APM Review: Advanced Titanium Alloy Design based on Additive Manufacturing!

Additive manufacturing, also known as 3D printing, is a revolutionary technology in modern manufacturing. In the past decade, additive manufacturing technology of metal materials has developed from rapid prototyping, small-scale production to large-scale industrial production. From the material point of view, one of the most significant advantages of additive manufacturing is the near net forming capability. Therefore, in addition to reducing the waste of raw materials, additive manufacturing has an unparalleled advantage in making hard-to-process materials such as titanium alloys or superalloys.

The innovation points
The interaction between additive manufacturing technology and alloy composition is systematically studied, that is, the microstructure and mechanical properties of alloy are determined by alloy composition and additive manufacturing technology. On the one hand, the complex thermal-kinetic process in additive manufacturing can affect the microstructure of alloys at different scales.
(1) The steep thermal gradient in the molten pool inhibits the potential nucleation capability in front of the solidification interface, resulting in the coarse columnar grain structure of most printed titanium alloys.
(2) The high cooling rate in additive manufacturing preserves most of the high-temperature phase (BCC phase) or induces martensite transformation in (α+β) titanium alloy.
(3) In addition, insufficient heat dissipation of the matrix can reduce the cooling rate of the molten pool, and the layer by layer thermal cycle will also impose inherent cyclic heat treatment on the material, leading to the decomposition of the metastable phase. Therefore, in alloy manufacturing and microstructure optimization, processing parameters should be designed according to the specific microstructure and processing technology required.

Conclusion
This paper systematically reviews the latest development of advanced titanium alloy additive manufacturing. The interaction between additive manufacturing process and alloy composition was studied and discussed from the perspective of alloy selection and design. Although additive manufacturing technology poses great challenges to fabricating defectless, isotropic and homogeneous metal parts, the non-equilibrium characteristics of additive manufacturing process actually help achieve some unprecedented microstructure, phase composition and composition structure. The aim of this paper is to propose a new perspective on the co-advancement of alloy design and process. Instead of just looking at additive manufacturing as a forming technology that produces near-net formed parts, we look at additive manufacturing as an irreplaceable method of material handling and design. Combining the structure design of alloy composition with the characteristics of additive manufacturing can greatly promote the design of advanced structural materials with controllable microstructure and properties in the era of 3D printing.