Effect of stress triaxiality and penny-shaped pores on tensile properties of laser powder bed fusion Ti-6Al-4V

In this study, the effect of internal penny-shaped pores on the strength and ductility of additively manufactured Ti-6Al-4V under uniaxial tension and notched tension loading was investigated. The behaviors of fully dense samples were compared to those of samples containing pores whose diameters ranged from 150 µm to 3000 µm within 6 mm diameter gauge regions. For uniaxial tension specimens, loss of strength occurred for samples containing pores larger than 870 µm (2.1% of the cross-sectional area), while ductility decreased for pores larger than 150 µm (0.07% of the cross-sectional area). The notched tension specimens – also with 6 mm diameter gauge regions and subject to greater stress triaxialities than uniaxial tension – were more severely affected by the pores; pores larger than 150 µm resulted in a reduction of strength, while all pore sizes significantly reduced ductility. Dense finite element simulations showed that plastic strain to failure was dependent on stress triaxiality in samples containing pores with a diameter of 540 µm (0.8% of the cross-sectional area) and smaller, while samples with larger pores failed with negligible plastic strain regardless of stress triaxiality. X-ray computed tomography showed negligible volumetric growth of pores for samples loaded to 75% of their displacement to failure.