Progress on Solidification Grain Morphology and Microstructure Control of Laser Additively Manufactured Large Titanium Components

The technological advantages of laser additive manufacturing (LAM) for high performance large critical metallic components are briefly introduced, and the main progresson control of solidification grain morphologiesand post-LAM heat- treatment microstructuresfor the LAMed large critical titanium components in the author's team issummarized.The epitaxial growth from the pool-bottom for columnar grain formation and surface heterogeneous nucleation for equiaxed grain formation are found to be the two dominant solidification mechanisms during the layerwiselaser additive manufacturing process. A completed set of solidification grain morphology control method was established and LAMedlarge titanium components with full columnar grains, full equiaxed grains and columnar/equiaxed mixed grains were produced by active controlling the solidification conditions during LAM process. A new special bi-modal microstructure was discovered during the post-LAM heat treatment process and its solid-state phase transformation theory is established.