R&D and Manufacturing of Metal Additive Manufacturing

Compared with conventional manufacturing methods such as casting, forging, welding, and powder metallurgy, metal additive manufacturing (AM) offers high geometric freedom, high material utilization, and strong capabilities for localized material deposition, while involving highly transient thermal histories. The micro-molten pool, a small and short-lived localized liquid-metal region generated by a moving heat source, serves as the fundamental metallurgical unit linking process parameters, compositional evolution, microstructure formation, and material properties. Repeated melting, rapid cooling, and cyclic reheating of the micro-molten pool generate steep temperature gradients, high solidification rates, and spatially heterogeneous thermal fields, causing solidification behavior to deviate substantially from conventional near-equilibrium conditions.

This presentation compares metal AM with conventional manufacturing processes in terms of forming principles, material utilization, geometric capability, thermal history, microstructure control, manufacturing scale, and application scenarios. Focusing on the coupled effects of micro-molten-pool solidification, solute diffusion, and phase transformations, a composition-design framework tailored to metal AM is established. In contrast to the conventional strategy of adapting traditional alloys to AM primarily through process-parameter optimization, this framework directly incorporates these physical-metallurgical mechanisms as constraints for alloy composition selection and optimization. Using TiAl alloys as a representative material system, the presentation illustrates how solidification-path control and diffusion-mediated homogenization can be integrated into the design of alloys specifically tailored for additive manufacturing.

This framework shifts alloy development from “process adaptation of conventional compositions” toward “active composition design for the transient states of micro-molten pools.” It provides a physical-metallurgical basis for simultaneously optimizing additive manufacturability, microstructural stability, and targeted material properties.

Yang Chen is a professor at Nanjing University of Science and Technology, China. He earned his BS degree from the Georgia Institute of Technology and his MS degree from the University of Michigan, Ann Arbor. After obtaining his PhD degree in materials science and engineering from the University of California, Los Angeles, he became a research scientist at Nanjing University of Science and Technology. His research is mainly focused on directional solidification and electron beam additive manufacturing of high-performance TiAl alloys.