Post heat treatment is essential for additively manufactured alloys to eliminate residual stress and in some cases further improve mechanical performance. This study systematically investigated the hardening response of a Ti-6Al-2Sn-4Zr-6Mo alloy processed by laser powder bed fusion (LPBF) to a one-step heat treatment. The results revealed significant hardening at both 500 °C and 650 °C. Most notably, an ultra-high peak-hardness of 563VHN was achieved within 5 mins of heat treatment at 650 °C due to a unique martensite-decomposed α+β microstructure consisting of alternating long β laths that are ∼5 nm thick and α laths that are ∼35 nm thick, and within the α laths are also short β laths that are ∼2 nm thick with an ∼11 nm inter-spacing. The influence of both types of β laths on the α lath thickness was established and related to the ultra-high hardness observed, which provides new insight for the design of new metastable LPBF-processed Ti alloys.
- Isothermal heat treatments
- Laser powder bed fusion
- Martensitic phase transformation
- Titanium alloy
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