Densification and microstructure formation mechanisms of 80 W-14Ni-6Fe fabricated by laser powder bed fusion

Abstract

Tungsten heavy alloys (WHAs) are typically refractory alloy, and machining tungsten alloy components at room temperature is a challenge. Currently, Laser additive manufacturing (LAM) provides a feasible route for machining complex tungsten alloy parts. In this study, the high relative density and almost defect-free 80 W-14Ni-6Fe specimens were successfully obtained via using laser powder bed fusion (LPBF). The densification, microstructure formation mechanisms and tensile properties of LPBFed tungsten alloy were systematically investigated. The results revealed that the relative density of tungsten alloy increases and then decreases with the laser energy density increases. Nearly full densification 80 W-Ni-Fe alloys were obtained when the volumetric energy density (VED) was 80–100 J/mm3. The typical microstructure contained irregular tungsten grain consolidation, W dendrites, spherical tungsten particles and Ni-Fe bonding phase, which was due to melting of partial tungsten particles during LPBF. Interestingly, many ultra-fine crystals occurred in the Ni-Fe matrix, which was closely related to the rapid heat and cooling during LPBF. Besides, there were two strengthening mechanisms in LPBFed 80 W alloy, respectively solid solution strengthening and dispersion strengthening. Hence, the 80 W-Ni-Fe alloy with optimum process parameters exhibited high tensile strength, and the ultimate tensile strength (UTS) reached 1064MP. This work will aid in the additive manufacturing of refractory metal alloys with excellent properties and expand the application prospects of tungsten alloys.