ScholarWorks@성균관대학교

초록

Ti-6Al-4V alloy fabricated via selective laser melting (SLM) inherently develops high residual stresses due to rapid cooling and steep thermal gradients. To address this, stress relief (SR) heat treatment was performed below the (3-transus temperature (0.3-0.5 Tm) to enable atomic diffusion without triggering full phase transformation. This study investigates the effects of SR treatment on microstructural evolution, dislocation density, residual stress, and mechanical properties. Residual stress was quantitatively evaluated using X-ray diffraction, while dislocation density was indirectly assessed through Kernel Average Misorientation (KAM) from EBSD analysis. With increasing SR temperature, lattice distortion was gradually relieved, and a notable decrease in dislocation density was observed beginning at 550 degrees C. A significant reduction in residual stress approximately 50 % compared with the As-Built condition was achieved even at 350 degrees C and was nearly eliminated at 650 degrees C. Microstructural recovery of alpha ' martensite into equilibrium alpha and (3 phases commenced at 550 degrees C, leading to a dual-phase alpha + (3 structure above 650 degrees C. Correspondingly, tensile strength declined while ductility increased. Overall, sub-transus SR treatment effectively relieved internal stresses, refined the microstructure, and improved the strength-ductility balance, making it a practical approach for enhancing the performance of SLM Ti-6Al-4V components.

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