<Abstract>

The “Holy Grail” of metal additive manufacturing is to manufacture reliable

high-performance metal parts with no or a minimal need of post processing.

However, Ti-6Al-4V parts made by selective laser melting (SLM) often suffer

from poor ductility and low toughness because of the predominant acicular α′

martensite contained in columnar prior-β grains. In practice, post heat treatment

is necessary. To overcome this deficiency, we have explored designing

innovative SLM processing routes to turn the unfavoured α′ martensite,

via in-situ decomposition, into lamellar (α+β) microstructures with tuneable

characteristic length scales. Such lamellar (α+β) microstructures lead to superior

mechanical properties which markedly exceed ASTM standards and outperform

the majority of Ti-6Al-4V fabricated by other additive manufacturing processes.

Furthermore, we find that the lattice parameter of the β phase in the (α+β) lamellae

falls into a specific range of 3.18–3.21 Å. Hence the lattice parameter of β phase

can serve as an indicator to predict whether significant martensite decomposition

has taken place in situ in Ti-6Al-4V made by SLM. This work marks an important

step forward in the understanding of how to tailor microstructure in situ for the

development of high-performance Ti-6Al-4V parts by SLM.

<全文連結>