Analyzing the effects of powder and post-processing on porosity and properties of electron beam melted Ti-6Al-4V

Abstract

Metal additive manufacturing techniques such as the powder-bed systems are developing as a novel method for producing complex components. This study uses synchrotron-based X-ray microtomography to investigate porosity in electron beam melted Ti-6Al-4V in the as-built and post-processed state for two different powders. The presence of gas porosity in the starting powder was shown to correlate to porosity in the as-built components. This porosity was observed to shrink after a hot isostatic press treatment, but grow following a subsequent heat treatment. Crystal plasticity simulations were used to observe the effects of various observed pore sizes on mechanical behavior under loading. IMPACT STATEMENTThis work combined µSXCT and crystal plasticity simulations to characterize porosity through each processing stage of EBM Ti-6Al-4V. Gas porosity was detected in the as-HIPed state, and growth was observed after subsequent heat treatment.

Review of the Methods for Production of Spherical Ti and Ti Alloy Powder

“…Another issue with the gas atomization is that the high-pressure gas used for atomization may be trapped in the liquid metal, which would remain to become gas pores or gas bubbles in the powder. These gas pores cannot be entirely eliminated even by HIP, 33 which is thus detrimental to the mechanical properties, especially fatigue properties.…”

Influence of Rapid Solidification on the Thermophysical and Fatigue Properties of Laser Additive Manufactured Ti-6Al-4V Alloy

“…Cunningham et al [49] investigated the effect of processing parameters on porosity of electron beam melted Ti-6Al-4V. The fatigue properties of a material are affected by porosity; these are points of weakness where cracks are initiated.…”

X-Ray Microcomputed Tomography in Additive Manufacturing: A Review of the Current Technology and Applications

“…32,40 It was indicated in Panwisawas et al 43 that small amounts of trapped gas between powder particles act as a nucleation site for spherical pores. Gas entrapped in the melt pool originating from the feedstock powder was identified in recent studies, such as in Cunningham et al 45 where the presence of porosity in the powder was correlated with porosity in the built EB-PBF parts.…”

“…92,93 The usefulness of this over conventional laser diffraction or microscopy is primarily that internal pores can be easily identified in powders, which might be trapped in the meltpool during the AM process. 45 It is also the only method through which the real sphericity, volume, and surface areas of particles can be determined, which can all be important parameters for ensuring flowability and eventually quality of the powder bed.…”