Cracking Behavior in Additively Manufactured Pure Tungsten

In this study, near fully dense(96.5%) pure tungsten bulks were additively manufactured and the cracking behavior was investigated. A crack network with a spacing of ～100 lm was observed in the fabricated bulks. It was observed that the laser scanning strategy, which could tailor the microstructure, affected the crack distribution pattern in fabricated tungsten.The calculated surface temperature difference(7300 K) was much higher than the cracking criterion(800 K) of tungsten,indicating that cracking is almost inevitable in laser additive manufacturing of tungsten. It could be concluded that crack network formed because the cracks emerged in every laser molten track and then interconnected in the layer-by-layer building process.

A review of tungsten fabricated via laser powder bed fusion

Tungsten and its alloys with high strength,thermal conductivity,and plasma radiation resistance are highly desirable for applications in medical,electronic and also nuclear facilities.However,the high melting point and high ductile–brittle transition temperature limit the fabrication of complex parts by using traditional methods,such as powder metallurgy.As a kind of additive manufacturing technology,laser powder bed fusion(LPBF)was used to fabricate tungsten and its alloys in recent years because of its high energy density and low action time.This paper reviewed the recent progress of LPBF fabricated tungsten.Two main challenges,which are the lack of density and cracking problem,are focused.The methods to solve these problems are reviewed.In terms of improving the density,decreasing oxygen content,optimizing the process parameter,and adopting spherical powder were proved effective.In terms of cracking problem,the method of alloying,such as adding secondary phase nanoparticles and alloy elements,could significantly reduce the cracking density.However,the crack problem has not been completely solved up to now.Finally,future developments and potential new research directions for LPBF tungsten are proposed.

Microstructure of a Ti–50wt% Ta alloy produced via laser powder bed fusion

Ti-Ta alloys have been widely studied for biomedical applications due to their high biocompatibility and corrosion resistance.In this work,nearly fully dense and in situ alloyed Ti-50 wt% Ta samples were fabricated by the laser powder bed fusion(LPBF) of mechanically mixed powders.With increased exposure time,and thereby increased laser energy density,insoluble Ta particles were almost dissolved,and a Ti-50 wt% Ta alloy was formed.Cellular and dendritic structures were formed due to constitutional undercooling,which was caused by the high cooling rate of LPBF process.Both retained βphases and α " phases were observed in the LPBFed Ti-50 wt% Ta alloy.The α" phase was found at the boundary of the cellular structures,where the tantalum content was not high enough to suppress the bcc lattice transition completely but could suppress the β phase→α’ phase transition.