Evaluation of HIP-parameter Effects on AM Titanium Ti-6Al-4V

Additive Manufacturing (AM) of titanium Ti-6Al-4V (Ti64) by Powder Bed Fusion (PBF) method results in metastable microstructure that differs significantly from the conventionally manufactured titanium. The high cooling rates in laser sintering allow the formation of very fine martensitic microstructure. Because of this different as-built microstructure, it can be suspected that the conventional post treatments, including Hot Isostatic Pressing (HIP), could be improved.

HIP treatment is commonly performed for aerospace and medical components for material densification and to modify microstructure. HIPping also affects to the mechanical properties of the material. The aim of the study was to investigate possibilities to renew current standard HIP-treatment (920°C, 100MPa, 2h) to better fit for AM Ti64 material. This was done by investigating the microstructure of AM Ti64 after different HIP treatments and link it to the static and dynamic mechanical properties and to fatigue fracture types of the material.

The results of the study indicate that the HIP-process can be further optimized to gain better results in terms of reducing porosity but also creating required strength and fatigue properties for AM Ti64. It was found that with a lower HIP-temperature and higher pressure, it is possible to reach smaller grain size leading to the better mechanical properties. The results indicate a need for AM specific post-treatments.