强磁场下退火对增材制造Ti-6Al-4V合金及其力学性能的影响

Improved Mechanical Properties of Additive Manufactured Ti-6Al-4V Alloy via Annealing in High Magnetic Field

摘要:

本文基于提出的一种崭新的磁场驱动方法有效地提高了激光选区熔化Ti-6Al-4V合金的力学性能。通过X射线衍射、光学显微镜、扫描电子显微镜和原子力显微镜，系统地表征了初始态和在7T强磁场下退火30分钟的样品的微观结构。其中，退火温度分别选取在低于β转变温度的400 ℃和800 ℃，以及高于β转变温度的1200 ℃。键合电荷密度不仅可以表征由Al和V原子引起的晶格畸变，还可以从电子和原子本质上揭示固溶强化机制和马氏体相变机制。由于退火时间较短，经7T强磁场400℃和1200℃退火的试样的极限抗拉强度和伸长率均比初始态的试样有所提高。上述结果表明，通过热和磁场的耦合效应，可以预期改变激光选区熔化Ti-6Al-4V合金的相变热力学，进而有效地优化其微观结构。这一设想的验证将有助于开发一种有效地提高增材制造材料的力学性能的新型磁场驱动方法。

Abstract:

In this work, a novel magnetic-field-driving approach is proposed and utilized to efficiently enhance the mechanical properties of selective laser melting Ti-6Al-4V. The microstructures of the as-built and the SLM specimens annealed at 400°C, 800°C below the β transus, and 1200°C above the β transus for 30 minutes in the high magnetic field of 7 T are comprehensively characterized in terms of X-ray diffraction, optical microscope, scanning electron microscope, and atomic force microscope. Lattice distortion induced by Al and V atoms are characterized by bonding charge density, providing an insight into the atomic and electronic basis for the solid solution strengthening mechanism and the martensitic transformation mechanism. Referring to the as-built speciments, the ultimate tensile strength and the elongation of annealed specimens at 400 °C and 1200°C in 7T high magnetic field were increased due to the short annealing time. Based on the coupling effect of force field induced by the heat and magnetic, it is expected that the microstructures of SLM Ti-6Al-4V would be conventionally optimized through changing the phase transformation thermodynamics. The validation of this hypothesis will pave a path to develop a novel magnetic-field-driving approach efficiently enhancing the mechanical properties of additive manufactured materials.