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The " Holy Grail " of metal additive manufacturing is to manufacture reliable high-performance me... more 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 a 0 martensite contained in columnar prior-b grains. In practice, post heat treatment is necessary. To overcome this deficiency, we have explored designing innovative SLM processing routes to turn the unfavoured a 0 martensite, via in-situ decomposition, into lamellar (aþb) microstructures with tuneable characteristic length scales. Such lamellar (aþb) 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 b phase in the (aþb) lamellae falls into a specific range of 3.18e3.21 Å. Hence the lattice parameter of b 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.
The " Holy Grail " of metal additive manufacturing is to manufacture reliable high-performance me... more 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 a 0 martensite contained in columnar prior-b grains. In practice, post heat treatment is necessary. To overcome this deficiency, we have explored designing innovative SLM processing routes to turn the unfavoured a 0 martensite, via in-situ decomposition, into lamellar (aþb) microstructures with tuneable characteristic length scales. Such lamellar (aþb) 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 b phase in the (aþb) lamellae falls into a specific range of 3.18e3.21 Å. Hence the lattice parameter of b 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.