Study of flow stress and spall strength of additively manufactured Ti-6-4 alloy

The use of additive manufacturing (AM) by Electron Beam Melting (EBM) or Selective Laser Melting (SLM) has extensively grown in the past few years. A major goal in AM is to manufacture materials with mechanical properties at least as good as traditionally manufactured materials. In this work we present the results of planar impact tests and Split Hopkinson Pressure Bar tests (SHPB) on Ti-6Al-4V manufactured by EBM and LSM techniques. Stress strain curves based on SHPB measurements at strain rate of about 1500 s-1 display similar plastic flow stresses for SLM and EBM processed Ti-6Al-4V alloys, and about 15% higher than reported for commercial Ti-6Al-4V alloy. Results of planar impact tests on SLM samples display slightly higher spall strength than EBM while the stress at Hugoniot elastic limit (HEL) is practically the same. Hugoniot elastic limit and spall strength estimates for EBM-and SLM-processed Ti-6Al-4V alloys are at least as high as values obtained for conventionally-processed alloys. The results of post mortem SEM analysis of the spall fracture have demonstrated significant differences in the spall fracture characteristics between the AM-processed and commercial Ti-6Al-4V alloys.