Influence of cooling rate on volume fraction of α massive phase in a Ti-6Al-4V alloy fabricated using directed energy deposition

The Effect of Decomposed Microstructure on Mechanical Properties of Additively Manufactured Ti-6Al-4V Alloy

“…Figs. 2 and 3 show the formation of α' and α m , respectively, within the prior β grain of the as-built DED Ti-6Al-4V alloy, as a result of high cooling rate (beyond 4000 K•s -1 ) in the DED process 10) . The α' generally appears as a needle-shaped morphology, as shown at the top layer of the specimens in Figs.…”

“…In DED Ti-6Al-4V, the microstructures of α' martensite and α massive phase (α m ) are generally formed due to the high cooling rate introduced during the process 10) . The α' and α m usually are observed with the appearance of acicular and sub-lamellar morphology, respectively 11) .…”

Directed energy deposition of metals: processing, microstructures, and mechanical properties

“…Ṫ in the DED process is determined to be 10 3 -10 4 K/s [23,44,87], which is two to three orders of magnitude lower than that of the LB-PBF process (10 5 -10 6 K/s) [43,164,167]. The ultrahigh Ṫ in LB-PBF processing is primarily due to the combination of low heat source energy, high scanning speed, and small melt pool size (Table 1).…”

“…The metallic components fabricated using DED have some distinct structural features (as compared to their CM counterparts), which stem from the specific thermal histories that feature high (10 3 –10 4 K/s) [23,44,87] coupled with repeated thermal cycling of the deposited layers, resulting in multi-scale, heterogeneous, and hierarchical structures. In this section, the mechanisms behind the formation and evolution of such microstructural features are discussed.…”

“…Both experimental and simulation studies reveal that primary dendrite arm spacing (PDAS, or cell spacing) is dominated by [43,157,165,166]. PDAS in AM steel components was observed to obey the relation [43]: in the DED process is determined to be 10 3 –10 4 K/s [23,44,87], which is two to three orders of magnitude lower than that of the LB-PBF process (10 5 –10 6 K/s) [43,164,167]. The ultrahigh in LB-PBF processing is primarily due to the combination of low heat source energy, high scanning speed, and small melt pool size (Table 1).…”