Chae Hobyung, Huang E-Wen, Woo Wanchuck, Kang Suk Hoon, Jain Jayant, An Ke, Lee Soo Yeol
Department of Materials Science and Engineering, Chungnam National University, Daejeon, 34134, Republic of Korea.
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010, Taiwan.
J Alloys Compd. 2021 Mar 15;857:157555. doi: 10.1016/j.jallcom.2020.157555. Epub 2020 Oct 13.
thermal cycling neutron diffraction experiments were employed to unravel the effect of thermal history on the evolution of phase stability and internal stresses during the additive manufacturing (AM) process. While the fully-reversible martensite-austenite phase transformation was observed in the earlier thermal cycles where heating temperatures were higher than A, the subsequent damped thermal cycles exhibited irreversible phase transformation forming reverted austenite. With increasing number of thermal cycles, the thermal stability of the retained austenite increased, which decreased the coefficient of thermal expansion. However, martensite revealed higher compressive residual stresses and lower dislocation density, indicating inhomogeneous distributions of the residual stresses and microstructures on the inside and on the surface of the AM component. The compressive residual stresses that acted on the martensite resulted preferentially from transformation strain and additionally from thermal misfit strain, and the decrease in the dislocation density might have been due to the strong recovery effect near the Ac temperature.
采用热循环中子衍射实验来揭示热历史对增材制造（AM）过程中相稳定性演变和内应力的影响。在早期热循环中，当加热温度高于A时，观察到完全可逆的马氏体-奥氏体相变，而随后的衰减热循环则表现出不可逆相变，形成逆转变奥氏体。随着热循环次数的增加，残余奥氏体的热稳定性提高，这降低了热膨胀系数。然而，马氏体显示出更高的压缩残余应力和更低的位错密度，表明增材制造部件内部和表面的残余应力和微观结构分布不均匀。作用在马氏体上的压缩残余应力主要源于相变应变，此外还源于热失配应变，位错密度的降低可能是由于在Ac温度附近有强烈的回复效应。
