3	19.30 × 10^3
Specific heat/C p	J (kg·K)^-1	132
Melting point/T m	K	3695
Initial temperature/T o	K	323
Latent heat of fusion/L f	J·kg^−1	2.20 × 10^5
Laser absorptivity/α	–	0.41
Laser beam radius/r b	mm	50 × 10^−3
Laser melting radius/r	mm	100 × 10^−3
Melting zone depth/H	mm	30 × 10^−3

Figure 2. Schematic diagram of the SLM process and the heat transfer in molten pool.

Figure 3. Optical images of SLM fabricated pure tungsten parts: (a) blocks fabricated with different linear energies; (b) 0.40 mm thin-wall tungsten part and specimens produced with η ₃ = 0.667 J/mm.

Figure 4. Surface morphology and roughness taken from horizontal surfaces of SLM fabricated pure tungsten: (a) SEM image showing regular laser tracks (η ₃ = 0.667 J/mm) and microcracks (inset image); (b) corresponding high-magnification SEM image showing massive nanocrystals in the liquid fronts; (c) the corresponding 3D topography image of the untreated fresh surface and (d) relationships between surface roughness and linear energy summarized from the 3D topography images.

Figure 5. Optical micrographs showing the pores in the horizontal cross-sections of pure tungsten produced by SLM with different linear energies (J/mm): (a) η ₁ = 0.500, (b) η ₂ = 0.625, (c) η ₃ = 0.667, (d) η ₄ = 0.750, (e) η ₅ = 0.833, (f) η ₆ = 1.000; (g) density graphs obtained from Archimedes and image analysis methods.

Figure 6. Microstructural observation and phase identification taken from horizontal cross-sections of SLM-produced pure tungsten: (a) low-magnification and (b) high-magnification OM macrographs; (c) low-magnification (inset) and high-magnification SEM morphologies, and (d) XRD patterns of powder and SLM-produced specimens.

Figure 7. SEM and EBSD analysis carried along the building direction (Z direction): (a) SEM image showing a crack along building direction and (b) Inverse pole figure showing the microstructure and grain orientation map of SLM-produced tungsten.

Figure 8. (a) The effect of laser linear energy on microhardness of SLM-processed pure tungsten and (b) compressive stress–strain curves of SLM fabricated pure tungsten with different laser linear energies.

Table 2. Comparison of the mechanical properties of pure tungsten fabricated by SLM and conventional processing methods.

Specimens	CYS (MPa)	UCS (MPa)	Strain (%)	Density (g/cm^3)	S a (μm)	HV
SLM η 1 = 0.500	868	978	5.97	97.82% (18.88 ± 0.02)	7.59	445 ± 39
SLM η 2 = 0.625	864	984	6.58	98.29% (18.97 ± 0.06)	8.10	448 ± 25
SLM η 3 = 0.667	882	1015	6.76	98.50% (19.01 ± 0.02)	6.74	461 ± 18
SLM η 4 = 0.750	791	933	8.65	97.98% (18.91 ± 0.05)	8.97	452 ± 31
SLM η 5 = 0.833	849	964	6.64	97.93% (18.90 ± 0.03)	7.46	467 ± 29
SLM η 6 = 1.000	860	962	6.36	97.72% (18.86 ± 0.04)	7.44	456 ± 41
CVD [41,42]	–	780–1480	–	≤99.79%	–	419 (4.5 GPa)
HIP [2,43]	1010	1180	–	≤98.00%	–	–
PM [44,45]	900	1000–1200	–	≤98.20%	–	344
SPS [7,39,46]	750	980	–	≤96.30%	–	372 (4 GPa)