Spall fracture in additive manufactured Ti-6Al-4V

Abstract

We present a study on the spall strength of additive manufactured (AM) Ti-6Al-4V. Samples were obtained from two pieces of selective laser melted (SLM, a powder bed fusion technique) Ti-6Al-4V such that the response to dynamic tensile loading could be investigated as a function of the orientation between the build layers and the loading direction. A sample of wrought bar-stock Ti-6Al-4V was also tested to act as a baseline representing the traditionally manufactured material response. A single-stage light gas-gun was used to launch a thin flyer plate into the samples, generating a region of intense tensile stress on a plane normal to the impact direction. The rear free surface velocity time history of each sample was recorded with laser-based velocimetry to allow the spall strength to be calculated. The samples were also soft recovered to enable post-mortem characterization of the spall damage evolution. Results showed that when the tensile load was applied normal to the interfaces between the build layers caused by the SLM fabrication process the spall strength was drastically reduced, dropping to 60% of that of the wrought material. However, when loaded parallel to the AM build layer interfaces the spall strength was found to remain at 95% of the wrought control, suggesting that when loading normal to the AM layer interfaces, void nucleation is facilitated more readily due to weaknesses along these boundaries. Quasi-static testing of the same sample orientations revealed a much lower degree of anisotropy, demonstrating the importance of rate-dependent studies for damage evolution in AM materials.

Dynamic properties of additively manufactured tantalum

“…These values have been plotted in figure 4 as individual data points in the USup plane, alongside a line representing the linear US-up relationship for conventional Ta taken from Marsh [8]. The data from this series is in good agreement with the existing Ta Hugoniot, a result which accords with previous investigations of AM metals under shock conditions [9][10]. For every shot except shot 2, the WAAM Ta sample returned a slightly higher shock velocity than the conventional Ta sample, a finding which is consistent with the higher calculated wave speed from the static sound speed measurements.…”

Structure/property characterization of spallation in wrought and additively manufactured tantalum

“…However, while there is a growing number of detailed structure-property studies of AM materials subjected to quasi-static and/or fatigue loading stress states, there remains to date few studies systematically quantifying their behavior at higher strain rates, shock loading, and/or when subjected to dynamic tensile 1D spallation loading [7][8][9]. Further, AM manufacturing of refractory pure metals and alloys has to date received little attention in contrast to alloys germane to aerospace and other industrial applications.…”

High‐rate characterization of additively manufactured Ti‐6Al‐4V using Taylor cylinder impact test: Experiments

“…As far as we know, the literature on AM material behavior under impact loading is scarce with very few exceptions. Among these, the work of Jones et al, 10 who investigated spall resistance in additively manufactured Ti‐6Al‐4V performing plate impact experiments, 11 is of particular relevance. They observed that flaws weaknesses resulting from the selected laser melting (SLM) manufacturing process were much more pronounced in the dynamic tests compared with the quasistatic tests.…”