Use of X-ray CT imaging to quantitatively analyze the effects of the pore morphology on the tensile properties of CP-Ti L-PBF materials

Controlling the shape, size, and arrangement of residual defects (pores) in additive-manufactured materials is essential for improving their strength and reliability. However, quantifying the shape and arrangement of individual pores in such materials remains a challenge. This study aimed to clarify the effect of pore configurations that determine the tensile properties of laser powder-based fusion (L-PBF) materials. First, the 3D pore-configurations of pure titanium L-PBF materials fabricated under different beam energy densities were visualized using high-intensity X-ray computed tomography (CT). Subsequently, the porosity, volume equivalent diameter, and sphericity of each pore were quantified by 3D analysis of each CT image, and their correlations with the tensile properties were analyzed. The results showed that, unlike conventional sintered materials, the 0.2% yield stress did not correlate with the porosity of the specimen, suggesting heterogeneity in the hydrostatic component of stress acting on pores. This was connected to periodic fluctuation in the local porosity of the layers sliced perpendicular to the building direction. Furthermore, for specimens fabricated under relatively low beam energy densities, the porosity of the lowest density sliced layer was negatively correlated with tensile strength and total elongation, whereby the local low-density layer dominated the tensile properties. For specimens fabricated under the high energy densities where keyholes were generated, the maximum pore diameter rather than the local layer porosity was more predominate. Thus, it is evident that local structures such as local low-density regions or larger pores dominate the ductile properties of Ti L-PBF materials in terms of their tensile properties.