Adiabatic shear bands in additively manufactured Ti-6Al-4V under high strain rate and elevated temperature conditions

Research interest in additively manufactured Ti-6Al-4V alloys has grown substantially for aerospace applications, where components frequently experience high temperatures and high strain-rate loading conditions. Thus, in this study, the dynamic mechanical behavior of a Ti-6Al-4V alloy manufactured using laser powder bed fusion (LPBF) was investigated using high-temperature compressive Split-Hopkinson Pressure Bar (SHPB) tests at strain rates of 1000 and 2000 s −1 , and across temperatures ranging from 298 to 773 K. Constitutive modelling of the acquired stress-strain was then conducted to allow simulation of their mechanical properties by means of three phenomenological models: modified Johnson-Cook, Hensel-Spittel, and modified Hensel-Spittel models. This was followed by extensive microstructural characterization, which revealed that the as-printed alloy primarily consists of a martensitic α’ structure within columnar prior β grains. After impact tests, the results provided evidence of multiple length scales of deformation localization developing within the microstructure: from slip bands within the basket-weave structure of activated α’ laths, to favorably oriented α’ grain boundaries, and eventually to transgranular adiabatic shear bands (ASBs) that cross the prior β grains and lead to fracture. The ASB half-width thickness increased and average distance between ASBs decreased with increasing strain rates and decreasing temperatures. Based on the findings, the instabilities in the microstructure brought about by the formation of the adiabatic shear bands at higher strain rates resulted in relatively high error when performing constitutive modelling. Specifically, among the constitutive models evaluated, the modified Hensel-Spittel model showed the lowest average absolute relative errors and highest correlation coefficients, with values of 5.51 and 0.95, respectively. • Impact tests using a Split Hopkinson pressure bar were used on additively manufactured titanium alloy at two strain rates. • Strain localization led to fracture of samples at 2000 s −1 at all temperatures, showing 45° cracks from the build direction. • Increase in adiabatic shear band half-widths at higher temperatures led to deviations in the constitutive model predictions.