In the application of laser powder bed melting technology, α+β duplex titanium alloy has a lot of applications in aerospace, Marine engineering, military equipment and biomedical fields because of its high specific strength, high temperature resistance, corrosion resistance, good biocompatibility, excellent weldability (forming parts without cracks) and other characteristics.
However, this technology is also faced with problems such as low density and severe anisotropy of microstructure properties, as well as difficulties in microstructure design for high strength and high toughness and creep resistance requirements of high strength and high fracture toughness.
(1) Laser powder bed melting process
In the process of laser melting/laser powder bed melting, the process parameters and scanning strategy have great influence on defect formation, residual stress and surface quality. High density samples can be obtained by reasonable combination of process parameters. Different types of defects can be introduced by too high or too low laser power and scanning speed parameters.
(2) The effect of forming process and subsequent heat treatment process on the microstructure
In this part, we introduce the α 'martensite structure of the original β columnar crystal, the α+β lamellar structure of the annealed α+β lamellar structure, the α+β double-lamellar or two-state structure of the solution aging α+β lamellar structure, and the α+β lamellar structure of the hot isostatic pressing. The influence of forming and heat treatment on microstructure evolution was discussed. As shown in Figure 4, in α+β STA treatment in the two-phase region, solution temperature and time can greatly affect the microstructure characteristics of primary α phase.
(3) The relationship between microstructure and performance
In this part, the effects of microstructure characteristics on tensile properties, fatigue properties, fracture toughness, creep and corrosion properties of laser powder bed melting titanium alloy are summarized. Compared with the titanium alloys prepared by traditional forging or casting process, the post-treated (including heat treatment/hot isostatic pressing/surface treatment) laser powder bed melting titanium alloys have better tensile, fatigue, fracture toughness and creep properties. In addition, we also proposed the contradiction of high strength/high fracture toughness/creep resistance obtained simultaneously in laser powder bed melting titanium alloy.
