金属增材制造中小孔孔隙形成机理研究
Mechanism of keyhole pore formation in metal additive manufacturing
摘要：
金属增材制造已经得到了研究机构和公司的广泛关注，以制造复杂的零件和功能梯度材料。然而，完工零件的孔隙率劣化了机械性能，甚至阻碍了金属增材制造的进一步应用。特别是，与小孔波动相关的小孔孔隙的机制尚未完全理解。为了揭示小孔的形成机理，本文采用一个综合考虑传热、液体流动、金属蒸发、Marangoni效应和达西定律的多物理场热流体流动模型对小孔的形成过程进行了数值模拟，并利用原位X射线图像对模拟结果进行了验证。模拟结果给出了小孔失稳引起的瞬时气泡形成过程以及瞬时气泡钉扎在凝固前沿时的运动过程。此外，小孔表面不均匀分布的后坐力也是小孔塌陷和侵彻的重要因素。此外，通过比较不同激光扫描速度下小孔的形成情况，发现小孔的形成对工艺参数非常敏感。小孔波动特征和小孔后壁的能量吸收率变化可以作为评价小孔孔隙形成可能性的指标。此外，在低环境压力下的模拟显示了提高小孔稳定性以减少甚至避免小孔孔隙形成的可行性。
英文摘要：
Metal additive manufacturing has gained extensive attention from research institutes and companies to fabricate intricate parts and functionally graded materials. However, the porosity of the as-built part deteriorates the mechanical property and even hinders the further application of metal additive manufacturing. Particularly, the mechanisms of keyhole pores associated with the keyhole fluctuation are not fully understood. To reveal the mechanisms of the keyhole pores formation, we adopt a multiphysics thermal-fluid flow model incorporating heat transfer, liquid flow, metal evaporation, Marangoni effect, and Darcy's law to simulate the keyhole pore formation process, and the results are validated with the in-situ X-ray images. The simulation results present the instant bubble formation due to the keyhole instability and motion of the instant bubble when it pins on the solidification front. Moreover, the unevenly distributed recoil pressure on the keyhole surface is an important factor for keyhole collapse and penetration. Furthermore, comparing the keyhole pore formation under different laser scanning speeds shows that the keyhole pore is sensitive to the manufacturing parameters. The keyhole fluctuation features and energy absorptivity variation on the rear keyhole wall could be metrics to evaluate the likelihood of the keyhole pore formation. Additionally, the simulation under a low ambient pressure shows the feasibility of improving the keyhole stability to reduce and even avoid the formation of keyhole pores.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
