Su Zhun,Lu Wenquan,Ding Zongye,Zhao Liang,Yang Fan,Li Jianguo,Hu Qiaodan
Laser powder bed fusion (LPBF) is used to fabricate complex-shaped, dense, and high-performance oxide ceramics. During LPBF, bubbles form and evolve in the melt pool and ultimately remain in the printed ceramics as pores, which significantly degrade the mechanical properties. Therefore, it is essential to understand the bubble behaviors during LPBF. Herein, we conducted an in-situ investigation of the bubble dynamics in the melt pool of homogeneously mixed Al 2 O 3 –Y 2 O 3 powders using synchrotron high-speed X-ray imaging. The formation, growth, motion, and evolution of bubbles, as well as the relationship between the instability of melt flow and bubble rupture during LPBF, were elucidated. The findings reveal that bubbles from the interstices within the powder bed grow following three distinct modes, i.e., uplift growth, gas channel attachment, and bubble coalescence. Furthermore, melt flow oscillations caused by the bursting of large bubbles can lead to local instability of the melt pool. Results from this study enhance the understanding of bubble dynamics during LPBF and may provide valuable insights for pore elimination in LPBF-processed oxide ceramics.
Laser directed energy deposition (LDED) additive manufacturing is promising in the fabrication of high-performance W-based heavy-alloys which are normally difficult-to-process due to their unique nature such as the extremely high melting point and high ductile-brittle transition temperature. In this work, a novel 95 W heavy alloy modified by nanosized Ni and Fe particles was manufactured by LDED process. The effects of laser power on the formation mechanisms of molten pool were investigated. It was found that a relatively high laser power could promote the complete melting of W powder and formation of regular molten pool morphology. The microstructures of laser-processed W heavy alloy showed columnar grains , cellular grains and equiaxed grains from bottom to top within the molten pool along the building direction. The three-dimensional finite element simulation revealed the temperature gradient ( G ), cooling rate ( C ) and solidification velocity ( S ) within the molten pool were different, which was responsible for the microstructural development. The bulk-form 95 W heavy-alloy part free of defects was produced at the laser power of 1400 W. The optimally processed 95 W heavy-alloy by LDED showed a high average nanohardness of 8.6 GPa and a sound wear performance with a low coefficient of friction (COF) of 0.5. The tensile tests also revealed the achievement of a combination of an excellent tensile strength of 541 MPa and an elongation of 0.99%. This work demonstrated that LDED was able to manufacture high-performance tungsten heavy-alloys in bulk form with outstanding mechanical properties .
危险品化学品经营许可证（带存储）