Strain localization in Ti-6Al-4V Widmanstätten microstructures produced by additive manufacturing

Abstract

Although Additive Manufacturing (AM) offers numerous performance advantages over existing methods, AM structures are not being utilized for critical aerospace and mechanical applications due to uncertainties in their structural integrity as a result of microstructural variations and defects arising from the AM process itself. With strain localization serving as a precursor for material failure, the impact of microstructural variations in Direct Metal Laser Sintering (DMLS) produced Ti-6Al-4V on strain localization is investigated through high resolution digital image correlation as a result of monotonic and cyclic loading for both stress relieved and mill annealed specimens. From the experimental characterizations, it was observed that the former β phase boundaries that enclose separate microtextured regions and the α lathe's major axis orientations play a critical role in the localization of strain with respect to the Widmanstätten microstructures exhibited by DMLS Ti-6Al-4V. The results show a potential opportunity to improve the performance of DMLS produced Ti-6Al-4V by decreasing the size of the β grains during the solidification process through higher cooling rates and a build strategy that avoids the reheating of solidified material as much as possible to prevent β grain growth.

Deformation and failure mechanisms of Ti–6Al–4V as built by selective laser melting

“…It has also been shown that there is not a correlation between the Schmid factor and high strain values measured by DIC in FCC materials [35]. On the other hand, Schmid law has been shown to be satisfactory to explain slip system activation in Ti-6Al-4V [14,36] and good correlation in the present study is also observed. Surface topography studies ( Fig.…”

“…High prismatic and basal Schmid factors also show good correlation with strain localization in the high aspect ratio ′ and ′ colonies respectively. However, correlation between strain localization in high aspect ratio ′ and high basal Schmid factor has also been reported in the literature [14]. At room temperature, the prismatic slip system in the α-Titanium displays the lowest critical resolved shear stress [32].…”

“…There are several methods for 3D printing metals including selective laser melting (SLM), selective electron beam melting (SEBM), directed energy deposition (DED) and binder jetting [5,6]. In the present study, we focus on selective laser melting (SLM) of Ti-6Al-4V that has attracted a lot of interest and results in a lamellar microstructure [7][8][9][10][11][12][13][14][15]. In SLM, a thin layer of metal powder is spread on a powder bed and selectively fused using a high power laser.…”

Mechanical response of a Laser Cladding repaired structure: localization of plastic strain due to microstructure gradient

“…In [31], tensile tests conducted with DIC at a macroscopic level underlines the fact that the existence of a microstructure gradient induces strain localization. Otherwise, other works use DIC at a smaller scale to highlight spatial distribution of strain within grains [4,7,9,29]. However, no study could be found where DIC is conducted at grain level in repaired microstructures.…”

Direct metal laser deposition of titanium powder Ti-6Al-4V

“…It is necessary to provide wide complex of researches and tests. Titanium alloys are used in the following additive technology: melting layer by layer powder by electron beam (EBM) [1,2] or laser (SLM, SLS methods) [3,4], feeding melted powder or wire by plasma arc [5,6] or laser (DMLD) [7,8]. We suggest using laser metal deposition technology for manufacturing of titanium parts.…”