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

Abstract

Selective laser melting (SLM) additive manufacturing of pure tungsten encounters nearly all intractable difficulties of SLM metals fields due to its intrinsic properties. The key factors, including powder characteristics, layer thickness, and laser parameters of SLM high density tungsten are elucidated and discussed in detail. The main parameters were designed from theoretical calculations prior to the SLM process and experimentally optimized. Pure tungsten products with a density of 19.01 g/cm3 (98.50% theoretical density) were produced using SLM with the optimized processing parameters. A high density microstructure is formed without significant balling or macrocracks. The formation mechanisms for pores and the densification behaviors are systematically elucidated. Electron backscattered diffraction analysis confirms that the columnar grains stretch across several layers and parallel to the maximum temperature gradient, which can ensure good bonding between the layers. The mechanical properties of the SLM-produced tungsten are comparable to that produced by the conventional fabrication methods, with hardness values exceeding 460 HV0.05 and an ultimate compressive strength of about 1 GPa. This finding offers new potential applications of refractory metals in additive manufacturing.

Selective Laser Melting and Remelting of Pure Tungsten

“…On the one hand, according to the Hall–Patch relationship, the decrease in grain size leads to an increase in yield strength . The ultimate compressive strength of the specimens with a scanning speed of 600 mm s −1 is 1197 MPa, as shown in Figure d, which reaches the highest value among our specimens and exceeds the value reported in other literature . On the other hand, the reduction of laser energy input elevated the defect level inside the samples, which slightly reduced the density of pure tungsten.…”

“…A relatively high laser power with high heat input is beneficial for tungsten melting . Unfortunately, further increasing laser power would lead to sintering loss and surface wrinkling for tungsten components, which can destroy the forming quality …”

“…When the hatch spacing and layer thickness were fixed during the SLM process, the volumetric energy input, E V , can be adapted to calculate the energy deposited in a single track. Thus, the linear energy is defined by the equationwhere P is the laser power and ν is the scanning speed. Based on the preliminary experiment, the laser power ( P ) and scanning speed ( ν ) were set in the range of 150–350 W and 200–800 mm s −1 , respectively.…”

“…It has been widely used in the production of a variety of alloys including titanium alloys, aluminum alloys, and stainless steel, providing the possibility for its application in producing tungsten. Tan et al . fabricated pure tungsten samples with a relative density of 98.5% using SLM.…”

Laser Powder Bed Fusion of Ti-rich TiNi lattice structures: Process optimisation, geometrical integrity, and phase transformations

“…Laser powder bed fusion (LPBF) produces parts in a layer-wise incremental manner using a laser to melt and consolidate thin layers of powders [10,11], providing an alternative approach to circumvent the challenges associated with traditional manufacturing methods of TiNi. Due to its localised heating and rapid cooling rates (up to 10 6 K/s), LPBF can reduce chemical segregation, cause grain refinement, and improve the mechanical behaviour [12].…”