Indexed by:Journal paper
First Author:Kaiwen Wei
Correspondence Author:Zemin Wang
Co-author:Xiaoyan Zeng
Journal:Materials Science & Engineering A
Included Journals:SCI、EI
Volume:709
Page Number:301-311
Date of Publication:2018-01-02
Impact Factor:4.652
Abstract:In the present work, selective laser melting technology (SLM) has been used to produce Ti-5Al-2.5Sn alpha titanium alloy and the influence of post-deposition heat treatments on microstructure and mechanical properties of the as deposited alloy has been in-depth analyzed for the first time. As-deposited Ti-5Al-2.5Sp exhibits a columnar prior-beta microstructure with martensitic alpha' needles filled inside and a small amount of grain-boundary alpha (alpha GB) stripes precipitated at the prior-grain boundaries. After subtransus heat treating at 600 degrees C to 750 degrees C for 2 h, incomplete recrystallization of the as-deposited microstructure occurs and the recrystallized alpha grains with equiaxed morphology nucleate mainly through grain boundary migration of the stripe-like alpha(GB), leading to a duplex microstructure composed of the soft recrystallized a and 75.1-97.6% high-strength alpha'. After subtransus heat treating at 850 degrees C to 950 degrees C for 2 h, complete recrystallization of the as-deposited microstructure occurs and the coarsening of recrystallized alpha grains becomes more pronounced at 950 degrees C. By contrasting, an excessively coarsened widmanstatten microstructure composed of alpha laths with lengths up to several hundred micrometers has been obtained after supertransus heat treating at 1100 degrees C for 2 h. Both of the as-deposited and heat-treated samples exhibit relatively weak textures, resulting in very little mechanical anisotropies. Because of the dominant alpha' microstructure, as-deposited possesses ultrahigh tensile strengths but also a poor elongation (7.7-8.2%) in comparison to the conventionally -fabricated Ti-5Al-2.5Sn. After the heat treatments, tensile strengths gradually decrease whereas elongation increases first and then decreases with the elevating annealing temperature, reaching its peak at 750 degrees C (14.4-15.2%). Finally, it has been proved that both elongations and tensile strengths of the 650-850 degrees C/2 h heat-treated samples can exceed those of the conventionally-fabricated Ti-5Al-2.5Sn. These findings provide some basis for the rapid fabrication of high-strength alpha titanium alloy products with a satisfactory ductility.