Simulation-informed laser metal powder deposition of Ti-6Al-4V with ultrafine α-β lamellar structures for desired tensile properties

Understanding the thermal history of a metal part during additive manufacturing (AM) is essential for process design and microstructural control. In this study, detailed thermal history simulation was carried out for laser metal deposition (LMD) of Ti-6Al-4V (wt%) using the Directed Energy Deposition (DED) module in Simufact Welding. The simulation identified necessary LMD conditions for in-situ decomposition of alpha '-martensite in Ti-6Al-4V with respect to build height. On this basis, rectangular Ti-6Al-4V coupons were fabricated and systematic microstructural characterisation confirmed in-situ decomposition of alpha ' into ultrafine alpha-beta lamellae in the as-built samples. In addition, the approximate in-situ transition time from alpha '-* alpha + beta (lamellar) during the LMD process was determined to be 30-40 s, which is two orders of magnitude faster than conventional isothermal decom-position of alpha '. The underlying reasons were analysed and attributed to precursor (clusters) development within the alpha '-martensite laths as well as at the alpha '-lath boundaries due to being frequently and rapidly heated to tem-peratures well above the beta transus, supported by recent literature. The as-built lamellar alpha-beta Ti-6Al-4V achieved yield strength of 951 +/- 10 MPa and tensile ductility of 8.18 +/- 1.8%. Other insights obtained from this simulation-based experimental study were discussed including microstructural control of tall titanium alloy components through in-situ decomposition of alpha '-martensite.

Automated summary

This study conducted detailed thermal history simulation for laser metal deposition of Ti-6Al-4V and confirmed the in-situ decomposition of alpha'-martensite during the process, providing insights for process design and microstructural control in additive manufacturing.