STUDY OF FLOW STRESS AND SPALL STRENGTH OF ADDITIVELY MANUFACTURED TI-6-4 ALLOY

The use of additive manufacture (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 material with mechanical properties at least as good as traditionally manufactured material. In this work we present results of planar impact tests and Split Hopkinson Pressure Bar tests (SHPB) on Ti-6-4 manufactured by EBM and LSM process. Part of the EBM-processed samples was post-processed by Hot Isostatic Pressing. 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. The results of post mortem analysis of the spall fracture will also be presented. Stress strain curves based on SHPB measurements at two different strain rates present similar plastic flow stresses for SLM and EBM processed Ti-6-4 alloy, while flow stress is about 15% higher than reported for commercial reference material. The EBM-processed alloy displays a slightly lower strain to failure compared to commercial Ti-6-4. Both commercial and EBM-processed Ti-6-4 alloys demonstrate an increase of strain to failure with decrease in the samples` aspect ratio. Possible mechanisms responsible for the observed differences in behavior between AM and commercial Ti-6-4 are discussed.