Spall damage in laser-powder-bed-fusion manufactured Ti-6Al-4V: Mechanisms and microstructure effects

Abstract

Spall damage of Ti-6Al-4V alloy fabricated via laser powder bed fusion (LPBF) is investigated via plate impact along the build direction (BD) and the transverse direction (TD), as regards its underlying mechanisms and microstructure effects. Conventional hot-rolled Ti-6Al-4V alloys processed with annealing and quenching are also examined for comparison. Hugoniot elastic limit (HEL) and spall strength of the LPBF-fabricated samples are derived from free-surface velocity histories, and are higher for the TD loading than for the BD loading. The LPBF-fabricated alloy has a lower HEL but similar spall strength compared to the conventionally fabricated alloys. Quantitative analysis of recovered samples reveals that, the number of cracks is smaller and the mean crack length is larger in the LPBF-fabricated and quenched hot-rolled samples containing α′ martensite laths than the annealed hot-rolled sample containing equiaxed α grains. For the LPBF-fabricated samples, the TD loading induces cracks of similar length along α′ grain boundaries (GBs) and α′{0001} planes, but much longer cracks along prior β GBs compared to the BD loading. Anisotropy in mechanical properties and damage is due to columnar prior β grains, morphological and crystallographic texture of α′ laths.