An experimental investigation into the micro-mechanics of spall initiation and propagation in Ti-6Al-4V during shock loading

Titanium alloys have long been considered candidate materials for use in monolithic armor systems due to their excellent specific mechanical properties and relative ease of manufacture. However, high production costs combined with a propensity to fail due to adiabatic shear band formation and spallation have limited the adoption of titanium alloys in armor systems. In this paper, the spall behavior of the workhorse titanium alloy, Ti-6Al-4V, is investigated via a series of plate impact experiments. Back-scatter electron (BSE) microscopy and electron back-scatter diffraction (EBSD) are carried out on recovered specimens to investigate the nature of spall initiation and propagation. It is found that spall initiation occurs by the nucleation of voids at the grain boundaries between plastically hard/soft grains of the dominant hcp α phase. Further, it is shown that spall then propagates via the growth/coalescence of the nucleated voids into facets, followed by the coalescence of the facets through highly localized ductile bridging. A number of suggestions are made to improve the spall resistance of titanium alloys based on these observations.